On synchronization in flow over airfoil with local oscillating flexible surface at high angle of attack using Lagrangian coherent structures

Lagrangian coherent structures (LCSs) are used to reveal the mechanism of high-lift airfoil with local oscillating at high angle of attack, as the frequency of local oscillation is synchronized with the characteristic frequency of the flow field. First, the forced excitation is used to control the oscillation of the local flexible surface, and the fluid-structure interaction model composed by local oscillating airfoil and unsteady fluid is established. Then, the unsteady flow around a 2-D local oscillating airfoil at high angle of attack is simulated and analyzed numerically by commercial software Fluent with the UDF function and the dynamic grid technique. The results show that the local oscillation can improve the lift of the airfoil. Moreover, as the frequency of the local oscillation is synchronized with the characteristic frequency of the flow field around the rigid airfoil, the lift could be enhanced significantly. Finally, the LCSs are introduced to study the mass transport between main flow and separation area as the frequency of local oscillation is synchronized with the characteristic frequency of flow field, from viewpoint of nonlinear dynamics. It is found that the stable manifolds and unstable manifolds are tangled with each other as time goes on, inducing the mass transport between the main flow and the separating area in a periodical way.

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