Numerical investigation of the unsteady effect on the onset of leading-edge separation in dynamic stall.

Numerical experiments are conducted to simulate airfoils pitching up at constant rates into the dynamic stall regime using the Beam and Warming algorithm for compressible Navier-Stokes equations. The Bladwin and Lomax algebraic turbulence model is used to mimic turbulent flow downstream of a point designated as the transition location. The investigation focuses on the leading edge, where, as experimental results indicate, a recirculating bubble is often present. It is found that the transition location has a dominating effect on the development of the flow and the evolution of the recirculation bubble which, in most cases, is the mechanism leading to the onset of separation and dynamic stall. In cases where the appearance of the bubble is prevented by some particular choices of the transition location, a supersonic region emerges, and numerical instability originated from there halts the simulations