The wake structures generated by rotating wings are studied numerically to investigate the complex vortex formation and evolution in both near-wake and far-wake regions. Flat rectangular wings with finite aspect ratios (AR = 1–8) that rotate from rest at an angle of attack ranging from 15° to 90° in a low Reynolds number regime (200–1600) are considered. Simulations were carried out using an in-house immersed-boundary-method-based incompressible flow solver. A detailed analysis of the vortex formation showed that the general wake pattern near the wingtip shifted from a single vortex loop to a pair of counter-rotating vortex loops with the enhancement of the leading-edge vortex (LEV) strength. Specifically, a stronger LEV due to the high angles of attack or high aspect ratios can induce an enhanced counter-pair trailing-edge vortex (TEV). As the TEV intensifies, a secondary tip vortex will be generated at the bottom corner of the wingtip, regardless of the wing geometry. This forms a pair of counter-rotating vortex loops around the wingtip. This type of wingtip vortex formation and evolution are found to be universal for the range of angle of attack and aspect ratio investigated. In addition to the vortex formation, surface pressure distribution and aerodynamic performance are also discussed. The findings from this work could help advance the fundamental understanding in the vortex dynamics of finite-aspect ratio rotating wings at a high angle of attack (>15°).

中文翻译：

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低雷诺数下旋转翼尖涡的形成和演化

对旋转机翼产生的尾流结构进行数值研究，以研究近尾流和远尾区域中复杂的涡旋形成和演化。考虑了具有有限纵横比 (AR = 1-8) 的扁平矩形机翼，它在低雷诺数范围 (200-1600) 中以 15° 到 90° 的攻角范围从静止旋转。使用基于浸入边界法的内部不可压缩流动求解器进行了模拟。涡形成的详细分析表明，随着前缘涡（LEV）强度的增强，翼尖附近的一般尾流模式从单个涡环转变为一对反向旋转的涡环。具体而言，由于大迎角或高纵横比而产生的更强 LEV 会导致增强的反对后缘涡流 (TEV)。随着 TEV 的增强，无论机翼几何形状如何，都会在翼尖的底角处产生次级翼尖涡流。这在翼尖周围形成了一对反向旋转的涡环。发现这种类型的翼尖涡旋形成和演化对于所研究的攻角和纵横比范围是普遍的。除了涡流的形成，还讨论了表面压力分布和空气动力学性能。这项工作的发现有助于推进对大攻角（> 15°）有限展弦比旋转机翼涡流动力学的基本理解。发现这种类型的翼尖涡旋形成和演化对于所研究的攻角和纵横比范围是普遍的。除了涡流的形成，还讨论了表面压力分布和空气动力学性能。这项工作的发现有助于推进对大攻角（> 15°）有限展弦比旋转机翼涡流动力学的基本理解。发现这种类型的翼尖涡旋形成和演化对于所研究的攻角和纵横比范围是普遍的。除了涡流的形成，还讨论了表面压力分布和空气动力学性能。这项工作的发现有助于推进对大攻角（> 15°）有限展弦比旋转机翼涡流动力学的基本理解。