Dynamic stall model with circulation pulse and static hysteresis for NACA 0012 and VR-12 airfoils

Airfoils undergoing dynamic stall often display a secondary lift peak after the lift has begun to decrease. A study of this phenomenon for the NACA 0012 and VR-12 airfoils shows that the secondary peak is followed by a damped oscillation in lift. It is found that this underdamped lift can be modeled by an ONERA-type equation for secondary lift that is driven by a simple pulse. It is known that the physical basis of this pulse is the attaching of a secondary vortex to the airfoil. The onset and duration of this pulse can be predicted in terms of angle of attack in a general time-domain model. When added to the present Ahaus-Peters stall equations, this new stall equation gives a total finite-state model for dynamic stall that can include the secondary stall peak.