Rotor airfoil profile optimization for alleviating dynamic stall characteristics

In order to alleviate the dynamic stall characteristics of rotor airfoil, a high-efficient optimization method is established by coupling the SQP method with CFD method. Aiming at improving the optimized efficiency, a new strategy of linear search is established to avoid the disturbance of the penalty factors, and the optimal efficiency improves more than 30% compared with traditional line search method. In order to reduce the design variables, the CST method is employed to parameterize the airfoil section. All the flow solutions were computed by solving the URANS equations, coupled with the Spalart-Allmaras turbulence model. To reduce pitching moment and drag coefficient under dynamic stall condition, a new airfoil has been optimized based on the OA209 airfoil by employing the present optimal method. Due to the inhibition of leading edge vortex, the peaks of pitching moment and drag coefficient of the optimized airfoil are decreased about 75.8% and 44.2% at point 1, 44.0% and 41.4% at point 2 compared with the OA209 airfoil. Moreover, the optimized airfoil has better lift stall characteristics compared with the OA209 airfoil. In addition, by comparing the 3-D dynamic stall characteristics of rotor blade, it is demonstrated that the peaks of pitching moment coefficients and drag coefficients of optimized airfoil are smaller than those of OA209 airfoil at different blade radial stations.