Physical analysis of the coherent motion during hysteretic static stall of Naca foil using proper orthogonal decomposition

Abstract

At static stall of airfoil, an hysteretic behavior (corresponding to an abrupt loss of lift) has been observed leading to a partially detached flow (called state I, upper increasing angle branch) and massively separated flow (called state II, lower decreasing angle branch). In order to predict the type of hysteretic loop that may occur or to quantify unsteady oscillatory flow in the near wake, experiments have been performed to explore laminar separation, transition and detachment of the boundary layer (Mittal and Saxena, 2000) but the keyphysical properties of the vortex shedding establishment during hysteretic loop is not clearly understood.