Abstract The aerodynamic performance of oscillating piezoelectric fans has been the focus of many research studies due to their potential as active cooling mechanisms for thermal management applications. These studies have typically focused on commercially available fans with flexible beams that are made to oscillate by tuning the alternating input voltages to the beam’s resonant frequency. Geometric variables such as fan height and length have previously been investigated; however, fan thickness has remained a fixed geometric constraint ( $${\mathcal {O}}\sim 0.1$$ O ∼ 0.1 mm) to allow feasible resonant frequencies to be achieved. This study investigates the influence of beam thickness on the flow field generated by an oscillating beam. The beam in this study is a rigid cantilever that is mechanically oscillated at a fixed amplitude and frequency thereby obviating the requirement to operate at resonance. Thicknesses of 1 and 3.7 mm are considered. A custom-designed particle-image velocity (PIV) facility was used to capture the induced phase-locked and time-averaged flow fields in two planes. The beams were noted to produce markedly different wakes within the oscillation plane. The 1-mm beam induced two distinct diverging jets—consistent with much of the literature on piezoelectric fans. In comparison, the 3.7-mm beam created two strong lateral wake regions with minimal fluid disturbance downstream of the beam tip. Out-of-plane measurements, as well as numerical models, revealed that fluid separation from the 3.7-mm beam is inhibited due to the more dominant influence of viscous friction on the larger, upper and lower surfaces of the rigid structure. The numerical analysis also revealed the significant influence of shed, counter-rotating vortex pairs on the pressure fields around the beam structures during the subsequent half-stroke. The results of this work may inform the design of oscillating fans for use in thermal management applications, as well as contribute to the literature on the complex phenomenon of flapping wing flight. Graphic abstract

中文翻译：

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厚度对悬臂梁振荡产生的流场的影响

摘要 振动压电风扇的空气动力学性能因其作为热管理应用的主动冷却机制的潜力而成为许多研究的焦点。这些研究通常集中在具有柔性梁的商用风扇上，这些风扇通过将交流输入电压调整到梁的谐振频率来振荡。先前已经研究了诸如风扇高度和长度之类的几何变量；然而，风扇厚度仍然是一个固定的几何约束（$${\mathcal {O}}\sim 0.1$$ O ∼ 0.1 mm）以允许实现可行的共振频率。本研究调查了梁厚度对由振荡梁产生的流场的影响。本研究中的梁是刚性悬臂梁，它以固定的振幅和频率进行机械振荡，从而避免了在共振下运行的要求。考虑了 1 和 3.7 毫米的厚度。定制设计的粒子图像速度 (PIV) 设施用于捕获两个平面中的感应锁相和时间平均流场。注意到光束在振荡平面内产生明显不同的尾流。1 毫米的光束引起了两个不同的发散射流——这与许多关于压电风扇的文献一致。相比之下，3.7 毫米的光束产生了两个强大的横向尾流区域，光束尖端下游的流体扰动最小。平面外测量以及数值模型表明，流体与 3. 由于粘性摩擦对刚性结构的较大的上表面和下表面的影响更大，因此 7 毫米梁被抑制。数值分析还揭示了在随后的半冲程中伞裙、反向旋转涡旋对对梁结构周围压力场的显着影响。这项工作的结果可以为用于热管理应用的振荡风扇的设计提供信息，并有助于有关扑翼飞行复杂现象的文献。图形摘要 这项工作的结果可以为用于热管理应用的振荡风扇的设计提供信息，并有助于有关扑翼飞行复杂现象的文献。图形摘要 这项工作的结果可以为用于热管理应用的振荡风扇的设计提供信息，并有助于有关扑翼飞行复杂现象的文献。图形摘要