Abstract This study explores the feasibility of using the vortex impulse approach, based on experimentally generated velocity fields to estimate the energy harvesting performance of a sinusoidally flapping foil. Phase-resolved, two-component particle image velocimetry measurements are conducted in a low-speed wind tunnel to capture the flow field surrounding the flapping foil at reduced frequencies of k = f c / U ∞ = 0.06–0.16, pitching amplitude of θ 0 = 75 ∘ and heaving amplitude of h 0 / c = 0.6 . The model results show that for the conditions tested, a maximum energy harvesting efficiency of 25% is attained near k = 0.14 , agreeing very well with published numerical and experimental results in both accuracy and general trend. The vortex impulse method identifies key contributions to the transient power production from both linear and angular momentum effects. The efficiency reduction at larger values of reduced frequencies is shown to be a result of the reduced power output from the angular momentum. Further, the impulse formulation is decomposed into contributions from positive and negative vorticity in the flow and is used to better understand the fluid dynamic mechanisms responsible for producing a peak in energy harvesting performance at k = 0.14 . At the larger k values, there is a reduction of the advective time scales of the leading edge vortex (LEV) formation. Consequently, the LEV that is shed during the previous half cycle interacts with the foil at the current half cycle resulting in a large negative pitching power due to the reversed direction of the kinematic motion. This vortex capture process significantly decreases the total cycle averaged power output and energy harvesting efficiency. These results show the link between the kinematic motion and LEV time scales that affect the overall power production.

中文翻译：

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基于涡旋脉冲理论的振翅式箔片能量采集器功率估算

摘要 本研究探讨了使用涡旋脉冲方法的可行性，基于实验产生的速度场来估计正弦拍动箔的能量收集性能。相位分辨的双分量粒子图像测速测量在低速风洞中进行，以捕获在 k = fc / U ∞ = 0.06–0.16 的降低频率下拍动箔周围的流场，俯仰幅度 θ 0 = 75 ∘ 和垂荡幅度 h 0 / c = 0.6 。模型结果表明，对于测试条件，在 k = 0.14 附近获得了 25% 的最大能量收集效率，在准确性和总体趋势方面与已发表的数值和实验结果非常吻合。涡旋脉冲方法确定了线性和角动量效应对瞬态功率产生的关键贡献。降低频率的较大值处的效率降低被证明是角动量输出功率降低的结果。此外，脉冲公式被分解为流动中正涡度和负涡度的贡献，并用于更好地理解负责在 k​​ = 0.14 处产生能量收集性能峰值的流体动力学机制。在较大的 k 值下，前缘涡 (LEV) 形成的平流时间尺度减少。最后，由于运动学运动的反向，在前一个半周期脱落的 LEV 在当前半周期与翼板相互作用，导致大的负俯仰功率。这种涡流捕获过程显着降低了总循环平均功率输出和能量收集效率。这些结果显示了运动学运动与影响整体功率产生的 LEV 时间尺度之间的联系。