SYNTHESIZED AIRFOIL DATA METHOD FOR PREDICTION OF DYNAMIC STALL AND UNSTEADY AIRLOADS

A detailed analysis of dynamic stall experiments has led to a set of relatively compact analytical expressions, called synthesized unsteady airfoil data, which accurately describe in the time-domain the unsteady aerodynamic characteristics of stalled airfoils. Under the present study, unsteady drag data were synthesized which provided the basis for successful expansion of the formulation to include computation of the unsteady pressure drag of airfoils and rotor blades. Also, an improved prediction model for airfoil flow reattachment was incorporated in the method. Application of this improved unsteady aerodynamics model has resulted in an improved correlation between analytic predictions and measured full scale helicopter blade loads and stress data. The results obtained clearly indicate that it is feasible to generalize the empirical parameters embedded in the present method over a range of angle of attack, Mach number, airfoil shape and sweep angle. However, the empirical parameters, corresponding to the various data sets synthesized to date were found to be insufficient for generalization of the parameters.