四旋翼无人机旋翼对机身非定常气动干扰特性

四旋翼无人机的旋翼对机身构成非定常气动干扰，影响整机的动力学特性。针对此问题，采用计算流体动力学(CFD)计算方法，在刚体假设和不可压流假设下获得无人机机身在前飞工况下受力与力矩的非定常变化情况，并进行风洞实验，验证CFD方法的合理性和计算结果的准确性。采用快速傅里叶变换方法，得到机身所受旋翼气动干扰的模态，从而在干扰力和力矩的变化频率与大小方面进行分析。结果表明：机身所受旋翼的气动干扰与旋翼的转速相关，并且可以由一个5阶傅里叶级数较好地拟合；相对于后旋翼，前旋翼对机身的气动干扰更强；经过简化，单1阶模态的傅里叶级数可以描述升力变化的主要特点，1~3阶模态的傅里叶级数可以描述阻力变化的主要特点；俯仰力矩的周期变化规律可以用单2阶模态的傅里叶级数描述，变化细节可以用1~4阶模态的傅里叶级数描述。

Transient Aerodynamic Interference between Rotor and Fuselage for a Quadcopter

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.