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首页> 外文期刊>Journal of the American Helicopter Society >A Visual Study of Vortex Instabilities in the Wake of a Rotor in Hover
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A Visual Study of Vortex Instabilities in the Wake of a Rotor in Hover

机译：悬停时转子尾流涡旋不稳定性的视觉研究

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摘要

A visual study of the instability characteristics of the helical vortex filaments trailing from the tips of a three-bladed lifting rotor in a water tank is presented. The rotor diameter was 25.4 cm, and its rotation rate ranged from 4 to 12 revolutions per second. Soon after their formation, the vortex filaments developed long- and short-wave instabilities. In the long-wave instability mode, two of the three vortices coming off the rotor orbited around each other and merged in about 0.4 of the theoretical orbit time of equistrength two-dimensional vortices, after which the third vortex joined the merger to form a single, apparently turbulent helical vortex filament. The wavelengths of the short-wave instabilities were about 0.4 of the wake radius, about 17 cycles over the circumference. The short waves exhibited a linear growth rate during the first half of their orbital motion and an exponential growth prior to merging. The linear growth rate was about 0.0034 D/rad. The e-folding time for the exponential growth rate was about 0.52 rad.
机译：可视化研究了从水箱中的三叶片提升转子的尖端拖曳的螺旋涡旋丝的不稳定性。转子直径为25.4厘米，转速为每秒4到12转。涡旋丝形成后不久，就形成了长波和短波不稳定性。在长波不稳定性模式下，三个旋涡中的两个旋涡从转子中绕过，并在等强度二维旋涡的理论轨道时间的约0.4的时间内合并，然后第三个旋涡加入合并，形成一个单一的，显然是涡旋螺旋涡流丝。短波不稳定性的波长约为尾波半径的0.4，在圆周上约为17个循环。短波在其轨道运动的前半段表现出线性增长率，在合并前呈指数增长。线性增长率约为0.0034 D / rad。指数增长率的电子折叠时间约为0.52 rad。

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