高提前比转子上的反向流动物理
Physics of Reverse Flow on Rotors at High Advance Ratios
摘要：
在大前进比条件下，当旋翼桨叶沿边飞行时，在前缘背风面形成强烈的旋涡结构。这对叶片空气动力学有意想不到的影响。由于转子旋转而产生的不同的起始速度梯度产生从轮毂延伸的反向流的包络。在几何后缘处观察到一个锐缘涡（SEV），该锐缘涡在叶片进入后退叶片侧后不久形成。当叶片后退时，SEV的尺寸和强度径向向内增大。SEV对流并随转子叶片一起发展，直至消散。本文在240 °方位角观测到一个相干涡旋。漩涡的大小和强度随着叶片的后退而增加，在270度之前停止增长。随着涡流强度的增加，在更高的提前比时，反向流包络线也增加。涡的固体旋转中心在低前进比下伸展，并在耗散阶段显示出破裂涡的迹象。SEV与叶片的接近导致表面静压的大偏移，这反过来又在后退叶片上产生显著的负升力。附着的、相干的尖缘涡显示出与三角翼前缘涡相似的形态特征。
英文摘要：
When a rotor blade encounters reverse flow in edgewise flight at high advance ratio, a strong vortical structure forms on the leeside of the sharp blade edge. This has unexpected effects on blade aerodynamics. A differential onset velocity gradient due to rotor rotation creates an envelope of reverse flow extending from the hub. A Sharp Edge Vortex (SEV) is observed at the geometric trailing edge, forming soon after the blade enters the retreating-blade side. The SEV grows radially inwards in size and strength as the blade retreats. The SEV convects and evolves along with the rotor blade until dissipation. In this paper, a coherent vortex is observed at 240 degrees azimuth. Vortex size and strength increase as the blade retreats, ceasing to grow before 270 degrees. The reverse flow envelope increases at higher advance ratios with increased vortical strength. The solid body rotation core of the vortex stretches at lower advance ratios and shows the signs of a burst vortex in the dissipation phase. The proximity of the SEV to the blade causes large excursions in surface static pressures which in turn generates significant negative lift on the retreating blade. The attached, coherent sharp edge vortex shows similar morphological features as the leading edge vortex on a delta wing.
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