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Parametric Analysis of a Large-Scale Cycloidal Rotor in Hovering Conditions
Abstract
In this work, four key design parameters of cycloidal rotors, namely the airfoil section;
the number of blades; the chord-to-radius ratio; and the pitching axis location, are
addressed, both having a strong effect on the rotor aerodynamic efficiency. To this aim,
an analytical model and a numerical approach, based on a finite-volume discretization
of 2D unsteady RANS equations on a multiple sliding mesh, are proposed and
validated against experimental data. A parametric analysis is then carried out
considering a large-scale cyclogyro, suitable for payloads above 100 kg, in hovering
conditions. Results demonstrate that the airfoil thickness significantly affects the rotor
performance; such a result is partly in contrast with previous findings for small- and
micro-scale configurations. Moreover, it will be shown that increasing the number of
blades could result in a decrease of the rotor efficiency. The effect of chord-to-radius
will demonstrate that c/R values of around 0.5 result in higher efficiency. Finally it is
found out that for these large systems, in contrast with MAV-scale cyclogyros, the
generated thrust increases as the PA is located away from the leading edge, up to
35% of chord length. Further the shortcomings of using simplified analytical tools in the
prediction of thrust and power in non-ideal flow conditions will be highlighted and
discussed.
... They concluded that the use of multi-DBDs could delay stall and achieve faster flow reattachment than the use of a single DBD, and an optimum position arrangement of the actuators must be chosen. Later, Xisto et al. [17] performed an unsteady CFD two-dimensional analysis of the effect of several blade geometrical parameters in hovering conditions. They concluded that, for large-scale applications, the rotor efficiency and thrust capability increases with blade thickness. ...
... To cancel the virtual camber effect on cyclorotors, one solution could be the use of geometrical cambered blades [17] in the rotor, which can improve rotor performance if the camber can be changed to the other direction in the upper and lower half of the rotating cycle. ...
... The lift coefficient comparison for the base case and the control law for the blades is shown in Fig. 19 using the first pair actuators located on the leading edge of the blades (as shown before in Figs. 17,18). It is clear that in each blade, the maximum lift coefficient is increased when using the control law as compared to the base case, depending on the position of each blade where the upper actuator is activated in the upper half and the lower one in the lower half but also we notice that between 300 to 350 and 30 to 70 and also between 120 to 160 there is a slight decrease in lift coefficient as compared to the base case because there is a time delay when the upper actuator is turned off while the lower actuation is turned on/off. ...
In the operation of cycloidal rotors the flow structure deformation, and associated curvature, limits the possibility of achieving an optimum working point. In this study, first, we started by performing a detailed analysis of the start-up characteristics of a cycloidal rotor in order to identify the evolution of kinematic and dynamic characteristics of its operation. Afterwards, we identified the effects of applying multiple plasma boundary layer control, of dielectric barrier discharge type. This application is defined in both sides of the blades, since in cyclorotor movement they change from pressure to suction side over one blade rotation. A control law is defined to regulate the operation of the plasma actuators as the rotor blade move in azimuthal direction. The coupled multi-physics simulation of the cyclorotor and plasma flow is performed by adding to Fluent two user define functions to model the complex cyclorotor movement and the plasma momentum effect. The k-x SST turbulence model is used in the computations. The study is performed for a cyclorotor comprised of six NACA 0016 blade profiles that rotate at 200 rpm. The results demonstrate the advantage of using multiple plasma actuators in order to control the blade flow field. In particular, the configuration with six actua-tors, three in each side, was the most effective, by improving the thrust by 2.3%, as compared to the base case, and achieving a reduction in power requirements of 0.9%.
... They concluded that the use of multi-DBDs could delay stall and achieve faster flow reattachment than the use of a single DBD, and an optimum position arrangement of the actuators must be chosen. Later, Xisto et al. [17] performed an unsteady CFD two-dimensional analysis of the effect of several blade geometrical parameters in hovering conditions. They concluded that, for large-scale applications, the rotor efficiency and thrust capability increases with blade thickness. ...
... To cancel the virtual camber effect on cyclorotors, one solution could be the use of geometrical cambered blades [17] in the rotor, which can improve rotor performance if the camber can be changed to the other direction in the upper and lower half of the rotating cycle. ...
... The lift coefficient comparison for the base case and the control law for the blades is shown in Fig. 19 using the first pair actuators located on the leading edge of the blades (as shown before in Figs. 17,18). It is clear that in each blade, the maximum lift coefficient is increased when using the control law as compared to the base case, depending on the position of each blade where the upper actuator is activated in the upper half and the lower one in the lower half but also we notice that between 300 to 350 and 30 to 70 and also between 120 to 160 there is a slight decrease in lift coefficient as compared to the base case because there is a time delay when the upper actuator is turned off while the lower actuation is turned on/off. ...
In the operation of cycloidal rotors the flow structure deformation, and associated curvature, limits the possibility of achieving an optimum working point. In this study, first, we started by performing a detailed analysis of the start-up characteristics of a cycloidal rotor in order to identify the evolution of kinematic and dynamic characteristics of its operation. Afterwards, we identified the effects of applying multiple plasma boundary layer control, of dielectric barrier discharge type. This application is defined in both sides of the blades, since in cyclorotor movement they change from pressure to suction side over one blade rotation. A control law is defined to regulate the operation of the plasma actuators as the rotor blade move in azimuthal direction. The coupled multiphysics simulation of the cyclorotor and plasma flow is performed by adding to Fluent two user define functions to model the complex cyclorotor movement and the plasma momentum effect. The k- SST turbulence model is used in the computations. The study is performed for a cyclorotor comprised of six NACA 0016 blade profiles that rotate at 200 rpm. The results demonstrate the advantage of using multiple plasma actuators in order to control the blade flow field. In particular, the configuration with six actuators, three in each side, was the most effective, by improving the thrust by 2.3%, as compared to the base case, and achieving a reduction in power requirements of 0.9%.
... 15 Xisto et al. performed parametric analysis on the cycloidal propeller in hover status. 16 They concluded that the best chord to radius ratio is about 0.5 and the best pitching axis location is 35% of blade chord from the leading edge. Gagnon et al. developed the analytical model for the cycloidal rotors. ...
... The blade swept area was deemed as thin actuator surfaces, across which the rotor imparts axial momentum into the flow. 2 Leger et al. proposed the equivalent rotor model. 15,16 In this model, the blade oscillation was simulated by Garrick model. The resultant velocity of blade was computed by the empirical equations. ...
... The numerical simulation can provide satisfactory solutions in the presence of adverse pressure gradients and dynamic stall. 16 Gagnon proposed the 3D numerical simulations based on sliding mesh technique using OpenFOAM. 17 All the models stated above can predict the aerodynamic forces with good accuracy. ...
In recent years, a lot of research work has been carried out on the cycloidal rotors. However, it lacks thorough understanding about the effects of the blade platform shape on the hover efficiency of the cycloidal rotor, and the knowledge of how to design the platform shape of the blades. This paper presents a numerical simulation model based on Unsteady Reynolds-Averaged Navier–Stokes equations (URANSs), which is further validated by the experimental results. The effects of blade aspect ratio and taper ratio are analyzed, which shows that the cycloidal rotors with the same chord length have quite similar performance even though the blade aspect ratio varies from a very small value to a large one. By comparing the cycloidal rotors with different taper ratios, it is found that the rotors with large blade taper ratio outperform those with small taper ratio. This is due to the fact that the blade with larger taper ratio has longer chord and hence better efficiency. The analysis results show that the unsteady aerodynamic effects due to blade pitching motion play a more important role in the efficiency than the blade platform shape. Therefore we should pay more attention to the blade airfoil and pitching motion than the blade platform shape. The main contributions of this paper include: the analysis of the effects of aspect ratio and taper ratio on the hover efficiency of cycloidal rotor based on both the experimental and numerical simulation results; the finding of the main influencing factors on the hover efficiency; the qualitative guidance on how to design the blade platform shape for cycloidal rotors. Keywords: Blade pitching motion, Cyclocopter, Cyclogyro, Cycloidal rotor, Dynamic stall
... One of the types of prospective propellers for aircraft is the cycloidal rotor [1][2][3][4]. It is a device with horizontal axis of rotation, to which the airfoils (blades) are arranged in parallel. ...
... Carrying out literature analysis allows establishing that for the rotors of the size ~1.0m, different authors offer the following optimal parameters: -the number of blades: 4 -6; A rotor version with a diameter D = 1.2 m, length L = 1.2 m with NACA 0016 profile with a chord length of 300 mm, and kinematics of blades identical to [1], [4], [5] was chosen for the test calculations. ...
... In most papers [1], [4], [5], [6], the URANS approach with Spalart Allmaras and -ω SST turbulence models are used to study the aerodynamics of rotor propulsors. In this paper, a more consummate two-parameter -ω SST turbulence model with the use of wall functions was chosen for calculation. ...
The paper is devoted to a numerical study of the characteristics of a cycloidal rotor depending on its construction features. It is established that the 2D simulation does not adequately resolve the investigated problem. This is connected with the complex three-dimensional structure of the flow formed by rotor. The 3D calculations allow detecting sucking in airflows into the end faces of rotor. This requires studying the effect of the end faces construction. Two rotor geometry options with open and closed end faces are considered. The significant dependence of formed flow structure behind the rotor, rotor thrust, and energy characteristics depending on the design of its end faces is established.
... Leger et al. developed a simulation model for the cycloidal rotor with good accuracy 15 . Xisto et al. performed parametric analysis on the cycloidal propeller in hover status 16 . They concluded that the best chord to radius ratio is about 0.5 and the best pitching axis location is 35% of blade chord from the leading edge. ...
... The blade swept area was deemed as thin actuator surfaces, across which the rotor imparts axial momentum into the flow 2 . Leger et al. proposed the equivalent rotor model 15,16 . In this model, the blade oscillation was simulated by Garrick model. ...
... Legar et al. performed 2D CFD analysis based on a finite-volume implementation of the incompressible URANS. The numerical simulation can provide satisfactory solutions in the presence of adverse pressure gradients and dynamic stall 16 . Gagnon proposed the 3D numerical simulations based on sliding mesh technique using OpenFOAM 17 . ...
... 2), airfoil shapes (Refs. 3,4), the Magnus effect on the rotor axle (Ref. 5), virtual camber (Refs. ...
... The resulting good agreement between CFD and the experiment is shown in the front view of Fig. 25 for which a 3D animation is also available online. 4 The inflow in both experiment and simulation exhibits a hemispherical component where the surrounding air is drawn by the rotor wake even downstream of the rotor. This suction effect is stronger for the air coming from the spanwise direction as for the radial direction. ...
A three-dimensional (3D) unsteady Reynolds averaged Navier–Stokes (URANS) computational fluid dynamics (CFD) toolkit for cycloidal rotors was developed and used to perform a parametric study. It included blade aspect ratio, side disks, pitch mechanism, blade camber, and shaft size. The influence of the pitch rod length showed the importance of the lift distribution between the upstream and downstream parts of the rotor cylinder. The application of blade camber significantly affected thrust and power, while having a limited effect on efficiency. A similar effect was obtained by varying the pitch rod lengths. The presence of a central axis in the rotor had a negligible effect on efficiency. The most significant impact on efficiency came from the side disks, which behaved similarly to winglets on fixed-wing aircraft. However, changing the aspect ratio of the blades showed a similar response to that of aircraft wings, but with a smaller effect, making it conceivable to fly a square-bladed cyclorotor without side disks. To verify the CFD model, a cycloidal rotor was also built using 3D printed parts and carbon fiber tubing. It was then operated on a test rig where thrust and power were measured for speeds ranging from 408 to 2528 RPM. On the test bench, the blades were pitched with a uniform asymmetric mechanism. The maximum nose-up pitch angle in upstream of the rotor axis was 34.8°. Due to its rotation around the rotor and its pitching in the opposite direction, the maximum nose-up pitch angle of the downstream blade was 38.6°. The obtained rotor thrust and power curves and the flow visualization around the rotor confirmed the validity of the CFD toolkit.
... at a uniform speed along their span, which allows the achievement of the best aerodynamic efficiency from each blade [12]. In fact, studies have shown that these propulsive systems can generate higher thrust per power unit than conventional screw propellers can when operating under a similar disk load [13]. In addition, by changing the pitching angle of the blades and controlling the rotational speed, the propulsive jet can be instantaneously controlled in terms of magnitude and direction, providing higher maneuverability and controllability to the aircraft [14]. ...
... At this time, a European consortium, under the project CROP (Cycloidal Rotor Optimized for Propulsion), developed several works which allowed the undertaking of various important conclusions regarding the use of cycloidal rotors in commercial aircrafts. Under this project, various works were performed, including analytical studies [27,28], numerical simulations [13,29,30] and experimental tests [31], and demonstrated that cycloidal rotors can be integrated with helicopters, allowing an increase in efficiency to about 60%, or with wings, allowing an efficiency increase of about 40% [32]. In a follow-up of this project, Habibnia and Pascoa [33][34][35] numerically studied the operation of cycloidal rotors under diverse conditions and altitudes, and demonstrated the possibility of optimizing these devices by implementing artificial neural network algorithms. ...
Airships are a method of transportation with reduced fuel consumption and great potential for different applications. However, these aerial vehicles still present considerable control and maneuverability problems. To overcome these issues, in the current work, we propose the use of plasma-enhanced cycloidal rotor thrusters to increase the controllability and maneuverability of airships. Numerical simulations are carried out to demonstrate the potential of plasma actuators to enhance the efficiency and thrust vectoring capabilities of cycloidal rotors. The fluid dynamics of the flow effects created via the operation of the cycloidal rotor is analyzed with and without plasma actuation. In addition, smart combined plasma actuation is proposed to further optimize the plasma-coupled cycloidal rotor device. The results demonstrated that by using this novel approach, the lift coefficient was increased by about 27%. To summarize, the obtained results for a rotational speed of 100 rpm are compared with results for 200 rpm, and it is demonstrated that for lower rotational speeds, the plasma effect is increased and more significant. This allows us to conclude that airships are an ideal application for plasma-enhanced cycloidal rotors, because since the lift is mostly generated via aerostatic principles, the plasma-enhanced thruster can be operated at lower rotational speeds and effectively increase the controllability and maneuverability of the aerial vehicle.
... Another important step was made by Wheatley [7,8], when he built an experimental stand on which he tested a 4-blade cycloidal rotor equipped with blades with the NACA 0012 profile. Author described the distribution and the way in which forces are generated on the rotor with determination of the relationships between them Important work was also performed in relation to the European CROP [9][10][11][12] (Cycloidal Rotor Optimized for Propulsion) project of 2015, which aimed to create a "radically different propulsion system for aerial vehicles". In a series of papers, the authors examined the influence of the geometrical properties of the cycloidal rotor itself on its aerodynamic efficiency and determined the optimal angles for MAVs equipped with a cycloidal rotor [13] developed a fully flying cyclocopter (UAV) that uses 2 cycloidal rotors for flight. ...
... The subject of the research was a cycloidal rotor fan (CRF) operating in a tunnel (Fig. 1). Based on the available scientific studies [10,11], it was decided to test a relatively small machine with a diameter of R=7cm and a span s=25 cm. A 4-blade variant of the fan was selected due to the popularity of this application ( Fig. 2) [11]. ...
Despite the wide possibilities of using a cycloidal rotor in the form of propulsion systems for unmanned aerial vehicles (UAV), cycloidal propellers for sea-going ships, rotors of wind turbines or sea or river cycloidal energy converters, there is practically no research on the use of this solution in the form of a cycloidal rotor fan (CRF) for HVAC (heat, ventilation & air conditioning) applications. The main features of such a machine, compared to conventional solutions, is a possibility of changing the flow direction only by changing pitch angles of the rotor blades. This study analysed two variants of the fan, first equipped with an asymmetrical CLARK Y profile, and other with a symmetrical NACA0012. Numerical simulation of cycloidal rotor fan developed in Ansys CFX was presented, that enables the simulation of fan operation. The results obtained from CFD for both variants were compared with those obtained during experimental measurements made with the use of Laser Doppler Anemometry (LDA). The comparison showed good agreement between the numerical analysis and the performed experiment. Despite the operation based on the same cycloidal regulation settings and rotation speed, the fan equipped with symmetrical blades slightly more curved the flow angle than the asymmetrical one.
... Between 2013 and 2014, the international CROP (Cycloidal Rotor Optimized for Propulsion) project aimed at introducing an innovative cycloidal rotor propulsion system to introduce a new concept for air vehicles, overcoming the traditional limitations of short take-off and landing, including the possibility of hovering [6,[21][22][23][24][25]. ...
... Point 0 is the geometrical center of the rotor, point E is the geometrical center of the mechanical cycloidal control moved by angle ε, point P is the blade pivoting point, while M is the point of attachment of the mechanical control gear arm with length L to the blade. Inclination angle θ can be described as in [25]: ...
Even though the cycloidal rotor concept has been around for almost a century, it is still not as popular as it should be. Most often it is used to propel unmanned aerial vehicles or sea-going ships, or it is applied as a river- or sea-energy converter. Despite the possibility of directing the flow by changing the inclination angle of blades and the possibility of working in both directions, there are no scientific studies on the use of the concept in HVAC (heat, ventilation and air conditioning). One of the most important elements characterizing the operation of the cycloidal rotor is the cycloidal function describing the change in the angles of the blades during rotation. To properly design a cycloidal rotor for a preferred application, an analysis of the rotor geometrical parameters must be performed and analyzed. This was performed on a four-blade rotor equipped with CLARK Y blades. Using Ansys CFX software, a CFD model of a fan operating with various cycloidal functions was created. The results were compared with the experimental data with the use of the LDA technique. Different velocity profiles were obtained despite the use of cycloidal functions with similar waveforms and small angular differences. This is due to the considerable sensitivity of the cycloidal regulation system to differences in the geometrical sizes that describe it.
... Cycloidal rotor is an attractive propulsion system for a wide range of aircraft applications. This type of propulsion system has very good maneuverability for various flight conditions, including hovering, and is mainly dedicated to vertical take-off and landing (VTOL) aircrafts [1] [4]. It was experimentally proved that besides good aerodynamic performance the cycloidal rotor produces little aerodynamic noise, what may be promising in terms to use it for fans. ...
... It was experimentally proved that besides good aerodynamic performance the cycloidal rotor produces little aerodynamic noise, what may be promising in terms to use it for fans. So far several analytical models were developed [4] [5] [6] which to-gether with experimental investigations were helpful in design process of cycloidal rotors. However, currently, the Computational Fluid Dynamics (CFD) allows to take into account unsteady phenomena and it is willingly used in design and analysis of the operation of the cycloidal rotor of various configurations [7] [8] [9] [10]. ...
In this work, the cycloidal rotor fan (CRF) performance was estimated by means of a numerical method based on Unsteady Reynolds Averaged Navier-Stokes equations (URANS). The fan with a cycloidal rotor belongs to the positive displacement machines of the rotary type. The numerical algorithm for simulation of the flow in the cycloidal rotor as well as postprocessing of the CFD results was prepared using Ansys CFX CEL. The methodology for the assessment of the CRF performance was proposed and verified. It was found out that the CRF performance strongly depends on the shape of the profile of the applied rotor blade. The NACA 0012 and CLARK Y profiles were tested for the same CRF structure and flow conditions. Also, the crucial importance for the CRF performance has the range of the blade pitch angle change.
... First of all the emphasis is placed on the ability of rapid change of thrust in force and direction, as well as relatively low noise level during rotor operation. Prototypes of the so-called cyclocopters (cyclogyros) of different scale and design are being created [1][2][3][4][5][6][7]. The influence of the number of blades, aspect ratio, chord, and the shape of the wing profiles on the efficiency of the rotors the papers describe. ...
The paper presents the results of an experimental and numerical study of the aerodynamic and thrust-energy parameters of a cycloidal rotor depending on the geometric features of the end faces. It has been shown experimentally and by numerical methods that the use of end disks with sharp edges leads to the formation of a separated flow and a decrease in the effective surface area of the wing. Various design options for end fairings are considered. The expediency of using inward-rounded fairings forming a uniform input flow to the entire plane of the rotor blades is shown. The use of fairings leads to an increase in aerodynamic efficiency of up to 8%. Changing the rotor design by placing blade control mechanisms inside a profiled end faces leads to an increase in efficiency of more than 12%.
... In contrast to conventional rotors, the motion of the fluid through the rotor is strongly bidimensional. Thus, researchers used two-dimensional (2D) CFD to analyze different cyclorotor features such as the interactions between the blades [6], alternative pitch functions [7], airfoil shapes [8,9], and Magnus [10], virtual camber [4,11,12], and other dynamic effects [13]. ...
This paper studied the influence of the Reynolds number on lift, power, and efficiency of a three-bladed cycloidal rotor in hover. In a parameter study, Reynolds numbers from 10,000 to 600,000 were investigated. The fluid mechanics were solved using incompressible 2D unsteady Reynolds-averaged Navier–Stokes (URANS) computational fluid dynamics (CFD). The CFD model was first carefully validated using experimental data for a pitching airfoil undergoing dynamic stall. The model was then verified to reproduce the shapes of both the force and power curves and the wake flow of a landmark cyclorotor experimental study. Two different flow regimes were identified: for the first regime Re ranged from 10,000 to 100,000 and two dynamic flow separations occurred, the first at maximum pitch angle and bottommost position of the blade and the second shortly afterwards. The second flow regime had Re from 200,000 to 600,000 and avoided the first separation due to the increased Reynolds number. Both separations were visible in the flow as well as in the azimuthal lift distribution. Regardless of the flow regime, rotation averaged lift and power followed the predictions of momentum theory, except for Re of 500,000. At this Re, a significant drop in power was observed and corresponds to findings of a 20-year old experimental study which were at the time classified as possibly wrong. This particular behavior at Re of 500,000 is explained by a change in shape of the downwash, which avoids flow separation as the blade starts to travel upwards.
... Although the cycloidal rotor was invented more than a century ago [1], it is not widely used nowadays. Mostly it is used as a propulsion of small unmanned aerial vehicles in aviation, in maritime its variant in the form of a cycloidal propeller is used for maneuvering the ship [2][3][4][5][6][7][8][9][10]. Thanks to its advantages, such as, the possibility of a quick change of the flow direction [9][10][11], higher flow efficiency than in the case of machines without cycloidal regulation and the possibility of using a Gurney flap (for fans) [12]. ...
A fan with cycloidal rotor (CRF) becomes a popular idea in wide application such as aviation, HVAC (heat, ventilation and air conditioning) or marine propeller systems. This is due to advantages such as direct control of the flow direction, larger flow rates than in a conventional machines without cycloidal control. In the presented article, velocity fields of CRF placed in a rectangular channel was measured, using Laser Doppler Anemomentry (LDA) method and thermoanemometric probe (TA).
... Andrisani et al. [14] presented a numerical study to define an optimal pitch schedule profile for cycloidal rotors that minimize the power average consumption for achieving higher thrust. Additionally, Xisto et al. [15] discussed the effects of blade number and advance ratio on the cyclorotor performance. They found that the rotor efficiency increased with blade thickness and also affected by the pitching amplitude, in which the best pitching axis location was at 35% chord length from the leading edge. ...
This study analyzes the effect of DBD plasma actuators on the unsteady flow of a cycloidal rotor with six blades of NACA 0016 type using computational fluid dynamics (CFD). The flow field modeling is performed through a sliding mesh technique that was used with k-ω SST turbulence model. The plasma body force generated by a dielectric barrier discharge DBD actuator is modeled with the phenomenological Shyy's model. The impact of plasma actuators on the flow is studied using two actuators located on the upper and bottom surfaces of the airfoil in each of the cyclorotor blades. Three cases are studied: actuation off; actuation over the upper surface of the blades; actuation over the bottom surface of the blades. The vorticity field and the evolution of the lift, thrust and power consumption are analyzed for when a control law is designed that combines both actuations based on the two last cases. The results show that the use of the proposed control law for plasma actuation improves the cyclorotor lift peak value per blade in 11% and the overall thrust by 1.5%. It is also demonstrated that the plasma actuator mitigates the virtual camber on the cyclorotor, this effect is named counter-virtual camber. We show that DBD actuators produce a reduction on the recirculation bubble at the blades suction surface. This effect is important to reduce the thickness of the blades, bringing improvements in terms of mitigating unsteady periodic mass acceleration in cyclorotors.
... Many experimental studies and computational fluid dynamics (CFD) computations have also been performed in order to analyze the generated thrust, and also the power required for hovering and forward flight conditions [1,16]. Xisto et al. [26] studied the geometrical effects on the performance of a cycloidal rotor. They concluded that the rotor efficiency and thrust capability increase with blade thickness. ...
Cycloidal rotors have the inherent ability to provide vectorized thrust with fast reaction times. However, their present efficiency levels restricts their routinely use as propulsion elements for air-vehicles. Efforts have been made to improve the performance of cycloidal rotors through the optimal combination of its geometric parameters. In the present work the performance improvement of cycloidal rotors is demonstrated using a different approach, namely by imposing an unsteady change on the dynamics and structure of the vortices developed around the blades. This required change on the flow field, around the blades, was applied by adding an harmonic vibration to the traditional cycloidal movement of the blades, thus causing the blades to vibrate as they describe their oscillating pitch movement. This research on the effect of harmonic vibration, on lift and drag coefficients, was done first for a single blade profile, and later for a full cycloidal rotor, and is based on the Takens reconstruction theorem and Poincaré map. Therefore, diverse test cases and conditions were considered: a single static airfoil, an oscillating blade profile, and a complete cycloidal rotor. We concluded that the optimal combination of harmonic vibration parameters, specifically; amplitude, phase angle and vibration frequency, under adequately tuned design conditions, can have a beneficial effect on cycloidal rotor performance.
... Each blade of the cycloidal rotor, in addition to oscillating around a fixed point, also rotates around the center of the rotor. The combined motion around these two points causes the blades to change their respective angles of inclination as described by Leger Monteiro et al. [1], Gagnon et al. [2], Xisto et al. [3]. Thus, at each rotation, the blades cyclically vary their respective angles of attack. ...
In the present work, a numerical study is carried out to compare the performance of seven
turbulence models on a single pitching blade of cycloidal rotor operating in deep dynamic stall regime at moderate Reynolds number. The investigated turbulence models were: (i) kω-SST (ii) kω-SST with γ (iii) Transition SST (γ–Reθ) (iv) Scale Adaptive Simulation (SAS) (v) SAS coupled with Transition SST (vi) SAS with γ (vii) Detached Eddy Simulation (DES) coupled with Transition kω-SST. The wake vortices evolution and shedding analysis is also carried out for the pitching blade. The performance of the investigated turbulence models is evaluated at various critical points on the hysterias loop of lift and drag coefficients. The predictions of the investigated turbulence models are in good agreement at lower angle of attack i.e. αu ≤ 20°. With the increase in the angle of attack, the performance of the investigated turbulence models deviated near the stall and post-stall angle of attack i.e αu ≥ 20° and αd ≥ 17°. The detailed quantitative analysis at critical
points showed that the predictions of SAS and Transition SST-SAS turbulence models are in better agreement with the experimental results as compared to the other investigated models. The wake vortices analysis and FFT analysis showed that the wake vortex characteristics of a blade pitching in the deep dynamic stall regime at moderate Reynolds number is significantly different than that for the low amplitude oscillating blade at the higher reduced frequency as available in the literature.
... Such interaction may improve thrust generation by delaying the stall onset on the downstream blades (Páscoa et al., 2012;Yu et al., 2013). However deterioration of the aerodynamic performance was also observed in a recent computational analysis of large-scale cyclogyros (Xisto et al., , 2015. Several experimental research activities were also realized over the years. ...
A cycloidal propeller is an aircraft propulsion system that is composed by several blades rotating about a horizontal axis perpendicular to the flight direction. The rotor blades prescribe a periodic change on their pitch angle over a cycle of rotation. Many experimental, analytical and numerical studies have been developed in order to calculate force production and power required as well as the real simulation of the blades motion and the cyclorotor mechanical system operation. An important aspect of cycloidal propellers is the study of their efficiency both in hovering state and in forward motion considering 3D effects. For this purpose, it is developed a two-dimensional and three-dimensional CFD model of a cyclorotor whose blades describe the cycloidal path imposed by the pitch mechanical system control. Then, it is taken into account the experimental data for the proper validation. With the validated model, it presented and analyzed the 3D flow field around the cyclorotor under different operating conditions.
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... Such interaction may improve thrust generation by delaying the stall onset on the downstream blades (Páscoa et al., 2012;Yu et al., 2013). However deterioration of the aerodynamic performance was also observed in a recent computational analysis of large-scale cyclogyros (Xisto et al., 2014a(Xisto et al., , 2015. Several experimental research activities were also realized over the years. ...
Vehicle of absolute cross‐country capability equipped with a rotor of two symmetrical balanced spirals of the aerodynamic profile, each of which has a relative rotation. The spirals are fixed above the vehicle body so that the rotor axis is positioned horizontally a short distance in front of the vehicle's center of gravity. To prevent air flow along the forming part, the internal separate walls perpendicular to axis of spiral are brought out to small distance exceeding the thickness of boundary layer. The formation of jets is controlled by an electronic system that monitors the steering commands of the car. Maneuvering the vehicle is performed through an electronic circuit that controls and controls the lighting of candles in different chambers of system. The system may be used for high efficiency conversion of flow energy in the jet stream and generate the additional lift force to support the power units in the stream.
Исследование направлено на разработку и апробацию методики численного моделирования аэродинамических и энергетических характеристик циклоидального ротора. За основу взята конфигурация ротора IAT21 L3. Для нее с использованием CFD-пакета ANSYS Fluent построена математическая модель и выполнен расчет. Проанализировано влияние скорости набегающего потока воздуха на движущийся ротор. Математическая модель и полученные результаты исследования могут быть использованы при создании летательных аппаратов с движителями роторного типа.
This article addresses the study of the aerodynamic and energy characteristics of a cycloidal rotor subject to the influence of the incoming flow. Cycloidal rotor is one of the perspective devices that provide movement of aircrafts. Despite the fact that the concept of a cycloidal rotor arose in the early twentieth century, the model of a full-scale aircraft has not been yet realized. Foreign scientists have developed models of aircraft ranging in weight from 0.06 to 100 kg. The method of numerical calculation of the cycloidal rotor from the article [1] is considered and realized in this study. The purpose of study was the development and testing of a numerical simulation method for the cycloidal rotor and study aerodynamic and energy characteristics of the rotor in the hovering mode and under the influence of the oncoming flow. The aerodynamic and energy characteristics of the cycloidal rotor, rotating at a speed of 1000 rpm with incoming flow on it with velocities of 20-80 km/h, were calculated. The calculation results showed a directly proportional increase of thrust with an increase of the incoming on the rotor flow velocity, but the power consumed by the rotor was also increased. Increase of the incoming flow velocity leads to the proportional increasing of the lift coefficient and the coefficient of drag. Up to a speed of 80 km/h, an increase in thrust and power is observed; at higher speeds, there is a predominance of nonstationary effects and difficulties in estimating the aerodynamic characteristics of the rotor. In the future, it is planned to consider the 3D formulation of the problem combined with possibility of the flow coming from other sides.
In this paper, the investigation of the cycloidal rotor fan (CRF) was presented. A CRF with four blades of the NACA0012 profile was used for the analysis. The CFD calculations were carried out by means of Ansys CFX commercial software. The experimental tests were done using velocity field measurement with the LDA technique. Numerical results were compared with experimental measurement in terms of velocity values. The CRF performance characteristic was prepared on the basis of experimental and numerical results.
Cycloidal rotor is a rotor whose blades pitch around the pitching axis and revolve around the rotor shaft that is parallel to blade. It can generate omni-directional thrust with high efficiency. In this paper, the numerical simulation models were validated by the wind tunnel experiments. Then physics of the cycloidal rotor in forward flight was studied. The effects of blade number and advance ratio were qualitatively discussed based on the numerical simulation results. Results of the analysis indicate that the rotor with more blades will result in smoother force curve, so that there will be lower vibration. However, the rotor with three or four blades will be the most efficient. The maximum forward flight efficiency is obtained from medium-to-high advance ratio. The efficiency is comparable with that of a screw propeller at the same Reynolds number. At low advance ratio, the peak lift on the blade can be observed when the blade is located at the lower left part of its trajectory. This is caused by positive blade pitch angle and relatively large inflow speed, which is similar to the downwash in the rotor cage under hovering status. From medium-to-high advance ratio, the thrust and lift primarily originated from the plunging motion of the blade. If the advance ratio is high enough, there will be negative horizontal force and positive torque, which means that the blade is taking energy from the inflow. Resultant force of the horizontal and vertical force does not vary too much with the advance ratio. But with the advance ratio approaching 1.0, the direction of the resultant force will point upwards and no horizontal force can be observed.
Purpose
– Cycloidal rotors, also known as cyclogyros, are horizontal axis rotary-wing machines with potential for Vertical Take-Off and Landing aircraft applications. The paper aims to devise and validate a new semi-empirical analytical model that is capable of assisting in the structural and aerodynamic design of cyclogyros.
Design/methodology/approach
– The analytical model comprises a purely analytical kinematic sub-component that is used for analyzing the structural feasibility of the rotor. Several geometrical parameters are assessed, e.g. the oscillation schedule of the blades as a function of the properties of the pitching mechanical system. The dynamic sub-component of the model is used for estimating the rotor thrust production and power consumption. This sub-component is semi-empirical and uses a calibration function that was devised using the available experimental data.
Findings
– For a set of initial conditions and geometrical parameters, the model is capable of providing a real animation of the cyclogyro operation. It is shown that the motion of the blades does not comply with the requirements of a perfect cycloidal curve. The study concerning the simulation of the virtual camber effect on the drum blades, with and without the pitch effect, shows that the virtual camber strongly depends on the chord-to-radius ratio and on the aircraft advance velocity.
Originality/value
– A new analytical model capable of assisting in the geometrical and aerodynamic design of cyclogyros is here proposed. The model is capable of providing approximate estimations of the cyclogyro thrust production and power consumption under operating design conditions.
A cycloidal rotor is an innovative horizontal axis propulsion system, which is utilized in the present study to develop a fully-controllable flying aircraft (known as "Cyclogyro"). The present 535 gram cyclogyro uses a hybrid configuration with two cyclorotors and a horizontal tail rotor. Since a cycloidal rotor relies on cyclic blade pitching for producing thrust and also for control, designing a reliable pitch mechanism that can provide the required blade pitching kinematics (depending on the advance ratio) is extremely important. A novel blade pitch mechanism has been developed, which is passively driven by centrifugal force, and could potentially be adapted to generate the required pitching schedules for efficient operation over a range of advance ratios. A simplified flightworthy version of this mechanism was implemented in the present cyclogyro. The mechanism was able to generate the appropriate blade kinematics and the thrust required for the vehicle to hover. Also, the present mechanism is designed such that it is possible to vary both amplitude and phasing of the cyclic blade pitching. A novel control strategy was developed using blade pitch amplitude (thrust magnitude) control for roll, phasing (thrust direction) for yaw and tail rotor for pitch control. The control strategy was implemented using a three gram onboard processor, which was used to stabilize the vehicle without a pilot, through a closed-loop feedback control system. This is the first flight-capable cyclogyro reported in the literature to utilize cycloidal rotors having both pitch amplitude and phase control. The successful flight for the present vehicle also validates the flightworthiness of this completely passive pitch mechanism design, which has great potential for efficient forward flight.
The highly efficient locomotion of birds, insects and fish is based on unsteady fluid dynamics. In recent years, research has focused on tapping into the potential that rests within these unsteady aerodynamic processes. However, most of the dynamic pitch and heave patterns encountered in nature are difficult to produce in an air vehicle that is propelled using rotating shaft power from an engine. To address this problem, this research assessed the feasibility and performance of a cycloidal propeller designed to utilize unsteady aerodynamic lift. A cycloidal propeller consists of one or more propeller blades mounted perpendicular to a rotating disk (see Figure 1). Contrary to current technical implementations of this type of propeller, dynamic pitch changes of a single blade mounted eccentrically to the propeller shaft in order to produce free leading edge stall vortices in the fluid are investigated. To generate thrust, a flow pattern that is the inverse of the von Karman vortex street is created in the fluid. The resulting time averaged flow field distant from the propeller is that of a jet. This type of propeller is particularly suited for low flow speeds, where state of the art propellers become inefficient due to flow separation on the blades. Potential applications include micro air vehicles that may use this device for propulsion as well as vertical take off and landing, and high altitude long endurance (HALE) aircraft that need to produce lift and thrust at low Reynolds numbers efficiently. The ability of a cycloidal propeller to produce similar efficiencies as dynamic pitch and heave motions reported in literature is demonstrated in this work.
In the following paper we perform an unsteady CFD analysis of the effect of several two dimensional blade geometrical parameters in the performance of CROP. The values will be analysed in terms of power loading (Thrust/Power) vs Disk Load (Thrust/Disk Area). The geometric parameters that we investigate include: blade thick-ness; rotor solidity (number of blades); and pitching amplitude.
In the following paper we introduce PECyT system for enhancing the aerodynamic efficiency of cycloidal rotors. For that purpose the incorporation of Dielectric Barrier Discharge plasma actuators for active flow control on a pitching airfoil, under deep-stall conditions, will be assessed using a numerical tool. Two different arrangements of DBD actuators will be analysed, namely single-and multi-DBDs configurations. For the single-DBD plasma actuator the effect of different modes of actuation on the lift coefficient will also be studied. We will show that the multi-DBD actuator, in a steady-actuation mode, could delay stall and allows for a faster reattachment of the flow. However during the downstroke phase of the pitching cycle the unsteady operation of a single-DBD gives us the best results in terms of lift coefficient.
Performance and flowfield measurements were conducted on a small-scale cyclorotor for application to a micro air vehicle. Detailed parametric studies were conducted to determine the effects of the number of blades, rotational speed, and blade pitching amplitude. The results showed that power loading and rotor efficiency increased when using more blades; this observation was found over a wide range of blade pitching amplitudes. The results also showed that operating the cyclorotor at higher pitching amplitudes resulted in improved performance, independently of the number of blades. A momentum balance performed using the flowfield measurements helped to quantify the vertical and sideward forces produced by the cyclorotor; these results correlated well with the force measurements made using load balance. Increasing the number of blades increased the inclination of the resultant thrust vector with respect to the vertical because of the increasing contribution of the sideward force. The profile drag coefficient of the blade sections computed using a momentum deficit approach correlated well with typical values at these low chord Reynolds numbers. Particle image velocimetry measurements made inside the cage of the cyclorotor showed that there are rotational flows that, when combined with the influence of the upper wake on the lower half of the rotor, explain the relatively low efficiency of the cyclorotor.
This study describes the control mechanism of a VTOL UAV cyclocopter. The cycloidal blades system (CBS), which is a thrust system of cyclocopter is composed of several blades rotating about a horizontal axis. To generate the required thrust, the pitch angles of the blades are periodically oscillated by a pitch control mechanism. And it can change both the magnitude and the direction of the thrust almost instantly. For the thrust control mechanism of the cyclocopter, the mathematical model is derived, and the control forces to control the magnitude and direction of the thrust are determined. In addition, it is designed and developed by radio-controlled actuators.
This paper investigates numerically the unsteady separated turbulent flows around an oscillating airfoil pitching in a sinusoidal pattern that induces deep dynamic stalls. The flow is in the regime of relatively low Reynolds number of the order of 105 based on the chord length of the airfoil. Both the URANS and the more advanced DES approaches are employed. The URANS is coupled with two advanced turbulence models, namely the RNG k−ε model and the Transition SST model (γ−Reθ model) and the DES is coupled with the SST k−ω model. A comparison with experimental data shows that the SST k−ω based DES approach is superior to the URANS approach and presents generally good agreement with the experimental data, although the prediction of experimentally observed peek stall angle of attack may not be warranted. The details of the complex flow development of the dynamic stall and the boundary layer transition have been discussed.
After reporting observations on the flight of gulls which indicated that the wing top moves with a cycloidal motion, the author proceeds to an analysis of this type of motion as it might be applied to the propulsion of aircraft. Various aspects of cycloidal propellers, including their efficiency, are discussed, and their application to heavier-than-air and lighter-than-air craft is urged. The advantages of this method of propulsion are discussed. Tests of model and full-size propellers are referred to, but are not included in the paper.
A cycloidal propeller is an aircraft propulsion system that is composed by several blades rotating about a horizontal axis perpendicular to the flight direction. The rotor blades prescribe a periodic change on their pitch angle over a cycle of rotation. Many experimental, analytical and numerical studies have been developed in order to calculate force production and power required as well as the real simulation of the blades motion and the cyclorotor mechanical system operation. An important aspect of cycloidal propellers is the study of their efficiency both in hovering state and in forward motion considering 3D effects. For this purpose, it is developed a two-dimensional and three-dimensional CFD model of a cyclorotor whose blades describe the cycloidal path imposed by the pitch mechanical system control. Then, it is taken into account the experimental data for the proper validation. With the validated model, it presented and analyzed the 3D flow field around the cyclorotor under different operating conditions.
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Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
This paper describes design and experimental works of a 100kg-or-heavier cyclocopter. A cyclocopter is a VTOL aircraft that has the Cycloidal Blade Systems (CBS). This system consists of a horizontal axis and several blades, which make it possible to change direction and magnitude of a thrust vector. The cyclocopter developed in this study has two CBS rotors and a horizontal tail rotor. To reduce drag, the cyclocopter has end plates, improved shape of trailing edge, and control arm. A new concept of control mechanism is proposed that uses a cam path. A stable hovering flight test is performed under tethered condition.
The aerodynamics of a cycloidal propeller operating in hovering flight is systematically studied using numerical method. By solving the time-dependent incompressible Navier-Stokes equations and using a dynamic mesh technique, the complex unsteady flow field around the cycloidal propeller and the time-varying aerodynamic forces are investigated. The wake flow deflection can be observed in the flow field of the cycloidal propeller, which results in a deflection of the thrust. Strong downwash around cycloidal propeller and unsteady interference between blades are induced by the rotation and pitch motion of the blade. The instantaneous vertical, horizontal and resultant thrusts fluctuate cyclically with the azimuths in a pattern similar to sinusoid, and although the direction of instantaneous resultant thrust varies in a comparatively large region during rotating, the direction of averaged resultant thrust produced in each revolution is almost constant at different rotation speeds. This is beneficial to the flight stability and maneuverability of a cyclogyro. When one blade moves upward, the aerodynamic forces of the blade are much higher than that produced when moving downward. With the increase of the blade number, the unsteady interference between blades and the wakes of other blades tend to be stronger, producing great effects on aerodynamic forces of the blades as well as the aerodynamic performance of cycloidal propeller.
This paper describes the systematic performance measurements conducted to understand the role of rotor geometry and blade pitching kinematics on the performance of a microscale cycloidal rotor. Key geometric parameters that were investigated include rotor radius, blade span, chord, and blade planform. Because of the flow curvature effects, the cycloidal-rotor performance was a strong function of the chord/radius ratio. The optimum chord/radius ratios were extremely high, around 0.5-0.8, depending on the blade pitching amplitude. Cycloidal rotors with shorter blade spans had higher power loading (thrust/power), especially at lower pitching amplitudes. Increasing the solidity of the rotor by increasing the blade chord, while keeping the number of blades constant, produced large improvements in power loading. Blade planform shape did not have a significant impact, even though trapezoidal blades with a moderate taper ratio were slightly better than rectangular blades. On the blade kinematics side, higher blade pitching amplitudes were found to improve the power loading of the cycloidal rotor. Asymmetric pitching with a higher pitch angle at the top than at the bottom produced better power loading. The chordwise optimum pitching axis location was observed to be around 25-35% of the blade chord. The power loading of the optimized cycloidal rotor was higher than that of a conventional microrotor.
Rotary wing aeroelasticity is a highly complex phenomenon involving coupling between flexible blade dynamics and unsteady aerodynamics including stall and unsteady wake effects. In this paper, a low-cost computational aeroelastic model including the structural coupling from geometric parameters and nonlinearities associated with structural modeling and dynamic stall, applicable to steady, level forward flight, has been developed. The differential equations of motion are solved in time domain in a sequential manner to obtain the response of all the blades in the rotor system, the dynamic inflow variables, and the sectional loads at every time step. A fourth-order Runge-Kutta integration scheme has been adopted for solving the differential equations. Iterations are carried out until convergence is achieved in blade response and helicopter trim. The effect of blade geometric parameters such as pretwist, hinge offset, and torque offset on aeroelastic response of a helicopter rotor system is investigated numerically. It is shown that the structural coupling from blade geometric parameters significantly influences the rotor blade response and loads.
In the paper it is proposed and described in detail a mathematical model that is able to assist in the design of cycloidal rotors. The method is formulated on a semi-empirical way including unsteady aerodynamic effects that are based on first principles. It is able to predict the overall generated thrust and the power required by the operation of the cycloidal rotor. The model also includes a kinematic package that can provide an instantaneous design and animation of the cycloidal rotor under different regimes of operation. For validation it was addressed three different rotor configurations where it was varied several rotor parameters, namely: pitch amplitude; pitching axis location; blade chord; airfoil thickness; phase angle of eccentricity. It was shown that the proposed model is able to provide a good estimation of thrust and power when compared with the experimental data from these different sources, showing that the semi-empirical approach could be applied in a more general way.
In the paper it is proposed and described in detail a mathematical model that is able to assist in the design of cycloidal rotors. The method is formulated on a semi-empirical way including unsteady aerodynamic effects that are based on first principles. It is able to predict the overall generated thrust and the power required by the operation of the cycloidal rotor. The model also includes a kinematic package that can provide an instantaneous design and animation of the cycloidal rotor under different regimes of operation. For validation it was addressed three different rotor configurations where it was varied several rotor parameters, namely: pitch amplitude; pitching axis location; blade chord; airfoil thickness; phase angle of eccentricity. It was shown that the proposed model is able to provide a good estimation of thrust and power when compared with the experimental data from these different sources, showing that the semi-empirical approach could be applied in a more general way.
Two dimensional numerical simulations of plasma actuator flow control of the ACHEON nozzle are conducted to give insight on the design of an experimental setup. Three configurations of the plasma actuators with single and multi AC-DBD actuators are used in steady mode of operation. AC-DBD actuators in standard mode (forward forcing mode), reverse mode (backward forcing mode) and plasma synthetic jets mode were used. Three different main groups of test cases were investigated by varying the reference velocity at the inlet of the nozzle stream from 4, 5 and 6 m/s. Moreover, each group includes four velocity ratios . The locations of the flow separation points are obtained numerically for all these cases and the plasma actuators are placed slightly upstream of these points leading to a system of seven DBD plasma actuators in the forward forcing mode over the Coanda surface. The induced thrust of the AC-DBD plasma actuators was estimated using a phenomenological model which considers the maximum achieved voltage and frequency from the experiments. Using an excitation voltage with maximum amplitude of 12 kVpp and frequency of 20 kHz, ionic wind was formed with 2.4 m/s velocity. The effects of plasma actuator are presented through change of the thrust and velocity angle and thrust vectoring efficiency. Preliminary results of the experimental set-up correlate well with the numerical design values.
Vertical axis (Cycloidal) propellers have been researched over the past Century for propulsion of aircraft, however they have never been used to successfully fly an aircraft. They are only being used on marine vessels. The attributes of the propeller are low noise, high thrust per horsepower and positive airship control.
This paper describes the systematic experimental and computational (2-D CFD) studies performed to obtain a fundamental understanding of the physics behind the lift and thrust production of a cycloidal rotor (cyclorotor) in forward flight for a unique blade pitching kinematics. The flow curvature effect (virtual camber and incidence due to the curvilinear flow) was identified to be the key factor affecting the lift, thrust and power of the cyclorotor in forward flight. The experimental study involved systematic testing of an MAV-scale cyclorotor in an open-jet wind tunnel using a custom built three-component balance by varying rotor chord/radius ratio and blade pitching axis location, since these two parameters have a strong impact on flow curvature effects. Because of the virtual camber/incidence effects and the differences in the aerodynamic velocities around the azimuth, the blades produce a small downward lift when they operate in the upper half of circular trajectory and a large upward lift in the lower half producing a net lift in the upward direction. The magnitude of this lift depends on the chord/radius ratio and the blade pitching axis location and the direction of lift depends on the sense of rotation. The positive thrust on the cyclorotor is produced when the blades operate in the rear half of the rotor, while they produce a small negative thrust as they operate in the frontal half. The lift per unit power of the rotor is increased with chord/radius ratio until a c=R of 0.67. Moving the pitching axis location closer to the leading edge also increased the lift producing efficiency of the cyclorotor. It was observed that the optimum chord/radius ratio for maximum thrust per unit power decreased with forward speed. A key conclusion was that the lift producing efficiency (lift per unit power) of the rotor (for a constant thrust) increased with forward speed while the thrust producing efficiency (for a constant lift) decreased with forward speed. This study also disproves the conventional argument that a cyclorotor needs two completely different pitching schedules for efficient hover and forward flight because it is clearly shown that a simple phase shifting of the hover kinematics could result in an efficient forward flight kinematics provided the cyclorotor has a high chord/radius ratio.
Rotocycloid propulsion presents interesting performance as a possible long-term alternative to helicopters in a far future. It will lead to increase the energy efficiency of VTOL vehicles. This paper focuses on optimization of an airship with the possibility up to 2000 h/year of photovoltaic propelled flight at a cruise speed about 20 m/s. This paper demonstrates the feasibility of this airship concept and presents a full dimensioning according to the CDE (Constructal Design for Efficiency) developed at University of Modena and Reggio Emilia. The proposed solution has been deeply analyzed and the analysis of performances has been presented. The results allow thinking to a novel class of vehicles designed specifically to take the maximum advantage by this propulsion method.
Surface DBD plasma actuators are novel means of actively controlling flow. They have shown promising ability in reducing drag, postponing transition from laminar to turbulent flow, suppression of separation, noise reduction and enhancement of mixing in differ
ent applications. The CFD simulation of the effect of plasma actuator in such kind of applications could provide more information, and insight, for optimization and design of close looped flow control systems. However, the fluid models for simulating
the formation of the plasma and its effect are computationally expensive such that, although they provide more detailed information about the physics related to the formation plasma, they are still not viable to be used in large scale CFD simulations. In this paper,
we present the modified version of a simpler model that predicts the thrust generated by the plasma actuator with acceptable accuracy and can be easily incorporated in CFD calculations. This model is also free of empirical fitting parameters, being based
on pure flow physics scaling.
A cyclorotor (also known as a cyclocopter or cyclogiro) is a rotating-wing system where the span of the blades runs parallel to the axis of its rotation. The pitch angle of each of the blades is varied cyclically by mechanical means such that the blades experiences positive angles of attack at both the top and bottom positions of the azimuth cycle. The resulting time-varying lift and drag forces produced by each blade can be resolved into the vertical and horizontal directions. Varying the amplitude and phase of the cyclic blade pitch can be used to change the magnitude and direction of the net thrust vector produced by the cyclorotor. Compared to a conventional rotor, each spanwise blade element of a cyclorotor operates at similar aerodynamic conditions (i.e., at similar flow velocities, Reynolds numbers, and angles of incidence), and so the blades can be optimized to achieve the best aerodynamic efficiency. Moreover, because the blades are cyclically pitched once per revolution (1/rev), unsteady flow mechanisms may delay blade stall onset and in turn may augment the lift produced by the blades. Albeit proposed to MAV-scale, its use on large scale vehicles turns problematic, and we proposed in this paper to address their stopovers. Furthermore, since the thrust vector of a cyclorotor can be instantaneously set to any direction perpendicular to the rotational axis, a cyclorotor-based air vehicle may ultimately show better maneuverability and agility as compared to a classical powered conventional rotor system. One major drawback of a cyclorotor is its relatively large rotating structure which might offer a weight penalty when compared to a conventional rotor.
Airships were the first air vehicles, which had the ability to generate lift without the use of aerodynamic flow around wings, also to enable controlled, powered flight, providing long endurance at low energy consumption. They were widely used before the 1940s, but their use decreased as their capabilities were exceeded by those of the airplanes. Their decline continued with a series of several accidents, including the burning of the hydrogen-filled Hindenburg, and the destruction of the USS Akron.
a b s t r a c t The influence of nanosecond pulse-driven, surface-mounted dielectric barrier discharge (DBD) actuators on a transonic flow is studied numerically. An airfoil representing turbo-machinery blades in transonic flow is considered as a test case. A two-dimensional fluid model of DBD is used to describe the plasma dynamics. The model couples fluid discharge equations with compressible Navier–Stokes equations. Simulations were conducted with an airfoil of NACA 3506 profile in a transonic condition of M = 0.75. When a nanosecond pulse voltage is used, with a rise and a decay time of the order of nanoseconds, a signifi-cant amount of energy is transferred in a short time from the plasma to the fluid, which leads to the formation of micro-shock waves and therefore to the modification of flow fea-tures. Moreover, a plasma energy deposition model is developed and presented by using the results of the plasma discharge model.
Effects of horizontal oscillations of the freestream velocity
superimposed on a pitch oscillating NACA0012 airfoil were investigated
using Computational Fluid Dynamics (CFD). The SST k-ω model
coupled with a low-Reynolds number correction was applied for Re
≈105, when the airfoil was undergoing dynamic stall. The
main parameter Φ, the phase difference between the freestream
oscillation and the airfoil oscillation, was varied from 0 to π. The
Φ variation resulted in several times amplitude dynamic loads when
Φ≤π/2 to several times damping dynamic loads for
Φ>π/2 where some dynamic stall loads were damped even below
static stall load values. It was found that Φ variation was divided
into two main ranges based on the values of the unsteady freestream
velocity at dynamic stall. The load variation also appeared with some
differences including the shape of the trailing edge vortex sheet before
stall, the circulation of the dynamic stall vortex pairs, the critical
angles, vortex growth time and the secondary lift peak location that are
discussed in detail.
The Cyclogiro is the name given by NASA researchers in the '30s to an aerodynamic configuration of several large aspect ratio rectangular airfoils with horizontal span, placed on the circumference of a vertical circle of radius of the order of the airfoil chord, and rotating around the circle center at high speed, with periodically changing angle of attack. This configuration produces aerodynamic forces that can be applied to lift and thrust, depending on the phase angle between the instantaneous position and angle of attack. The original approach was to install such rotors instead of an aircraft wing, and thus combine the lift & thrust producing functions. As a result of the state of knowledge of unsteady aerodynamics at the time disparities between predictions and measured forces remained unexplained. This, combined with low efficiency resulted in the concept being abandoned. In the present study the concept is revisited, as a possible propulsor/lift generator for a hover-capable micro-UAV. Preliminary analysis showed that scaling down to rotor airfoil sizes of 10-15 cm span and 2 cm chord will reduce the centrifugal forces to manageable proportions while the aerodynamic forces would be comparable to those obtained by conventional rotors. A series of experiments was performed, showing disparities of up to 30theory. Visualization showed that this difference resulted mainly from interactions between single foil wakes with the following foils, and a numerical study confirmed the magnitude of the effects, in good agreement with the experiments.
A combined experimental and numerical study of a cyclogiro, rotor operating at Reynolds numbers,about 40,000 has been conducted. The study reveals complex flow field with complex (unsteady) interactions between the blades and the wakes of other blades. In spite of this complexity, time-averaged integral forces acting on the rotor can be predicted by a simple momentum theory, properly corrected for thrust-producing area of the rotor and for large Magnus effect. The effective thrust producing area was estimated to be about half of its projected area, suggesting that the effectiveness of a cyclogiro rotor may be comparable with that of a heavy-loaded helicopter rotor.
A cyclocopter propelled by a cycloidal blade system is a new concept of vertical takeoff and landing aircraft. The cycloidal blade system, which can he described as a horizontal rotary wing, offers powerful thrust levels and a unique ability to change the direction of the thrust almost instantly. This paper investigates the development of the cyclocopter with four rotors, file aircraft was designed through computational fluid dynamics and finite element structural analyses. Elliptic blades and a swash plate were applied to the rotor system to improve the rotor performance and control mechanism. Efficient dc brushless motors and lithium-polymer batteries were used for power transmissions. Almost all parts of the rotor blades and fuselage were manufactured out of composite material. Thrust and required power were measured experimentally on the test bed. The experimental result shows that the cyclocopter on produce sufficient thrust for both hovering and low-speed forward flight.
The cycloidal propeller, which can be described as a horizontal rotary wing, offers powerful thrust levels, and a unique ability to change the direction of the thrust almost instantly. In this work, cycloidal propulsion system was designed and implemented with sinusoidal low pitch system to investigate the fundamental characteristics of hovering states. Before experimental study, computational analysis was made in commercial CFD tool, CD Adopco/Star- CD. This work gives schematic view of flow field around rotor. And it predicts the load variation on a blade with respect to revolution and the total thrust from cycloidal rotor, at specific condition. CFD analysis also makes it possible to check the camber effect. The propulsion system was built up with sinusoidal low pitch control mechanism. Thrust, power and efficiency were measured for various conditions of parameter setting. It was accomplished by designing the equipment which can change the rotational radius, number of blade, phase angle of eccentricity and amplitude of eccentricity.
Among the purely aeronautical applications, near-horizontal axis as well as horizontal axis devices are considered. The former cover the radial-lift propeller or 'self-propelling' wing; the latter cover Magnus effect and related systems; cyclogiro systems and horizontal-axis propeller systems with cyclic pitch. A limited investigation of non-aeronautical applications of HARWAS is also made, which covers wing-rotor type windmills, cyclogiro windmill turbines, Magnus effect ship propulsion and cycloidal ship propulsion. Approximately 1200 references are listed. A series of cross-index tables is also included to provide a quick means for the reader to determine the content and availability of the references. An analysis of the various lift systems pertinent to the HARWAS field is made with a view to potential air vehicle applications. Over 20 original aeronautical applications are identified and evaluated in the light of recent advances in power plants, transmissions and lightweight structural techniques. This analysis points out the extraordinary variety of HARWAS and identifies promising new aeronautical systems. A preliminary performance and design study of two promising HARWAS concepts is also reported. The two concepts are the STOL logistics aircraft using a rotating airfoil flap and the amplified high-pitch cyclogiro for application to the composite aircraft mission.
The cycloidal-rotor (cyclorotor) is a revolutionary flying concept which
has not been systematically studied in the past. Therefore, in the
current research, the viability of the cyclorotor concept for powering a
hover-capable micro-air-vehicle (MAV) was examined through both
experiments and analysis. Experimental study included both performance
and flow field measurements on a cyclorotor of span and diameter equal
to 6 inches. The analysis developed was an unsteady large deformation
aeroelastic analysis to predict the blade loads and average aerodynamic
performance of the cyclorotor. The flightworthiness of the cyclorotor
concept was also demonstrated through two cyclocopters capable of
tethered hover. Systematic performance measurements have been conducted
to understand the effect of the rotational speed, blade airfoil profile,
blade flexibility, blade pitching amplitude (symmetric and asymmetric
blade pitching), pitching axis location, number of blades with constant
chord (varying solidity), and number of blades at same rotor solidity
(varying blade chord) on the aerodynamic performance of the cyclorotor.
Force measurements showed the presence of a significant sideward force
on the cyclorotor (along with the vertical force), analogous to that
found on a spinning circular cylinder. Particle image velocimetry (PIV)
measurements made in the wake of the cyclorotor provided evidence of a
significant wake skewness, which was produced by the sideward force. PIV
measurements also captured the blade tip vortices and a large region of
rotational flow inside the rotor. The thrust produced by the cyclorotor
was found to increase until a blade pitch amplitude of 45° was
reached without showing any signs of blade stall. This behavior was also
explained using the PIV measurements, which indicated evidence of a
stall delay as well as possible increase in lift on the blades from the
presence of a leading edge vortex. Higher blade pitch amplitudes also
improved the power loading (thrust/power) of the cyclorotor. When
compared to the flat-plate blades, the NACA 0010 blades produced the
highest values of thrust at all blade pitching amplitudes. The NACA
blades also produced higher power loading than the flat plate blades.
However, the reverse NACA 0010 blades produced better power loadings at
lower pitching amplitudes, even though at high pitch amplitudes, regular
NACA blades performed better. Among the three NACA sections (NACA 0006,
NACA 0010 and NACA 0015) tested on the cyclorotor, NACA 0015 had the
highest power loading followed by NACA 0010 and then NACA 0006. The
power loading also increased when using more blades with constant chord
(increasing solidity); this observation was found over a wide range of
blade pitching amplitudes. Asymmetric pitching with higher pitch angle
at the top of the blade trajectory than at the bottom produced better
power loading. The chordwise op timum pitching axis location was
approximately 25--35% of the blade chord. For a constant solidity, the
rotor with fewer number of blades produced higher thrust and the
2-bladed rotor had the best power loading. Any significant bending and
torsional flexibility of the blades had a deleterious effect on
performance. The optimized cyclorotor had slightly higher power loading
when compared to a conventional micro-rotor when operated at the same
disk loading. The optimum configuration based on all the tests was a
4-bladed rotor using 1.3 inch chord NACA 0015 blade section with an
asymmetric pitching of 45° at top and 25° at bottom with the
pitching axis at 25% chord. The aeroelastic analysis was performed using
two approaches, one using a second-order non-linear beam FEM analysis
for moderately flexible blades and second using a multibody based
large-deformation analysis (especially applicable for extremely flexible
blades) incorporating a geometrically exact beam model. An unsteady
aerodynamic model is included in the analysis with two different inflow
models, single streamtube and a double-multiple streamtube inflow model.
For the cycloidal rotors using moderately flexible blades, the
aeroelastic analysis was able to predict the average thrust with
sufficient accuracy over a wide range of rotational speeds, pitching
amplitudes and number of blades. However, for the extremely flexible
blades, the thrust was underpredicted at higher rotational speeds and
this may be because of the overprediction of blade deformations. The
inclusion of the actual blade pitch kinematics and unsteady aerodynamics
was found crucial in the accurate sideward force prediction.
The viability of a cyclorotor for powering a hover-capable micro air vehicle (MAV) was examined by making performance and flow field measurements. Parametric studies were conducted to determine the dependence of performance on rotational speed, the amplitude of the blade pitch, the blade airfoil shape, and blade flexibility. All of the experiments were conducted using a three-bladed cyclorotor system, which was built light enough to be used on an actual flight-capable MAV. While higher blade pitch angles were found to improve performance and increase the power loading of the cyclorotor, significant bending and torsional flexibility of the blades had a deleterious effect on performance. Blade section camber also proved to be detrimental to overall performance. Force measurements showed the presence of a significant sideward force on the cyclorotor (along with the vertical thrust force), analogous to that found on a spinning circular cylinder. Particle image velocimetry (PIV) measurements made in the wake of the cyclorotor provided evidence of a significant wake skewness, which was produced by the sideward force. The thrust produced by the cyclorotor was found to increase until a blade pitch angle of 45° was reached without showing any signs of blade stall. This behavior was also explained using the PIV measurements, which indicated evidence of a stall delay as well as possible increases in lift on the blades from the presence of a leading edge vortex.
In recent years, interest has been growing in a new class of very small flight vehicles called micro air vehicles (MAVs). Hover capability is highly desirable with respect to the mission requirements of these vehicles. Due to the small size of MAVs and the low Reynolds number regime in which they operate, scaling down conventional rotorcraft configurations to the MAV scale may not yield optimum performance. Unconventional vehicle configurations can be explored to realize high endurance hover capable MAVs. This paper investigates the hover performance of a small-scale cycloidal rotor to determine its viability for use in a micro air vehicle. A 6 inch diameter prototype rotor was constructed and tested to determine the effects of number of blades, blade pitch angle, and rotational speed on thrust output and power requirements. Pressure distribution was measured to obtain insight into the downwash and flow through the rotor. An analytical model, using a combination of vertical axis wind turbine theory and an indicial solution for the aerodynamic response was developed to predict rotor performance, and was validated with the experiments. The performance of the cycloidal rotor was compared to that of a conventional rotor of the same diameter in terms of power loading. Based on the analytical model and the experimental results, a conceptual design of an MAV utilizing cycloidal propulsion was developed. The conceptual cyclo-MAV utilizes two cycloidal rotors, providing thrust, propulsion, and control. Complete vehicle weight is envisaged to be 240 g, with two three-bladed rotors of six inches diameter.
This paper provides a study of the NACA0012 dynamic stall at Reynolds numbers 105 and 106 by means of two- and three-dimensional numerical simulations. The turbulence effect on the dynamic stall is studied by statistical modelling. The results are compared with experiments concerning each test case. Standard URANS turbulence modelling have shown a quite dissipative character that attenuates the instabilities and the vortex structures related to the dynamic stall. The URANS approach Organised Eddy Simulation (OES) has shown an improved behaviour at the high Reynolds number range. Emphasis is given to the physical analysis of the three-dimensional dynamic stall structure, for which there exist few numerical results in the literature, as far as the Reynolds number range is concerned. This study has shown that the downstroke phases of the pitching motion are subjected to strong three-dimensional turbulence effects along the span, whereas the flow is practically two-dimensional during the upstroke motion.
An experimental investigation was conducted to study the flow around a cycloidal propeller. Flow fields were obtained using a particle image velocimetry system whose data acquisition was synchronized with the propeller’s angular position. The chord-based Reynolds number was Re
c = u
rc/υ = 1.4 × 104, where u
r is the rotational velocity of the propeller and c is the chord length of the airfoil. Flow characteristics such as mean velocity, vorticity and the RMS value of velocity fluctuation were derived from the measurements. The results demonstrated the presence of a downwash around the propeller during the generation of lift. Detailed observations around each airfoil visualized distinct vortex shedding and reattaching flow at certain phase angles of the propeller.
Graphical Abstract
Simplified unsteady aerodynamic and inertial force models were developed for a cycloidal propeller system operating at small forward speeds. These models were used to support the development of a VTOL concept demonstrator vehicle. The nature of the blade motion showed that interactions between the blades could be neglected to first order. The downwash through the rotor could not be neglected because of the induced angle of attack caused by the downwash. The total force was compared with wind tunnel data produced by Wheatley in the 30's and a ground test system developed for this project. It was found that the estimates produced by the model agreed with the total force and power to within 10% for the Wheatley data. Agreement between the model and the current tests was within 5% for the total force and power. The inertial loads were used to design the blade structure, the support structure, and the blade motion system. It was found that the inertial loads were much larger than the aerodynamic loads. The aerodynamic effect of forward motion or wind moving toward the propeller was defined. It was modeled as a constant velocity induced flow through the propeller that induced an angle of attack of the blades. It was found that the cycloidal propeller was very susceptible to wind gusts, but that the resultant force from the wind gust could be easily damped out. The same forward motion model was used to simulate downwash. By modeling the downwash as a constant velocity flow through the propeller, the lift and thrust of the propeller was linked to the induced flow velocity. The effect of the induced flow velocity was then linked back to its effect on the lift and thrust produced by the propeller. Mode of access: Internet via the World Wide Web. System requirements: Internet connectivity; World Wide Web browser software; Adobe Acrobat Reader. Title from title screen. Electronic book in PDF. Thesis (M.S.)--Mississippi State University. Department of Aerospace Engineering. Includes bibliographical references.
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