The aerodynamic performance of an isolated coaxial rotor in forward flight is analyzed by a high-fidelity computational fluid dynamics (CFD) approach. The analysis focuses on the high-speed forward flight with an advance ratio of 0.5 or higher, which is the ratio of the forward speed to the rotor tip speed. The effect of the degree of the rolling moment on the rotor thrust, called lift offset, is studied in detail. The coaxial rotor model is a pair of contrarotating rotors, each rotor consisting of two untwisted blades with a radius of 1.016 m. The pitch angle of the blades is controlled by both collective and cyclic as in a conventional single main-rotor helicopter. CFD analysis is performed using a flow solver based on the compressible Navier-Stokes equations with a Reynolds-averaged turbulence model. Laminar/turbulent transition in the boundary layer is taken into account in the calculation. The rotor trim for target forces and moments is achieved using a gradient-based delta-form blade pitch angle adjusting technique in conjunction with CFD analysis. The reliability of the calculations is confirmed by comparison with published wind tunnel experiments and two comprehensive analyses. Applying the lift offset improves the lift-to-effective drag ratio (lift-drag ratio) and reduces thrust fluctuations. However, in the case where the advance ratio exceeds 0.6, the lift-drag ratio drops significantly even if the lift offset is 0.3. The thrust fluctuation also increases with such a high advance ratio. Detailed analysis reveals that the degradation of aerodynamic performance and vibratory aerodynamic loads is closely related to the pitch angle control to compensate for the reduction in thrust on the retreating side due to the increased reverse flow region. It is effective to reduce the collective and longitudinal cyclic pitch angles for the improvement of the aerodynamic performance of coaxial rotors with an appropriate lift offset.

通过高保真计算流体动力学 (CFD) 方法分析了前向飞行中隔离同轴转子的空气动力学性能。分析侧重于前进比为0.5或更高的高速前飞，前进比是前进速度与旋翼叶尖速度的比值。详细研究了滚动力矩的大小对转子推力的影响，称为升力偏移。同轴转子模型是一对反向旋转的转子，每个转子由两个半径为 1.016 m 的未扭曲的叶片组成。与传统的单主旋翼直升机一样，叶片的俯仰角由集体和循环控制。CFD 分析是使用基于可压缩 Navier-Stokes 方程和雷诺平均湍流模型的流动求解器进行的。计算中考虑了边界层中的层流/湍流转变。目标力和力矩的转子配平是使用基于梯度的三角形叶片桨距角调整技术结合 CFD 分析实现的。通过与已发表的风洞实验和两项综合分析的比较，证实了计算的可靠性。应用升力偏移可提高升力与有效阻力比（升阻比）并减少推力波动。然而，在前进比超过0.6的情况下，即使升力偏移为0.3，升阻比也会显着下降。推力波动也随着如此高的提前比而增加。详细分析表明，气动性能和振动气动载荷的下降与桨距角控制密切相关，以补偿因回流区域增加而导致的后退侧推力的减少。减小总距和纵向循环桨距角对于提高具有适当升力偏移的同轴转子的气动性能是有效的。