Combining Passive Control Method for Dynamic Stall Control

Abstract

To demonstrate the benefits of a combined nose droop and Gurney flap for improving dynamic stall and poststall aerodynamic characteristics of a rotor airfoil, numerical investigations and design optimization have been performed. As a means of passive flow control, a fixed nose droop has been deliberately employed together with a Gurney flap. For shape optimization, droop location and droop angle were selected as design variables for the fixed nose droop, and the flap length was chosen as a design variable for the Gurney flap. Bousman's function plot was employed to define the objective function and constraint conditions. A feasible direction-based optimizer and a higher-order response surface method were harnessed to handle the highly nonlinear properties of dynamic stall. By the use of this methodology, optimum design was carried out to enhance lift and pitching moment characteristics simultaneously; at.the same time, the unfavorable effects of the overall movement of the pitching moment coefficient induced by droop and the Gurney flap was reduced. It is also proved that by utilizing a 22.7-deg droop at the 0.275 chord droop position and a 1.14% chord Gurney flap, the stall can be delayed by a maximum lift coefficient increased by 13%, a maximum negative pitching moment reduced by 60%, and the lift-to-drag ratio increased accordingly. The present combined passive control methods and design result show significant improvement of aerodynamic performance in Bousman's plot in terms of lift and pitching moment.