Design optimization of passive control devices for dynamic stall control

Abstract

Design optimization was performed to improve dynamic stall characteristics of rotor airfoil by deliberately combining two kinds of passive control devices, namely, the fixed nose droop and Gurney flap. The location and droop angle were selected as design variables for fixed nose droop and for Gurney flap the flap length as a design variable. Bousman's function plot was employed to define objective function and constraint conditions. A feasible direction based optimizer and a higher order response surface method were employed to handle highly nonlinear characteristic of dynamic stall. Using this methodology, optimum design was carried out so as to improve lift and pitching moment characteristics simultaneously, while limiting the unfavorable effects of pitching moment coefficient induced by the increase of droop angle. It was found from the series of optimizations that the stall was remarkably alleviated when using 21° droop of 0.3125 chord droop position and 1.3% chord Gurney flap. The maximum lift coefficient was found to increase 14% and the negative pitching moment and the maximum drag coefficient were reduced by 84% and 80% respectively. These design result indicate that the present design method for combined passive control device might be a useful concept for designing rotor airfoil with massive stall. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.