Cycloidal Rotor Research Articles

Aerodynamic assessment of the cycloidal rotor fan

This paper presents numerical and experimental testing of a cycloidal rotor fan (CRF). The tested cyclorotor is made of four NACA0012 profile blades. CFD calculations using the Ansys CFX® tool and the LDA measurement technique are performed to determine the fan performance for different operating parameters, i.e. rotational speed and the rotor blade maximum swing angle values. One initial position of the blades corresponding to one air-flow direction is considered only. The comparison between the numerical results and the experimental LDA measurements is satisfactory and encouraging further investigation.

Role of Blade Flexibility on Cycloidal Rotor Hover Performance

In this paper, the aeromechanics of a cycloidal rotor (or cyclorotor) is investigated to understand the effect of blade flexibility on the performance of the rotor in hover. Toward this, experiments are conducted on cyclorotors using moderately and highly flexible blades. These studies show that, with increasing blade flexibility, the rotor thrust decreases; whereas the power consumption increases, leading to a significant drop in power loading (thrust/power). To investigate these phenomena, a coupled aeroelastic model of cyclorotor is developed by coupling an unsteady aerodynamics model with a beam-based structural model and is systematically validated with experimental results. The aerodynamic model contains rigorous modeling of various physics behind the operation of the cyclorotor, such as the nonlinear dynamic virtual camber, the effect of near and shed wakes, and the leading-edge vortex. In comparison with a second-order nonlinear structural model, inclusion of a geometrically exact structural model proves to be essential in accurate prediction of rotor deflections and performance. Based on a systematic analysis performed using the validated model, it is observed that the large torsional deflections of the blades are a key reason for the drop in thrust. The torsional deflections are mainly produced by centrifugal force and nonlinear moments due to bending curvatures.

Numerical Modeling of Stall and Poststall Events of a Single Pitching Blade of a Cycloidal Rotor

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-shear stress transport (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, and (vii) detached eddy simulation (DES) coupled with transition kω-SST. The wake vortices evolution and shedding analysis are 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 deg. 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 fast Fourier transport analysis showed that the wake vortex characteristics of a pitching blade are significantly different than those for the low amplitude oscillating blade at the higher reduced frequency.

Numerical and Experimental Investigation of the Fan with Cycloidal Rotor

Abstract 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.

Aeroelastic Analysis of a Cycloidal Rotor Under Various Operating Conditions

The aeroelasticity of a cycloidal rotor in forward flight is investigated using an analytical and a numerical model; the latter is based on a multibody dynamics approach. Three experimental sources are used to validate the multibody model. The influence of the number of blades, their stiffnesses, and their skin thicknesses are investigated. At high pitch angles, before stall and flexibility effects occur, increasing the number of blades produces more thrust for the same power. Flexibility and skin thickness considerably affect the required pivot rod strength and blade deformation. Simply supported blades exhibit severe deformations when compared to clamped blades. Thrust and power are both influenced in a similar and moderate way by flexibility. The rotor response to wind gusts is also analyzed. The angular velocity of the rotor significantly affects the response of the rotor to wind gusts. The direction of the gusting wind has an important influence on power, whereas thrust increases regardless of wind direction. Finally, the rotor response lags minimally behind the arrival of the gust.

Parameter Estimation of Wave-Induced Oscillatory Ship Motion for Wave Filtering in Dynamic Positioning

By means of wave filtering a dynamic positioning system for ships can be developed which does not counteract high-frequency, wave induced oscillatory ship motion. For high-performance and energy-efficient operation, the wave filtering parameters must be adjusted according to the environmental conditions. This prevents unnecessary wear and tear of the propulsion system while still achieving a high level of control performance. If the characteristics of the wave disturbance vary during operation, an online update of the filter parameters is required in order to maintain the control performance. The filter parameter which is significantly influenced by the varied wave spectrum is the peak frequency of the wave-induced oscillatory ship motion. Hence, the online estimation of the peak frequency is the topic of this paper. The approach adopted is to determine the peak frequency based on the parameter identification of a low order auto regressive model. The practical problems that arise are addressed and modifications are proposed. The algorithms shown are tested and compared on the basis of real experiments on a model scaled ship with Voith-Schneider Propellers. The results show the improved reliability of the proposed detail solutions in terms of numerical robustness and capability for practical real-time application in continuous operation.

The effects of dynamic-stall and parallel BVI on cycloidal rotor

PurposeThis paper aims to investigate the mechanisms lying behind the cycloidal rotor under hovering status.Design/methodology/approachExperiments were conducted to validate the numerical simulation results. The simulations were based on unsteady Reynolds-averaged Navier–Stokes (URANS) equations solver and the sliding mesh technique was used to model the blade motion. 2D and 2.5D simulations were made to investigate the 3D effects of turbulence. The effects of pressure and viscosity were compared to study the significance of the blade motion on force generation.FindingsThe 2.5D numerical simulation cannot produce more accurate results than the 2D counterpart. The pitching motion of the blade results in dynamic stall. The dynamic stall vortices induce parallel blade vortex interaction (BVI) upon downstream blades. The interactions between the blades delay the stall of the blade which is beneficial to the thrust generation. The blade pitching motion is the dominant contributor to the force generation and the turbulence is the secondary. Strong downwash in the rotor cage varied the inflow velocity as well as the effective angle of attack (AOA) of the blade.Practical implicationsCycloidal rotor is a propulsion device that can provide omni-directional vectored thrust with high efficiency and low noise. To understand the mechanisms lying behind the cycloidal rotor helps the authors to design efficient cycloidal rotors for aircraft.Originality/valueThe authors discovered that the blade pitching motion plays primary role in force generation. The effects of the dynamic stall and BVI were studied. The reason why cycloidal rotor can be more efficient was discussed.

The effects of advance ratio and blade number on the forward flight characteristics of cycloidal rotor

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.

Reciprocating Geared Mechanism with Compliant Suspension

We present a novel cycloidal geared mechanism with a continuous rotational input featuring a reciprocating translational output. A statically balanced compliant mechanism suspends an annulus driven by a cycloidal rotor. The freedom and constraint topology design method is used to synthesize the compliant suspension. A fixed transmission ratio of 15 results from the ratio between the cycloidal rotor and the annulus. The static balancing conditions of the suspension are developed analytically, and validated using finite-element modeling and experimental results. Moreover, the estimation of the frictional loss as a function of the stiffness of the compliant members is derived using a force analysis of the system and verified using experimental data. A case study on a mechanical watch yields dimensions for the prototype, which is fabricated in silicon using deep reactive ion etching. Experiments show that energy loss as a function of the stiffness of compliant members is marginal and independent of the position of the compliant suspension. [2016-0260]

A Dynamic Allocation Strategy for Voith Schneider Propeller

To ensure a ship’s capability of Dynamic Positioning, the propulsion system of the vessel is usually designed over-actuated, meaning the ship has more control inputs than degrees of freedom. The distribution of thrust demands of some higher-level controller onto the available thrusters, the thrust allocation, is an essential problem and due to the over-actuated problem not trivial. Furthermore, the thrust should be delivered fast and precisely to achieve good positioning results. The usage of a Voith Schneider Propeller allows thrust generation with these properties but spans a new problem due to complex modeling and increased number of control variables. The paper on hand presents a thrust allocation algorithm which utilizes the dynamic advantages of Voith Schneider Propeller. The algorithm uses a two-step approach consisting of Quadratic Programming optimization and external tracking algorithms for calculation of power-optimal propulsion control. The proposed strategy is compared to a non-linear, multi-criteria optimization which is based on high quality open-water characteristics. The results show strong similarities though the computational time can be significantly reduced by usage of the proposed allocation.

Improving the aerodynamic performance of a cycloidal rotor through active compliant morphing

ABSTRACTCycloidal rotors are a novel form of propulsion system that can be adapted to various forms of transport such as air and marine vehicles, with a geometrical design differing significantly from the conventional screw propeller. Research on cycloidal rotor design began in the early 1930s and has developed throughout the years to the point where such devices now operate as propulsion systems for various aerospace applications such as micro air vehicles, unmanned air vehicles and compound helicopters. The majority of research conducted on the cycloidal rotor’s aerodynamic performance have not assessed mitigating the dynamic stall effect, which can have a negative impact on the rotor performance when the blades operate in the rotor retreating side. A solution has been proposed to mitigate the dynamic stall effect through employment of active, compliant leading-edge morphing. A review of the current state of the art in this area is presented. A two-dimensional, implicit unsteady numerical analysis was conducted using the commercial computational fluid dynamics software package STAR CCM+, on a two-bladed cycloidal rotor. An overset mesh technique, otherwise known as a chimera mesh, was used to apply complex transient motions to the simulations. Active, compliant leading-edge morphing is applied to an oscillating NACA 0015 aerofoil to attempt to mitigate the dynamic stall whilst maintaining the positive dynamic lift coefficient (Cl) contributions. It was verified that by applying a pulsed input leading-edge rotational morphing schedule, the leading-edge vortex does not fully form and the large flow separation is prevented. Further work in this investigation will focus on coupling the active, leading-edge motion to the cycloidal rotor model with the aim to maximise aerodynamic performance.

Development of a meso-scale cycloidal-rotor aircraft for micro air vehicle application

This paper describes the design, controls system development, and hover testing of a 60 -g meso-scale cycloidal-rotor based (cyclocopter) micro air vehicle. The cycloidal rotor (cyclorotor) is a revolutionary vertical take-off and landing concept with a horizontal axis of rotation. The twin-cyclocopter utilizes two optimized cyclorotors and a horizontal tail rotor used to counteract the pitching moment generated by the cyclorotors. An innovative light-weight and high strength-to-weight ratio blade design significantly reduced cyclorotor weight and improved aerodynamic efficiency. In addition, increasing the virtual camber and incidence (by increasing chord-to-radius ratio) and using a symmetric pitching schedule with a maximum ± 45° pitching amplitude also improved rotor efficiency. Due to gyroscopic coupling and inherent instability of the cyclocopter, a closed-loop feedback control system was implemented using a custom autopilot weighing 1.5 g. The 60-g meso-scale twin-cyclocopter successfully demonstrated stable, sustained hover.

Two-dimensional and three-dimensional numerical simulations of cycloidal propellers in hover

The cycloidal propellers for micro aerial vehicle scale cyclocopter in hovering status were studied in this paper based on the URANs solver using 2D, 2.5D, 3D half blade and 3D full blade model. The results from all numerical models were validated with the experimental results. It was found that 2.5D model cannot produce more accurate results than 2D model, hence results from 2D model were employed to discuss cycloidal rotor with infinite blade span. It was also indicated that the 3D half blade model produced the same results as 3D full blade model, but was more efficient than 3D model. The numerical simulation results of cycloidal rotor with finite (3D model) and infinite span (2D model) were compared. The results indicated that for the 2D cycloidal rotor with large blade pitching amplitude, there were leading edge and trailing edge vortices due to dynamic stall, which resulted in parallel blade vortex interactions. The parallel blade vortex interactions will also induce the fluctuation of aerodynamic forces. For the 3D blade with small aspect ratio, the flow was dominated by 3D dynamic stall and blade vortex interactions. The 3D flow due to finite blade span resulted in smooth dynamic stall and can weaken the parallel blade vortex interactions induced by dynamic stall vortices, hence no strong aerodynamic force fluctuation was observed. The perpendicular blade vortex interactions caused by blade tip vortices can induce cross flow when the azimuth angle of the rotor is between 270° and 360°, which reduces the strength of downwash in the region where the rotor azimuth angle is between 180° and 360°. This results in much smaller side force. Although sometimes the time-averaged aerodynamic forces obtained by 2D and 3D model were quite close to each other, the physics lying behind is quite different. Hence, it was not correct to use the 2D models to discuss the principles of cycloidal rotors with finite blade span.

Optimal pitching schedules for a cycloidal rotor in hovering

Purpose The purpose of this paper is to define an optimal pitching profile for the blades of a cycloidal rotor which minimizes the mean power consumption for a given mean thrust of the rotor. Design/methodology/approach A simple analytical model of the kinematics and aerodynamics of a cycloidal rotor is defined first to obtain expressions for thrust and power depending on the pitching profile and geometrical parameters of the rotor. Then, Lagrange optimization is applied to obtain the optimal pitching schedule under hovering conditions. Finally, results of the theoretical analysis are compared with those of a two-dimensional computational fluid dynamics (CFD) model. Findings Results of the optimization suggest that the optimal profile is a combination of sinusoidal functions. It is shown that the adoption of the optimal pitching schedule could improve the power efficiency of the rotor by approximately 25 per cent. Practical implications The possibility to increase the efficiency of a cycloidal rotor by acting on its pitching schedule could be a significant factor of success for this alternative propulsion concept. Originality/value The present work represents the first attempt at a definition of an optimal pitching profile for a cycloidal rotor. Moreover, although being carried out on the basis of simplified analytical considerations, the present investigation sets a methodological framework which could be successfully applied to the design of similar kinds of systems.

Parametric Analysis of a Large-Scale Cycloidal Rotor in Hovering Conditions

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. The four parameters, which have a strong effect on the rotor aerodynamic efficiency are analyzed with an analytical model and a numerical approach. The numerical method is based on a finite-volume discretization of two-dimensional Unsteady Reynolds Averaged Navier-Stokes 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 values of around 0.5 result in higher efficiency. Finally it is found out that for these large systems, in contrast with micro-scale cyclogyros, the generated thrust increases as the pitching axis 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.

DEFINITION OF TOOL PROFILE FOR TOOLING ROTOR OF GEROTOR TRANSMISSION IN CONDITIONS ROUNDING

The article is devoted to problems of designing tools for machining for processing the surface cycloidal rotor of gerotor gear. Such tools are in particular hobbing cutters and worm wheels. Despite the fact that the above described tools are known in the world, virtually no information about the method of designing. Mostly it mathematical apparatus that would allow us to build a profile of this tools. Based on the analysis for the rotary tool rake and graphic-analytical synthesis was formulated and solved the problem of the existence of discriminant (tangent curve) of family rotor position, and received its equations, which have advantages over numerical and graphical-analytical methods of construction and are relatively easy for the user. The research results can be used as an engineering methodology in the design and manufacture of hobbing cutters and grinding wheels for machining rotors gerotor gear under the conditions of rounding.

Investigation of unsteady aerodynamics effects in cycloidal rotor using RANS solver

ABSTRACTThe 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.

Aerodynamic models for cycloidal rotor analysis

Purpose Few modeling approaches exist for cycloidal rotors because they are a prototypal technology. Thus, the purpose of this study was to develop new models for their analysis and validation. These models were used to analyze cycloidal rotors and a helicopter that uses them instead of a tail rotor.

Aerodynamic optimization of cyclorotors

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.

Roll Damping Using Voith Schneider Propeller: a Repetitive Control Approach

Abstract: Voith Schneider propellers are potential propulsion systems for dynamic positioning in offshore applications because of their fast and accurate thrust generation. An overlaid roll damping control by the same propulsion system is possible to reduce the influence of external disturbances. The paper at hand presents simulation results of roll damping control using a repetitive control approach. Repetitive control is a highly effective control technique for the compensation of periodic disturbances, or for exact tracking of periodic reference signals. Simulation results of repetitive control in roll damping will be compared with those from a classical approach. The simulation models as well as the disturbance signals are based on theoretical considerations as well as on verifying experiments in a towing tank. The robustness of the method has been investigated according to deviations from a purely periodic excitation as well as to the influence of propulsion saturation.