Flow instability on airfoil separation control at optimum actuation frequency

Abstract eng:
The present study reveals a role of flow instabilities in the spatially developing disturbance induced by a synthetic jet device (SJ) with an optimum actuation frequency, which improves a separation-control capability around an airfoil. For this purpose, a high fidelity flow computation (large-eddy simulation) is conducted, where the chord Reynolds number and angle of attack are set to be 63,000 and 12 [deg], respectively. The linear stability analysis is conducted to detect an unstable mode of the wall-normal fluctuation in the separation controlled flows. In the well-controlled flows, the harmonics of the input fluctuation directly enhances the Kelvin-Helmholtz instability which linearly develops in the separated shear layer, followed by higher- and lower-frequency modes that are triggered by the most unstable modes (nonlinear growth regime). The process above effectively enhances a turbulent transition and generation of large-scale coherent vortices.

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