Low-Frequency Oscillation over NACA0015 Airfoil Near Stall at High Reynolds Number

摘要

The unsteady flows past a NACA0015 airfoil near stall at a high Reynolds number are investigated numerically using the delayed detached-eddy simulation with adaptive coefficient model. The unsteady feature is primarily represented by a low-frequency oscillation, attributed to the quasi-period movement of the separation point. Correlation analysis between the instantaneous lift coefficient and separation point location indicates that the two signals present nearly in-phase behavior. Other unsteady characteristics such as the trailing-edge vortex shedding and instability of the upper surface shear layer are also analyzed. Since the Strouhal number corresponding to the movement of the separation point based on the projected airfoil height Sth varies significantly with the angle of attack, the normalized Strouhal number based on the length of the recirculation region StL is observed to have a value of approximately 0.036 and be insensitive to the angle of attack.