升力偏置对共轴刚性旋翼前飞气动特性的影响

为了分析升力偏置对共轴刚性旋翼前飞气动特性的影响，建立了基于雷诺平均Navier-Stokes方程的计算流体力学方法进行共轴旋翼流场求解，采用嵌套网格方法模拟桨叶运动，采用双时间方法进行时间推进。针对不同升力偏置状态，采用基于"差量法"的共轴旋翼高效配平策略进行操纵量配平。通过对Harrington-1旋翼性能的计算，验证了方法的有效性。对比计算了共轴刚性旋翼在不同前进比和升力偏置量下的气动性能和流场特征，结果表明：双旋翼操纵量在小前进比状态有明显差别，在大前进比状态基本一致；在相同拉力状态，随着升力偏置量的增大，共轴旋翼升阻比先升高后降低，其阻力却不断增大，不同前进比状态的最大升阻比对应的升力偏置量不同；双旋翼相遇时桨叶拉力出现脉冲式波动，由于流场被前行桨叶所主导，因此后行桨叶拉力波动幅值更大，且波动幅值随升力偏置量的增加而增大。

Influence of lift offset on rigid coaxial rotor aerodynamic characteristics in forward flight

In order to analyze the influence of lift offset on the aerodynamic characteristics of coaxial rigid rotors in forward flights, a computational fluid dynamics method based on the Reynolds averaged Navier-Stokes equations is established to solve the coaxial rotor flow field. The nested grid method is used to simulate the blade motion, and the dual-time method is used for time propulsion. A high-efficiency trim strategy based on the "delta method" is adopted to trim the control pitches for coaxial rotor at different lift offset states. The validity of the method is verified by calculating the performance of Harrington-1 rotor. The aerodynamic performance and the flow field characteristics of the coaxial rigid rotor at different advance ratios and lift offset states are calculated and compared. The results show that the control pitches of the coaxial rotor are significantly different at small advance ratio, and the trimmed pitches of the dual rotors tend to be the same at high advance ratio. Under the same thrust condition, with the increase of the lift offset, the lift-drag ratio of the coaxial rotor increases first and then decreases, while the drag as the lift offset increases. At different advance ratios, the maximum lift-drag ratios correspond to different lift offsets. When the dual rotors meet with each other, the blade thrusts fluctuate impulsively. Meanwhile, since the flow field is dominated by the advancing blade, the amplitude of the thrust fluctuation of the retreating blade is larger than that of the advancing blade, and the amplitude increases with the increase of the lift offset.