Abstract
The present work investigates the natural low-frequency flow oscillation phenomenon using large-eddy simulation. Four simulations were carried out for flow around a NACA 0012 airfoil with Reynolds number of 50,000 and Mach number M∞=0.4 at angles of attack of 9.25, 9.29, 9.4, and 9.6 deg. The results clearly indicate that natural low-frequency flow oscillation is taking place. The oscillations are self-sustained and caused by periodic bubble forming and bubble bursting on the suction side. The low-frequency oscillation phenomenon was found to exist over a range of angles of attack near stall. Computed maximum reverse flow inside the bubble indicates an absolute instability mechanism. The time- and span-averaged flowfield as well as the instantaneous turbulent flowfield illustrated the dynamics of low-frequency oscillation near stall. The location of transition is shown to move downstream during bubble bursting. Spectral analysis of the surrounding acoustic field reveals that the observed phenomenon affect...
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