Lack of flexibility limits the performance enhancement of man-made flapping wing Micro Air Vehicles (MAVs). Active chordwise deformation (bending) is introduced into the flapping wing model at low Reynolds number of Re = 200 in the present study. The lattice Boltzmann method with immersed boundary is adopted in the numerical simulation. The effects of the bending amplitude, bending frequency and phase lag between bending and flapping on the propulsive performance are analysed. The numerical results show that all the chordwise deformation parameters including the bending amplitude, bending frequency and phase lag have a great influence on the flow field, Leading-Edge Vortex (LEV), Trailing-Edge Vortex (TEV) and previous Leading-Edge Vortex (pLEV) of the deformable flapping wing, which leads to the variation of the propulsive performance. With decreasing bending amplitude and increasing bending frequency, both the thrust and energy dissipation coefficients increase. The highest thrust coefficient and highest energy dissipation coefficient occur at a phase lag of 180°. On the other hand, strong dependence of the propulsive efficiency on the vortex tangle is found. The highest propulsive efficiency is obtained for the present model at a dimensionless bending amplitude of 0.2, bending frequency of 0.7Hz, and phase lag of 0°.

中文翻译：

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弦向变形对前飞扑翼推进性能的影响

缺乏灵活性限制了人造扑翼微型飞行器（MAV）的性能提升。本研究将主动弦向变形（弯曲）引入到低雷诺数 Re = 200 的扑翼模型中。数值模拟采用浸没边界的格子Boltzmann方法。分析了弯曲幅度、弯曲频率和弯曲与拍打之间的相位滞后对推进性能的影响。数值结果表明，包括弯曲幅度、弯曲频率和相位滞后在内的所有弦向变形参数对流场、前缘涡（LEV）、后缘涡（TEV）和之前的前缘涡都有很大影响。 (pLEV) 的可变形扑翼，这导致推进性能的变化。随着弯曲幅度的减小和弯曲频率的增加，推力和能量耗散系数都增加。最高推力系数和最高能量耗散系数出现在 180° 的相位滞后处。另一方面，发现推进效率对涡缠结有很强的依赖性。本模型在无量纲弯曲幅度为 0.2、弯曲频率为 0.7Hz 和相位滞后为 0° 时获得了最高的推进效率。