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Three dimensional simulation of J-shaped Darrieus vertical axis wind turbine
Abstract
The present research aims to investigate the concept of J-shaped blade in a straight–bladed Darrieus type VAWT in terms of output torque and power by employing high-fidelity 3D numerical simulations. Theoretically, since the J-shaped blades can benefit from the lift and drag forces simultaneously, this combined forces help the turbine possess faster operation at low wind speeds, thereby resulting in the termination of self-starting problem and improving power coefficients, especially at low and moderate tip speed ratios. In this study, NACA0015 is served as the base airfoil and has been modified to generate the desired J-shape profile. The attained results indicate improvements on torque and power coefficients, more specifically in the first half of revolution namely 0° < θ < 180°. Additionally, the amplitude of power and torque oscillation in each revolution has been curtailed and shifted up. A chunk of these improvements can be attributed to the inherent geometry of J-shaped profile through which the generated vorticities are trapped inside the blade and released behind the rotor. Not only that, the volumetric representation of turbulent kinetic energy discloses that the wake region behind the J-shaped rotor is free from slow dissipation of vorticities and possesses much less turbulency.
... This duct functions by accelerating and channeling airflow towards the rotor blades, thereby increasing the mass flow rate through the turbine [5]. consistently produced positive torque across the operating range [31]. This finding suggests improved self-starting capabilities and potentially higher overall efficiency. ...
... While J-shaped airfoils have demonstrated promise in enhancing VAWT self-starting torque and overall performance, as evidenced by [30,31], it's crucial to acknowledge recent findings that suggest potential limitations under specific operating conditions. Research by [32] presents contrasting results, indicating that J-shaped blade designs might not improve performance for Darrieus-type VAWTs operating in the high TSR zone (high tip speed ratio) with solidity values ranging from 0.1 to 0.2. ...
... Notably, the studies by Zamani et al. [30,31] that highlighted the benefits of J-shaped airfoils did not explore this particular operating regime. ...
As the demand for sustainable energy sources continues to rise, improving the efficiency of existing renewable technologies is crucial. This study investigates the aerodynamic performance of J-shaped blade design for H-Darrieus VAWT with the objective of enhancing starting torque and overall efficiency. A 2D URANS CFD model was employed to simulate the airflow around the J-shaped blades. The model underwent a comprehensive verification and validation process. This rigorous approach ensured the model's fidelity, enabling a systematic comparison of the J-shaped blade's aerodynamic performance with conventional NACA0015 airfoils. The numerical analysis reveals a significant enhancement in starting torque, with a 142% increase observed at low tip speed ratios (λ = 0.2). This finding positions the J-shaped blade as a promising solution to address the challenge of initiating rotation in low-wind environments, particularly relevant for urban applications. Furthermore, the simulations demonstrate comparable torque production between the J-shaped blade and the NACA0015 airfoil under typical operating conditions. The J-shaped blade exhibits improved torque uniformity and reduced wake turbulence intensity. This study highlights the potential of the J-shaped blade design to revolutionize VAWT technology by offering advancements in increased efficiency, reduced fatigue stresses on the turbine structure, and optimized energy generation.
... However, the area of flow structure remains less studied by researchers. In first 3D numerical study by Zamani et al., 26 it was outlined that the aforementioned blades exhibited a moderate rise in value of average torque for the TSRs up to 1.6. Despite their results, the importance of vortices was not thoroughly analyzed. ...
... 28 Limited number of studies have considered the J-type VAWTs in 3D. 26 In a recent study, Farzadi et al. 29 extensively studied the effect of flow properties such as turbulence intensity and wind speed on the performance of J-type VAWTs using a 3D numerical simulation. They indicated that the blade's interaction and impact of tip vortices in J-type blades are more pronounced than straight blades. ...
... Their comparative analysis against the K-ω and K-ε models revealed that employing the K-ω SST turbulence model yielded results that closely aligned with the experiments. Noteworthy studies such as those by Rezaeiha et al., 2 Ardaneh et al., 31 Zamani et al., 22,26 and Farzadi et al. 29,32 successfully applied the K-ω SST model in both 2D and 3D simulations of VAWTs, achieving commendable outcomes. This turbulence model, characterized by the provided equations (Equations 4 and 5), has been adopted in the current research for resolving transient 3D incompressible turbulent airflow over VAWTs. ...
There is a growing demand to improve the performance of vertical axis wind turbines to facilitate their commercialization for application in urban areas. This study utilizes a 3D numerical analysis to examine the influence of different vortices generated on turbine efficiency with straight and J‐type blades. The numerical simulation of this study employs the Reynolds‐Averaged Navier–Stokes equations and sliding mesh techniques to more accurately model the rotational motion of blades about the turbine axis in relation to the wind. Comparing the output torque and the flow field at different span‐wise sections, the J‐type blades achieve better performance at mid‐spans where the effect of stall vortices is dominant. Conversely, the lower performance of J‐type blades is seen at tip spans due to stronger tip vortices. Investigations also reveal the criticality of the downwind region on the overall performance at high tip speed ratios. It is observed that by increasing the height, the tip vortices are limited to the tip sections, and stall vortices expand further along the blade. At TSR = 1, the improvement by J‐type blades rises from 10% at a height of 0.8 m to 44% at 3 m. The growth in height at lower wind speeds becomes more beneficial. Compared to the straight blades, the self‐starting generated torque by J‐type blades for heights of 0.8, 1.2, and 1.6 m, are improved by 15.6%, 26.9%, and 34.7%, respectively. Overall, it is concluded that by increasing the blade height, the superiority of the J‐type blade becomes more noticeable as the blade mainly contributes to suppressing the stall vortices effect where the tip vortices effect is not presented.
... Building upon the concept of cambered airfoils, research by Zamani et al. [30,31] conducted a comparative analysis of VAWT performance using different blade designs. Their studies compared turbines with DU 06-W-200 airfoils (a cambered design) to those with conventional NACA0015 airfoils (symmetrical). ...
... consistently produced positive torque across the operating range [31]. This finding suggests improved self-starting capabilities and potentially higher overall efficiency. ...
... While J-shaped airfoils have demonstrated promise in enhancing VAWT self-starting torque and overall performance, as evidenced by [30,31], it's crucial to acknowledge recent findings that suggest potential limitations under specific operating conditions. Research by [32] presents contrasting results, indicating that J-shaped blade designs might not improve performance for Darrieus-type VAWTs operating in the high TSR zone (high tip speed ratio) with solidity values ranging from 0.1 to 0.2. ...
As the demand for sustainable energy sources continues to rise, improving the efficiency of existing renewable technologies is crucial. This study investigates the aerodynamic performance of a novel J-shaped blade design for H-Darrieus VAWT with the objective of enhancing starting torque and overall efficiency. A 2D URANS CFD model was employed to simulate the airflow around the J-shaped blades. The model underwent a comprehensive verification and validation process. This rigorous approach ensured the model's fidelity, enabling a systematic comparison of the J-shaped blade's aerodynamic performance with conventional NACA0015 airfoils. The numerical analysis reveals a significant enhancement in starting torque, with a 142% increase observed at low tip speed ratios (λ = 0.2). This finding positions the J-shaped blade as a promising solution to address the challenge of initiating rotation in low-wind environments, particularly relevant for urban applications. Furthermore, the simulations demonstrate comparable torque production between the J-shaped blade and the NACA0015 airfoil under typical operating conditions. The J-shaped blade exhibits improved torque uniformity and reduced wake turbulence intensity. This study highlights the potential of the J-shaped blade design to revolutionize VAWT technology by offering advancements in increased efficiency, reduced fatigue stresses on the turbine structure, and optimized energy generation.
... But under usual operating settings, this can also result in a loss in turbine performance. Zamani et al. [6,7] examined a turbine with NACA0015-based blades and DU 06-W-200 airfoils in 2D and 3D and compared the outcomes with similar J-shaped-based turbines. Observing the spinning of 3D NACA-based blades, it was discovered that they exhibited negative torque values, a behavior that might potentially be ascribed to stall effects. ...
... This research aims to create an optimized J-shaped blade to enhance the Darrieus turbine's performance by encouraging resilient, sustainable infrastructure that is built and run to have the least negative effects on the environment that maintains the Darrieus turbine's performance while improving starting torque, utilizing a NACA0015 airfoil as a model. The earlier research on J-shapes [5][6][7] and the more recent study [10] concentrated on blades with a hollow and hair-like form; however, they did not investigate the inner shape of the construction. Thus, this study evaluates the performance of J-shaped blades with an interiorfilled construction. ...
... The setup was equivalent to that of [6,7,11,12,13,14,27,28]. The J-shaped airfoil's cavity size and placement were determined based on very similar studies carried out in [6,24,15]. ...
This research introduces a novel J-shaped aerofoil designed to enhance the performance of H-Darrieus Vertical Axis Wind Turbines (VAWTs). A comprehensive comparison is conducted between the J-shaped aerofoil and the standard NACA 0015 airfoil to assess their impact on turbine efficiency. The study employs a two-dimensional, incompressible, transient, and turbulent flow model to capture airflow around the turbine blades. Model verification and validation are carried out through systematic evaluation of various parameters, including mesh sizes, time steps, turbulent models, and discretization techniques. Computational Fluid Dynamics (CFD) simulations give useful insights into the aerodynamic features of H-Darrieus VAWT blades, indicating greater performance of the J-shaped airfoil over conventional designs. Results suggest that blades with the J-shaped aerofoil demonstrate increased overall performance and, notably, a 142% increase in beginning torque compared to the normal NACA 0015 type. This research not only contributes a new and efficient aerofoil design for vertical axis wind turbines but also offers full knowledge of its aerodynamic benefits via rigorous simulation and analysis.
... They found that the solid symmetrical airfoils have higher lift-to-drag ratio values as compared to their J-shaped airfoils. Zamani et al. 24,26 investigated the J-shape of DU-06-W-200 and NACA 0015 airfoils on the Darrieus type VAWT performance at low wind speed. The outcomes indicate that the aerodynamic performance is improved significantly at the first half revolution [0 < azimuthal angle (h) < 180 ] of the turbine. ...
... The J-shaped blade design offers good starting torque due to the incorporation of drag forces (F D ) and also compensate the deficiency of adequate lift forces (F L ) in low wind speed areas. 26 Mohamed 11 criticized the J-shaped Darrieus VAWT with NACA 0015, NACA 0021, and S1046 airfoils in terms of performance and noise generation. The author reported that the J-shaped blade profiles reduce the performance and noise of the turbine at a high k range (2-6). ...
... Furthermore, the present 2D numerical simulation outcomes are also compared with the three-dimensional (3D) numerical results of Zamani et al., 26 as shown in Fig. 21(b). This comparison is based on the same k, V, and h ranges. ...
Wind energy is one of the most eminent renewable sources for the generation of power. The increasing enthusiasm toward the advancement of small-scale Darrieus type straight-bladed vertical axis wind turbines (SB-VAWTs) can offer a potential remedy for addressing power shortage and the unpredictability of climate conditions. These particular wind turbines provide distinct advantages over their counterparts due to their linear blade design and uncomplicated structure. However, enhancements are required in their aerodynamic efficiency and self-initiation capabilities. These challenges stem from using traditional straight blade configurations and symmetrical airfoils. By substituting these conventional elements with J-shaped straight blades and along with cambered airfoils, these issues can be effectively overcome. The current study aims to investigate the effect of J-shaped straight blades with a series of cambered airfoils to improve the aerodynamic performance and starting torque of small-scale Darrieus type SB-VAWTs. Therefore, experimental and numerical studies are conducted to analyze the J-shaped airfoil impact with various opening ratios systematically. The J-shaped blade profile is designed by eliminating some portion toward the trailing edge of a conventional airfoil. This analysis demonstrated that the J-shaped blade incorporating a cambered NACA 4418 airfoil outperforms its alternative cambered airfoil designs. The performance of SB-VAWT improves by about 25% by the J-shape of the cambered NACA 4418 airfoil with a 70% opening ratio. Moreover, the use of J-shaped airfoils enhances the self-starting torque of SB-VAWT compared to conventional airfoils.
... A J-shape is obtained by removing a section of a standard NACA airfoil from the trailing edge of the blade, either on the pressure or the suction side. Such shape modification has been shown to increase the acquirable energy by improving the selfstarting and power generation capabilities of a wind turbine subject to low wind speeds, as the turbine can use both lift and drag forces [7]. The authors investigated numerically a VAWT built with J-shaped blades generated from NACA 0015 airfoils with a transient solver and the k-ω SST turbulence model [7]. ...
... Such shape modification has been shown to increase the acquirable energy by improving the selfstarting and power generation capabilities of a wind turbine subject to low wind speeds, as the turbine can use both lift and drag forces [7]. The authors investigated numerically a VAWT built with J-shaped blades generated from NACA 0015 airfoils with a transient solver and the k-ω SST turbulence model [7]. A blade chord length of 0.4 m and a rotor diameter of 2.5 m were considered. ...
... The k-ω SST turbulence model is commonly used in CFD simulations dealing with VAWTs [6][7][8]23], and the corresponding equations can be found in the Appendix A [24]. When using this model, the computational cost per simulation is usually increased due to the fine mesh needed at the walls (ideally y + < 1) when compared to the realizable kmodel with standard wall functions, where a coarser grid is considered at the walls (30 < y + < 300). ...
Small vertical axis wind turbines (VAWTs) are often considered suitable for use in urban areas due to their compact design. However, they are also well known to offer poor performance at low wind speeds, which is a common situation in such environments. An optimised 3D J-shaped VAWT was designed from standard NACA 0015 blades and analysed numerically through computational fluid dynamics (CFD). A finite element analysis (FEA) was also carried out to ensure the model’s structural integrity. Optimal results were obtained with aluminium alloy hollow blades and stainless-steel struts with X-shaped beams, with internal ribs. Numerical results showed that the J-shaped VAWT achieved an 18.34% higher moment coefficient compared to a NACA 0015-based VAWT, indicating better self-starting abilities.
... The computational mesh used in the simulations is further illustrated in Figure 10b, emphasizing its background [35]. Figure 10c displays the mesh structure of the 3D computational domain [54]. The computational mesh around the combined Darrieus and the front view of the mesh near the blades are depicted in Figure 10d [17]. ...
... It is necessary to critically evaluate the chosen cluster layout and its implications on flow interactions, including the sensitivity to turbine spacing and the impact of turbine wakes. Principal dimensions and boundary conditions of the computational domain are provided in Figure 11d [54]. It is crucial to critically evaluate their adequacy for capturing the flow physics and turbine behavior, considering the representativeness of the dimensions and the influence of domain truncation. ...
... The schematic representation of a Darrieus with a J-shaped section is depicted in Figure 14a [54], emphasizing the optimized curved profile of the turbine blades. A critical evaluation of the J-shaped section's performance gains, starting torque, power generation efficiency, and structural integrity is essential. ...
This critical review delves into the impact of Computational Fluid Dynamics (CFD) modeling techniques, specifically 2D, 2.5D, and 3D simulations, on the performance and vortex dynamics of Darrieus turbines. The central aim is to dissect the disparities apparent in numerical outcomes derived from these simulation methodologies when assessing the power coefficient (Cp) within a defined velocity ratio (l) range. The examination delves into the prevalent turbulence models shaping Cp values, and offers insightful visual aids to expound upon their influence. Furthermore, the review underscores the predominant rationale behind the adoption of 2D CFD modeling, attributed to its computationally efficient nature vis-à-vis the more intricate 2.5D or 3D approaches, particularly when gauging the turbine’s performance within the designated l realm. Moreover, the study meticulously curates a compendium of findings from an expansive collection of over 250 published articles. These findings encapsulate the evolution of pivotal parameters, including Cp, moment coefficient (Cm), lift coefficient (Cl), and drag coefficient (Cd), as well as the intricate portrayal of velocity contours, pressure distributions, vorticity patterns, turbulent kinetic energy dynamics, streamlines, and Q-criterion analyses of vorticity. An additional focal point of the review revolves around the discernment of executing 2D parametric investigations to optimize Darrieus turbine efficacy. This practice persists despite the emergence of turbulent flow structures induced by geometric modifications. Notably, the limitations inherent to the 2D methodology are vividly exemplified through compelling CFD contour representations interspersed throughout the review. Vitally, the review underscores that gauging the accuracy and validation of CFD models based solely on the comparison of Cp values against experimental data falls short. Instead, the validation of CFD models rests on time-averaged Cp values, thereby underscoring the need to account for the intricate vortex patterns in the turbine’s wake—a facet that diverges significantly between 2D and 3D simulations. In a bid to showcase the extant disparities in CFD modeling of Darrieus turbine behavior and facilitate the selection of the most judicious CFD modeling approach, the review diligently presents and appraises outcomes from diverse research endeavors published across esteemed scientific journals.
... They reported that a rotor develops a good starting ability with an inner opening ratio of 0.48 and 0.60 and an outer opening ratio of 0.72 and 0.84. Similarly, several researchers [25][26][27][28][29] have suggested that the new shapes of the blade profile having inner or outer openings improve the start-up condition and the performance of the Darrieus rotor. The above research concludes that the Darrieus rotors have faced one primary issue, i.e., the self-starting problem. ...
... Hill et al. [31] have investigated the physics of the self-starting ability of the small-scale Darrieus rotors. The starting problem of the Darrieus rotor can be resolved by using a blade profile constructed in such a way that it can use the advantages of both F L and drag force (F D ) [25][26][27][28][29]. The benefit of this blade profile is the good start-up torque as it functions due to a drag-based mechanism like Savonius rotor blades and simultaneously enhances the overall C P of the VAWT because it is lift-based like the Darrieus rotor [32]. ...
... Further, self-starting is another main issue for Darrieus-type VAWTs due to their blade shape, specifically those VAWTs employed for small-scale energy generation. Moreover, few researchers [7,25,26] have used airfoils with an opening to improve the self-starting of Darrieus-type VAWTs. For this case, they used symmetrical airfoils in the rotors; therefore, they did not find a better performance in rotors at low TSRs. ...
Darrieus type straight-bladed vertical axis wind turbines (SB-VAWTs) are more appropriate for generating electricity than other VAWTs mostly suitable for regions having low to medium wind speed. The installation of SB-VAWTs faces start-up problems, which limits its applicability in low wind speed environments. The start-up problem arises mainly due to the cross-sectional blade profile and is the crucial parameter for blade design. To overcome this issue, it is aimed to study the influence of the J-shape airfoil with various opening ratios in the Darrieus type SB-VAWTs in terms of starting torque and aerodynamic performance. The design of a J-shape airfoil is created by removing a portion towards the trailing edge of the conventional NACA 4415 airfoil on its upper or lower surface. This analysis displays a maximum power coefficient of 0.517 when the Darrieus type SB-VAWT utilizes upper cut J-shape airfoils with opening ratio of 0.8, at the tip speed ratio (TSR) of 1.6. These values are higher than the power coefficient (0.486) of conventional NACA 4415 airfoil at the same TSR. The SB-VAWT depicts a lower performance while it employs the lower cut J-shape airfoils. Furthermore, the present study demonstrates that the power and torque coefficient of SB-VAWT improves by about 31% when the opening ratio of upper cut J-shape airfoil is varied from 0.1 to 0.8.
... However, a decrease in the turbine performance also appeared in normal working conditions and the authors reported internal cut ratios between 0.48 and 0.6, and external cut ratios between 0.72 and 0.84 as favourable options for their turbine [19]. Other studies by Zamani et al. [20,21] showed an increase in turbine performance in normal working conditions, in addition to a starting torque enhancement. They conducted 2D studies of a turbine with DU 06-W-200 airfoils [20], and 3D studies of a turbine with NACA0015-based blades [21], and compared the results with the corresponding J-shaped based turbines (J-shapes created from DU 06-W-200 airfoils for the 2D case, and J-shapes created from NACA0015-based blades for the 3D case). ...
... Other studies by Zamani et al. [20,21] showed an increase in turbine performance in normal working conditions, in addition to a starting torque enhancement. They conducted 2D studies of a turbine with DU 06-W-200 airfoils [20], and 3D studies of a turbine with NACA0015-based blades [21], and compared the results with the corresponding J-shaped based turbines (J-shapes created from DU 06-W-200 airfoils for the 2D case, and J-shapes created from NACA0015-based blades for the 3D case). Negative torque values were obtained during the rotation of the 3D NACA-based blades, which were explained by stall effects [21]. ...
... They conducted 2D studies of a turbine with DU 06-W-200 airfoils [20], and 3D studies of a turbine with NACA0015-based blades [21], and compared the results with the corresponding J-shaped based turbines (J-shapes created from DU 06-W-200 airfoils for the 2D case, and J-shapes created from NACA0015-based blades for the 3D case). Negative torque values were obtained during the rotation of the 3D NACA-based blades, which were explained by stall effects [21]. However, the J-shaped airfoils produced overall greater torque with no negative values. ...
The need for an increase in energy harvesting has led to novel ideas and designs to extract more power from wind. One innovative solution is through the use of J-shaped blades for Darrieus vertical axis wind turbines (VAWTs), which is based on the removal of a portion of a conventional blade, either on the pressure or suction side. Although improvements in the self-starting capabilities of VAWTs have been reported when using such blades, the literature only studied hollow blades, showing a hair-like structure. This work numerically investigates six different J-shaped designs. A turbine comprising NACA0015-based blades forms the base case and is used to evaluate the 2D numerical models. Results show that blades with an external cut systematically outperform those designed with an internal cut. In addition, all proposed cut-based designs are shown to improve the starting torque of the turbine, reaching a 135% increase compared to the base model.
... The shed vortices mix the high-energy airflow above the boundary layer with the low-energy airflow within the boundary layer; this mixing strengthens the momentum and energy of the fluid near the wall, makes the fluid moves further along the blade surface, delays airflow separation, and increases the lift [125][126][127][128][129][130][131]. The effect of VGs is sensitive to their geometric parameters, including their profile, height and array configuration, spacing, and incidence angle [132]. There are two types of VG arrays, namely co-rotating and counter-rotating VGs, as shown in Fig. 20. ...
... Zamani et al. [132,133] proposed a J-shaped blade (Fig. 23), which was designed by eliminating a fraction of the pressure side of the common airfoil. The effectiveness of the J-shaped blade was validated by comparing VAWTs adopting J-shaped NACA 0015, NACA 0018, NACA 0030, and DU06-W-200 airfoils with VAWTs adopting corresponding smooth airfoils; the results indicated that the J-shaped blade evidently improved the self-starting capability and power efficiency of the turbines. ...
... VAWT with J-shaped airfoil blades[132]. ...
Floating vertical-axis wind turbines (VAWTs) display considerable advantages over horizontal-axis wind turbines (HAWTs) due to their Omni directionality, better structural scalability, and higher system stability. VAWTs are therefore experiencing a regained interest for use in large-scale offshore wind energy generation. However, the aerodynamic performance of lift-type VAWTs is lower than that of HAWTs. To provide more guidance for the performance improvement of VAWTs, this article reviews the existing approaches to aerodynamic performance enhancement from the perspectives of geometric parameters, flow control methods, blade shape modification, power augmentation devices, hybrid systems, and variable pitch control. Additionally, the findings of various investigations on the performance improvement of VAWTs are summarized.
... Researchers have been studying ways to improve the efficiency of vertical axis wind turbines by using different techniques to achieve this end (Elsakka et al., 2019;Marinić-Kragić, Vučina, and Milas, 2019;Zhu et al., 2019;Saad et al., 2020). It has been determined some airfoil profiles that have a higher static torque than conventional ones, in order to improve the self-start capability (thus reducing the cut in speed, which is the necessary wind speed to start rotating the wind turbine), reducing the time it passes without generating energy and thus increasing the energy generated over time (Zamani et al., 2016;Sengupta, Biswas, and Gupta, 2016;Batista et al., 2016;Zwierzchowski et al., 2017). ...
... That use of drag force to generate more static torque reduces the cut in speed, which is very important (Sengupta, Biswas and Gupta, 2016). Jshaped is a profile that is basically a combination between the two profiles previously shown: it has a "shell" that drives the turbine using the drag force (like Lenz2), and also has an aerodynamic shape that generates lift forces such as S815 (Zamani et al., 2016), as shown in Figure 5. This format basically consists of a profile NACA 0015 with its upper portion removed, thus making the turbine have a better self-start capability, and still having good aerodynamics compared to the original profile NACA 0015. ...
Wind Energy, Convergent omnidirectional nozzle guide, Vertical Axis Wind Turbine, Energy Efficiency Wind energy, considered a stable alternative, can be implemented in cities by means of vertical axis wind turbines, which have better performance against turbulent flow compared to horizontal axis turbines. However, this type of turbine has not evolved technologically significantly in the last few centuries, being the horizontal axis turbines more studied and developed, due to the theoretical better efficiency of these turbines, which creates room for improvement. Therefore, vertical axis wind turbine will be studied and the performance of some enhancements will be analyzed aiming a more efficient harvesting of wind energy. In this regard, a flow augmentation system is proposed to be integrated with the wind turbine. In addition, the Lenz 2, S815 and JShaped airfoil shapes will be analyzed by Computational Fluid Dynamics – CFD technique on the ANSYS software for comparison of static torque generated by the wind turbine against wind flow for different angular positions of the turbine. Analyzing the gains obtained with the integration of the flow augmentation system proposed, achieving, this way, results regarding to cut in speed and overall efficiency of the shapes. Results show that the use of the convergent omnidirectional nozzle guide increased the overall static torque of all turbines, which would decrease the cut in speed, as well as its increased effectiveness on drag driven airfoils.
... Placing a cylindrical structure at the airfoil's leading edge can delay dynamic stall and improve the lift-to-drag ratio by about 30.7% [35]. A comparison of the power coefficient between a vertical-axis wind turbine (VAWT) featuring novel J-shaped blades and a traditional wind turbine with standard symmetrical airfoils was conducted using 3D Computational Fluid Dynamics (CFD) simulations [36]. Earlier studies have concentrated on investigating the effect of the tower's shadow on the efficiency of large wind turbines [37][38][39]. ...
An experimental investigation was carried out to understand the effects of LEP (leading-edge protuberance) blades on the structural characteristics of VAWTs. A series of experiments were performed on VAWTs with straight and LEP blades for a wide range of wind velocity (6 m/s to 20 m/s) and pitch angles (−20° to 20°), and the structural excitations on the VAWT structure were measured using a triaxial accelerometer in each case. The raw acceleration data were extensively processed in the time and frequency domains to identify the variation in structural excitation caused by the unsteady wind and aerodynamic loads on the VAWT structure. Understanding the aerodynamic changes and their impact on structural characteristics is essential. The current study examines how LEP influences the structural excitation of VAWTs. However, a great deal of aerodynamic variation was observed for the LEP blades, so the straight blades of the VAWT were replaced with various modified LEP blades, for which a similar set of experiments was carried out. The study presents a better performance (self-starting, stall-mitigating) for VAWTs with LEP 3 and 2 blades, with a significant reduction in the excitation of loads due to wind load and the changes in aerodynamics observed in the along- and across-wind directions.
... Among both profile blades, V-shape profile blade enhances the power coefficient of 20% compared to straight profile blade. Zamani et al. [9] developed a new airfoil design called J-shape profile by eliminating some of the maximum thickness from the pressure side using NACA 0015 profile. It is found out from this study that the maximum power coefficient obtained with this new design is 0.6146 whereas the conventional blade profile is 0.5835 at azimuthal angle 100°. ...
The demand of renewable energy is increasing rapidly as it is cheaper, eco-friendly and sustainable compared to non-renewable energy sources. Wind energy is one of the renewable energy sources where wind turbines are used to harness the available kinetic energy from the wind stream. Wind turbines are classified as horizontal axis wind turbines (HAWTs) and vertical axis wind turbines (VAWTs). As VAWTs are less efficient to generate power compared to HAWTs, so there is a scope for researchers to improve the efficiency of such turbines. Different methods are used for the performance enhancement of H-Darrieus vertical axis rotors such as blade shape modification, surface modifications, leading edge modification, etc. In this study, NACA 6409 blade profile has been chosen and elliptical- and square-shaped dimples are imposed on pressure side of the profile to study the effect on the aerodynamic characteristics namely lift coefficient (CL), drag coefficient (CD) and CL/CD. It is found that elliptical-shaped dimple has improved the CL/CD values of airfoil blade compared to square-shaped dimple. Addition of two dimples on the pressure side like one at 25% and another at 50% of chord, led to the improved CL/CD value to 5.94 from 4 (clean blade).
... A significant drawback of U-type Darrieus and V-shaped VAWTs is their complex design and manufacturing processes, which make them expensive. While the J-shaped Darrieus VAWT showed better performance than the V-shaped Darrieus VAWTs during self-starting conditions and at low TSRs, the total torque decreased at TSRs above 2.25 due to the lower lift coefficient (C L ) of the J-shaped blades [57]. In another effort to enhance the efficiency of VAWTs, the Gurney flap (GF) significantly improved the aerodynamic performance of VAWTs at reduced rotational velocities. ...
Wind energy, being renewable, cost-effective, and environmentally friendly, has attracted global attention. However, due to suboptimal performance and limited research, vertical axis wind turbines (VAWTs) lag behind horizontal axis wind turbines (HAWTs) in commercial applications, particularly for large-scale installations. This study aims to improve the self-starting capability of the Darrieus VAWT. While some parameters, such as the number of blades (N) and solidity (σ), have been studied extensively, the airfoil shape has not received as much attention. This study compares the performance of National Advisory Committee for Aeronautics (NACA) airfoils and Selig airfoils at a Reynolds number (Re) of 40,673. The investigation revealed that the NACA0015 airfoil exhibited the highest peak power coefficient (Cp). Further analysis utilizing an advanced double multiple stream tube (DMST) code in MATLAB increased the peak Cp by adjusting the thickness-to-camber ratio (t/c) of the NACA0015 airfoil, resulting in a 12.50 % increase in the maximum achievable Cp at a Re of 40,673. This study compared four modes of VAWT operation, utilizing the NACA0015 airfoil and a modified NACA0015 airfoil for both straight-bladed and embossed-bladed VAWTs. The results showed that the modified NACA0015 airfoil for embossed-bladed VAWTs exhibited the best self-starting capability and rotation at wind velocities of 1 to 9 m s-1. Additionally, the self-starting force required by embossed-bladed VAWTs was lower than that needed by straight-bladed VAWTs due to the ability of the embossed material to enhance airflow attachment to the VAWT and suppress turbulence.
... The blade profile significantly affects the aerodynamic performance of the wind turbines. A J-shaped blade was proposed by , where the authors removed a fraction of the pressure side of the conventional airfoils and observed that the proposed configuration had better power output compared to the conventional airfoils [26]. Tip vortices at the tip of the blade negatively affect the turbine's aerodynamic performance and, hence, need to be minimized. ...
Developing countries like Bangladesh is facing immense challenges to cope up with the increasing energy demand due to the rapid population growth. While every country is looking forward to exploring all the renewable sources available, wind energy is one of the least explored sectors in the countries having low average wind speeds. This study provides a systematic review of the promising wind turbine modification methods to achieve satisfactory power output. It is found that, in the recent times, blade shape modification, active and passive flow control and incorporation of power augmentation devices are the topics of interest to the researchers due to their reliability in enhancing the power coefficients of the wind turbines. It is observed that approximately 16.30% and 23.26% improvement in the power coefficients are possible due to the incorporation of dimples on the airfoil and gurney flap, respectively. Moreover, diffuser-type power augmentation devices result in a maximum 216% improvement in the power coefficient compared to the conventional turbines. It is expected that augmentation of more than one approach (shape modification, active and passive flow control and incorporation of power augmentation devices) can result in even better aerodynamic performance compared to each of them alone.
... While these configurations demonstrated good efficiency at low tip speed ratios (TSR), they fell short in achieving higher efficiency at high TSR, making them less effective than the conventional designs as Hosseini and Goudarzi (2019) stated. However, the research of Zamani et al. (2016) stated that the introduction of the J-type airfoil design for the Darrieus rotor, which combines the drag type characteristics of the Savonius rotor with the lift type characteristics of the Darrieus rotor, has shown promising results. This research indicated that the J-type airfoil enhanced the self-starting capability and achieved better peak efficiency compared to conventional Darrieus rotors due to its balanced utilization of the lift and drag forces. ...
This study aims to improve the performance of the vertical axis wind turbine using a J-type airfoil shape. In this study we used an optimal airfoil shape called Opt-VF that was obtained in previous research using an optimization method of the Kriging surrogate model approach. We aimed to improve the performance of the optimal airfoil utilizing the J-type airfoil shape, by the realization of good balance to utilize lift and drag forces. 2D computational fluid dynamics (CFD) simulations and experimental performance measurements were performed to confirm the efficiency of the J-type airfoil designs. We designed/evaluated various types of the Jtype airfoils to find the most efficient condition for the optimal airfoil. We also performed flow visualizations to observe the difference between the original and J-type airfoils in detail. Some J-type airfoils achieved better performance than the original optimal airfoil, by generating higher pressure in the inner side of the J-type airfoil and obtaining higher velocity wind flow around the leading edge at certain rotational angles. Finally, experimental evaluations were conducted to compare with the CFD results. Same trends could be confirmed between the CFD and experimental results. In the experimental evaluations, maximum values of power coefficient were increased about 7% and 4% at the cases of two-blades and three-blades, respectively, compared to the original Opt-VF airfoil. These results demonstrated the effectiveness introducing the J-type airfoil shape in the optimal airfoil.
... The results show that the modification improves the selfstarting and the nominal power by 3% compared to the conventional profile Du 06-W-200. This technique was applied to another prototype profiled by NACA0015, which improved the power curve and 6% of the nominal power (Zamani et al., 2016b). By modifying the mean camber line of a NACA0018 SD-VAWT blade profile, Ma et al. (2018) improved the power of SD-VAWT by 26.82% compared to the baseline prototype. ...
The blade profile selection is paramount for the efficient operation of straight Darrieus wind turbines in terms of torque and power generation. In this work, we have used the Kline-Fogleman Airfoil (KFA) design for the wind turbine blades. The concept of KFA design aims to cause flow separation, vortex formation, and reattachment establishment before the trailing edge. Thus, geometric tests on have been performed on the baseline airfoil NACA0015 as one of the best profiles for operating a straight Darrius wind turbine. A two-dimensional Computational Fluid Dynamic (CFD) model using the two-equation Shear Stress Transport k-ω (SST k-ω) turbulent model was developed in ANSYS/FLUENT software to assess the aerodynamic efficiency of the modified airfoil. Two designs (KFA-2 and KFA-4) were tested initially in the static case. The effects of the opening step angle and its curvature diameter were studied for an angle of attack’s range of -20° to +20°. The rounded KFA-4 design with an opening step angle of 93.6° led to a significant improvement in the lift-to-drag ratio thus, aerodynamic efficiency. Finally, the straight KFA-4 design with the opening step angle of 93.6° revealed a the most advantageous effects on the operation of a straight Darrieus wind turbine for a Tip Speed Ratio less than 1.6 (TSR<1.6). It allowed a noticeable reduction of the dead zone and TSR corresponding to the nominal power, thus consequently improving the starting torque and delaying torque stall.
... Many studies have focused on increasing the VAWT's performance. [17][18][19][20][21][22]. These upgrades may primarily be divided into three groups: optimizing [23][24][25], adding a device [26][27][28], and utilizing aerodynamic interaction [29][30][31][32][33]. Experimental investigations have looked at performance factors in other research [12][13][14][15][16]. Their experimentation with several blade types suggests creating a hybrid turbine. ...
The need to increase the energy efficiency and energy harvesting of vertical axis wind turbines is growing as a consequence of the quick expansion in the energy sector. Therefore, it is crucial to comprehend how a turbine operates. In this study, the more often used VAWT—vertical axis wind turbine—has been experimentally evaluated. Various performance graphs have been produced as a result. At various wind speeds, S1014 and S1020 airfoils are employed. Aspect ratio and angle of attack were noted, and the performance of the turbine was investigated in relation to the impact of the current produced by the turbulence generating plate. The subsonic wind tunnel setup utilized during the testing consisted of a 15 W DC motor and a 0.1 Nm torque meter. The findings demonstrated that the S1014 type blade profile was more efficient and boosted performance of the two types.
... J-shaped straight Darrieus (Figure 8 I) (Zamani et al., 2016) • Improves the self-starting ability. • Less turbulency and noise. ...
The need for energy and electricity has been increasing globally, and this means more power is required from the power plants. Power plants, however, will then continue harming the earth because of the greenhouse gasses produced while generating energies that contribute to global warming. Using renewable sources to produce clean energies is one of the sustainable methods to deal with such challenges. Wind energy is one of the renewable sources, which is accessible anywhere on earth, creating green energy. Wind turbines are mainly categorized into Horizontal Axis Wind Turbines (HAWT) and Vertical Axis Wind Turbines (VAWT). This paper firstly presents a general comparison between the HAWTs and VAWTs. Then, it presents mathematical modelling for the aerodynamic factors of HAWT and Darrieus VAWT to assist the researchers to understand some key design aspects of wind turbines, such as lift/drag ratio, tip speed ratio, power coefficient, and torque coefficient. Also, this paper presents a review of the aerodynamic performance of the recent VAWT designs to help researchers to identify and choose the best model among the Savonius and Darrieus rotors for further development or designing a new model at different wind conditions. This comparison review shows that for a large scale HAWT upwind 3 bladed wind turbines are the most optimum. The helical Savonius rotors perform better by having positive torque coefficient at all azimuth angles. Moreover, helical Darrieus was found to produce lesser noise and suitable for conventional areas. hybrid Savonius-Darrieus rotors can solve the self-starting challenge of the VAWTs, and they are suitable at low wind speeds. At last, this review shows some of the recent hybrid Savonius-Darrieus rotors which would help to solve the low efficiency of Savonius rotor and self-starting challenge of Darrieus rotors.
... • A Maximum 14.56 % increase in C p was observed with a low solidity turbine having three deformable blades [143]. Feasibility and Effectiveness: Stall angle delayed, aerodynamic performance increase with rise of camber for a large range of AOAs J-shaped airfoil [144][145][146] Straight Bladed VAWT DU06-W200, NACA 0008, NACA 0015, NACA 0024 Re = 5 × 10 5 , 1.6 × 10 5 ...
The decline of fossil fuel reserves and stringent environmental regulations demands an extensive use of renewable energy sources. Wind turbine power generation is rapidly increasing, and researchers oversee new challenges and solutions every day. This paper critically reviews the flow control techniques and strategies for improving the wind turbine efficiency. The development of controlling and mitigation strategies for dynamic stall requires an understanding of flow mechanisms such as wake formation, downstream vortex, flow separation , and vortex shedding. The aforesaid phenomena significantly lead to the formation of dynamic stall (Tip speed ratio < 4). This review paper extensively discusses the mechanism of dynamic stall formation and its effects on the performance of vertical axis wind turbines along with the recent developments in mitigation techniques (enhances power coefficient by 50-60 %). It highlights the main aspects involved in performance and stability enhancement of vertical axis wind turbines such as objective functions, design constraints, airfoil dynamics , models, flow control, and optimization techniques. The results of various mitigation approaches are critically analysed, and the most effective techniques are identified. Hence, this review article provides a complete information on the constraints and solution strategies involved in vertical axis wind turbine and opens new possibilities for further research for enhancing the aerodynamic performance. Introduction The wind turbine is a leading technology for extracting energy from wind. It has been extensively studied with the dwindling fossil fuel reserves and the growing awareness on building environmental friendly energy supplies. The sustainability metric assessment on the lowest relative emissions of greenhouse gases, lower use of water, and the most favourable social impacts showed the dominance of wind power on hydropower, photovoltaic and geothermal energy [1]. With an addition of 77.6 GW in the year 2022, the projected global wind power capacity is 906 GW, as shown in Fig. 1 [2]. The Indian government recently set a target of 450 GW of overall renewable energy by 2030, with wind energy and solar photovoltaic estimated to account for 36 % of total installed capacity [3]. The future of wind power is mainly dependent on the development of vertical axis wind turbines (VAWTs) because of their applicability in low wind regions, especially urban areas [4-9]. The VAWTs can be classified into two main categories, i.e., drag and lift-based [10,11]. The Savonius rotor is driven by the aerodynamic drag force acting in the direction of the wind, whereas lift-based turbines (Darrieus and H-type) experience the force acting in the perpendicular direction of wind flow. Savonius rotors work at lower wind speeds than Darrieus rotors, resulting in better self-start capabilities. In contrast, the performance of Savonius rotors in terms of power coefficient is lower than that of the other VAWTs due to the limitation of a lower tip speed ratio [12-18]. VAWTs possess omnidirectional behaviour, higher scalability, and better performance in chaotic, unstable, and turbulent flow conditions [16,19-22]. VAWTs also exhibit a higher degree of sustainability than horizontal axis wind turbines (HAWTs) because of its simplified design layout and low maintenance with no yaw or pitch mechanics, lower noise pollution, better safety, lower operational tip ratio, lower centre of mass, and the generator not being limited to the top of the tower [14,23-30]. Over the last decade, on-site implications of the VAWTs have been observed to gain more attention with the increase in its self-starting abilities [14,31-36]. The VAWT is also proven to be a more feasible technology because of its lower installation, operation, and maintenance costs. In general, VAWTs (>10 MW), which are larger in size, provide a lower cost of energy (COE) when compared to HAWTs [16]. There are also certain challenges associated with VAWTs, such as the formation of a wake on the VAWTs blade, which is one of the most
... Masoumeh Gharaati et al. [15] found through numerical simulation that if the torsion direction of the spiral blade changes, the influence of the spiral blade on the wake characteristics will be reversed. Zamani et al. [16,17] designed a J-shaped blade that can benefit from both lift and drag, and numerical simulation analysis showed that the self-starting performance of the J-shaped blade is better. Wang et al. [18] also designed a new Darrieus vertical-axis wind turbine, and the results show that the new adaptive blade can significantly suppress flow separation on the blade surface. ...
In this paper, based on the lift-type wind turbine, an adaptive double-drive lift–drag composite vertical-axis wind turbine is designed to improve the wind energy utilization rate. A drag blade was employed to rapidly accelerate the wind turbine, and the width of the blade was adaptively adjusted with the speed of the wind turbine to realize lift–drag conversion. The aerodynamic performance analysis using Fluent showed that the best performance is achieved with a blade curvature of 30° and a drag-type blade width ratio of 2/3. Physical experiments proved that a lift–drag composite vertical-axis wind turbine driven by dual blades can start when the incoming wind speed is 1.6 m/s, which is 23.8% lower than the existing lift-type wind turbine’s starting wind speed of 2.1 m/s. At the same time, when the wind speed reaches 8.8 m/s, the guide rail adaptive drag-type blades all contract and transform into lift-type wind turbine blades. The results show that the comprehensive wind energy utilization rate of the adaptive dual-drive lift–drag composite vertical-axis wind turbine was 5.98% higher than that of ordinary lift-type wind turbines and can be applied to wind power generation in high-wind-speed wind farms.
... There is every prospect for the occurrence of dynamic stall. It is generally known that the dynamic stall will delay the stall angle of operating airfoil through which it can gain higher lift coefficients owing to the extended range of its operational points before the new postponed stall [49]. No stall is occurring; the blade wake becomes very thick and the boundary layer is detached on the suction side when the angle of attack becomes large [9]. ...
The comparative assessment carried out in this paper aims to investigate the results driven from our 2D and 3D CFD modeling of H-Darrieus, based on the URANS approach. It describes the aerodynamic operation of H-Darrieus that has been used for several numerical investigations since 2010. The k-ω SST has been used to reproduce the flow structures developing in the wake. The maximal 2D and 3D power coefficients that have been achieved are Cp=0.4016 and Cp=0.5734, respectively for λ=3.0976. The maximal 2D and 3D absolute error, which is corresponding to the power coefficient assessment were equal respectively to 14.9714% and 29.1582%. They were calculated at λ=2.5183 and λ=3.0976. Our parametric study showed that the increase range of the power coefficient, while taking into account the 3D aerodynamic effects becomes larger than that obtained by 2D calculations. This range is defined in 3D modeling between λ=1.85 and λ=3.10, while it is defined in 2D modeling by the interval having the bounds λ=2.05 and λ=3.10. The necessary contours to conduct our confrontation between the 2D and 3D approach and to describe the flow structures developing around H-Darrieus were constructed and discussed.
Graphical abstract
... Weakened tip vortices cause performance improvement due to the presence of a winglet. Wang and Zhuang (2017) Fig. 15j) is studied by Zamani, Nazari, et al. (2016b). The numerical study exhibits that a C P max value of 0.3358 was observed at a TSR of 1.6. ...
The global demand for small and medium-scale wind energy production necessitates the development of vertical axis wind turbines for centralized and decentralized energy applications. The best performances of the Darrieus vertical axis wind turbines under specific locations and environmental conditions are obtained using performance improvements. However, several shortcomings and operational challenges restrict their on-ground implementations and scalability. One of the challenges in developing new turbine configurations with greater efficiency is the lack of benchmarking strategy for turbine configurations from past researchers. The present work utilizes a hybrid approach for the benchmark studies, consisting of qualitative and quantitative analysis of past research in the Darrieus vertical axis wind turbines. The relevant turbine configuration parameters and features are benchmarked by examining performance attributes and augmentation techniques. Bibliometric and Scientometric analysis of past research is employed to ensure the relevancy of data. A predefined sorting level is used to evaluate the qualitative and quantitative data. The qualitative analysis is performed by capturing relevant information from the literature. In contrast, the quantitative analysis uses data envelopment analysis to identify potential configurations through models such as input-oriented Charnes Cooper Rhodes, input-oriented Banker Charnes Cooper, and output-oriented Banker Charnes Cooper models. The present study reveals that input-oriented Charnes Cooper Rhodes and input-oriented Banker Charnes Cooper models are more suitable for benchmark studies. A detailed qualitative and quantitative analysis is performed, discussed, and used for benchmarking. Finally, this study concludes with highlights from the developed benchmarks.
Graphical abstract
... As an example of the modification of the airfoil, the J-shaped profile, which is designed by eliminating a portion of either the pressure or suction side, has been utilised to assist the turbine start-up ability by increasing the torque generation at the low tip speed ratios. However, there are just a few studies existing in the literature that examine how the J-shaped airfoil affects the overall performance of the turbine, including the self-starting capability (Celik, 2021;Celik et al., 2022;Mohamed, 2019;Sun et al., 2020;Zamani et al., 2016aZamani et al., , 2016b. ...
The present study proposes a novel hybrid blade design that is the combination of a conventional airfoil, namely the NACA0018, and its J-shaped profile to increase the torque generation at the start-up stage of the turbine while decreasing the potential efficiency loss at the high tip speed ratios. Therefore, a new 2D-based design methodology was proposed, and depending on this methodology, different hybrid blade configurations were determined for the investigation of the overall and self-starting performance of the H-type Darrieus vertical axis wind turbine. Due to the inherent shape of the proposed hybrid blade, a 3D CFD dynamic start-up model, which is based on the fluid-turbine interaction, was built and used to evaluate the performance of the different configurations of the hybrid blades. The results indicate that although the proposed design methodology is based on the 2D-CFD calculations, it enables a quicker prediction of the aerodynamic performance of the proposed hybrid blades compared to the 3D-based CFD simulations. Furthermore, the findings also clearly illustrate that the new proposed hybrid blade designs not only overcome the self-starting issue of the turbine but also provide a wider turbine operating range and an improvement in the turbine peak efficiency in contrast to the losses caused by J-shaped airfoils.
... Further, hybrid rotor having Savonius rotor inside H-Darrieus rotor has high power coefficient than the hybrid rotor with Savonius rotor below the H-Darrieus rotor [20]. The starting performance of Darrieus turbine was improved by modifying the airfoils to J-shaped profile [21]. Similarly, Chen et al. [22] investigated the parameters of turbine having modification in the profile of Darrieus rotor. ...
... The occurrence of dynamic stall is highly probable. As reported in Zamani et al. [46], it is well-known that dynamic stall can delay the stall angle of the operating airfoil, allowing it to achieve higher lift coefficients by extending the operational range of its points before experiencing a new postponed stall. However, when the angle of attack becomes large, the blade wake becomes very thick and the boundary layer is detached on the suction side, without experiencing any stall [4]. ...
In the present study, a comparative assessment is conducted to evaluate the outcomes derived from two-dimensional (2D) and three-dimensional (3D) computational fluid dynamics (CFD) models utilizing the unsteady Reynolds-averaged Navier–Stokes (URANS) approach. The focus lies on the aerodynamic performance of the H-Darrieus vertical axis wind turbine, which has been the subject of numerous numerical investigations since 2010. The k−ω shear stress transport (SST) turbulence model is employed to replicate the flow structures evolving in the turbine wake.The maximum power coefficients attained through 2D and 3D modeling are reported as Cp=0.4016 and Cp=0.5734, respectively, at a tip speed ratio (λ) of 3.0976. The maximum 2D and 3D absolute errors, corresponding to the evaluation of the power coefficients, are determined to be 14.9714% and 29.1582%, respectively. These errors are calculated at λ=2.5183 and λ=3.0976. The parametric study conducted herein reveals that the range of the power coefficient enhancement, considering 3D aerodynamic effects, surpasses that obtained from 2D calculations. In 3D modeling, this range is delineated between λ=1.85 and λ=3.10, whereas, in 2D modeling, it is defined by the interval bounded by λ=2.05 and λ=3.10. The essential contours for comparing the 2D and 3D approaches and for characterizing the flow structures developing around the H-Darrieus turbine are generated and analyzed.
... The vertical axis wind turbine (VAWT) is another wind turbine with two small and large scales [9]. Small-scale VAWTs perform better than HAWTs in urban areas, where the wind environment is complex, due to their ability to work in varied wind directions, adaptability to turbulent flows [14], and reduced noise levels [15], [16], [17]. For offshore applications, VAWTs are more promising than HAWTs due to their lower center of gravity, ease of manufacturing, reduced installation and maintenance costs, and greater scalability to larger sizes [18], [19]. ...
This study proposes an application of vertical-axis wind turbines to power telecom towers in off-grid areas. Telecom services play a critical role in a country, and the majority of the people use its service in daily life. Moreover, this network is growing. Despite this development, it is essential to decarbonize the telecom power supply. Literature suggests replacing telecom towers' traditional fossil fuel energy with sustainable energy such as solar and wind resources. According to countries' investment and interest, wind energy currently has the fastest energy resource development. Since there are many off-grid telecom towers, using the wind turbine is an excellent choice. However, it must be considered which type and wind turbine(s) installation is appropriate, economical, and low-maintenance costs. Small-scale vertical-axis wind turbines are one of the best options among available resources; with this suggestion, they can be installed on the telecom tower, which has extensive economic and technical advantages. Furthermore, the hybrid power supply of vertical-axis wind turbines and fuel cells makes the telecom tower supply fully green and clean.
... The modified rotor uses lift and drag forces for operation and yields improved starting torque and conversion efficiency compared to the conventional Darrieus rotor. The J-shaped rotor has also been reported to have lower fatigue stress, further assisting in trapping vortices by a special cup-shaped blade, leading to less turbulence and vibrations (Zamani et al., 2016b). ...
Darrieus rotor is a promising technology for hydrokinetic and wind energy harvesting applications. However, the Darrieus rotor suffers from the problem of poor starting performance. The present research highlights solutions to improve the poor starting performance of the Darrieus rotor by introducing the hybrid rotor. Further, a comparative performance evaluation of conventional vertical axis Darrieus and hybrid rotors has been investigated numerically. The most widely used S-series S-1046 hydrofoil has been utilized by hybrid and Darrieus rotors. Further, two semicircular blades are used for the Savonius part of the hybrid rotor. The size of the Savonius part is optimized to obtain maximum performance from the hybrid rotor. Analyzing the flow field distributions across the turbine vicinity has highlighted various possible reasons. The study results have demonstrated that the hybrid rotor yields an exceptional increment of about 159.41% in the torque coefficient under low tip speed ratio (TSR) regimes (during initial starting) compared to the Darrieus rotor. However, due to the Savonius rotor's presence, the hybrid rotor's maximum power coefficient is reduced slightly compared to the maximum operating point of the Darrieus rotor. Further, the hybrid rotor yields a wider operating range than the single maximum operating point by the Darrieus rotor. The present investigations will assist the designers in selecting the site-specific hydrokinetic technology suitable for efficient and optimum use of hydrokinetic potential.
... In recent years, VAWTs have gained more attention, especially for urban and offshore applications, where they are considered more suitable than HAWTs [2]. Small-scale VAWTs perform better in urban areas due to their ability to adapt to turbulent flows, work in varied wind directions [3], and produce reduced noise levels [2] [4] [5] [6]. The scope of VAWT applications has extensive perspective, and there is a gap in the wake loss model for this type of turbine. ...
The purpose of this research is to develop a theoretical method for predicting the wake region downstream of the flow from a top view of a vertical axis wind turbine (VAWT) and to examine the wake loss effects of the VAWT. Previous literature has reported that the wake region of the VAWT is not symmetric, and it's downstream is similar to a circular cylinder wake street. The airflow of the VAWT is turbulent, and the inviscid incompressible flow can be applied to its range. Therefore, the current study analyzed the flow over a cylinder with circulation to investigate the velocity, pressure coefficient, and tip speed ratio and to observe the similarity between the cylinder and the VAWT. The results of this study demonstrate remarkable similarity, particularly with respect to the asymmetry of the wake region due to the distinct velocity speed in two opposite locations of the VAWT. Moreover, the pressure coefficient functionality and curvature are similar to the available measurements of the VAWT. This model can be further developed and examined under varied conditions to provide a theoretical wake loss model for VAWTs. This will lead to the expansion of VAWTs' applications in green, sustainable, and clean energy production.
... In terms of improving the characteristics of wind turbines, various design modifications and optimizations as well as innovative design ideas have been investigated. The influence of blade shape parameters on self-starting and energy extraction efficiency has attracted scientists' attention [17][18][19][20]. However, others have focused on improving the performance by using composite blades [21,22]. ...
Aims: Researchers are more and more focused on finding ways to optimize renewable energy sources. One of the more promising of these renewable energies is wind energy. However, these wind resources are very localized and selective. There is also significant potential for wind resources available at low densities or low wind speeds. The objective of this research is to exploit these resources. Methodology: To do so, this study proposes a new wind generating device coupled with a flow convergent in order to increase its performance at low wind speed. This new wind device is designed under Solidworks and analyzed with Matlab software. Several parameters are simulated. The effect of the pulley transmission ratio on the mechanical values of the generator, the impact of 33 the operating gas in terms of angular velocity, power and torque on the generator shaft was clearly determined. Results: It appears that the power at the input of the wind device is multiplied by the square of the ratio of the output and input velocities, the flow passing through the convergent being constant. The torque on the generator decreases with the increase of the transmission ratio while its speed increases. However, for a fixed transmission ratio, the speed remains constant while the torque and power increase with the speed at the inlet of the convergent. On the other hand, it is noted that, the lower the adiabatic coefficient of the gas used, the higher the power generated. Conclusion: When used with a wind device, the output parameters of the convergent will result in better mechanical efficiency, which greatly improves electrical power generation.
... Another study on the straight blade VAWT gurney flap's performance noticed that the maximum power output of 21.32% and it is also found that the gurney flap increased the blade tangential force in the upstream area . Three dimensional CFD simulations on J shaped blade made of NACA0015 profile for different TSR is done and it was observed that at TSR of 1.6, the considered turbine showed best power coefficient value of 0.3358 (Zamani, 2016). ...
Utilization of Carbon Dioxide for Preparation of Polyurethanes without Using the Toxic Isocyanates
... The cut or opening ratio is defined as the ratio between the cut length starting from the trailing edge to the chord length. Zamani et al. [33] investigated the performance of the NACA0015 J-shaped Darrieus vertical axis wind turbine using 3D numerical simulations. They found that the J-shaped blade's profile outperforms conventional blades and enhances the starting torque with lower fatigue stress on the shaft and the bearings. ...
In this work, the effect of the inner opening ratio on the J-shaped airfoils aerodynamic performance was studied and documented for symmetrical airfoils. Three different airfoil thicknesses were investigated: small (NACA0008), medium (NACA0015), and large (NACA0024). For each airfoil thickness, effects of three inner opening ratios were analyzed: one-third, one-half, and two-thirds. The performance of each opening ratio was compared with the performance of the solid airfoil “zero opening ratio” for different angles of attack between 5 deg and 20 deg. All designs were simulated using the computational fluid dynamics (CFD) technology against experimental results for solid NACA4412 airfoil in the University of Wisconsin-Milwaukee (UWM) and other published experimental data. It was found that large eddy simulation yields accurate solutions with a smaller number of mesh cells compared to the k–ω turbulence model but with much longer computational time. The lift-to-drag ratio for all studied airfoils has a maximum value for solid airfoils compared to those equipped with openings. For airfoils equipped with 00.00% opening ratio “solid,” NACA0015 airfoil has the maximum lift-to-drag ratio. Furthermore, it was found that NACA0008 equipped with a 33.33% opening ratio has the best performance of all studied J-shaped airfoils.
... In fact, numerical simulation of complex configurations using a single-solver architecture code [27][28][29] is not a 22 very elegant solution, but rather a compromise, since it is only a simple extension of its ability to handle single-body 23 configurations. As the code has only one input/output interface, the user has to package the mesh blocks and runtime 24 control parameters of all components into a single grid file and a single input file respectively for the program to read 25 [30, 31]. ...
This paper presents a novel computational fluid dynamics (CFD) framework for flow simulation of complex configurations containing relatively moving components. The framework is based on the dynamic overset grid method and is intrinsically parallel. The user only needs to decompose complex configurations into topologically simple components according to the geometric features and generate high-quality computational meshes around these components. The framework can then automatically instantiate multiple fully functional CFD solvers to solve the flow fields on the meshes of all components simultaneously in a one-to-one correspondence. Thus, the geometric relationships of the components are transformed into concurrent states of the instance solvers, and accordingly, their flow fields are coupled through the intercommunication among instance solvers. The framework is implemented in a parallel environment based on the Message Passing Interface (MPI). An instantiation space is formed by splitting the world communicator into desired number of fully functional sub-communicators. Within this space, the same number of independent solvers with complete input and output interfaces can be instantiated from the same template solver. The data coupling between instance solvers is realised using the dynamic overset grid method, and the whole process is achieved automation by approaches of collision detection, Exact Inverse Maps (EIM) -based donor cell search, and robust Implicit Hole Cutting (IHC). Numerical results show that the framework is effective for configurations with complex topologies, and it is particularly suitable for numerical simulations of array configurations with relatively moving components.
... It was established that thicker airfoils perform better at low tip-speed ratios (TSRs) due to a longer duration of attached flow and a high solidity turbine performs better at lower TSRs. Zamani et al. (2016) employed 3D CFD simulations to examine the influence of J-shaped blades on VAWT performance at low and moderate TSRs. It was found this unique blade shape improved the turbine self-starting and aerodynamic efficiency characteristics. ...
The vertical axis wind turbine (VAWT) configuration has many advantages for an offshore wind turbine Installation. In this paper, the three dimensional (3D) computational fluid dynamics analysis of a large-scale 5 MW VAWT is conducted. At the optimum tip-speed ratio (TSR), the VAWT maximum inline force was 75% larger than the maximum lateral force. It was found the dynamic stall effects cause the VAWT flow field to become increasingly asymmetrical at the mid-span plane, when the TSR is reduced. The attachment of end plates to the blade tips, resulted in a performance improvement during the upwind phase with the average blade torque coefficient in this range being increased by 4.71%. Conversely, during the blade downwind phase a reduction in performance was found due to the increase in drag from the end plates and the average blade torque coefficient in this phase was reduced by 23.1%.
... Hydrokinetic energy is one important type of clean renewable energy, which does not generate toxic pollution or greenhouse gases in the process of electricity production. Much research has demonstrated that turbine technologies are highly related to the cost and performance of energy production in both offshore and onshore areas [1,2]. In this study, we focus on analyzing the performance of vertical axis water turbines [3,4], which are suitable for hydrokinetic energy harvesting in regions such as rivers, estuaries, and canals. ...
We conduct performance analyses of a family of vertical axis water turbines (VAWTs) under single-phase water and two-phase open channel flow conditions using unsteady Reynolds-averaged Navier-Stokes (URANS) numerical simulations. The performance, including self-starting capability and energy harvesting efficiency, of a recently developed hybrid Darrieus-Modified-Savonius (HDMS) design is examined under single-phase water flow conditions. With a two-way coupled fluid-structure interaction (FSI) approach, we demonstrate that the water turbine has excellent self-starting capability. After that, the effects of the Reynolds number, tip speed ratio (TSR), and geometric design of the turbine, including turbine size, solidity, and number of blades, are systematically studied. Since the main function of the modified Savonius rotor is to assist self-start, and this part has a negligible effect on energy harvesting performance when the turbine is under stable operation, only the Darrieus rotor is studied under two-phase open channel flow conditions to save computational cost. A key finding is that larger blockage ratios result in better energy harvesting performance of the water turbines. When the blockage ratio is 60% and the TSR of the turbine is 5.0, the power coefficient of the water turbine can reach up to 73%, which exceeds Betz's limit.
... It has been proven that the cylindrical shaft decreases the power of the device by about 2.5% compared to the non-shaft configuration. Zamani et al. [21] addressed the J-shape configuration, emphasizing its advantages in terms of power and torque. By cutting at the maximum thickness of the pressure side, they determined the NACA 0015 airfoil and the J-shape. ...
The Darrieus wind turbine has a low starting torque, which is one of its main disadvantages. The main objective of the present study is to design an advanced Darrieus wind turbine capable of self-starting at low wind speeds without extra components. This will allow us to utilize this sort of wind turbine in less windy regions, such as urban areas. The new design relied solely on the blade profile for exploiting the drag force caused by the wind on the blades. The profile modifications under consideration included a variety of cavity shapes, numbers, sizes, and positions on the blade surface. The Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations were numerically solved in combination with the SST k-ω turbulence model. The characteristics of power and torque, as well as their flow fields, were studied. The results demonstrated that the maximum enhancements of power and torque coefficients were achieved using a single cavity located on the upper surface of the trailing edge of the airfoil, namely UST airfoil. A maximum improvement of 18% for power coefficient was obtained using a UST airfoil with a Tip Speed Ratio (TSR) of 3.5. The UST airfoil has a circular shape with a diameter equal to 0.08 of airfoil chord length. The airfoil with a single cavity performed noticeably better than the airfoil with a dual cavity. However, the ULST airfoil which consisted of two cavities located on upper and lower surfaces of the airfoil trailing edge generated the maximum power coefficient among other airfoils. The ULST airfoil generated a CP value of 0.27 at TSR = 3.5, representing a maximum improvement of 17% over an airfoil without a cavity.
The The wind turbine converts the kinetic energy of the wind current into the rotational energy of the rotor shaft. The use of vertical axis wind turbines as a source of clean energy production is of great importance. Among the advantages of vertical axis wind turbine over horizontal axis wind turbine are low production cost, lightweight, the efficiency of the installation, and use in residential zones. The darriues blades of vertical axis wind turbines are more in the kind of straight or helical blades. The central difficulty of Darius vertical axis wind turbines is their primary self-starting, which is the basis of this study. They increase self-initiation at low speeds. For this purpose, Darius vertical axis wind turbine was designed and built-in CATIA software. NACA0015 is made for airfoils and the material used for straight and porous blades is plain aluminum sheet and porcelain embossed sheet, both of which are series alloys of aluminum and the equipment used in manufactured and calibrated Manufacturing and calibrating. The result showed that the Ambas blade wind turbine needs less torque to start up to a speed of 9m/s than the vertical blade axis wind turbine.
Due to the high consumption of energy in recent years and global efforts to replace fossil fuels with clean energy, the need for high-efficiency renewable energy systems has become necessary. Small VAWTs are suitable candidates for clean energy production, due to their advantages over other power systems; nevertheless, their aerodynamic performance is modest. This paper attempts to improve the Darrieus VAWT performance by examining the turbine design parameters through the CFD method by adopting the SST k-ω turbulence model and finding the optimum turbine by utilizing the Kriging optimization model. Finally, by using the suggested optimized turbine, the economic analysis conducted to assess the total net present cost indicated the ideal hybrid power. The CFD results from different parameters show that the three-bladed turbine achieved maximum Cp and turbine with σ = 1.2 and optimal Cp by 34.4% compared to the medium solidity. The symmetrical airfoil t/c of 21% registered 19% and 48% performance enhancement at λ = 2.5 in comparison to t/c = 15% and 12%, respectively. Increasing the H/D ratio results in a better performance at the initial TSR, while a low H/D attained the highest Cp value. The stall condition can be delayed in low TSRs with toe-out blades upstream and obtained an increase of 22.4% in power obtained by β= −6° compared to the zero pitch angle. The assistance of auxiliary blades working in a wider range of TSR is shown and the turbine starting power augmented by 75.8%. The Kriging optimization model predicted the optimal Cp = 0.457, which can be attained with an optimal turbine with N = 3, σ = 1.2, NACA 0021 airfoil, AR = 0.8, and β= −6° operating at λ = 2.8. Finally, the results of the economic analysis indicate that the hybrid energy system consisting of a VAWT, a battery, and a converter can be applied for satisfying the site load demand with a lower net present cost and cost of energy compared to other feasible hybrid energy systems.
COVID-19 has disrupted all aspects of human life. To mitigate the impact of the pandemic, several efforts have been taken, including by Indonesian scholars abroad. This book entitled Indonesia Post-Pandemic Recovery Outlook: Strategy towards Net-Zero Emissions by 2060 from the Renewables and Carbon-Neutral Energy Perspectives explores energy sustainability and climate change issues and how it can progress further. There are also discussion on the delays caused by the COVID-19 pandemic to a few major renewable energy projects that should have been done in 2020-2021. Comprising of 14 chapters, this book is divided into three sections. The first part, Indonesia's Current Position and Strategy for Renewable Energy, explores Indonesia's current position and strategy on New and Renewable Energy. This chapter also explores Indonesia's commitment towards Net-Zero Carbon Emission 2060. Second, Carbon-Free and Renewable Energy in Indonesia, discusses the status of renewable energy use in the world, elaborate on the carbon impact of energy shift from fossil to renewable sources, and introduce a new criterion in renewable energy: carbon-neutral energy. The last part, Indonesia's New Strategy to Achieve Net-Zero Emission in 2060, explores the macroeconomic benefits of renewable and carbon-neutral energy deployment which are increasing energy security, fueling GDP development, creating job opportunities, enhancing human welfare, and achieving gender equality. We hope that this book can be a valuable reference for stakeholders, policymakers, as well as society to recover from the pandemic crisis and find better solutions to benefit future generations.
This study focuses on the blade design and optimization of Dual Darrieus Wind turbines (DDWTs). Based on Genetic Expression Programming (GEP) model, a power prediction formula CP=f(Δ, β, θ), containing radius difference Δ, chord ratio β, and offset angle θ, is proposed in this study. Hence, the power coefficient of various blade layouts can be directly calculated, corresponding to their optimum TSR. Meanwhile, orthogonal array L9 (3⁴) and Modified Additive Model (MAM) are combined to ensure the representative sample and consider the interaction effects. Additionally, each configuration in dataset requires to execute Computational Fluid Dynamics (CFD) analyses under various Tip Speed Ratios (TSRs) to figure out the highest power coefficient. The optimum layout of double-layer blades, derived from Taguchi Method and CP=f(Δ, β, θ), features the parameter combination as radius difference Δ of 0.25 m and chord ratio β of 3, which can improve the power output by 7.5%. The power prediction formula established by GEP is competent to approximate CP value of double-layer blades precisely which is verified by the correlation index R² = 0.993 and supplementary CFD cases. The proposed methodology indicates that DDWTs deserve to be further researched and developed.
This article provides a comprehensive review about passive flow control devices (PFCDs) implemented in lift‐type vertical axis wind turbine (LVAWT), focusing on the underlying flow physics mechanisms and to what extents they can improve the LVAWT performance. In addition, some novel concepts that can be potentially implemented in future are also presented. Based on literature review, it is observed that PFCDs can enhance the power generation of LVAWT up to 172.73% compared with a clean LVAWT. However, this significant improvement still needs to be evaluated carefully by considering the economic feasibility aspect, because PCFDs can increase the design complexity, weight penalty and manufacturing cost of LVAWT. Furthermore, it is essential to design and evaluate the effectiveness of PFCDs using a full VAWT configuration by considering the blade rotating effects and blade‐to‐blade interactions. Finally, evaluation of PFCDs needs to be performed at all ranges of tip speed ratios ( TSRs ) operation conditions, as there are clear evidences on the correlation between LVAWT performance and different range of TSRs .
This article is categorized under: Sustainable Energy > Wind Energy
Vertical-axis wind turbines are considered to be a better choice for cities and isolated semi-urban areas. However, it is difficult to control their power outputs, especially at high wind speeds, which can potentially cause damage to the generator or the wind turbine structures. In this study, a tree-shaped quad-rotor wind turbine with an active yaw system was proposed to not only effectively control the wind turbine power output but also increase its shutdown capability under survival conditions. To evaluate the proposed design concept, experimental prototypes of the wind turbine and the active yaw system were built and tested in a wind tunnel. To simulate real working conditions, the rotor freely rotated with the change of the wind speed and turbine yaw angle and drove a generator to charge a 24-volt battery. The charging power was measured in the experiments. It was found that the power-extraction efficiency of the quad-rotor configuration was 23% larger than that of the single-rotor configuration. The rotor speed was effectively controlled by changing the turbine’s yaw angle. Under different wind speeds, the total power output of the wind turbine could be stabilized at the given rate. Under survival conditions, the active yaw system was able to adjust the turbine plane parallel to the wind direction and shutdown the rotors to minimize the rotors’ aerodynamic torques, preventing the generators from overspeeding.
The depletion and the adverse effect on the environment caused by fossil fuels are critical reasons to divert the power generation medium into non-fossil fuels (hydro, wind, solar, and biomass). In recent years, the hydrokinetic system appeared as robust technology in the renewable power sector. The present study summarized the modifications done by various researchers on single and hybrid cross-flow HKT (hydrokinetic turbine) to enhance turbine performance characteristics. An effort has been made to present the experimental and numerical techniques for performance assessment of the cross-flow hydrokinetic system. There are various measuring instruments are available to measure the parameters such as water flow velocity, angular speed of the turbine, and torque output. These instruments, along with the experimental setup used by different investigators, have been reported in this study. There are various numerical methods are widely adopted to visualize the hydrodynamic behavior of hydrokinetic systems. Given this, several influential CFD parameters have been reviewed in the present study. This paper will assist in further development of the design and performance of the cross-flow hydrokinetic system.
This present paper leads to investigation of blade-fluid interactions of cambered blade H-Darrieus rotor having EN0005 airfoil blades using comprehensive Computational Fluid Dynamics (CFD) analysis to understand its performance in low wind streams. For several blade azimuthal angle positions, the effects of three different low wind speeds are studied regarding their influence on the blade-fluid interactions of the EN0005 blade rotor. In the prevailing studies by various researchers, such CFD analysis of H-Darrieus rotors are very less, hence it is needed to improve their steady-state performance in low wind velocities. Such a study is also important to obtain important performance insights of such thin cambered blade rotor in its complete rotational cycle. It has been seen that the vortex generated at the suction side of the EN0005 blade rolls back to its leading edge due to the camber of the blade and thus a peak velocity occurs near to the nose position of this blade at its leading edge, which leads to peak performance of this rotor. Again, in the returning phase of the blade, a secondary recirculating vortex is generated that acts on the pressure side of EN0005 blade rotor that increases the performance of this cambered EN0005 blade rotor in its downstream position as well. Here, the aerodynamic performances have been compared considering Standard k-ω and SST k-ω models to check the better suited turbulence model for the cambered EN0005 blade H-Darrieus rotor in low tip speed ratios.
In this study, the performance of offshore wind turbines at low tip speed ratio (TSR) is studied using computational fluid dynamics (CFD), and the performance of offshore wind turbines at low tip speed ratio (TSR) is improved by revising the blade structure. First, the parameters of vertical axis offshore wind turbine are designed based on the compactness iteration, a CFD simulation model is established, and the turbulence model is selected through simulation analysis to verify the independence of grid and time step. Compared with previous experimental results, it is shown that the two-dimensional simulation only considers the plane turbulence effect, and the simulation turbulence effect performs more obviously at a high tip ratio, while the three-dimensional simulation turbulence effect has well-fitting performance at high tip ratio. Second, a J-shaped blade with optimized lower surface is proposed. The study showed that the optimized J-shaped blade significantly improved its upwind torque and wind energy capture rate. Finally, the performance of the optimized J-blade offshore wind turbine is analyzed.
In this study, the structure of the trailing edge of the vertical axis offshore wind turbine blade is modified. First, according to the method of parameterization, the offshore wind turbine model is established, and a series of characteristics of the offshore wind turbine are obtained. Second, we add flaps with different lengths to the trailing edge of NACA0021 airfoil to obtain different dynamic characteristics. The angle of the additional trailing edge flaps is modified. Finally, a simulation model for the modified airfoil of the vertical axis offshore wind turbine is reestablished, and the variable characteristics of the performance is studied. Through the optimization and analysis of the blade structure, this study has obtained the best parameters of the length and angle of the offshore wind turbine blade trailing edge flap. The optimization of the blade structure changes the flow field around the blade, which significantly improves the maximum wind energy capture rate and self-starting ability of the vertical axis offshore wind turbine.
In this paper, the dynamic stall of S809 airfoil that widely used in horizontal axis wind turbine, in different reduced frequencies is investigated. The simulation was carried out numerically handling Navier-Stokes equations. For this purpose, the segregated solver with SIMPLE algorithm was chosen to solve the momentum equations. The effect of turbulence on the flow field is taken into account using Shear Stress Transport (SST)
K-ω
turbulence model. The obtained numerical results are compared with experimental and a few numerical results. The results indicate that the
K-ω
SST model is in good agreement with experimental results for both steady and unsteady conditions. Furthermore, a non-dimensional parameter, relating the acceleration of unsteady free stream velocity and acceleration of pitch motion (known as reduced frequency), is also investigated. In addition, the results show that any increase in the reduced frequency increases the instantaneous aerodynamic characteristics of oscillating airfoil.
An experimental campaign using Particle Image Velocimetry (2C-PIV) technique has been conducted on a H-type Vertical Axis Wind Turbine (VAWT) to create a benchmark for validating and comparing numerical models. The turbine is operated at tip speed ratios (TSR) of 4.5 and 2, at an average chord-based Reynolds number of 1.6e5 and 0.8e5. At both TSR, the velocity fields are presented in the mid (symmetry) plane of the blade for eight azimuthal positions. The velocity fields are directly derived from PIV, while the loads are obtained through an integral approach presented by Noca et al. The experimental data of the velocity fields around the airfoil and the loads on the blade are used for numerical validation. The aim of evaluating the two different TSR is identifying the effect of Dynamic Stall (DS), which is not present at the higher TSR, while dominant at the lower. The DS phenomenon is numerically very hard to model, so a solid benchmark for a VAWT in DS is of great interest. The aim of the paper is to present the experimental flow fields, and the validated loads on the blades for both TSR. © 2015, American Institute of Aeronautics and Astronautics Inc. All rights reserved.
In the present work, a recently developed in-house 2D CFD code is used to study the effect of gas turbine stator blade roughness on various performance parameters of a two-dimensional blade cascade. The 2D CFD model is based on a high resolution flux difference splitting scheme of Roe (1981). The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the zero-equation turbulence model of Baldwin-Lomax (1978) and two-equation Shear Stress Transport (SST) turbulence model. For the smooth blade, results are compared with experimental data to validate the model. Finally, a correlation between roughness Reynolds number and loss coefficient for both turbulence models is presented and tested for three other roughness heights. The results of 2D turbine blade cascades can be used for one-dimensional models such as mean line analysis or quasi-three-dimensional models e.g. streamline curvature method.
In this paper, the viscous and inviscid flow fields of a gas turbine blade cascade are investigated. A two-dimensional CFD solver is developed to simulate the flow field through VKI blade cascade. A high resolution flux difference splitting scheme of Roe is applied to discretize the convective part of Navier–Stokes equations. Baldwin Lomax (BL) model is used to account for turbulent effects on the viscous flow field of the blade cascade. For validation of the code, the flow field was solved by Ansys Fluent commercial software. The flow solution was done by third order flux difference splitting scheme of Roe and k–ω turbulence model. The findings show that the high turbulent and the shock creation in the flow field, lead to the same results in viscous and inviscid flows. Also, the results show that the grid and solver’s focus must be on the precise prediction of the shock effects, when the shock is occurred in the domain.
A two dimensional vertical axis wind turbine's model was established in this paper, and two dimensional unsteady incompressible N-S equations and Realizable kɛ− turbulence model were solved with software FLUENT. SIMPLC algorithm was applied, combined with the sliding grid technology; the influence of rotational speed to the flow structure of vertical axis wind turbine was discussed. The results showed that, the rotation of wind turbine had significant influence on wake, and higher the rotational speed, the greater reduction of the wake velocity. The wake velocity restored gradually away from the rotational part. There was much larger turbulent kinetic energy near the tail of the wind turbine's blade. The value of turbulent kinetic energy reduced gradually away from the rotational part, and the flow restored the stratospheric state gradually. With the increase of wind turbine's rotational speed, the value of turbulent kinetic energy in calculation domain increased too. The results showed that the flow structure of vertical axis wind turbine's rotational process could be revealed effectively by numerical simulation, provided theoretical reference for the engineering design of the vertical axis wind turbine.
This paper presents an implementation of the Generalized Grid Interface (GGI) for OpenFOAM. It is used to couple multiple non-conformal regions into a single contiguous domain at matrix level. The main advantage of the Generalized Grid Interface comes from removing the requirement to adjust the topology of the mesh at the interface between two non-conformal meshes. Instead, a set of weighting factors is evaluated in order to properly balance the flux at the GGI interface. Evaluation of the GGI weighting factors is based on the precise computation of the patch faces intersection on each side of the coupling interface as follows from discretisation. This is complicated due to the different grid resolution of the mesh on each side of the interface. This paper describes the choice and implementation of robust and quick algorithms for computing the GGI weighting factors. Furthermore, for turbomachinery simulations in particular, various derived forms of GGI are used regularly. Cyclic GGI, partial GGI and mixing plane GGI are all variants of the basic GGI interface that are needed for various use cases. Finally, it is very important that the GGI interface can be used for parallel OpenFOAM simulations on clusters of computers; otherwise, this would impose a severe limit on the size of the problems. This paper will show the current state of development of the Generalized Grid Interface for turbomachinery simulations and steps towards its generalisation and parallelisation.
In this paper, a computational fluid dynamics analysis using the FLUENT package 6.2 was carried out to predict the performance characteristics such as power coefficient (Cp), torque coefficient (Ct), and tip speed ratio of a combined three-bucket Savonius and three-bladed Darrieus rotor for various overlap conditions, namely, 16.2%, 20%, 25%, 30%, and 35%. In the upper part of the rotor model, there was a three-bucket Savonius rotor of bucket diameter of 8 cm and height of 10 cm, whereas, in the lower part, there was a three-bladed Darrieus rotor of blade diameter of 8 cm and height of 10 cm. A two-dimensional unstructured computational grid was developed for the combined Savonius–Darrieus rotor model. A k-&Vegr; turbulence closure model with enhanced wall treatment function was chosen. A first-order upwind discretization scheme was adopted for pressure-velocity coupling of the flow. The values of Cp and Ct obtained computationally were then compared with those of the values of Cp and Ct obtained experimentally for all the overlap conditions. The experimental values of Cp and Ct for different overlap conditions were obtained from the tests conducted previously in an open-circuit subsonic wind tunnel available in the department. The comparison of experimental and computational studies is quite encouraging.
This document describes the enhancement of the aeroelastic stability analysis with the program system ARLIS by applying aerodynamic results obtained from 3D CFD computations. As a main goal a coupling between the CFD-solver and ARLIS by exchanging aerodynamic loads and deformations is envisioned.
The suitable hybrid configuration of Darrieus lift-type and Savonius drag-type rotors for stand-alone wind turbine-generator systems is discussed using our dynamic simulation model. Two types of hybrid configurations are taken up. Type A installs the Savonius rotor inside the Darrieus rotor and Type B installs the Savonius rotor outside the Darrieus rotor. The computed results of the output characteristics and the dynamic behavior of the system operated at the maximum power coefficient points show that Type A, which has fine operating behavior to wind speed changes and can be compactly designed because of a shorter rotational axis, is an effective way for stand-alone small-scale systems. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 150(4): 13–22, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20071
This study presents numerical simulations of a cross-flow vertical-axis marine current turbine (straight-bladed Darrieus type) with particular emphasis on rotor-performance prediction and hydrodynamic characteristics. Numerical investigations of a model turbine (power coefficient and flow behaviour) were undertaken using developed computational models. Turbine design was studied using a time-accurate Reynolds-averaged Navier–Stokes (RANS) commercial solver (Fluent v. 6.3). A physical transient-rotor-stator model with a sliding mesh technique was used to capture change in flow field at a particular time step. A shear stress-transport k-ù turbulence model was used to model turbulent features of the flow. Developed model can effectively predict hydro-dynamic performance of a vertical-axis marine current turbine.
The aerodynamic behavior of a vertical axis wind turbine (VAWT) is analyzed by means of 2D particle image velocimetry (PIV),
focusing on the development of dynamic stall at different tip speed ratios. The VAWT has an unsteady aerodynamic behavior
due to the variation with the azimuth angle θ of the blade’s sections’ angle of attack, perceived velocity and Reynolds number.
The phenomenon of dynamic stall is then an inherent effect of the operation of a VAWT at low tip speed ratios, impacting both
loads and power. The present work is driven by the need to understand this phenomenon, by visualizing and quantifying it,
and to create a database for model validation. The experimental method uses PIV to visualize the development of the flow over
the suction side of the airfoil for two different reference Reynolds numbers and three tip speed ratios in the operational
regime of a small urban wind turbine. The field-of-view of the experiment covers the entire rotation of the blade and almost
the entire rotor area. The analysis describes the evolution of the flow around the airfoil and in the rotor area, with special
focus on the leading edge separation vortex and trailing edge shed vorticity development. The method also allows the quantification
of the flow, both the velocity field and the vorticity/circulation (only the results of the vorticity/circulation distribution
are presented), in terms of the phase locked average and the random component.
As the demand for renewable energy grows, the use of small wind turbines becomes increasingly attractive. Turbines using vertical-axis geometries are particularly suited to the urban environment by virtue of their operation being independent of wind direction. However, such designs have received much less attention than the more common ‘propeller type’ designs and the understanding of some aspects of their operation remains weak. This is particularly true of their starting characteristics. Indeed, some authors maintain that they cannot start without external assistance.
In this investigation a numerical model is used to simulate the starting of an H-rotor Darrieus turbine under steady wind conditions. Experimental wind-tunnel data for a small prototype is presented, demonstrating unaided start-up of a three-bladed Darrieus in a steady wind. Discrepancy between the modelled and experimental results demonstrate that modelling remains constrained by the quality of data on aerofoil characteristics.
A fluctuating inflow around the surface of rotor blade in the spanwise direction presents a more significant challenge in the performance of wind turbine. In this paper, three-dimensional (3D) experimental and computational investigations of a straight-bladed VAWT (Vertical Axis Wind Turbine) are proposed and analyzed with two straight blades. In wind tunnel experiments, LDV (Laser Doppler Velocimeter) system is presented to investigate the influence of spanwise direction on the straight-bladed of NACA0021 symmetric airfoil in unsteady wind condition. In numerical analysis, 3D transient CFD (Computational Fluid Dynamics) models have been performed to simulate the flow field characteristics of VAWT at the same experimental conditions as wind tunnel experiments. From comparing the results of wind tunnel experiments and numerical analysis, it is found that momentum amount is the largest at the blade center height and the smallest at the blade tip. Furthermore, it is well able to predict the experimental results using CFD model based on k- ε Shear Stress Transport turbulence model.
Providing high starting torque and efficiency simultaneously is a significant challenge for vertical axis wind turbines (VAWTs). In this paper, a new approach is studied in order to modify VAWTs performance and cogging torque. In this approach, J-shaped profiles are exploited in the structure of blades in which by eliminating the pressure side of airfoil from the maximum thickness toward the trailing edge. This new profile is a new type of VAWT airfoil using the lift and drag forces resulting in the better performance at low TSRs. To simulate the flow fluid of the VAWT along with J-shaped profiles originated from NACA0018 and NACA0030, a two-dimensional computational analysis is conducted. The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the two-equation Shear Stress Transport (SST) turbulence model. The main goal of this study is to investigate the effects of J-shaped straight blade thickness on the performance characteristics of VAWT. The results obtained indicate that opting for the higher thickness in J-shaped profiles for the blade sections leads the performance and cogging torque of VAWT to enhance dramatically.
This paper presents a straight-bladed VAWT (vertical axis wind turbine) model for the evaluation of aerodynamic forces and inertial contributions to rotor blade deformation. In this paper, a two-bladed VAWT is proposed and analyzed with CFD (computational fluid dynamics) and wind tunnel experiments in three-dimensional (3D) investigation. In wind tunnel experiments, pressure measurement system is presented to measure the pressure acting on a single blade of straight-bladed VAWT in the spanwise direction. In numerical analysis, 3D CFD models have been performed to simulate the aerodynamic forces characteristics of VAWT with k–ε SST (Shear Stress Transport) (k–ε) turbulence model. From comparing the results of the wind tunnel experiments and numerical analysis, it is found that the fluid force decreased with the increase of spanwise positions excluding the position of support structure. Furthermore, according to the result from six-component balance, the waveforms of the power coefficient Cpw have similar characteristics and show smaller values than CFD calculations.
In this study a 3 kW straight–bladed Darrieus type Vertical Axis Wind Turbine (VAWT) is investigated numerically using OpenFOAM computational fluid dynamic package. The newly proposed J-Shaped profile is used as the blade airfoil in the simulation. The J-Shaped profile is designed by means of eliminating a fraction of pressure side of Du 06-W-200 airfoil. The main purpose of this investigation is the improvement of the VAWT starting torque using J-shaped profile. The power curves for both conventional and J-shaped profiles are calculated and the torque variation is obtained at different azimuth angles. In addition, the vorticity and pressure field surrounding the wind turbine is presented. The results indicate that the performance of turbine is optimized for J-shaped profile which eliminates the pressure side of airfoil from the maximum thickness toward the trailing edge. Moreover, by employing this J-Shaped profile, the wind turbine performance is intensified TSRs and self-starting of turbine is improved.
This paper shows the results of an experimental investigation into the effect of changes in solidity on the performance of a Vertical Axis Wind Turbine. Two VAWT configurations are used, one of solidity σ = 0.26 (chord C = 0.03 m) and the other with σ = 0.34 (C = 0.04 m). The turbine performance coefficient (Cp) was measured over a range of tip speed ratios and Particle Image Velocimetry (PIV) was used to determine the flow field around both turbine configurations.Performance (Cp-λ) curves for the two VAWTs are compared at the same Reynolds numbers to investigate the effects of solidity alone on the performance and aerodynamics of each configuration. The higher solidity (σ = 0.34) VAWT attained a similar maximum Cp but with a narrower Cp-λ curve than the lower solidity VAWT. The performance differences between the two VAWT configurations at two tip speed ratios are explained in detail using PIV around both VAWT rotor blades. This allows the linking of detailed aerodynamics to the performance and it was shown that the generation and shedding of stall vortices started earlier on the lower solidity VAWT than the higher solidity VAWT, thus limiting the rotor efficiency.
The flow field around a vertical axis wind turbine (VAWT) is very complicated mainly due to the continuous variation of the geometrical angle of attack and resultant flow velocity to blade during rotation. This paper has attempted to compile the assessment study the flow field around a small straight-bladed VAWT. Two dimensional unsteady flows around the VAWT are investigated through the use of the Laser Doppler Velocimeter (LDV) system, operating at three different tip speed ratios in wind tunnel experiments. Meanwhile, the geometrical angles of attack and the resultant flow velocities are calculated using local wind velocity and direction. From the results of these experiments, it has been found that a wide low wind velocity field emerges in the wind turbine׳s internal region and continues into the downstream region. As the tip speed ratio increases, the area of low wind velocity also expands. Furthermore, moving from the upstream to the downstream region, the velocity deficit becomes greater in the free stream direction. Finally, large turbulence intensity is generated in the plane of wind turbine rotation.
In this paper, the power performance of straight-bladed VAWT is experimentally investigated by wind tunnel experiment and field test. The test rotor is two-bladed with NACA0021 airfoil profile. A survey of varying unsteady wind parameters is conducted to examine the effects of blade pitch angle, Reynolds number and wind velocity on the power performance of VAWT. Moreover, the flow field characteristics are obtained through measuring the wind velocity by Laser Doppler Velocimeter (LDV) system in the wind tunnel experiment and three-cup type anemometers in field test. Power and torque performance are obtained through a torque meter installed in rotor shaft of the wind turbine. Experimental results estimated from the measured values from field test and wind tunnel experiment are compared. In this research, power performance and flow field characteristics are discussed and the relationship between operating conditions and wind velocity are verified. These results provided a theoretical guiding significance to the development of VAWT simplified.
Small wind turbine performance and safety standard for straight-bladed Vertical Axis Wind Turbine (VAWT) have not been developed in the world because of the lack of fundament experimental data. This paper focuses on the evaluation of aerodynamic forces depending on several numbers of blades in wind tunnel experiment. In the present study, the test airfoil of blade is symmetry airfoil of NACA 0021 and the number of blades is from two to five. Pressure acting on the surface of rotor blade is measured during rotation by multiport pressure devices and transmitted to a stationary system through wireless LAN. And then, the aerodynamic forces (tangential force, normal force etal.) are discussed as a function of azimuth angle, achieving a quantitative analysis of the effect of numbers of blades. Finally, the loads are compared with the experimental data of six-component balance. As a result, it is clarified that the power coefficient decreases with the increase of numbers of blades. Furthermore, the power which is absorbed from wind by wind turbine mainly depends on upstream region of azimuth angle of θ=0°~180°. In this way, these results are very important for developing the simple design equations and applications for straight-bladed VAWT.
Energy is an essential ingredient for socio-economic development and economic growth of a country. Energy is available in two different forms, fast depleting or non-renewable (coal, fuel, natural gas) and renewable (solar, wind, hydro etc). Wind is one of the potential renewable energy sources due to its abundance in the atmosphere in different scales of high, medium and low ranges. Vertical axis wind turbine (VAWT) can be installed in low wind speed regime for performing various small-scale functions ranging from electrifying a built environment to pumping water especially in remote places where grid-connected electricity is a scarce. Amongst various VAWT rotors, H-type Darrieus rotor has become more popular in the built environment for their straight blade designs and simpler construction features. However, the major problem facing such VAWT rotor is their non-self-starting characteristics due to symmetrical blade designs. Replacing VAWT's conventional blades with unsymmetrical blades and increasing rotor solidity could make potential solution to the above problem. However, there is still hardly any quantitative measure of the self-starting, torque, power coefficient etc. with increased rotor solidity so as to obtain some performance insights of high solidity unsymmetrical blade H-Darrieus rotor in low wind speed condition. In this paper a three-bladed H-type Darrieus rotor equipped with unsymmetrical S1210 blades is investigated first for its self-starting characteristics with different rotor solidities (from 0.8 to 1.2) at various azimuthal positions. Then the power coefficients (Cp) are evaluated for these solidities at various wind speeds. It will be shown that high blade solidity is in fact desirable for overall better performance of the rotor. There is an optimum rotor solidity at which power coefficient is the highest. And the maximum Cp of 0.32 is obtained for rotor solidity 1.0 and wind speed 5.7 m/s. The results are compared with some other symmetrical/unsymmetrical blade H-Darrieus rotors. Though the operating range is reduced but, for higher static and dynamic torque and comparable power coefficient with respect to existing rotors, the present rotor could be used for various small-scale applications especially that require high torque like pumping, grinding etc.
This thesis reports on a numerical and experimental investigation of the unsteady loading of high solidity vertical axis wind turbines (VAWTs). Two-dimensional, unsteady Reynolds averaged Navier-Stokes simulations of a small scale, high solidity, H-type Darrieus vertical axis wind turbine revealed the dominant effect of dynamic stall on the power production and vibration excitation of the turbine. Operation of the turbine at low blade speed ratios resulted in complex flow-blade interaction mechanisms. These include; dynamic stall resulting in large scale vortex production, vortex impingement on the source blade, and significant flow momentum extraction.
To validate the numerical model, a series of full-scale experimental wind tunnel tests were performed to determine the aerodynamic loading on the turbine airfoils, vibration response behaviour, and wake velocity. In order to accomplish this, a complex force measurement and wireless telemetry system was developed. During the course of this investigation, high vibration response of the turbine was observed. This resulted in conditions that made it difficult or impossible to measure the underlying aerodynamic loading. A vibration mitigation methodology was developed to remove the effect of vibration from the measured aerodynamic forces. In doing so, an accurate and complete measurement of the aerodynamic loading on the turbine blades was obtained.
Comparison of the two-dimensional numerical model results to the experimental measurements revealed a considerable over-prediction of the turbine aerodynamic force and power coefficients, and wake velocity. From this research, it was determined that the three-dimensional flow effects due to the finite aspect ratio of the turbine and blades, as well as parasitic losses, could be accounted for through the application of inlet velocity and turbine height correction factors. In doing so, the two-dimensional numerical model results could be properly scaled to represent the three-dimensional flow behaviour of the turbine prototype. Ultimately, a validated VAWT design tool was developed.
This paper presents a CFD model for the evaluation of energy performance and aerodynamic forces acting on a straight-bladed vertical-axis Darrieus wind turbine. The basic principles which are currently applied to BE-M theory for rotor performance prediction are transferred to the CFD code, allowing the correlation between flow geometric characteristics (such as blade angles of attack) and dynamic quantities (such as rotor torque and blade tangential and normal forces). The model is proposed as a powerful design and optimization tool for the development of new rotor architectures for which test data is not available. After describing and validating the computational model against experimental data, a full campaign of simulation is proposed for a classical NACA 0021 three-bladed rotor. Flow field characteristics are investigated for several values of tip speed ratio, allowing a comparison among rotor operation at optimum and lower C(p) values, so that a better understanding of vertical-axis wind turbines basic physics is obtained. (C) 2011 Elsevier Ltd. All rights reserved.
Straight Darrieus wind turbine has attractive characteristics such as the ability to accept wind from random direction and
easy installation and maintenance. But its aerodynamic performance is very complicated, especially for the existence of dynamic
stall. How to get better aerodynamic performance arouses lots of interests in the design procedure of a straight Darrieus
wind turbine. In this paper, mainly the effects of number of blades and tip speed ratio are discussed. Based on the numerical
investigation, an assumed asymmetric straight Darrieus wind turbine is proposed to improve the averaged power coefficient.
As to the numerical method, the flow around the turbine is simulated by solving the 2D unsteady Navier-Stokes equation combined
with continuous equation. The time marching method on a body-fitted coordinate system based on MAC (Marker-and-Cell) method
is used. O-type grid is generated for the whole calculation domain. The characteristics of tangential and normal force are
discussed related with dynamic stall of the blade. Averaged power coefficient per period of rotating is calculated to evaluate
the eligibility of the turbine.
Unsteady flowfields of a two-dimensional oscillating airfoil are calculated using an implicit, finite-difference, Navier-Stokes numerical scheme. Five widely used turbulence models are used with the numerical scheme to assess the accuracy and suitability of the models for simulating the retreating blade stall of helicopter rotor in forward flight. Three unsteady flow conditions corresponding to an essentially attached flow, light-stall, and deep-stall cases of an oscillating NACA 0015 wing experiment were chosen as test cases for computations. Results of unsteady airloads hysteresis curves, harmonics of unsteady pressures, and instantaneous flowfield patterns are presented. Some effects of grid density, time-step size, and numerical dissipation on the unsteady solutions relevant to the evaluation of turbulence models are examined. Comparison of unsteady airloads with experimental data show that all models tested are deficient in some sense and no single model predicts airloads consistently and in agreement with experiment for the three flow regimes. The chief findings are that the simple algebraic model based on the renormalization group theory (RNG) offers some improvement over the Baldwin-Lomax model in all flow regimes with nearly same computational cost. The one-equation models provide significant improvement over the algebraic and the half-equation models but have their own limitations. The Baldwin-Barth model overpredicts separation and underpredicts reattachment. In contrast, the Spalart-Allmaras model underpredicts separation and overpredicts reattachment.
The vertical axis wind turbines are simple in construction, self-starting, inexpensive and can accept wind from any direction without orientation. A combined Savonius–Darrieus type vertical axis wind rotor has got many advantages over individual Savonius or individual Darrieus wind rotor, such as better efficiency than Savonius rotor and high starting torque than Darrieus rotor. But works on the combined Savonius–Darrieus wind rotor are very scare. In view of the above, two types of models, one simple Savonius and the other combined Savonius–Darrieus wind rotors were designed and fabricated. The Savonius rotor was a three-bucket system having provisions for overlap variations. The Savonius–Darrieus rotor was a combination of three-bucket Savonius and three-bladed Darrieus rotors with the Savonius placed on top of the Darrieus rotor. The overlap variation was made in the upper part, i.e. the Savonius rotor only. These were tested in a subsonic wind tunnel available in the department. The various parameters namely, power coefficients and torque coefficients were calculated for both overlap and without overlap conditions. From the present investigation, it is seen that with the increase of overlap, the power coefficients start decreasing. The maximum power coefficient of 51% is obtained at no overlap condition. However, while comparing the power coefficients (Cp) for simple Savonius-rotor with that of the combined configuration of Savonius–Darrieus rotor, it is observed that there is a definite improvement in the power coefficient for the combined Savonius–Darrieus rotor without overlap condition. Combined rotor without overlap condition provided an efficiency of 0.51, which is higher than the efficiency of the Savonius rotor at any overlap positions under the same test conditions.
This paper presents a combined experimental and computational study into the aerodynamics and performance of a small scale vertical axis wind turbine (VAWT). Wind tunnel tests were carried out to ascertain overall performance of the turbine and two- and three-dimensional unsteady computational fluid dynamics (CFD) models were generated to help understand the aerodynamics of this performance.
Wind tunnel performance results are presented for cases of different wind velocity, tip-speed ratio and solidity as well as rotor blade surface finish. It is shown experimentally that the surface toughness on the turbine rotor blades has a significant effect on performance. Below a critical wind speed (Reynolds number of 30,000) the performance of the turbine is degraded by a smooth rotor surface finish but above the turbine performance is enhanced by a smooth surface finish. Both two bladed and three bladed it, rotors were tested and a significant increase in performance coefficient is observed for the higher solidity rotors (three bladed rotors) over most of the operating range. Dynamic stalling behaviour and the resulting large and rapid changes in force coefficients and the rotor torque are shown to be the likely cause of changes to rotor pitch angle that occurred during early testing. This small change in pitch angle caused significant decreases in performance.
The performance coefficient predicted by the two dimensional computational model is significantly higher than that of the experimental and the three-dimensional CFD model. The predictions show that the presence of the over tip vortices in the 3D simulations is responsible for producing the large difference in efficiency compared to the 2D predictions. The dynamic behaviour of the over tip vortex as a rotor blade rotates through each revolution is also explored in the paper.
Two new two-equation eddy-viscosity turbulence models will be presented. They combine different elements of existing models that are considered superior to their alternatives. The first model, referred to as the baseline (BSL) model, utilizes the original k-omega model of Wilcox In the inner region of the boundary layer and switches to the standard k -epsilon model in the outer region and in free shear flows. It has a performance similar to the Wilcox model, but avoids that model's strong freestream sensitivity. The second model results from a modification to the definition of the eddy-viscosity in the BSL model, which accounts for the effect of the transport of the principal turbulent shear stress. The new model is called the shear-stress transport-model and leads to major improvements in the prediction of adverse pressure gradient flows.
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