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Two-Equation Eddy-Viscosity Turbulence Models for Engineering Applications
... The choice of turbulence model is crucial in accurately simulating chemically reactive flows. For this investigation, the k-ω Shear Stress Transport (SST) model [35] was selected due to its ability to handle boundary layer interactions and free shear flows. This hybrid approach applies the k-ω formulation within boundary layers and transitions to the k-formulation in regions outside solid boundaries, ensuring robust performance across diverse flow conditions. ...
... Compressibility contributes to dissipation terms Y k and Y ω and plays a role in the generation of turbulent kinetic energy outlined below [35]: ...
Scramjet engines hold significant promise for hypersonic propulsion, yet the complexities of supersonic combustion pose considerable challenges. Computational Fluid Dynamics (CFD) offers a cost-effective approach to studying turbulent reactive flows in such systems, particularly addressing the critical turbulence-chemistry interactions that differ from conventional combustion. This study employs two-dimensional Reynolds-averaged Navier-Stokes (RANS) simulations to evaluate a novel strut-dual cavity flame holder in scramjet combustors. Among various configurations analyzed, the double-step cavity demonstrated a superior balance, achieving high combustion efficiency with moderate total pressure loss. The numerical model was validated against experimental data, confirming its reliability and predictive accuracy. The findings highlight the effectiveness of integrating cavity-based geometries with strut injectors in enhancing fuel-air mixing and stabilizing combustion. This research underscores the strut-dual cavity flame holder's potential as a practical solution for advancing scramjet performance in hypersonic applications.
... Finer mesh elements were generated close to the interest zone and a smooth transition from smaller to larger element sizes was achieved. To capture the effect of turbulent flow, k-ω SST turbulence model was preferred (Menter, 1994). ...
This paper presents a numerical procedure for investigating the dynamic behaviour of a planar steel frame subjected to turbulent wind loads. The main objective is to emphasize the modal distribution of top lateral displacements induced by time varying wind forces. Time histories of pressure and forces were acquired for a time period of 600 s from a Computational Fluid Dynamic (CFD) analysis. Air flow over rectangular bluff bodies was modelled in a bounded CFD domain in order to simulate wind’s stochastic behaviour in the presence of roughness. Simulated pressure in the CFD analysis is transferred as time-varying load applied on a steel shear frame. The studied structure is mathematically modelled as a dynamic multi-degree-of-freedom (MDOF) system directly related to its constituent stiffness, mass and damping matrices. Forced vibrations induced by highly arbitrary wind forces are dealt with Duhamel’s Integral to emphasise the modal decomposition of the overall lateral displacements response. Wind load function defined as a time-history of discrete force values requires the use of Simpson’s 1/3 Rule for numerical integration.
... The inlet boundary conditions included the stagnation parameters (pressure and temperature), the flow direction and the quantities essential for turbulence modelling: the intensity of the turbulence and the length scale. The entire study implemented the second-order "High-Resolution" discretization of convective fluxes 56 and Menter's k − ω SST turbulence model 57 . At the outlet, the average static pressure in the area p st out was used (Fig. 9, b). ...
This sensitivity study is focused on understanding the rate at which blade thickness can affect the risk of high-cycle fatigue failure in an impeller of a centrifugal compressor. The investigated Ti-alloy impeller serves to compress and deliver feed air into the combustion chamber of the jet-engine commercially known as DGEN 380. The risk of blade resonance at take-off exists between the tangential eigenmode with four nodal diameters and the fourth engine-order excitation source. The study uses weak coupling of the fluid- and structural numerical solvers to simulate the resonant vibrations of three impeller designs with lower, baseline and higher blade thickness. The transient aerodynamic pressure load is first estimated with the use of harmonic balance Fourier-transformation method. The load is afterwards applied to the structural harmonic-response model and the vibratory stresses are computed for a series of critical damping ratios. The following assessment of safety factors is done based on the Haigh diagram built-up with the use of Goodman equation. The requirement of minimally '10^9' cycles to failure is applied to ensure that the blades sustain the resonance for a reasonably long period. The results indicate no potential high-cycle fatigue issues in baseline- and thicker designs. Safe operation of the thinner design is strongly affected by the system damping and its sustainable operation could not be guaranteed. The findings of the study should be useful to mechanical engineers solving the coupled fluid-structural problems in aerospace-, power- and environmental sectors.
... Despite the fact that the flow over the T106 blade is actually simulated in LES regime (we use a mesh with proper resolution), the RANS branch is required in the region downstream the inlet boundary and upstream the VSTG source to conduct unsteady RANS solution (see Section 2 for details). We use the recent version of the IDDES based on the Menter k − ω SST model [17] and ∆ SLA [19,26] dynamic subgrid scale. ...
Methodology for studying effects associated with periodic unsteady impact of neighbouring rows in turbomachines is presented. The two-stage procedure of an investigation is as follows: simulation using an approach based on solving the Reynolds-averaged Navier–Stokes equations (RANS) of an entire turbomachine at the first stage and scale-resolving simulation (SRS) of a particular row at the second. The methodology exploits the following methods and technologies, which are implemented in the NOISEtte computational algorithm: the nonlinear harmonics method as a RANS approach to obtain unsteady inflow parameters for SRS; the hybrid Improved Delayed Detached Eddy Simulation approach for SRS of the row under detailed study. SRS considers using the dynamic synthetic turbulence generator in a form of volumetric source terms (VSTG) to reproduce unsteady periodic turbulent perturbations. A dynamic version of the VSTG, the parameters of which depend on the flow upstream the source region, is formulated. Details of the parallel heterogeneous implementation of the dynamic VSTG are discussed. To demonstrate the applicability of the presented methodology, a simulation of non-stationary effects in a cascade of T106 low-pressure turbine blades was performed.
... The comparison between Reynolds Averaged Navier-Stokes (RANS) simulations and large eddy simulations (LES) results showed that turbulence modelling has a very large influence. Figure 3 compares the results of Menter's (1994) shear-stress transport model (SST) and Nicoud's (1999) wall-adapting local eddy-viscosity model (WALE) with experimental data, showing that RANS qualitatively predicts the vapour distribution incorrectly, while LES correctly reproduces the cavitation distribution. This shows a strong interaction between turbulence/vortices and cavitation, which is also seen experimentally in water by Lu et al. (2012). ...
This article presents an experimentally validated computational fluid dynamics (CFD) model for localising and quantifying cavitation erosion in oil hydraulic valves using large eddy simulation (LES) turbulence modelling and the cavitation erosion indices by Nohmi. Cavitation erosion, a significant factor limiting the lifespan and performance of hydraulic valves and pumps, is challenging to simulate accurately due to factors like vapour-gas cavitation separation, cavitation model parameterisation for mineral oil and accounting for the influence of air. A test rig is shown that enables an adjustable air content, the separation of gas and vapour cavitation and optical access to the cavitating valve flow. The visualisation data from this rig was used to parametrise and validate the Zwart–Gerber–Belamri vapour cavitation model for mineral oil and to include the effect of free air, achieving excellent results. The model is used to quantify cavitation erosion load, with the cavitation indices accurately reflecting erosion location, shape and intensity as well as the damping effect of air. The simulation method is suitable for industrial use to reduce cavitation erosion in hydraulic components by optimising the flow path.
... While k-epsilon is robust and widely used, it may not provide the highest accuracy near walls. An alternative, the k-omega model, tends to perform better in areas with strong pressure gradients and boundary layer effects but was not used in this analysis (Menter 1994). ...
Ensuring occupant comfort and energy efficiency is a cornerstone of building design, yet existing Building Performance Simulation (BPS) tools often lack the detailed modelling required for human-centric design and advanced control strategies. This paper addresses this gap, by integrating a detailed human thermal representation into the ESP-r building simulation tool, along with deeper integration within ESP-r's Computational Fluid Dynamics (CFD) domain. The developed model enhances the accuracy of human thermal interaction modelling by incorporating variable metabolic rates, internal heat loads, and a dynamic clothing model in whole-building simulations.
The approach described, balances computational efficiency with the need for detailed, localized insights into indoor conditions, making it suitable for studying the impact of indoor micro-climatic effects on human comfort. To validate the integrated modelling approach, simulation results were compared against a published experimental CFD benchmark, showing mean absolute errors of 0.2–0.53°C for temperature and 0.012–0.017 m/s for air velocity. The integrated model was applied to a naturally ventilated building, to assess the influence of temporal variations of local conditions on occupant thermal states; such an analysis is not possible through the individual application of CFD, building simulation or human thermal models, and demonstrates the novelty and potential of the combined approach in facilitating more detailed analysis indoor conditions and occupant comfort and in advancing human-centric building modelling and simulation.
... Dirichlet boundary conditions were adopted for the front, upper and lower boundaries, imposing an estimated far-field velocity distribution obtained via a supporting Reynoldsaveraged Navier-Stokes (RANS) simulation. The k-ω shear-stress transport model (Menter 1994) was employed for the RANS simulation, where a circular domain with a radius of 200c is considered. For the outlet, the boundary condition developed by Dong et al. (2014) is used, preventing the uncontrolled influx of kinetic energy through the outflow boundaries. ...
Opposition control (OC) is a reactive flow-control approach that mitigates the near-wall fluctuations by imposing blowing and suction at the wall, being opposite to the off-wall observations. We carried out high-resolution large-eddy simulations to investigate the effects of OC on turbulent boundary layers (TBLs) over a wing at a chord-based Reynolds number ( ) of . Two cases were considered: flow over the suction sides of the NACA0012 wing section at an angle of attack of , and the NACA4412 wing section at an angle of attack of . These cases represent TBLs subjected to mild and strong non-uniform adverse pressure gradients (APGs), respectively. First, we assessed the control effects on the streamwise development of TBLs and the achieved drag reduction. Our findings indicate that the performance of OC in terms of friction-drag reduction significantly diminishes as the APG intensifies. Analysis of turbulence statistics subsequently reveals that this is directly linked to the intensified wall-normal convection caused by the strong APG: it energizes the control intensity to overload the limitation that guarantees drag reduction. The formation of the so-called virtual wall that reflects the mitigation of wall-normal momentum transport is also implicitly affected by the pressure gradient. Control and pressure-gradient effects are clearly apparent in the anisotropy invariant maps, which also highlight the relevance of the virtual wall. Finally, spectral analyses indicate that the wall-normal transport of small-scale structures to the outer region due to the APG has a detrimental impact on the performance of OC. Uniform blowing and body-force damping were also examined to understand the differences between the various control schemes. Despite the distinct performance of friction-drag reduction, the effects of uniform blowing are akin to those induced by a stronger APG, while the effects of body-force damping exhibit similarities to those of OC in terms of the streamwise development of the TBL although there are differences in the turbulent statistics. To authors’ best knowledge, the present study stands as the first in-depth analysis of the effects of OC applied to TBL subjected to non-uniform APGs with complex geometries.
... The shear stress transport(SST) k-ω turbulence model was selected due to its accomplished previous studies in the simulation of turbine analysis performance [41][42][43][44]. The SST k−ω turbulence model combines the advantages of the k−ω model in the near-wall region with the k−ε model's ability to handle free-stream turbulence [45,46]. Compared to other turbulence models, such as the standard k−ε, the SST k−ω model offers superior performance in predicting separation and nearwall turbulence, which are crucial for evaluating the efficiency and effectiveness of the turbine under varying flow conditions [47,48]. ...
Hydrokinetic turbines are crucial for sustainable power generation, but their performance is often impacted by floating debris and sediment transport, which can damage turbine blades. Sediment retention enhances the turbine's lifespan and reduces maintenance by preventing blade erosion, cavitation and clogging. Protective grates reduce abrasive particle entry, minimising blade wear. They also avoid buildup of sediment, lowering the risk of blockages and cavitation, which harm efficiency and accelerate degradation. This study presents the numerical performance of Darrieus‐type vertical axis hydrokinetic turbines under the impact of straight and Coanda type grate protection structures. The effects of these two types of grate structures with different design angles on turbine power coefficient (CP) and torque coefficient (CT) were investigated using the ANSYS Fluent program. The dynamic mesh technique simulated the turbine rotation and the semi‐implicit method for pressure‐linked equations (SIMPLE) was applied with a shear stress transport (SST) k‐ω turbulence model. The turbine's efficiency was compared and the results were evaluated for steady and unsteady flow conditions. The highest power coefficients were obtained as 0.230 and 0.264 for steady and unsteady flow, respectively, in the Coanda grate with a 30° central angle. The highest power coefficients were obtained as 0.215 and 0.247 for steady and unsteady flow, respectively, in the straight grate design with a 60° inclination angle. The sediment retention capacities of Coanda grates (30° central angle) and straight grates (60° inclination angle) with varying particle size distributions were further investigated using the discrete phase model (DPM) under steady flow conditions.
... The shear-stress transport (SST) k-ω model is used in this study to solve the turbulent flow equation developed by Mentor [40]. This model is formed by converting the k-ε model into the k-ω formulation to accurately simulate the near-wall region and the free-stream independence of the k-ε model in the zones which are far away from the walls. ...
Effective thermal management is crucial for safe, high-performance operation of lithium-ion batteries in electric vehicles (EVs). However, conventional passive or active cooling methods alone struggle to provide sufficient heat dissipation while maintaining uniform battery temperatures. This computational study investigates a hybrid thermal management system combining lateral phase change material (PCM) layers for temperature stabilization with vertical liquid cooling channels. The system was evaluated for a lithium-ion pouch cell module with PCM thicknesses ranging from 1 to 7 mm (melting point 26 • C) and a 0.5 mm liquid coolant channel using Novec-774 at 15-20 • C inlet and 90 lpm flow rate. Key findings reveal the 7 mm PCM achieved superior thermal regulation, constraining mean/maximum cell temperatures to 32.5 • C/39.1 • C compared to 113.8 • C/188.1 • C for the ineffective 1 mm case. Lower coolant inlet temperatures further enhance the performance, with a 5 • C inlet yielding 24.6 • C/29.2 • C mean/max, versus 26.0 • C/29.8 • C at 15 • C inlet. The hybrid passive-active approach combines lateral heat absorption via PCM with vertical forced convection cooling to effectively regulate battery temperatures. The proposed approach achieves superior cooling with up to 73 % reduction in maximum temperature compared to conventional liquid cooling, while maintaining temperature uniformity within 5 • C across the battery module.
... The k − ω Shear Stress Transport (SST) two equations eddy-viscosity model developed by Menter et al. (1994) is a blend between k − ω and k − ε formulations. The k − ε formulation is used in the free-stream, to avoid the dependence of k − ω on the free-stream turbulence intensity. ...
This paper proposes the numerical investigation of the scale effects in open water for two tip-raked marine propellers. The turbulence model k − ω SST is applied for full-scale simulations, while the transition model γ − Re θ is used in model-scale. The hydrodynamic performance at different loading conditions is analyzed, and predictions indicate small Reynolds number effects for these two unconventional propellers. Whereas the predicted propeller efficiency is within a 2% relative deviation from measurements in model-scale, efficiency predictions in full-scale quantitatively deviate from the extrapolated-to-full-scale values, particularly at high advance ratios. Skin friction distributions and limiting streamlines at model-, with and without transition model, and full-scale are analyzed at the design conditions. It is concluded that the negligible predicted scale effects are related to the considerably dissimilar boundary layer flows at different Reynolds numbers and to the vortex shedding behind the blunt trailing edge for one of the two propellers. Finally, it is noted that k − ω SST predicts more significant scale effects than γ − Re θ when also used to compute model-scale results. This behavior emphasizes the importance of using a transition model for low-Reynolds number flows.
... Given that the turbulent viscosity μ t in the momentum equation is unknown, it is necessary to introduce a turbulence model in order to solve for its value. The turbulence model employed in this paper is the SST k-ω turbulence model [24], which combines the respective advantages of k-ω turbulence model and the k-ε turbulence model. The mixed function F 1 is introduced as the control, and the k-ω turbulence model is employed to calculate the viscous bottom layer directly on the near wall, while the k-ε turbulence model is used to enhance stability on the far wall. ...
To investigate the differences and similarities in vortex and cavity characteristics between translational and rotational domain hydraulic machines, the NACA0009 hydrofoil and a self-designed impeller blade were selected as representative cases in the translational and rotational domains. STAR-CCM+ software was utilized to simulate the multiphase flow, and the experimental results of NACA0009 hydrofoil from EPFL were employed to validate the accuracy of the simulation. The following conclusions were drawn from the analysis of the simulation results: Firstly, both types of hydraulic machinery generate similar vortex types, including the tip leakage vortex (TLV), tip separation vortex (TSV), and secondary tip leakage vortex (S-TLV). However, each type also exhibits unique vortices, such as the perpendicular vortex (PV) in the translational domain and the trailing edge vortex (TEV) in the rotational domain. Secondly, the TLV is initially weak but continuously absorbs other vortices, thereby strengthening itself as it develops. Additionally, the blades in the rotational domain must achieve a higher speed to produce the same level of cavitation as those in the translational domain. Finally, the attached cavitation (AC) on the blade surface is repelled by the spin of the TLV, which cannot promote the generation of tip leakage vortex cavitation (TLVC). The primary source of TLVC is the tip separation vortex cavitation (TSVC). The strengths of cavitation and vortices differ between the rotational and translational domains, leading to varying effects on the equipment.
... In Cartesian tensor form, these equations can be represented as follows: (2), corresponds to the mean strain rate tensor, while the expression − ‾ ρ U ´ I U ´ j accounts for the stresses resulting from turbulent fluctuations, known as Reynolds stresses, with the overbar signifying a time-averaged value. ANSYS Fluent was utilized for the simulations, with the k-ω Shear Stress Transport (SST) turbulence model [36], grounded in the Boussinesq approximation [37]. This approach incorporates two extra transport equations for turbulence kinetic energy and its dissipation to capture the effects of Reynolds stresses in the RANS equations. ...
The flow dynamics and performance of tandem foils, both with and without ground effect (GE), continue to present challenges that are critical to understanding and optimizing aero/hydrodynamic systems, particularly for applications in next-generation wing-in-ground (WIG) effect vehicles, sailing yachts, and hydrofoil vessels. The performance of foils in GE (IGE) versus out of GE has not been extensively compared. This comprehensive study investigates the aero/hydrodynamic performance and flow dynamics of tandem foils using NACA 4412 section at moderate Reynolds number. To isolate the effects of spacing and ground clearance (H), both foils were set at a fixed angels of attack to negate the influence of decalage angle. The design variables examined include horizontal and vertical spacing between the foils, as well as H. Performance comparisons in both GE and out-of-GE conditions were presented, focusing on lift-to-drag ratio, lift and drag, and foil-to-foil interaction dynamics. Numerical simulations were conducted using the finite-volume method to solve the incompressible Reynolds-averaged-Navier-Stokes equations with the shear-stress transport k-ω turbulence model with gamma-transition model. Results indicate that the superiority of tandem foils is highly configuration-dependent. IGE, tandem foils exhibit a significantly higher lift-to-drag ratio than in out-of-GE conditions, where their performance is often lower than that of isolated foils. Positive G between the foils were found to enhance aero/hydrodynamic efficiency, suggesting that optimizing the gap distance can lead to performance improvements. The stagger distance plays a critical role in altering the static pressure distribution due to foil-to-foil interactions. Notably, under certain interference conditions, the fore foil can experience reduced drag or even generate thrust, offering potential advantages for specific aero/hydrodynamic applications. These findings provide new insights into the behaviour of tandem foils and may inform the design of next-generation WIG vehicles, hydrofoil vessels, tandem sails, and other systems where foil interactions are significant.
... Turbulence was modeled using Menter's shear stress transport model [35], along with the ...
In this study, Large Eddy Simulation (LES) is employed to investigate the self-excited detonative tangential combustion instability in a laboratory-scale rocket combustor with multiple impinging-type injectors. Auto-ignition was initiated with an initial condition of 2000 K in the combustor. It was found that the pressure fluctuations generated by ignition did not dissipate, instead, a pair of rotating waves in CW and CCW direction are steepened, promoting the interaction between the pressure wave-heat release rate. The interaction between these pressure waves and the heat release further developed the rotational motion of the heat release zone. This rotational motion coupled with the rotating pressure waves, ultimately establishing a dominant rotating direction. The coupled rotating wave and heat release eventually lead to resonant behavior, resulting in the development of detonative tangential mode instability. During limit cycle operation, the observation of a detonation cell structure further confirmed that tangential mode combustion instability can evolve into a rotating detonation. Comparing this evolution process with the deflagration-to-detonation transition (DDT), it was found to closely resemble the DDT process.
... Model constants [28] α 1 = 0.31, β i,1 = 0.075, β i,2 = 0.0828, σ k,1 = 1.176, σ ω,1 = 2.0, σ k,2 = 1.0, σ ω,2 = 1.168. ...
The impact of fuel injection positioning along the bottom‐wall cavity with aft‐wall divergence in a parallel‐injection, reacting flow environment has been examined through numerical analysis. This simulation employs the two‐dimensional Reynolds‐averaged Navier–Stokes equations coupled with the shear stress transport k–ω turbulence model and a single‐step reaction chemistry model for the fuel–air combustion process. Fuel injection locations at the cavity's fore wall, bottom wall, and aft wall are assessed and compared with a baseline Deutsches Zentrum für Luft‐ und Raumfahrt scramjet combustor. The analysis of numerical results based on varying fuel injection locations reveals that aft‐wall injection enhances the recirculation zone, improving fuel residence time and leading to better mixing and combustion performance. Furthermore, this configuration achieves a 20% reduction in combustor length required for complete combustion, with a 27% increase in total pressure loss due to shock waves emanating from the cavity edges, compared with the baseline model.
... In this paper, the interaction between fluid flow and heat transfer is modeled using various RANS turbulence models taken from the library of the package itself. The standard k-ε model of Launder and Sharma [47], the k-ω model of Wilcox [48] and the SST model of Menter [49] were used to model turbulence. ...
This paper discusses the hot subsonic and near-sonic axisymmetric submerged stationary jets flowing from a nozzle with a radius of 25.4 mm. The Mach number at the nozzle exit is 0.376 for a subsonic jet, and for a near-sonic jet, it is 0.985. The Reynolds number for both problems was equal to 5600. A two-fluid turbulence model was used to study these problems. The numerical results of this model were obtained for both the full elliptic and simplified parabolic systems of equations. The SIMPLE procedure was applied to the numerical implementation of the complete elliptic system of equations. In the parabolic system of equations, the marching method of integrating equations in the longitudinal direction is used. The results of the two-fluid model are compared with the results of other known RANS turbulence models, which were obtained using the COMSOL Multiphysics ® package, as well as with the experimental data from the NASA database.
... Continuity and RANS equations were used as the governing equations. The k-ω shear stress transport turbulence model (Menter 1994) was employed, and a second-order scheme was used in both space and time. Steady simulations were performed to compute the open-water performance of the propeller and towed resistance of the hull without propulsion for analyzing the thrust deduction fraction. ...
This paper presents the design of a ducted propeller for the DARPA SUBOFF submarine. The numerical analysis of the propeller’s hydrodynamic performance—using computational fluid dynamics (CFD)—is also presented. In our study, CFD simulations were performed to predict the propeller performance, and a ducted propeller consisting of a screw, a nozzle, inlet guides, and stators was designed for the SUBOFF model under a self-propulsive condition. The hydrodynamic performance of the ducted propeller was simulated and compared with that of an open propeller (an Istituto Nazionale per Studi ed Esperienze di Architettura Navale (INSEAN) E1619 propeller without a nozzle). The propulsive efficiency was almost equivalent to that of the INSEAN E1619 propeller. Unsteady propeller thrusts were analyzed using a Fourier series, and the amplitudes of the dominant harmonics were higher than those for the INSEAN E1619 propeller. Cavitation performance was qualitatively evaluated by analyzing the flow field around the propeller, which could be suppressed more for the ducted propeller than for the open propeller. Although further studies to improve the hydrodynamic performance are needed, this study demonstrated the fundamental capability of a ducted propeller on an underwater vehicle to enhance the hydroacoustic performance by balancing the propulsive performance over an open propeller.
Improved ship design and market demands have driven the adoption of multi-propeller systems for propulsion in recent years. This study examines the hydrodynamic performance of two KP505 propellers arranged in various transverse and longitudinal spacings, utilizing an in-house CFD code. The numerical simulations employ the URANS method with the SST k-ω turbulence model and a structured overset grid approach. First, standardized mesh and time-step convergence studies are conducted following ITTC recommendations. The hydrodynamic results for the KP505 propeller are compared with experimental data to validate the reliability of the method. Subsequently, over 40 propeller arrangements with varying transverse and longitudinal spacing are simulated. Thrust, torque, and efficiency under different operating conditions are calculated, and key flow field data are analyzed. Finally, the interference characteristics between propellers at different positions are examined by comparing the results with those of a single KP505 propeller. The findings indicate that the high-speed wake generated by the upstream propeller significantly affects the hydrodynamic performance of the downstream propeller. This interaction diminishes as the transverse spacing between the propellers increases. To ensure the propulsion efficiency of the two-propeller configuration, the transverse spacing should not be less than one times the diameter of the propeller.
This paper presents a numerical study of the optimization of the geometric parameters of a four-bladed Darrieus vertical-axis wind turbine (VAWT) with a NACA 0021 aerodynamic profile. The aim of the study was to increase the aerodynamic efficiency of the turbine by selecting optimal values of the rotor diameter and blade chord length. The Taguchi method using an orthogonal array was used as an optimization method, which reduced the number of necessary calculations from 77 to 20 while maintaining the reliability of the analysis. CFD modelling was performed in the ANSYS 2022 R2 Fluent software environment based on a two-dimensional non-stationary model, including a full rotor revolution and an analysis of the steady-state mode for the twentieth cycle. As a result of the analysis, the optimal parameters were determined: rotor diameter D = 3 m and chord length c = 0.4 m. Additionally, for the selected configuration, the numerical model was validated by constructing the dependence of the power coefficient Cp on the tip speed ratio λ in the range from 0.2 to 2.8. The maximum value of Cp was 0.35 at λ = 2.2, which is an increase of ~64% compared to the least efficient rotation mode in the considered range of λ. The obtained results allow us to conclude that the Taguchi method can be used in combination with CFD modelling for fast and accurate optimization of the aerodynamic parameters of low-power wind turbines.
The stability of axial flow pumps is significantly affected by the tip leakage vortex (TLV), which is generated through the entrainment of the main flow. This study explores the effects of circumferential grooving in the rotor chamber on the tip leakage vortex of an axial flow pump by using the SST k-ω turbulence model. Numerical results were validated with prototype pump experiments. At the design condition, circumferential grooves positioned near the blade leading edge enhance both the pump’s efficiency and head. Grooves implemented at the mid-chord to trailing-edge regions are relatively close to those of the prototype pump. The implementation of grooves at both leading and trailing regions resulted in significantly degraded performance compared to the other two cases. However, at reduced flow rates, grooving in the rotor chamber leads to a decline in performance. Grooves positioned near the blade’s leading edge interfere with the ingress of the TLV into the suction side, suppressing vortex formation. Vortex structures and low-pressure regions are closer to the blade, reducing flow instability. In contrast, grooving in the middle and rear rotor chamber induces instability in the tip region. These findings offer theoretical guidance for suppressing the TLV and enhancing the stability of axial flow pumps.
Complex air pollution, including particulate matter and ozone, is a significant environmental issue in China, with volatile organic compounds (VOCs) as key precursors. Traditional ground-based monitoring methods struggle to capture the vertical distribution and changes of pollutants in the troposphere. To address this, we developed a vertical monitoring and sampling platform using a quadcopter unmanned aerial vehicle (UAV). The platform, equipped with lightweight quartz sampling canisters and miniaturized sensors, collects air samples for VOC analysis and vertical data on meteorological parameters and particulate matter. Performance tests showed the quartz canisters had less than 15% adsorption loss, with sample storage stability exceeding 80% over three days. Sensor data showed strong correlations with standard instruments (R2 > 0.80). Computational fluid dynamics simulations optimized the sampler’s inlet position and ascertained that ascending flight mitigates rotor-induced air recirculation. Field campaigns were conducted at six sites along the Chengdu Metropolitan Circle Ring Expressway. Vertical data from 0~300 m revealed particulate matter concentrations peaked at 50~70 m. Near-surface VOCs were dominated by alkanes, while aromatics were found concentrated at 150~250 m, indicating significant regional transport influences. The results confirmed the platform’s effectiveness for pollutant distribution analysis.
Shockwaves induce considerable flow separation loss; it is essential to reduce this using the flow control method. In this manuscript, a method for suppressing flow separation in turbomachinery through a constant adverse-pressure gradient was investigated. The first-passage shock was split into a compression wave system of the vane suction surface. The aim of this was to reduce loss from shockwave/boundary layer interactions (SWBLIs). This method promotes the performance parameters of the supersonic compressor cascade. The investigation targets were a baseline cascade and the improved system. Both cascades were numerically studied with the aid of the Reynolds-averaged Navier–Stokes (RANS) method. The simulation results of the baseline cascade were also validated through experimentation, and a further physical flow analysis of the two cascades was conducted. The results show that the first-passage shockwave was a foot above the initial suction surface, with a weaker incident shock along with a clustering of the compression wave corresponding to the modified cascade. It was also concluded that the first-passage shockwave foot of the baseline cascade was replaced with a weak incident shock, and a series of compression waves emanated from the adopted negative-curvature profile. The shock-induced boundary layer separation bubble disappeared, and much smaller boundary layer shape factors over the SWBLI region were obtained for the improved cascade compared to the baseline cascade. This improvement led to a high level of stability in the boundary layer state. Sensitivity analyses were performed through different simulations on both cascades, unveiling that the loss in total pressure was lower in the case of the updated cascade as compared to the baseline.
Energy-saving device (ESD) plays an important role in mitigating the emission of greenhouse gases in ship industry. It is necessary to study a promising ESD, a gate rudder, for its great potential in promoting energy efficiency. In the present study, ship resistance and self-propulsion simulations were conducted to investigate the energy-saving effects of gate rudder using a viscous in-house CFD solver. First, verification and validation studies were performed to estimate the accuracy and reliability of the numerical method and the results are in good agreement with experimental data. Afterward, resistance and self-propulsion simulations of a crude carrier equipped with the conventional rudder and the gate rudder were carried out respectively. Ship resistance and self-propulsion characteristics with different sailing velocities and propeller revolution rates were compared to study the energy-saving ability of the gate rudder as well as its effects on ship hydrodynamic performance. The results indicate that the gate rudder can greatly optimize the energy efficiency of the ship. Meantime, the ship equipped with the gate rudder shows better resistance and propulsion performance in a self-propelled state.
This study deals with three-dimensional numerical simulation of the drop spreading of water-in-oil (W/O) emulsions with different concentrations of dispersed phase on a solid oleophilic wall. The apparent viscosity values measured by rotational and drop impact viscometry (DIV) are used to describe high-shear rate rheological behavior; the Hershel–Bulkley emulsions are modeled for shear-thinning behavior. The vortex flow from dispersed phase microdroplets in the spreading drop volume and in the boundary layer is modeled using the standard k–ε and Langtry–Menter k–ω shear stress transport models, respectively. Due to the proper packing of the dispersed phase, the influence of vortex flow on the maximum spreading is strongest at a mean emulsion concentration of 30 wt. %, as well as at higher drop impact velocities U0. As U0 rises, a fourfold increase in the vorticity magnitude is found in the vicinity of the boundary layer. The study employs a DIV-based approach to estimate the viscosity at shear rates relevant to drop impact that are not accessible with conventional rheological methods, thereby confirming the complexity of emulsion rheology at high shear rates. In interconnected numerical simulation of complex rheology and vortex flow of the dispersed phase of emulsions with respect to maximum spreading, the validity of the empirical expression for predicting the maximum spreading factor of emulsion drops βmax = 0.82(We/Oh)0.15 [Semyonova et al., “Dynamic and kinematic characteristics of unsteady motion of a water-in-oil emulsion droplet in collision with a solid heated wall under conditions of convective heat transfer,” Int. Commun. Heat Mass Transfer 137, 106277 (2022)] is substantiated. The results are critical in developing the emulsions in terms of high-shear rate rheology and optimizing ink spray, inkjet, and drop-on-demand processes.
The present study investigates the flow dynamics surrounding offshore wind turbine OWT foundations, focusing on the interaction of wind and water flows with two prevalent foundation types: mono-pile and tripod designs. Computational simulations and analyses were conducted on the substructures of these OWTs using the ANSYS-Fluent v16.5 software package. The primary objective was to predict critical parameters, including directional drag force coefficients, interface velocities, and pressure distributions. To model realistic oceanic conditions, pseudo-periodic wave patterns were implemented at the inlet boundary. The flow regime was characterized by logarithmic vertical velocity profiles at low interfacial velocities, ranging from 2.23 m/s to 3.01 m/s. This computational approach revealed anisotropic constraints imposed on the foundations under unidirectional flow conditions. The drag coefficients obtained from the simulations highlighted significant vertical flux exchanges in proximity to the OWT structures, with a particularly pronounced downward flow near the tripod foundation design. Additionally, the study demonstrated that variations in wind speed within the specified range did not substantially impact pressure distributions or strain rates. However, these changes were found to influence skin friction coefficients, indicating a sensitivity of these hydrodynamic parameters to wind speed variations. The analysis of flow streamlines around the mono-pile foundation showed a smooth and well-defined pattern, whereas the flow around the tripod foundation exhibited more complex, interleaved, and turbulent streamlines. This distinction in flow behavior is believed to contribute to the observed downward vertical flux exchanges near the tripod.
Vertical-axis wind turbines (VAWTs) offer key advantages such as independence from wind direction, low manufacturing costs, and reduced noise levels, making them highly suitable for urban and offshore wind energy applications. Among various VAWT designs, the J-shaped VAWT demonstrates improved energy capture at low and medium tip speed ratios (TSRs) compared to symmetrical blade VAWTs, which has garnered increased interest in recent years. However, the mechanisms by which J-shaped blades enhance VAWT performance remain insufficiently explored. In this paper, the high-resolution three-dimensional Improved Delayed Detached Eddy Simulation was employed to investigate the evolution and interaction of complex vortex systems in J-shaped and symmetrical blade VAWTs at varying TSRs, aiming to deepen the understanding of J-shaped blade effects on wind turbine aerodynamic performance. The results indicate that the tip vortex plays a role in inhibiting flow separation, while the J-shaped blade generates a stronger tip vortex, conferring upon it an advantage in suppressing flow separation and delaying dynamic stall. Additionally, the smaller pressure differential between the root and tip of the J-shaped blade reduces cross-flow on the blade surface, thereby reducing susceptibility to flow separation. Therefore, as the blade enters the dynamic stall region at low and medium TSRs, the J-shaped blade achieves a higher lift coefficient than the symmetrical blade, yielding greater torque, and enhancing wind energy utilization.
In aeroengines, the turbine entry temperature profile determines the characteristics of the cooling system, including the flow field occurring in the cavity positioned between the stator rim and the rotor platform, which is used to provide end-wall cooling while ensuring no flow ingestion to prevent harmful configurations. The local flow field depends on the relative position between the blade rows, on the geometry of the cavity, on the rotational speed, and on the mass flow. The flow structures within the cavity may be described by high-fidelity simulations, which are still too onerous at engine-relevant conditions. However, URANS solvers provide information about integral-scale structures development and interaction. In this paper, the results obtained from three unsteady simulations of a high-pressure turbine stage considering different cavity flow rates and rotational speeds are presented. The comparison between the experimental data obtained at the von Karman Institute for Fluid Dynamics, and the numerical results allows for analyzing the interaction between the cavity flow and the main flow. Pressure and velocity fields are analyzed to describe both the sealing mechanism and the formation of secondary flows in the presence of secondary air. It is demonstrated that the occurrence of ingestion regions depends on the potential interaction between the vanes and the blades, and that the wake shed by the vane trailing edge determines the intensity of the phenomena. The secondary flows analysis shows that the stream exiting the cavity impacts the arrangement and strength of the hub passage vortex.
Deep sea submersible simulation has become an effective means of predicting the motion of deep-sea submersibles. The deep-sea operating environment is complex, and deep-sea submersibles are often affected by the interference of ocean currents. This article combines CFD numerical calculation method and six degree of freedom motion simulation modeling method to conduct simulation research on direct flight motion under ocean current interference. This article takes a deep-sea manned submersible as the research object, obtains the lateral ocean current interference force through numerical calculation, and applies the calculated ocean current interference force information to the motion equation of the deep-sea submersible, so as to simulate and study the motion response of the submersible to ocean currents during actual navigation. By comparing with the motion under no ocean current conditions, it can be seen that ocean current has a significant impact on heading and attitude. This study can provide reference for practical manipulation and has certain engineering significance.
This study explores a novel morphing blade design methodology to enhance the aerodynamic performance of the NREL 1.5 MW wind turbine while addressing structural constraints. The proposed approach applies targeted morphing to the leading and trailing edges of the blade sections, utilizing a streamlined parameterization framework with four shape variables per airfoil: two deflection angles and two deformation starting points. The morphing process is modeled using an m-degree shape function and optimized with a genetic algorithm to maximize power generation while minimizing structural displacement and thrust forces. Turbine performance is initially assessed using Blade Element Momentum (BEM) theory and validated through high-fidelity Computational Fluid Dynamics (CFD) simulations based on the Reynolds-Averaged Navier–Stokes (RANS) equations and the k-ω turbulence model. Results demonstrate significant power coefficient improvements of up to 23.8%, 10%, and 7% at wind speeds of 11.5 m/s, 8 m/s, and 4 m/s, respectively, compared to the baseline configuration. These findings highlight the potential of morphing blade technologies to improve energy efficiency in wind turbines while adhering to practical structural limitations.
Microplastics (MPs) have emerged as a major pollutant in aquatic ecosystems, primarily originating from industrial activities and plastic waste degradation. Understanding their transport dynamics is crucial for assessing environmental risks and developing miti-gation strategies. This study employs Computational Fluid Dynamics (CFD) simulations to model the trajectory of MPs in section B of the Salado Estuary in the city of Guayaquil, Ecuador, using ANSYS FLUENT 2024 R2. The transient behavior of Polyethylene Tereph-thalate (PET) particles was analyzed using the Volume of Fluid (VOF) multiphase model, k-omega SST turbulence model, and Discrete Phase Model (DPM) under a continuous flow regime. Spherical PET particles (5 mm diameter, 1340 kg/m 3 density) were used to establish a simplified baseline scenario. Two water velocities, 0.5 m/s and 1.25 m/s, were selected based on typical flow rates reported in similar estuarine systems. Density contour analysis facilitated the modeling of the air-water interface, while particle trajectory analysis revealed that at 0.5 m/s, particles traveled 18-22.5 m before sedimentation, whereas at 1.25 m/s, they traveled 50-60 m before reaching the bottom. These findings demonstrate that higher flow velocities enhance MP transport distances before deposition, emphasizing the role of hydrodynamics in microplastic dispersion. While limited to one particle type and idealized conditions, this study underscores the potential of CFD as a predictive tool for assessing MP behavior in aquatic environments, contributing to improved pollution control and remediation efforts.
The selection of T-groove end face seals (T-EFS) with optimized structural parameters, based on operating conditions, is critical to regulating gas flow into the bearing chamber in aero-engine accessory gearboxes. Therefore, according to the actual forced of T-EFS, based on the force equilibrium, the leakage model for T-groove end face seals is modeled by considering the change in closing force due to the spring stiffness, after verifying the accuracy, the effect of structural and operational parameters on sealing characteristics are analyzed. The results show: the proposed modelling can accurately solve and analyze the sealing characteristics of non-contact end face seals. The increase of preload spring force can reduce leakage, but the increase of revolving speed and pressure ratio can increase leakage. Among them, pressure ratio has the most considerable effect. Increasing the number of grooves can make leakage increase exponentially, increasing groove depth can make leakage increase logarithmically, and increasing groove width ratio can increase leakage. Among them, the number of grooves has the greatest effect.
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