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首页> 外文期刊>Journal of the American Helicopter Society >Wake Structure and Kinematics in the Vortex Ring State
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Wake Structure and Kinematics in the Vortex Ring State

机译：涡环状态下的尾迹结构和运动学

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High-resolution computational simulations of the vortical wake of a rotor operating both near to and within the vortex ring state have been conducted using Brown's vorticity transport model. The nonlinear vortex kinematics of the wake is exposed using three-dimensional visualizations of the simulated flow field. To reveal the vortex dynamics that underpin the highly unsteady flow within the vortex ring state, a rotor with just one blade was modeled. This blade was decoupled aerodynamically from the surrounding velocity field so that it acted merely as a source of trailed vorticity. The investigation identified a significant change in the dominant dynamics of the wake as it swapped from the tubular form that is characteristic of hover or very low speed descent into the toroidal geometry of the vortex ring state. Initial vortex "pairing" leads to rotation of vortex filaments away from their original attitude. This phenomenon plays an important role in regulating the downwash that the rotor can produce and thus in precipitating the onset of the vortex ring state. The considerable and persistent coherence of the vortical structure of the wake when in the vortex ring state is revealed, despite these disturbances, as are the mechanisms that lead to both small-scale and large-scale wake breakdown events. Simulations show the balance between the vortex pairing and short-wave instability modes to be different in the vortex ring state at high descent speed, where the wake lies above the rotor, compared to in the vortex ring state at low descent speed when the wake lies predominantly below the rotor. This yields subtle differences to the kinematics and structure of the wake in the two cases.
机译：使用布朗的涡度输运模型已经对在涡流环状态附近和在涡流环状态内运行的转子的涡流尾流进行了高分辨率的计算仿真。尾流的非线性涡旋运动学是使用模拟流场的三维可视化显示的。为了揭示支撑旋涡环状态下高度非恒定流的旋涡动力学，对仅具有一个叶片的转子进行了建模。该叶片在空气动力学上与周围的速度场脱钩，因此它仅充当拖尾涡流的来源。研究发现，当尾流从呈悬停或极低速下降特征的管状形式转换为涡流环态的环形几何形状时，其主要动力学特性发生了显着变化。初始涡旋“成对”导致涡旋细丝旋转离开其原始姿态。这种现象在调节转子可能产生的向下冲洗中并因此在促使涡旋环状态开始起着重要作用。尽管存在这些干扰，但仍揭示了处于涡流环状态时尾流旋涡结构的相当大且持续的连贯性，以及导致小规模和大规模尾流崩溃事件的机制。仿真显示，在尾流位于转子上方的高下降速度时，涡流环状态与短波不稳定性模式之间的平衡不同，而在尾流处于低下降速度时，涡流环状态下的下降速度较低。主要位于转子下方。这在两种情况下对尾流的运动学和结构产生了细微的差异。

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