Research On The Near-surface Effect Of Rotary-wing UAV

In recent years,rotorcrafts have attracted attentions due to their lightness,flexibility and small size,and their application scenarios have gradually enriched.In some scenarios,the aircraft operates in a confined environment,where it may experience proximity effects with nearby structures such as the ground,ceiling,and wall.The aerodynamic characteristics will change,which may affect the flight path and control stability of the aircraft.In order to avoid the adverse effects of the proximity effect and even to convert it into favorable features,the study of the mechanism of the proximity effect becomes significant.In this paper,the proximity effect of the small-rotor UAV is studied.Aiming at the aerodynamic characteristics of the rotor,various proximity effects are tested and analyzed by numerical simulation technology and experimental method.The main research work is as follows:Firstly,the definition of the proximity effect of the small-rotor aircraft is clarified,and the proximity effect is classified into various situations according to the shape,position and function of the near-structure.The computational fluid dynamics basics and the workflow of the numerical simulation methods are elaborated.Secondly,the numerical simulations of the infinite proximity effect and the finite proximity effect are carried out respectively.We obtained the rotor thrust data and the visual flow field through simulations.The rotor thrust data shows that the effect of the proximity effect is closely related to the position and shape of the plane.Based on the rotor thrust data,mathematical models are established for the change of rotor thrust caused by proximity effect.The fitting curves indicate that the models can accurately describe the rotor thrust variation under the proximity effect.Based on the visual flow field,the principle of proximity effect is analyzed and discussed.The results show that the proximity effect affects the flow direction,pressure and vorticity distribution of the flow field around the rotor,which affects the rotor thrust.Thirdly,the flight control simulation of the quadrotor was carried out.The dynamic model of the quadrotor was established.Then the controller with rotor thrust feedforward compensation was designed and the stability of the system was analyzed.In flight control simulation environment we simulates the height control of the quadrotor in the near-surface environment.The simulation results show that the height control effect of the quadrotor is not effective under the ceiling effect,and the control effect is greatly improved after the rotorthrust feedforward compensation.Finally,the rotor thrust validation experiment and the flight control experiment in the near-surface environment were carried out.The results of the rotor thrust validation experiment are in good agreement with the numerical calculations,and the models we built can accurately describe the rotor thrust variation in the actual environment,which verifies the conclusions we drew from the computer numerical simulation and the models we built.Applying the controller designed,we successfully conduct the actual flight of the quadrotor in the near-surface environment,verifying the control simulation results,which proves the correctness and practicability of our proximity effect research.