Cheng Xin, Sun Mao
Institute of Fluid Mechanics, Beijing University of Aeronautics and Astronautics , Beijing , China.
PeerJ. 2017 Mar 9;5:e3002. doi: 10.7717/peerj.3002. eCollection 2017.
Most of the previous studies on Weis-Fogh clap-fling mechanism have focused on the vortex structures and velocity fields. Detailed pressure distribution results are provided for the first time in this study to reveal the differences between the full and the partial clap-fling motions. The two motions are studied by numerically solving the Navier-Stokes equations in moving overset grids. The Reynolds number is set to 20, relevant to the tiny flying insects. The following has been shown: (1) During the clap phase, the wings clap together and create a high pressure region in the closing gap between wings, greatly increasing the positive pressure on the lower surface of wing, while pressure on the upper surface is almost unchanged by the interaction; during the fling phase, the wings fling apart and create a low pressure region in the opening gap between wings, greatly increasing the suction pressure on the upper surface of wing, while pressure on the lower surface is almost unchanged by the interaction; (2) The interference effect between wings is most severe at the end of clap phase and the start of the fling phase: two sharp force peaks (8-9 times larger than that of the one-winged case) are generated. But the total force peaks are manifested mostly as drag and barely as lift of the wing, owing to the vertical orientation of the wing section; (3) The wing-wing interaction effect in the partial clap-fling case is much weaker than that in the full clap-fling case, avoiding the generation of huge drag. Compared with a single wing flapping with the same motion, mean lift in the partial case is enhanced by 12% without suffering any efficiency degradation, indicating that partial clap-fling is a more practical choice for tiny insects to employ.
以往大多数关于韦斯-福格拍击-甩动机制的研究都集中在涡旋结构和速度场上。本研究首次提供了详细的压力分布结果，以揭示完全拍击-甩动运动和部分拍击-甩动运动之间的差异。通过在运动的嵌套网格中数值求解纳维-斯托克斯方程来研究这两种运动。雷诺数设定为20，这与微小飞行昆虫的情况相关。研究结果如下：(1) 在拍击阶段，翅膀合拢，在翅膀之间的闭合间隙中形成高压区域，大大增加了翅膀下表面的正压力，而相互作用对翅膀上表面的压力几乎没有影响；在甩动阶段，翅膀甩开，在翅膀之间的张开间隙中形成低压区域，大大增加了翅膀上表面的吸力，而相互作用对翅膀下表面的压力几乎没有影响；(2) 翅膀之间的干扰效应在拍击阶段结束和甩动阶段开始时最为严重：会产生两个尖锐的力峰（比单翼情况大8-9倍）。但由于翼型的垂直取向，总力峰主要表现为阻力，几乎没有升力；(3) 部分拍击-甩动情况下的翼-翼相互作用效应比完全拍击-甩动情况下弱得多，避免了巨大阻力的产生。与以相同运动方式拍动的单翼相比，部分拍击-甩动情况下的平均升力提高了12%，且效率没有任何下降，这表明部分拍击-甩动是微小昆虫更实际的选择。
