流场中柔性体摆动尾迹模态分析

Modal Analysis for the Wake of Flapping Flexible Body in Flow Field

在自然界和实际工程问题中,柔性体和流体的流固耦合现象广泛存在。本研究应用浸入边界方法模拟了柔性体在流场中从静止到稳定运动的过程,发现在摆动柔性体的尾迹中存在3种模态:即由强度较小的卡门涡街过渡为无规律的混沌状态,最后当摆动稳定后尾迹区呈现强度较大的卡门涡街;随着柔性体抗弯强度减小,柔性体摆动尾迹中的涡量增大,模态转变时间提前,而当摆动状态稳定后,抗弯强度对尾迹影响不明显,但对应的阻力系数并不是对应减小,只有合适的抗弯强度才能减少柔性体在流场中的阻力。此问题的探讨对生物学运动的反应时间差异和提高工程效率具一定的参考意义。

Flow-structure interaction problems are ubiquitous in nature. In this paper, the Immersed Boundary Method （IBM） is introduced to simulate the process of the flapping flexible body in the flow field from static status to steady movement, and we found that there are three modes in the wake of flapping flexible body, i.e. the small strength Karman vortex street will change into the irregular chaotic state from the beginning, and it will be showed great strength Karman vortex street in the wake when the flapping movement is steady. With the bending strength decreases, the vorticity increased and the time of modal translation is moved up. When the flapping state is stability, the bending strength do not show obvious effects on the wake in flow field, but the drag coefficients are not decreased, just only the suitable bending strength will reduce the drag of flexible body in flow field. It is a certain reference value to discuss this question for the biological differences in response time and the improvement of engineering efficiency.