This study is conducted to investigate the aerodynamic characteristics of a coaxial rotor in low-speed forward flight using a high-fidelity computational fluid dynamics (CFD) solver. Numerical simulations are performed on the coaxial rotor and its isolated upper and lower rotors at two small advance ratios, 0.12 and 0.24. Interaction events in the flowfield, especially blade-vortex-interaction (BVI), are studied in detail. As the forward speed increases, the airload distributions become concentrated on the front part of the disk. Fluctuations in the loading indicate self-BVIs within each rotor, and blade-crossover events and rotor-to-rotor BVIs between the coaxial upper and lower rotors. Principal BVI events are identified in the well-captured wake structures by the 8th-order TENO reconstruction scheme. Self-BVIs on all rotors reduce in strength as the forward speed increases, while rotor-to-rotor BVIs on the coaxial lower rotor increase in strength with the increasing forward speed. In the coaxial configuration, the wake of the upper rotor is induced to move backwards and downwards due to the exertion of the lower rotor wake. The wake of the coaxial lower rotor features the most complex flow nature among all rotors. At both advance ratios, the coaxial lower rotor experiences a parallel rotor-to-rotor BVI, causing highly impulsive loading fluctuations along the blade span.

中文翻译：

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低速前飞同轴旋翼系统气动相互作用数值研究


本研究旨在使用高保真计算流体动力学 (CFD) 求解器研究低速前向飞行中同轴旋翼的空气动力学特性。对同轴转子及其隔离的上下转子在两个小提前比（0.12和0.24）下进行了数值模拟。详细研究了流场中的相互作用事件，特别是叶片涡相互作用（BVI）。随着前进速度的增加，空气载荷分布集中在盘的前部。负载波动表明每个转子内的自身 BVI，以及同轴上转子和下转子之间的叶片交叉事件和转子间 BVI。通过 8 阶 TENO 重建方案在清晰捕获的尾流结构中识别出主要的 BVI 事件。所有转子上的自 BVI 强度随着前进速度的增加而减小，而同轴下转子上的转子到转子 BVI 的强度随着前进速度的增加而增加。在同轴配置中，由于下转子尾流的作用，导致上转子尾流向后和向下移动。同轴下转子的尾流是所有转子中流动性质最复杂的。在两种提前比下，同轴下转子都会经历平行的转子间 BVI，从而导致沿叶片跨度的高度脉冲载荷波动。