Bistable flow dynamics of airfoil stall under varying angle of attack: A stochastic model with multiplicative noise

Abstract

We focus on the intermittent bistable stall dynamics of an airfoil under varying angle of attack. We propose a one-dimensional Langevin equation where the stochastic forcing depends on the state of the system -- high-lift attached flow or low-lift detached flow -- and where the deterministic potential depends continuously on the angle of attack. The model, identified based on the flow statistics and dynamics, reproduces the S-shaped lift curve, as well as the flow dynamics. It also predicts the nature of the bifurcations that the flow undergoes as the angle of attack varies.