Lift-drag Characteristics And Experimental Study On Rotorcraft For Mars Exploration

Mars exploration will deepen human’s understanding of the evolution of Earth and the origin of life because of similar physical environment between Mars and Earth.At present,the ground detection of Mars is mainly based on the way of Mars rover.The complex ground environment of Mars,however,affects the visibility and mobility of Mars rover to a certain extent.Mars Unmanned Aerial Vehicle(UAV)is another possibility for Mars exploration because of thin atmosphere on Mars.The compact structure as well as vertical take-off and landing capability gives coaxial rotorcrafts a unique advantage in various Martian UAVs.The different working conditions between Mars rotorcrafts and Earth rotorcrafts is that the former possesses low Reynolds number and high Mach number.Low Reynolds number will lead to laminar flow separation which will reduce the lift produced by rotor,while high Mach number will cause vortex at the tip of blade which will reduce the mechanical efficiency of rotor.In this thesis,for the rotor system of Mars rotorcrafts,the lift-drag characteristics model of blade is built and a suitable blade configuration for use under low Reynolds number and high Mach number condition is proposed.By the method of experiment,not only the correctness of blade lift-drag characteristics model is verified but also coupling effect between upper and lower rotor of the coaxial rotor system is studied.By the method of Computational Fluid Dynamic(CFD),the airfoil suitable for low Reynolds number and high Mach number is selected considering the geometric parameters of airfoil.Based on the Blade Element Momentum Theory(BET),a liftdrag characteristic model of rectangular blade is established and a method for predicting the thrust of a blade using airfoil simulation results is proposed.The influence of planeform on the lift-drag characteristics is studied and blade design for low Reynolds number and high Mach number condition is carried out.Rotor lift-drag characteristics testing system including Martian Atmosphere Simulator(MAS),single-rotor lift-drag characteristics testing devices and coaxialrotor lift-drag characteristics testing device is developed.MAS is used for simulating the atmosphere pressure of Mars atmosphere.Single-rotor lift-drag characteristics testing devices are used for testing the lift-drag characteristics of various single rotors,while coaxial-rotor lift-drag characteristics testing device is used for obtaining the relationship between the thrust generated by the rotor system when the upper and lower rotors rotate simultaneously and the sum of thrust generated by the rotor system when the upper and lower rotor rotate alone.The experiment of lift-drag characteristics test on rectangular blade is carried out.The correctness of the rectangular blade lift-drag characteristics model is verified and the optimal collective angle of the rectangular blade during hovering is obtained.The experiment of lift-drag characteristics test on taper blades is carried out,and the relationship between characteristics of blades which possess different taper is obtained.The experiment of airflow coupling between upper and lower rotors of coaxial rotor system is carried out in order to obtain the relationship between the thrust generated by the rotor system when the upper and lower rotors rotate simultaneously and the sum of thrust generated by the rotor system when the upper and lower rotor rotate alone.