Jet flows induced by pitching cantilever plates provide a power-efficient solution for fluid acceleration and cooling enhancement. In such applications, the time-averaged (mean) properties of the induced jet flows are of great importance. We report a combined experimental and numerical study on the three-dimensional (3-D) characteristics of the mean jet downstream of a harmonically pitching cantilever plate in a quiescent fluid. These characteristics are then correlated with the transient 3-D vortex structures emanated from the trailing and side edges. Our particle image velocimetry and 3-D numerical simulations reveal that the mean induced jet has two distinct regions – a shrinking region immediately downstream of the trailing edge followed by an abrupt expansion region – separated by a necking point. We investigate the transient 3-D wake vortex evolution downstream of the plate to help elucidate the physics underlying the geometry of the mean jet. Our observations suggest that the breakdown of the shed vortex structure and reorientation of the consequent substructures are the primary factors governing the shape of the jet. These factors in turn are controlled primarily by the plate width and the amplitude of the oscillations. The results presented in this study improve our understanding of the complicated 3-D geometry of the induced mean jet in oscillating plates and facilitate optimal design of devices that operate based on this principle, such as piezoelectric fans.

中文翻译：

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静止流体中俯仰板诱发射流的三维特性

由倾斜悬臂板引起的射流为流体加速和冷却增强提供了一种节能的解决方案。在此类应用中，诱导射流的时间平均（平均）特性非常重要。我们报告了对静态流体中和谐俯仰悬臂板下游平均射流的三维 (3-D) 特性的联合实验和数值研究。然后将这些特征与从后缘和侧缘发出的瞬态 3-D 涡旋结构相关联。我们的粒子图像测速和 3-D 数值模拟表明，平均诱导射流有两个不同的区域 - 紧靠后缘下游的收缩区域，然后是突然膨胀区域 - 由颈缩点分隔。我们研究了板块下游的瞬态 3-D 尾涡演化，以帮助阐明平均射流几何形状的物理基础。我们的观察表明，脱落涡结构的破坏和随之而来的子结构的重新定向是控制射流形状的主要因素。这些因素又主要由板宽度和振荡幅度控制。本研究中提出的结果提高了我们对振荡板中诱导平均射流的复杂 3-D 几何形状的理解，并促进了基于该原理运行的设备（例如压电风扇）的优化设计。我们的观察表明，脱落涡结构的破坏和随之而来的子结构的重新定向是控制射流形状的主要因素。这些因素又主要由板宽度和振荡幅度控制。本研究中提出的结果提高了我们对振荡板中诱导平均射流的复杂 3-D 几何形状的理解，并促进了基于该原理运行的设备（例如压电风扇）的优化设计。我们的观察表明，脱落涡结构的破坏和随之而来的子结构的重新定向是控制射流形状的主要因素。这些因素又主要由板宽度和振荡幅度控制。本研究中提出的结果提高了我们对振荡板中诱导平均射流的复杂 3-D 几何形状的理解，并促进了基于该原理运行的设备（例如压电风扇）的优化设计。