Cycloidal Rotor Research Articles

Coupled Active Control Technique for Oscillating Blades in a Cycloidal Rotor Using CFD and ANN Analysis by Including 3D End Wall Effects

Cycloidal rotors have shown to be susceptible to achieving larger efficiency enhancements when being subjected to various designs and operating conditions. In this work, an improvement on the performance of a unmanned aerial vehicle (UAV)-scale cycloidal rotor is demonstrated at hovering mode and for various operating conditions with three end wall designs. The novel concept of actively controlling the pitching oscillations at different rotational speeds is obtained from a coupled methodology of computational fluid dynamics (CFD) and artificial neural network (ANN). In this approach, rather than a free-sided rotor, the effects of employing single and double end walls are targeted for optimizing the operation at hover state. A detailed database from numerous combinations of operating conditions is obtained from CFD predictions. Over 18 principal parameters are processed and computed along the continuous 360° circular trace, which is showing novel results. Subsequent to performing a precise database from the rotating-oscillating blades under various operating conditions for all three designs, the ANN approach is trained from the CFD data for optimization analysis and to propose the optimum pitching schedules by using a parametric study on the cyclorotor performance at each operating condition. Because each design can be used in its specific application, the optimum operating state for each of the end wall designs is further illustrated and reported as baseline data. The coupled analysis from CFD and ANN methodologies reports the efficiency achieved with free sides, doubled end walls, and a single side end wall, respectively. Moreover, employing a single side end wall results in 18.8% efficiency, and the double-sided model in 13.6% efficiency reduction compared with the free-sided cyclorotor. The computations on horizontal and vertical force productions are revealing an 8% and 11% higher horizontal force for the free-sides design than those of double end wall and single end wall models, and an average of 7% and 16% higher values in vertical force generation in double end wall model compared with free-sided and single end wall designs.

Active control assessments towards optimizing the performance of a cycloidal rotor at hover

The present study demonstrates an improved performance of cycloidal rotors by actively controlling the pitching oscillations and rotational speeds. The computational fluid dynamics (CFD) coupled with artificial neural network (ANN) were the methodologies used in the optimization analysis for the hover-state operation rather than the take-off mode under ground effects [1]. The former is carried out to obtain numerical predictions at various operating conditions for an UAV-scale cyclorotor. The oscillating-rotating blades and the corresponding flowfield is computed unsteadily along the complete circular trace for performance considerations. From CFD simulations, the optimum operational state is predicted for a 30∘ and 500 (rpm) pitch angle and rotating speed, respectively. On a second step, by training the ANN with the CFD database at various operating conditions and parameters, the ANN was then capable of analyzing the optimum states for operating at different conditions. The pitching oscillation schedule is then optimized for each rotational speed by using ANN and for each azimuthal location over the traversing trace. This will imply to perform on-board control in active mode for the blades, rather than assigning constant pitching oscillations for all operating states. This active control concept showed to be a potential approach to enhance the cyclorotor efficiency by 12 percent in average.

Model experiments with different cycloidal propeller algorithms using same electric controller

This article presents a methodology of controlling the cycloidal propeller electronically in model scale by an experimental approach. It establishes the function of single-unit controlled multiple propeller models such as Kirsten-Boeing and Voith-Schneider propeller. It also deals with the execution of different maneuvering cases like straight acceleration, autopilot, zigzag, crash stop. Blade motors independently control the pitching of the propeller-blades unlike the mechanism of the conventional cycloidal propeller. PID control and heuristic control are investigated for this purpose. Mathematical models for system identification, pulse generation, position, and speed control of propeller blades, and disc and synchronizations are demonstrated. Based on model experimental results, advantages/disadvantages of PID and heuristic control are discussed.

Parametric optimization of a cyclogiro aircraft design for efficient hover with aeroelastic considerations

A minimization procedure is proposed to orient the design of a vertical take-off and landing drone towards sustainability. The vehicle is a novel cycloidal rotor drone and the principal objective is to yield the best ratio of payload to power consumption. The drone blades, rotor arms, and frame are designed for fused deposition modeling additive manufacturing with polylactic acid. 10 variables for the geometry, operation parameters, and material infill percentages are explored in search of the optimum design. A special derivation procedure allows obtaining the symbolic equations for the weight and power consumption of the drone. This permits optimization with a hybrid genetic and gradient method and exploring a broad range of aircraft sizes. 7 constraint equations ensure that the necessary assumptions made for the derivation remain valid and that the structural strength is adequate. For each new configuration, this method allows to quickly find a new optimum design using a desktop computer. Also, modifying the constraints, variables, or objective function is straightforward. Finally, the resulting design has a power loading of 0.0876 N/W.

Performance Optimization of Forward-Flight and Lift-Up Phases in a Cycloidal Rotor Using an Active Control Mechanism

AbstractCycloidal rotors have revealed a noticeable potential to be further enhanced when running at different operating conditions. The present work demonstrates the active control methodology in ...

Cycloidal rotor coupled with DBD plasma actuators for performance improvement

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.

An attempt to measure cycloidal rotor fan in a rectangular duct

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).

Optimization study on the drain mode of cycloidal rotor oil pump

Optimization study on the drain mode of cycloidal rotor oil pump

Nonlinear Aeroelastic Coupled Trim Analysis of a Twin Cyclocopter in Forward Flight

The paper discusses the development of a nonlinear aeroelastic coupled trim model of a twin cyclocopter in forward flight. The twin cyclocopter consists of two cycloidal rotors as main thrusters and a conventional nose rotor for pitch-torque balance. It is shown that five control inputs [mean and differential revolutions per minute (RPM), mean and differential phase offset of cycloidal rotors, RPMs of nose rotor] are needed to balance three moments and two forces on a cyclocopter in forward flight while forces along the lateral direction remain balanced at all stages. Alternatively, the mean and differential pitch amplitude of cycloidal rotors can be used as control inputs while keeping the RPMs of cycloidal rotors constant. In this coupled trim procedure, blade aeroelastic response equations and vehicle trim equations are solved together by simultaneously updating control inputs and blade response. The present model is validated with previously published data by the authors on the performance of a trimmed cycloidal rotor at different forward speeds. Once systematically validated, the model is used to understand the trim behavior of a micro-air-vehicle-scale twin cyclocopter in forward flight. One major conclusion from this study is that the center of gravity of the vehicle is desired to be as close to the cycloidal rotor as possible in order to decrease the required power.

Optimisation scheme applied to the Voith-Schneider propulsion system using genetic algorithm

ABSTRACT This paper is presented to calculate the hydrodynamic characteristics of the Voith-Schneider Propeller (VSP) and its optimisation scheme applied to the vessels using genetic algorithm (GA). VSP is an efficient propulsion system in manoeuvring of service vessels such as tugs, offshore vessels, workboats and some other vessels. In this study, hydrodynamic forces of thrust and torque are considered as objective functions, whereas four geometrical parameters of VSP, i.e. disk radius (R), chord (c), span (b) and pitch ratio (e), are considered as variables. A simple GA optimisation scheme is applied to the VSP system to find the optimum values of the VSP parameters to achieve the highest efficiency, in which the thrust and torque are calculated through the practical formulas. The calculated results of the open-water characteristics at various geometrical parameters are presented and validated against experimental data. Finally, the optimisation scheme is applied to two VSP systems employed for two vessels of Voith Water Tractors (VWT) and Offshore Support Vessels (OSV). The optimisation results showed that the efficiency of VSP improved by 6.2% and 1.6% for OSV and VWT vessels, respectively.

Cycloidal Rotor-Blade Tip-Vortex Analysis at Low Reynolds Number

This study provides the first in-depth analysis of the formation, strength, and convection of cycloidal rotor tip vortices. The measurements of blade force and tip vortex using particle image velocimetry were conducted for different blade aspect ratios and pitch kinematics at a chord-based Reynolds number of 18,000. Particle image velocimetry was employed to investigate vortex development at increasing vortex ages and the early development for varying azimuthal locations. The instantaneous blade force measurements on the cycloidal rotor showed a decrease in nondimensional lift with decreasing blade aspect ratio. The aspect ratio of the blade did not affect the shape of the vortex convection trajectory. However, the rate of downward convection increased with increasing aspect ratio due to the higher thrust produced. The tip vortices showed self-similarity in the velocity and the circulation profiles. The measurements indicate that the vortex core experiences a logarithmic growth and the swirl velocity experiences a logarithmic decay due to viscous diffusion. The tip-vortex strength varied cyclically with blade azimuthal location due to the cyclic variation of blade pitch angle and the dynamic virtual camber effects. This periodic variation in the tip-vortex strength leads to a periodic variation in the induced flow velocity on the blade.

Numerical Analysis of a Cycloidal Rotor under Diverse Operating Conditions and Altitudes

<div class="section abstract"><div class="htmlview paragraph">The current paper presents the numerical study of the downwash flowfield characteristics in a cycloidal rotor at close-ground altitudes. In an aircraft equipped with this kind of thruster, the downwash flow plays significant role in different flight modes. The interaction of this downwash jet with ground in effective altitudes is studied using CFD simulations in OpenFOAM. Several operating conditions such as pitching oscillation angles, rotation speeds and height levels are all considered in this work. The results declare that close-ground operating states affects the performance of cyclorotors. The vertical and horizontal forces of a single blade is also analyzed in a complete cycloid in different operating conditions. A lead and lag in maximum and minimum extremes of force curves of a single blade is obtained while being subjected to different functional conditions. The presented results highly support an active control methodology to be taken for both pitching oscillations and rotation speeds as essential strategy for operating at optimum state.</div></div>

Aerodynamic mechanisms in bio‐inspired micro air vehicles: a review in the light of novel compound layouts

Modern designs of micro air vehicles (MAVs) are mostly inspired by nature's flyers, such as hummingbirds and flying insects, which results in the birth of bio-inspired MAVs. The history and recent progress of the aerodynamic mechanisms in bio-inspired MAVs are reviewed in this study, especially focused on those compound layouts using bio-inspired unsteady aerodynamic mechanisms. Several successful bio-mimicking MAVs and the unsteady high lift mechanisms in insect flight are briefly revisited. Four types of the compound layouts, i.e. the fixed/flapping-wing MAV, the flapping rotary wing MAV, the multiple-pair flapping-wing MAV, and the cycloidal rotor MAV are introduced in terms of recent findings on their aerodynamic mechanisms. In the end, future interests in the field of MAVs are suggested. The authors' review can provide solid background knowledge for both future studies on the aerodynamic mechanisms in bio-inspired MAVs and the practical design of a bio-inspired MAV.

Effects of blade aspect ratio and taper ratio on hovering performance of cycloidal rotor with large blade pitching amplitude

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.

Symmetric Versus Asymmetric Pitching of a Cycloidal Rotor Blade at Ultra-Low Reynolds Numbers

This paper provides a fundamental understanding of the unsteady aerodynamic phenomena on a cycloidal rotor blade operating with symmetric as well as asymmetric pitching at ultralow Reynolds numbers () by using a combination of experimental (force and flowfield measurements) and computational fluid dynamics (CFD) studies. The instantaneous blade fluid dynamic forces on a rotating cycloidal rotor blade were measured, which, along with particle image velocimetry (PIV) based flowfield measurements revealed the key fluid dynamic mechanisms acting on the blade. A two-dimensional CFD analysis of the cycloidal rotor was developed and systematically validated using both force and flowfield measurements. The CFD flow solution and PIV-measured flowfield correlated well, especially in the upper half of the circular blade trajectory, and both showed the formation and shedding of strong dynamic stall or leading-edge vortices at high pitch amplitudes, which is the reason for the stall delay and force enhancement. The dynamic virtual camber induced by the flow curvature decreased the blade lift in the upper half due to negative induced camber; however, the lift increased in the lower half due to positive camber. Therefore, introducing an asymmetry in pitch kinematics with higher pitch in the upper half and lower pitch in the bottom half counteracted this inherent lift asymmetry and improved efficiency through a more uniform lift production.

A 2.5D numerical study on open water hydrodynamic performance of a Voith-Schneider propeller

Marine cycloidal propeller (MCP) is a special type of marine propulsors that provides high maneuverability for marine vessels. In a MCP, the propeller axis of rotation is perpendicular to the direction of thrust force. It consists of a number of lifting blade. Each blade rotates about the propeller axis and simultaneously pitches about its own axis. The magnitude and direction of thrust force can be adjusted by controlling the propeller pitch. Voith-Schneider propeller (VSP) is a low-pitch MCP with pure cycloidal blade motion allowing fast, accurate, and stepless control of thrust magnitude and direction. Generally, low-pitch cycloidal propellers are used in applications with low speed maneuvering requirements, such as tugboats, minesweepers, etc. In this study, a 2.5D numerical method based on unsteady RANS equations with SSTk-ωturbulent model was implemented to predict the open water hydrodynamic performance of a VSP for different propeller pitches and blade thicknesses. The numerical method was validated against the experimental data before applying to VSP. The results showed that maximum open water efficiency of a VSP is enhanced by increasing the propeller pitch. Furthermore, the effect of blade thickness on open water efficiency is different at various advance coefficients, so that the maximum efficiency produced by the VSP decreases with increasing blade thickness at different propeller pitches.

An Attempt to Evaluate the Cycloidal Rotor Fan Performance

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.

Force and flowfield measurements to understand unsteady aerodynamics of cycloidal rotors in hover at ultra-low Reynolds numbers

This paper provides a fundamental understanding of the unsteady fluid-dynamic phenomena on a cycloidal rotor blade operating at ultra-low Reynolds numbers (Re ∼ 18,000) by utilizing a combination of instantaneous blade force and flowfield measurements. The dynamic blade force coefficients were almost double the static ones, indicating the role of dynamic stall. For the dynamic case, the blade lift monotonically increased up to ±45° pitch amplitude; however, for the static case, the flow separated from the leading edge after around 15° with a large laminar separation bubble. There was significant asymmetry in the lift and drag coefficients between the upper and lower halves of the trajectory due to the flow curvature effects (virtual camber). The particle image velocimetry measured flowfield showed the dynamic stall process during the upper half to be significantly different from the lower half because of the reversal of dynamic virtual camber. Even at such low Reynolds numbers, the pressure forces, as opposed to viscous forces, were found to be dominant on the cyclorotor blade. The power required for rotation (rather than pitching power) dominated the total blade power.

Experimental Studies on a Mesoscale Cycloidal Rotor in Hover

This paper details the performance and flowfield measurements on a mesoscale cycloidal rotor (rotor radius of 1 in.), which operates at ultralow Reynolds numbers () and uses a design different from previous cycloidal rotor studies. The mesoscale rotor uses a cantilevered blade with a flat-plate airfoil and low-aspect-ratio elliptical blade planform. A three-component balance was developed to measure the vertical and sideward thrust, torque, and rotation frequency as the number of blades, pitch amplitude, and blade aspect ratio were varied. The studies showed that the highest efficiency was achieved with higher number of blades (4–6), high pitch amplitude (40–45 deg), and moderate aspect ratios. Phase-locked flowfield measurements were conducted using a particle image velocimetry (PIV) technique in two different orientations: chordwise and spanwise. PIV measurements show that the flowfield on the present mesoscale cycloidal rotor is highly three-dimensional and unsteady, characterized by the growth and shedding of leading-edge vortices and a trailing-edge vortex sheet similar to that seen on flapping wings; strong root and tip vortices that interact with each other to create an undulating wake; skewed inflow; and the strong interaction of the slip stream from the upper blade on the lower blade.

Investigation of the effects of end faces design on parameters of cycloidal rotor

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.