Prediction of Dynamic Stall and Unsteady Airloads for Rotor Blades

A detailed study of the wind tunnel test data of oscillating airfoils has led to a relatively simple formulation, involving a compact set of dynamic parameters, which accurately predicts the unsteady aerodynamic coefficients of airfoils during dynamic stall. One of the main features of the formulation is that it adequately accounts for the effects of the formation and streamwise movement of the vortex shed from the airfoil leading edge during dynamic stall. Based upon this formulation, a new method has been developed that determines the unsteady aerodynamic loading acting on rotor blades operating in stall. The effects of the azimuthal variation in aerodynamic sweep angle and Mach number are appropriately incorporated in the method. The synthesized unsteady lift and pitching moment hysteresis loops match very will with the two-dimensional test data. The results of a limited correlation study involving the application of the present method to full scale helicopter rotor blades indicate improved correlation between analytical predictions and the test data.