Unsteady Aerodynamic Analysis Of H-type Tilt Rotor UAV

With its unique aerodynamic layout,the H-type tilt-rotor UAV takes into account the vertical take-off and landing of the multi-rotor UAV,as well as the ability of the fixed-wing UAV to fly at high speed.However,its complicated motion state also creates more problems of aerodynamic interference.This paper analyzes the aerodynamic interference of the H-type tilt rotor UAV in three modes: multi-rotor mode,over-tilt mode and fixed-wing mode.Firstly,the geometric model of each flight state is established,then according to its unique aerodynamic layout and complex structural characteristics,setting up a method for generating a tilt rotor flow field grid.Finally,Basing on the structural characteristics of the H-type tilt-rotor UAV,the sliding grid model method and k-? SST turbulence model are used to establish the H-type tilt-rotor UAV unsteady constant value simulation method.According to the established numerical simulation method to calculate the isolated rotor model,by contrasting the experimental value and the CFD calculated value to verify the reliability of the numerical simulation method.According to the numerical calculation method,the aerodynamic interference calculation and analysis of the UAV in multi-rotor mode,over-tilt mode and fixed-wing mode are carried out,and ultimately obtaining the influence law of aerodynamic interference of various pneumatic components in different flight modes.In multi-rotor mode,under the hovering state,the downwash flow of the rotor directly acts on the nacelle.Then the nacelle generates a certain downward load,which causes a certain loss of the hovering performance of the aircraft.At this point,The downward load of the fuselage accounts for about 10% of the total rotor tensiontension.under vertical ascent,the aircraft's overall lift gradually decreases as the ascent speed increases.In the overtilt mode,the rotor / short cabin aerodynamic interference is mainly at 0 to 35 degrees in the initial stage of the tilt transition;the aerodynamic interference is the strongest when the mid-stage tilt transition is 45 to 65 degrees.There is a significant interference with the wing;at the last stage of the tilt transition,it mainly refers to the aerodynamic interference of the front rotor / wing and front rotor / rear rotor./ With the gradually increase of the tilt Angle and the the forward flow velocity,the aerodynamic interference of the wing gradually weakens,and the aerodynamic interference of the front rotor / rear rotor gradually increases.In the fixed-wing mode,the aerodynamic interference of the H-type tilt-rotor UAV mainly comes from the disturbance of the front rotor / wing and the front rotor / rear rotor.The drag in the state makes a certain loss of the cruise performance of the aircraft;although the front rotor will add to the lift on the wing,it will also reduce the lift-to-drag ratio of the whole aircraft.