Department of Aerospace Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, Republic of Korea.
Chungnam National University, Daejeon 34134, Republic of Korea.
Bioinspir Biomim. 2024 Jul 15;19(5). doi: 10.1088/1748-3190/ad5e50.
This study investigates the role of leading-edge (LE) curvature in flapping wing aerodynamics considering hovering and forward flight conditions. A scaled-up robotic model is towed along its longitudinal axis by a rack gear carriage system. The forward velocity of the robotic model is changed by varying the advance ratiofrom 0 (hovering) to 1.0. The study reveals that the LE curvature has insignificant influence on the cycle-average aerodynamic lift and drag. However, the time-history lift coefficient shows that the curvature can enhance the lift around the middle of downstroke. This enhanced lift is reduced from 5% to 1.2% aschanged from 0 to 1.0. Further flow examinations reveal that the LE curvature is beneficial by enhancing circulation only at the outboard wing sections. The enhanced outboard circulation is found to emanate from the less stretched leading-edge vortices (LEVs), weakened trailing-edge vortices (TEVs), and the coherent merging of the tip vortices (TVs) with the minor LEVs as observed from the phase-lock planar digital particle image velocimetry measurements. The far-wake observation shows that the LE curvature enhances the vorticity within the TV, helping to reduce the overall flow fluctuations in the far field. These findings can be extended to explain the predominantly straight LE wing shape with a small amount of curvature only observed near the wing tip for flapping fliers with Re from 10to 10.
本研究考察了前缘（LE）曲率在考虑悬停和前飞条件下扑翼空气动力学中的作用。一个按比例放大的机器人模型通过齿条齿轮 carriage 系统沿其纵轴被拖曳。通过改变前向速度比（advance ratio）从 0（悬停）到 1.0，改变机器人模型的前进速度。研究表明，LE 曲率对周期平均气动力升力和阻力的影响不大。然而，升力时程系数表明，曲率可以在下降冲程的中间部分增强升力。当从 0 变为 1.0 时，这种增强的升力从 5%降低到 1.2%。进一步的流动研究表明，LE 曲率通过仅在外翼段增强循环是有益的。在外翼段观察到增强的循环是由于前缘涡（LEV）较少拉伸、尾流涡（TEV）减弱以及尖端涡（TV）与较小的 LEV 相干合并。远尾迹观察表明，LE 曲率增强了 TV 内的涡度，有助于减少远场的整体流动波动。这些发现可以扩展到解释为具有小曲率的主要直 LE 机翼形状，仅在具有 Re 从 10 到 10 的扑翼飞行器的翼尖附近观察到。
