No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The effects of advance ratio and blade number on the forward flight characteristics of cycloidal rotor
Abstract
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.
The blade of a cycloidal propeller rotates while revolving at a constant speed, such that the angle of attack against the oncoming flow changes constantly. This characteristic working principle determines the unique hydrodynamics of cycloidal propellers. In this study, a cycloidal propeller with five blades of NACA 0012 airfoil was numerically simulated using a simplified two-dimensional model via STAR-CCM + software. The convergence of the hydrodynamical behaviors of the modeled propeller was confirmed in order to determine the gridding scheme, with special emphasis on the y⁺ value for the blade surface, the mesh size for the computational domain, and the time step length for the simulation. The thrust, torque, and efficiency of pulsations relative to the centers of blade rotation, which were set at different positions, were computed, and the flow field and vortex distribution of were analyzed. Finally, the hydrodynamic performance of the cycloidal propeller under different operating conditions (e.g., center of blade rotation, eccentricity, advance speed, and rotary speed) were compared to determine the conditions that maximized propeller performance. The findings from this work should serve as a useful reference for improving propeller performance, as well as for optimizing future propeller designs.
The cycloidal propeller for a Micro-Aerial Vehicle (MAV)-scale cyclogyro in hover was studied using a 2D Reynolds-averaged Navier-Stokes equations solver. The effects of the blade dynamic stall, parallel Blade Vortex Interaction (BVI), inflow variation and flow curvature were discussed, based on the results of numerical simulation. The results from the 2D Computational Fluid Dynamics simulation indicated that the blade of the cycloidal rotor is actually performing a pitching oscillation, if observed in a moving reference frame. The dynamic stall vortices shed from the upstream blade cause intense parallel BVI on the downstream blade. The interaction will induce upwash and downwash on the downstream blade. This changes the effective reduced frequency and actually delays the stall of the blade, which is beneficial to the thrust generation. There is also strong downwash in the rotor cage and it changes the inflow velocity experienced by the blade. The downwash and flow curvature can either be beneficial or harmful to the thrust generation. The combined effects of dynamic stall, parallel BVI, inflow variation and flow curvature cause large aerodynamic force peaks and ensure the cycloidal rotors work at very low rotation speeds with high thrust. This guarantees that the cycloidal rotors possess at least the same level of hover efficiency as screw propellers.
This paper presents a 2D computational investigation on the dynamic stall phenomenon associated with unsteady flow around the NACA0012 airfoil at low Reynolds number (Rec≈105). Two sets of oscillating patterns with different frequencies, mean oscillating angles and amplitudes are numerically simulated using Computational Fluid Dynamics (CFD), and the results obtained are validated against the corresponding published experimental data. It is concluded that the CFD prediction captures well the vortex-shedding predominated flow structure which is experimentally obtained and the results quantitatively agree well with the experimental data, except when the blade is at a very high angle of attack.
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 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.
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.
This paper describes the systematic design and development of a hover-capable cyclocopter/cyclogyro, which is a 100-yearold vertical takeoff and landing (VTOL) concept that was invented during the early 20th century. The cyclocopter is an aircraft that utilizes cycloidal rotors (cyclorotors), a revolutionary horizontal axis propulsion concept that appears to be aerodynamically more efficient than a conventional rotor. Another key advantage of the cyclorotor is its thrust vectoring capability, which is utilized in the present study for attitude control. The present vehicle has a twin-cyclorotor and a horizontal tail rotor configuration where each of the rotors is powered using independent motors. A novel attitude control technique is developed using differential rotational speed control and thrust vectoring of the cyclorotors for rolling and yawing and horizontal tail rotor for pitch control. Using this control strategy, for the first time in the history, the stable flight of a cyclocopter was demonstrated.
The numerical simulations for cycloidal propellers based on five airfoils with different thickness are presented in this paper. The CFD simulation is based on sliding mesh and URANS. The result of CFD simulation indicates that all test cases share similar flow pattern. There are leading edge vortex and trailing edge vortex due to blade dynamic stall. Interaction between the vortices shed from upstream blade and the downstream blade is observed. There is also variation of the flow velocity encountered by the blade due to downwash in the cycloidal rotor cage. These factors result in large fluctuations of the aerodynamics forces on the blade. The comparison of the forces and flow pattern indicates that the thickness of the airfoil is very important parameter that influents the flow pattern and hence the performance of the cycloidal propeller.
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.
This paper summarizes the state of knowledge of cyclogyro theory and development in order
to aid those working on researching and designing cyclogyros. A cyclogyro is a horizontal-
axis rotary-wing aircraft. While no cyclogyros have ever been successfully flown, the concept
offers an alternative to helicopters and other VTOL aircraft with several potential advantages.
Research on cyclogyro development was first begun in the 1930's and at least one prototype
was actually built. With the recent interest in small UAV’s and the
development of lightweight electric motors and batteries, interest in the cyclogyro has been
renewed in the last decade. There exists a considerable void between modern works and the
significant amount of research and testing was performed in the first half of the twentieth
century. Many of the early reports are difficult to locate, and there is a lack of continuity
between the works in this field. The goal of this work is to present an overview of the several
widely varied sources in order to reduce the likeliness of redundant efforts, encourage
collaboration and advancement, and help facilitate cyclogyro evaluation in light of modern
materials and technologies.
This paper describes the aeroelastic model to predict the blade loads and the average thrust of a micro air vehicle (MAV) scale cycloidal rotor. The analysis was performed using two approaches, one using a non-linear FEM analysis for moderately flexible blades and second using a multibody based large-deformation analysis (especially applicable for extremely flexible blades). An unsteady aerodynamic model is included in the analysis with two different inflow models, uniform inflow 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 analysis clearly showed that the reason for the reduction in the thrust producing capability of the cycloidal rotor with blade flexibility may be attributed to the large nose-down elastic twisting of the blades in the upper half cylindrical section which is not compensated by a nose-up pitching in the lower half section. The inclusion of the actual blade pitch kinematics and unsteady aerodynamics was found crucial in the accurate lateral force prediction. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc.
A cyclocopter propelled by the cycloidal blade system, which can be described as a horizontal rotary wing, is a new concept of VTOL vehicle. In this paper, structural design and analysis are carried out for the aerodynamically optimized cyclocopter rotor system. Design variables such as stacking sequence (ply angles), number of plies and locations of spars of composite blade are determined through MSC/NASTRAN, RSM and some other optimizing processes. The maximum stress obtained by static analysis of each parts of the rotor is within the failure criteria. The rotor system is designed for the purpose of avoiding possible dynamic instabilities by inconsistency between frequencies of rotor rotation and some low natural frequencies of rotor. Also dynamic analysis for the airframe which supports the rotor, engine, etc. is carried out.
Abstract Acyclocopter,propelled by the ,cycloidal blade system, which can be described as a horizontal rotary wing, is a new concept of VTOL vehicle. In this paper, cyclocopter rotor system is optimized for design variables such as radius of rotor, rotating speed, maximum pitch angle, chord and span of blade, number of blades and airfoil. To apply response surface methodology, datum acquired by STAR-CD for aerodynamic ,design ,variables and MSC/NASTRAN for ,structural ,ones. Genetic algorithm is used to find the optimal values from the constructed,response ,surface ,while ,objective functions are thrust, required power and stress of blade.
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.
The characteristics of the unsteady boundary layer and stall events occurring on an oscillating NACA 0012 airfoil were investigated by using closely spaced multiple hot-film sensor arrays at Re {=} 1.35 {×} 10(5) . Aerodynamic forces and pitching moments, integrated from surface pressure measurements, and smoke-flow visualizations were also obtained to supplement the hot-film measurements. Special attention was focused on the behaviour of the spatial-temporal progression of the locations of the boundary-layer transition and separation, and reattachment and relaminarization points, compared to the static values, for a range of oscillation frequency and amplitude both prior to, during and after the stall. The initiation, growth and rearward convection of a leading-edge vortex, and the role of the laminar separation bubble leading to the dynamic stall, as well as the mechanisms responsible for the stall events observed at different test conditions were also characterized. The hot-film measurements were also correlated with the aerodynamic load and pitching moment results to quantify the values of lift increment and stall angle delay as a result of the observed boundary layer and stall events. The results reported here provide an insight into the detailed nature of the unsteady boundary-layer events as well as the stalling mechanisms at work at different stages in the dynamic-stall process.
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.
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.
If your new or interested in the field of CFD this book with introduction to cfd by john d anderson should be in your personal library.
Experimental investigation of the effect of rotor geometry and blade kinematics on the performance of a MAV-scale cycloidal rotor
- M Benedict
- T Jarugumilli
- I Chopra
Benedict M, Jarugumilli T and Chopra I. Experimental
investigation of the effect of rotor geometry and blade
kinematics on the performance of a MAV-scale cycloidal
rotor. In: Proceedings of the American helicopter society
specialists' meeting on unmanned rotorcraft and network
centric operations, Tempe, AZ, USA, 25-27 January
2011.
Design and development of unmanned VTOL cyclocopter
- S J Kim
- I S Hwang
- H Y Lee
Kim SJ, Hwang IS, Lee HY, et al. Design and development of unmanned VTOL cyclocopter. In: Aerospace
science and technology proceedings, North Carolina,
USA, 12-14 August 2004.
Two dimensional and three dimensional numerical simulation of cycloidal propellers in hovering status In: The 54th AIAA aerospace sciences meeting, AIAA science and technology forum and exposition 2016
- Y Hu
- Hl Zhang
- Gq Wang
Aerodynamics of the cyclogiro
- G Iosilevskii
- Y Levy
Iosilevskii G and Levy Y. Aerodynamics of the
cyclogiro. In: 33rd AIAA fluid dynamics conference and
exhibit, Orlando, FL, USA, 2003, AIAA-2003-3473.
Development of a four-rotor cyclocopter
- I S Hwang
- Min
- Lee Sy
Design, development and flight testing of a twin-rotor cyclocopter micro air vehicle
- M Benedict
- R Gupta
- I Chopra
Benedict M, Gupta R and Chopra I. Design, development and flight testing of a twin-rotor cyclocopter
micro air vehicle. In: Proceedings of the 67th annual
national forum of the American Helicopter Society,
Virginia Beach, VA, USA, 2011.