Pre-Stall Wall-Pressure Characteristics of a CD Airfoil

A DNS of a CD airfoil at pre-stall conditions was conducted to characterize wall pressure statistics in terms of power spectral density (PSD) of wall pressure, convection velocity and spanwise coherence. Wall PSD on the suction side confirms a decay slope of^−2.2 which is consistent with previous experimental and numerical results. Neither Smolyakov nor Panton and Linebarger models for convection velocity are able to predict convection velocity for the pre-stall airfoil. The ratio of spanwise coherence length to displacement thickness in the separated boundary layer increases at low frequencies relative to attached boundary layers but remained similar at higher frequencies. At low frequencies, spanwise coherence length scales better with a turbulence length scale defined by Prandtl’s mixing length than with displacement thickness.