Multi-Objective Airfoil Optimization Under Unsteady-Freestream Dynamic Stall Conditions

Aimed at alleviating dynamic stall, an optimization method for rotor airfoils is proposed considering the unsteady-freestream circumstance and pitching motion. The method is based on the unsteady Reynolds-averaged Navier-Stokes equations, kriging model, and non-dominated sorting genetic algorithm II (NSGA-II). Three objective functions are built for minimizing the area of lift hysteresis loop, value of peak drag, and peak pitching moment. An optimized airfoil with larger maximum thickness, maximum camber, and upper leading-edge radius is obtained based on the baseline SC1095 airfoil. Besides, the optimized airfoil shows smaller local thickness and camber near the trailing edge. The results show that the flow separation and dynamic stall are suppressed or alleviated under both design and off-design conditions, attributed to a significant reduction of negative pressure peak and adverse pressure gradient. The dynamic stall is also alleviated for the rotor configured with the optimized airfoil in forward flight. This indicates that the optimized airfoil performs well in a rotor environment.