Validated Dynamic Stall Simulation of Pitching Low Reynolds Number Airfoils

Abstract

Deep dynamic stall is one of several complex behaviors that result in extreme variation of the aerodynamic loads on small wind turbine (SWT) blades during unsteady wind conditions. In this study, unsteady Reynolds-averaged Navier–Stokes simulations are performed for two low Reynolds number (Re) airfoils where sinusoidal pitching is applied to replicate the dynamic stall that occurs on rotating SWT blades. The SD 7037 airfoil is simulated at Re=4.1x10⁴ and a pitching reduced frequency of k=0.08, and the S833 airfoil is at Re=1.7x10⁵ and k=0.06. The simulated lift coefficient and dynamic stall timing agree with experimental data, which is attributed to the wall-normal resolution of the mesh and is an advancement from the early prediction of stall seen consistently in previous numerical studies. The accurate prediction of dynamic stall is found to be dependent on the correct simulation of the bursting of the laminar separation bubble (LSB), which initiates the complete separation of the boundary layer and the formation of a leading-edge vortex. The γ-Reθ,t k-⍵ model combined with the use of a fine mesh at the airfoil leading edge results in an accurate simulation of the bursting LSB and the correct prediction of the deep dynamic stall.