When a helicopter rotor undergoes flow separation, the drag of the rotor increases substantially, as does the power demand, which seriously affects the aerodynamic performance and flight safety of the helicopter. Therefore, it is crucial to research how to suppress the flow separation of rotor blades. An active control technique based on a coflow jet (CFJ) at the rotor blade tip was employed in this study to suppress the flow separation over the rotor. The mechanisms and behavior were investigated. The rotor flow field was numerically simulated by solving the Reynolds-averaged Navier–Stokes equations with the finite volume method. The turbulence model was SST, and the rotor motion was simulated using the overset mesh technique. After applying CFJ control, the airflow from the injection slot at the leading edge of the rotor increased the energy of the mainstream in the near-wall area, which enhanced its ability to resist the adverse pressure gradient. A flow separation was effectively suppressed, both on the advancing and retreating sides, which improved the aerodynamic performance of the rotor. During the whole rotation period, the thrust coefficient of the rotor increased by up to 5.6%, the moment coefficient decreased by as much as 26.8%, and the equivalent lift-to-drag ratio increased by up to 44.0%. Moreover, the effects of the CFJ parameters on the flow separation suppression of the rotor are researched. These results may provide a foundation for the development of aerodynamic performance improvement for helicopter rotor based on a CFJ.

中文翻译：

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基于Coflow Jet的直升机旋翼主动流动控制

当直升机旋翼发生气流分离时，旋翼阻力大幅增加，动力需求也随之增加，严重影响直升机的气动性能和飞行安全。因此，研究如何抑制转子叶片的分流至关重要。本研究采用基于转子叶片尖端的共流射流 (CFJ) 的主动控制技术来抑制转子上的流动分离。研究了机制和行为。通过用有限体积法求解雷诺平均 Navier-Stokes 方程对转子流场进行数值模拟。湍流模型为SST，并使用重叠网格技术模拟转子运动。采用CFJ控制后，转子前缘喷口的气流增加了近壁区主流的能量，增强了其抵抗逆压梯度的能力。在前进和后退侧都有效地抑制了流动分离，从而提高了转子的气动性能。在整个旋转期间，转子的推力系数最多增加5.6%，力矩系数减少最多26.8%，等效升阻比增加最多44.0%。此外，研究了CFJ参数对转子分流抑制的影响。