Research On Hover Lift-drag Characteristics Of Mars Helicopter Rotor System

In the exploration of Mars surface environment by using Mars rover,its detection speed is slow and efficiency is low,and its work is also affected by unknown factors such as Mars surface environment,so it is difficult to avoid sand pits and other dangerous areas in advance.There is a thin atmosphere near the surface of Mars,which provides the necessary conditions for the development of a high altitude exploration terrain Mars helicopter flight.As a kind of aerial exploration platform to assist Mars rover to complete the exploration task,Mars helicopter can realize autonomous take-off and landing,and complete surface exploration and path planning for the target areas difficult to reach by Mars rover.In addition,the fixed-point take-off and landing function of Mars helicopter can also assist Mars rover to complete soil sample collection.Due to the low pressure and low temperature environment on Mars,the low Reynolds number and high Mach number flight environment of Mars helicopter lead to the significant decrease of lift drag ratio of rotor airfoil of Mars helicopter,which leads to the decline of rotor thrust of Mars helicopter.At the same time,a low Reynolds number will lead to the laminar flow separation and separation bubble phenomenon on the rotor surface of Mars helicopter,resulting in the significant increase of rotor power loss.Therefore,it is difficult for conventional earth helicopters to have enough lift and aerodynamic efficiency in the unique Martian atmosphere.At present,there are many gaps in the structural design,aerodynamic characteristics analysis and ground simulation experiments of the rotor system of Mars helicopter.In order to improve the hovering lift drag characteristics of the helicopter rotor system in the low Reynolds number flow field environment,the structural parameters and flight parameters o f the helicopter rotor system in the Martian atmosphere are analyzed in this paper.Based on the blade element momentum theory(BEMT)and the action disk theory,the aerodynamic parameter distribution of each element in the span direction of the rotor system is analyzed.The hover performance of the single-rotor system is predicted.The finite element method(FEM)is used to study the effect of the two-dimensional airfoil geometric parameters and flight parameters on the lift-drag characteristics.By simulating the unique low Reynolds number and high Mach number flight environment of the Martian atmosphere,the effects of various geometric parameters of the airfoils are comprehensively compared.Ba sed on the simulation results,a low Reynolds number airfoil suitable for working in the Martian atmosphere is selected.The hover performance of the single rotor with the low Reynolds number airfoil is predicted.Using the Martian Atmosphere Simulator(MAS),the rotor hovers performance setup is used to amplify the aerodynamic characteristics.The generated thrust and torque of the single rotor system are measured.The theoretical model's prediction results are compared with the experimental results,and the accuracy and reliability of the prediction of the theoretical model are verified.A low Reynolds number rotor blade with a uniform inflow ratio model is proposed based on the single-rotor design method and the blade element momentum theory.The aerodynamic parameter distribution in the span direction of the rotor blade with continuous plane shape can be analyzed with the finite element metho d.The hover performance of the single-rotor system in the Martian atmosphere can also be predicted.Based on the finite element method,the effect of the geometric parameters and flight parameters of the three-dimensional low Reynolds number single-rotor number blades on the rotor blade's hover performance is studied.The rotors with different rotor blade shapes and twists are comprehensively compared by simulating the unique low Reynolds number and high Mach number flight environment of the Martian atmosphere.Finally,a low Reynolds number blade suitable for working in the Martian atmosphere is selected.Using the Martian Atmosphere Simulator and the single rotor hover performance setup,the single-rotor system's generated thrust and required torque are directly measured.The theoretical model's prediction results are compared with the experimental results,and the accuracy of the optimal results obtained by the numerical simulation method is verified.A dynamic model of the coaxial rotor system is proposed based on aerodynamics analysis and action disk theory.The four types of extreme hover conditions of the coaxial rotor system and the dynamic characteristics of the coaxial rotor system in the presence of rotor eccentricity are analyzed.Based on the single-rotor blade element momentum theory and considering the coupling effect of the flow field between the upper and lower blades,a theoretical model of the blade element momentum of the upper and lower rotors of the coaxial rotor system is proposed.Combined with the finite element method,the effect of eccentric distance between rotor centers of the coaxial rotor on the coaxial rotor system's hover performance is analyzed,and the structural parameters of the coaxial rotor system are optimized.The torque between the upper and lower rotors of the coaxial rotor system is matched by varying the lower rotor's rotational speed.The effect of eccentric distance between the rotor centers of the coaxial rotor on the rotor system's hover performance is also investigated.The split coaxial rotor hovers test setup is used to measure the generated thrust directly and the coaxial rotor system's required torque.By comparing the theoretical model's prediction results with the experimental results,the accuracy of the numerical simulation method's optimization results is verified.A separate hover stand for the rotor system of a Mars helicopter is developed.The Mars atmospheric environment simulation system is used to simulate the atmospheric environment of Mars.The hovering lift drag characteristics of the optimized NACA airfoil,low Reynolds number blade,and twin-rotor system of the Mars helicopter are experimentally studied.The experimental results show that: for a helicopter with a mass of 2.0 kg,the pitch angles corresponding to the maximum aerodynamic efficiency and the maximum power load of the single rotor system with NACA 6904 airfoil are 30° and 2130 r/min,respectively,and the corresponding power load is 0.0498 N/W.The experimental results show that the coaxial rotor system's rotor spacing should not be less than 134.9 mm.Based on the active matter's theoretical capacity equation,the helicopter hovering time in Mars atmosphere is about 18.4 min.In this paper,the lift drag characteristics of the rotor system of Mars helicopter in hover are studied,which provides a theoretical basis and reference for developing the rotor system of Mars helicopter.This paper's research results have a certain theoretical significance and engineering practice value for the research of Mars helicopter-related technology.