Abstract This paper investigates both acoustics and performance of a lift-offset coaxial rotor based on a first-principles and high-fidelity CFD (Computational Fluid Dynamics) and CSD (Computational Structural Dynamics) loose coupling approach in high-speed forward flight at different vehicle pitch attitudes. The pitch attitudes selected for this research are − 5 ∘ , 0∘, and 5∘. Detailed aerodynamic analyses are performed at two flight speeds: 150 (278 km hr − 1 ) and 200 knots (370 km hr − 1 ). A total of six major unsteady aerodynamic interactions are identified: 1) hub-wake interaction, 2) self-BVI (blade-vortex interaction), 3) parallel rotor-to-rotor BVI, 4) blade-crossover events, 5) root-induced BVI, and 6) reversed-flow-edge-vortex interactions. The strength of these interactions is found to be dependent on vehicle pitch attitude. The cases with a negative pitch attitude show significantly stronger impulsive pressure pulses, which is found to be induced by parallel rotor-to-rotor BVIs of the lower rotor. It is shown that the positive and zero pitch attitude cases tend to dominate the acoustic region on the starboard side of the coaxial rotor, whereas the negative pitch attitude case shows higher acoustic pressure peaks on the port side. Overall, the high-speed case with a positive pitch attitude shows significant improvement in rotor aerodynamic efficiency, rotor acoustics, and vehicle power performance at high speed. The hemispherical acoustic simulation results also show that the noise is less likely to propagate in the forward direction at a positive pitch attitude in high-speed forward flight.

中文翻译：

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具有俯仰姿态的升力偏置同轴旋翼在高速向前飞行中的气动噪声

摘要 本文基于第一性原理和高保真 CFD（计算流体动力学）和 CSD（计算结构动力学）松散耦合方法研究了不同飞行器高速前飞中升力偏置同轴转子的声学和性能。投球态度。本研究选择的俯仰姿态为 − 5 ∘ 、 0∘ 和 5∘ 。详细的空气动力学分析在两种飞行速度下进行：150 (278 km hr − 1 ) 和 200 节 (370 km hr − 1 )。总共确定了六种主要的非定常空气动力学相互作用：1) 轮毂-尾流相互作用，2) 自 BVI（叶片-涡流相互作用），3) 平行转子到转子 BVI，4) 叶片交叉事件，5) 根- 诱导 BVI，和 6) 反向流动 - 边缘 - 涡流相互作用。发现这些相互作用的强度取决于车辆俯仰姿态。具有负俯仰姿态的情况显示出明显更强的脉冲压力脉冲，这是由下转子的平行转子到转子 BVI 引起的。结果表明，正和零俯仰姿态情况倾向于支配同轴转子右舷的声学区域，而负俯仰姿态情况在左舷侧显示出更高的声压峰值。总体而言，具有正俯仰姿态的高速情况在高速下转子空气动力学效率、转子声学和车辆功率性能方面显示出显着改善。半球声学仿真结果还表明，在高速向前飞行中，噪声以正俯仰姿态向前方传播的可能性较小。