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首页> 外文期刊>Journal of the American Helicopter Society >High Resolution Trailing Vortex Measurements in the Wake of a Hovering Rotor
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High Resolution Trailing Vortex Measurements in the Wake of a Hovering Rotor

机译：悬停转子尾流中的高分辨率尾随涡流测量

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摘要

High-resolution three-dimensional velocity field measurements and flow visualization results were acquired in the flow field near the tip of a rotor blade operating in hover. Using three-component laser Doppler velocimetry (LDV), the measurements documented the trailing vortex formation, the initial core structure, and the viscous evolution of the vortex properties. The test conditions covered a range of wake-ages from as young as one-degree, up to about one rotor revolution. For each wake age, vortex core properties were estimated from the velocity field measurements. The high spatial resolution obtained with LDV has shown that the tip vortex core radius can be less than 3% chord at early wake-ages, but grows asymptotically as it ages. A significant axial velocity deficit (on the order of the peak swirl velocity) existed in the vortex core at early wake-ages, but the deficit rapidly diminished as the vortex aged. Using a Richardson parameter combined with flow visualization, the results suggest that the inner core of the vortex is mostly laminar at the vortex Reynolds numbers tested in this experiment. It was found that bands of turbulent eddies, originating from an adjacent vortex sheet, underwent a re-laminarization process as they were entrained into the vortex core. The evidence suggests that the entire tip vortex structure is neither fully laminar nor fully turbulent, but is instead in a continuous state of dynamic evolution with a region of relatively slow laminar diffusion and a region of accelerated turbulent diffusion. It is suggested that the variation of peak swirl velocity is the result of the competing influences of an inviscid roll-up process, relaminarization inside the vortex core, and viscous diffusion around the core boundary.
机译：在悬停工作的转子叶片尖端附近的流场中获得了高分辨率的三维速度场测量和流场可视化结果。使用三分量激光多普勒测速仪（LDV），测量结果记录了尾随的旋涡形成，初始岩心结构以及旋涡特性的粘性演变。测试条件涵盖了从小到一度到大约一转转子的唤醒范围。对于每个尾流年龄，根据速度场测量值估算涡流核心特性。用LDV获得的高空间分辨率表明，在早期醒来时，尖端涡旋芯半径可以小于弦的3％，但是随着年龄的增长，其渐近增长。在早期醒来时，涡流核中存在明显的轴向速度赤字（按峰值旋流速度的顺序），但随着涡旋的老化，该赤字迅速减小。使用Richardson参数与流动可视化相结合，结果表明，在本实验中测试的涡旋雷诺数下，涡旋的内层大部分为层流。已发现，由于涡流带被夹带到涡流核中，因此产生了湍流涡流，这些涡流源自相邻的涡流片。证据表明整个尖端涡结构既不是完全层流也不是完全湍流，而是处于动态演化的连续状态，具有相对缓慢的层流扩散区域和加速的湍流扩散区域。有人认为，峰值涡旋速度的变化是无粘性卷起过程，涡旋核内部的再分层以及核边界周围粘性扩散的竞争影响的结果。

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