四旋翼无人机旋翼对机身非定常气动干扰特性

The rotors of a quadcopter cause transient aerodynamic interferences to the fuselage, which impacts the overall aerodynamic characteristics. Based on a typical quadcopter model, the computational fluid dynamics (CFD) method is used to obtain the transient changes in force and moment under the condition of forward flight with the assumption of rigid body and incompressible flow. Wind tunnel test was implemented for verifying the rationality of CFD method and the accuracy of calculated result. The fast Fourier transform (FFT) method is adopted to obtain the modal of aerodynamic interference for further investigating of the change frequencies and amplitudes of interference force and torque. The results show that the aerodynamic interference is highly correlated with the rotation rate of rotors. Such interference can be fitted by a fifth-order Fourier series. In this model, compared with the rear rotors, the front rotors have larger impact on the fuselage. The change in the lift force can be simplified and described by the first-order Fourier series, the change in the drag force can be described by the first-third-order Fourier series, and the major periodical variation of pitching moment changes can be described by a single second-order Fourier series. The first-fourth-order Fourier series are capable of describing the detail of variations.