Research On The Design Of Cycloidal Propeller For Micro Cyclocopter

The cyclocopter propelled by a cycloidal blade system is a new concept of vertical takeoff and landing aircraft.The cycloidal propeller is a concept of rotary-wing system,whose blade span runs parallel to the rotation axis and perpendicular to the flight direction.Owing to its high aerodynamic efficiency,low noise and vectored thrust,it has become one of the greatest concerns in the field of micro air vechile.However,due to its unique characteristics such as strong unsteadiness,much more studies on the mechanism and design method still need to be done.On one hand,there wasn't any record on the flycable cyclocopter before this study;on the other hand,there is still no systematic design method on how to improve the efficiency of cycloidal propeller,and the work mainly concenterate on the experiments.Aiming to solve the above problem,the thesis firstly conducted the research on the mechanism of the cyclocopter,and a micro cyclocopter was designed and the capability of controlled flight for the cyclocopter was validated;then,the paper focuses on the aerodynamics and the design method of the cycloidal propeller.The contents of this paper are listed as follows,(1)A prototype of micro cyclocopter is developed and the design method of cyclocopter is explored.The control pricnciple of flight attitude for the cyclocopter is analyzed,and the thrust allocation approach and the computational method of endurance is established as well.The aerodynamic performance of cycloidal propeller is investigted based on the Mcnabb model;the experimental setup is established and the geometric configuration of blade is selected according to the orthogonal design method.The parameter matching method of propulsion systems is also put forward.Lastly,the prototype of micro cyclocopter is developed,whose capability of controlled flight is validated by the free flight test.The endurance is found to be relatively low due to the inadequate aerodynamic efficiency of cycloidal propeller,which indicates that there is a need to develop the design approach to improve the efficiency of the cycloidal propeller.(2)The aerodynamics of a micro cycloidal propeller operating in hovering flight is systematically studied to enhance the understandings about the cycloidal propeller and cyclocopter,and provide some theoretical basis for the development of high efficient cycloidal propeller.The two dimensional numerical simulations are conducted on the cycloidal propellers based on the dynamic mesh method.And the mesh generation method,moving mesh method,remeshing strategy and the choice of the turbulence model are investigated in detail to improve the convengence and accuracy.The comparisons between the computational results and experimental data show its good capability of simulating the aerodynamics of cycloidal propeller.Based on the above validation,the characteristics of time-averaged thrusts,instantaneous flow field,thrusts,blade aerodynamics and interference between blades are investigated in detail.(3)By using the unsteady numerical simulation method,the influence on aerodynamic performance of the key design parameters is systematically studied.Based on the two dimensional unsteady numerical simulation method present above,the effects of blade number,airfoil,pitching axis,pitching amplitudes and pitching asymmetric setup on the thrusts and aerodynamic power are investigated in detail,providing a direct guide to the design of the cycloidal propeller.(4)A fast unsteady two dimensional aerodynamic optimization method of airfoil for cycloidal propellers based on the sliding mesh method is developed,which can consider the effects of multi-blades coupling interferences.In this approach,the two dimensional cycloidal propeller is simulated as a whole,and the figure of merit is selected to be the optimizimation objective;the CST airfoil parameterization method is adopted to describe the airfoil profile;given the computational accuracy and computational cost,the cycloidal propeller is simulated by using the sliding mesh technique,and the approximation model is established by the surrogate model to be optimized.Using the proposed approach,the optimization is conducted on a micro 4-bladed cycloidal propeller with NACA 0015 airfoil,and the optimized results show that the figure of merit is increased by 18.31% at the design rotation speed,showing the importance of the airfoil optimization design to improve the aerodynamic efficiency of cycloidal propeller.Besides,the optimized result is qualitatively consistent with the conclusions from the experimental parametric studies,indicating the efficiency of the present method.(5)A new three-dimensional aerodynamic performance computational approach is established to achieve fast and accurate prediction of the thrust and aerodynamic power of cycloidal propellers,which is based on the lifting-line method,free wake model and L-B dynamic stall model.Firstly,the semi empirical and semi theoretical Leishman Beddoes model is introduced to compute the unsteady lift and drag coefficient of the blade element.Then,to improve the convergence and steadbility during calculation,the single streamtube model is coupled with the Leishman-Beddoes model to predict a uniform inflow velocity through the cycloidal propeller disc,which is set to be the initial induced velocity.Besides,to consider the three dimensional effects,the blade is modeled by the lifting line method,and the free wake model is utilized to model the dynamics of cycloidal propeller wake.The Vatista viscous vortex model is adopted to correct the induced velocities calculated by the Bivort-Savart law,to avoid the instability during computation.Finally,the validations show that the results from the present model agree reasonably well with the overall experimental data and the CFD results,indicating the relatively high computational speed and accuracy of the proposed approach.Based on the validation of the controlled flight of the micro cyclocopter,this thesis is mainly focused on the design method for cycloidal propellers,the conclusions can provide some useful basis for the design of cycloidal propeller,and the proposed design method has great significance on improving the aerodynamic efficiency and the endurance of the cyclocopter,hence a good theoretical and engineering value.