A robust design for a winglet based on NURBS-FFD method and PSO algorithm

Drag reduction has always been the emphasis and difficulty in aircraft design. For a large air freighter or airliner, the induced drag accounts for about 40% of the total drag in the cruise phase. In this case, a robust design for a winglet is implemented to an initial wing of an aircraft. For the purpose of reducing the number of design variables, the NURBS based free form deformation (NURBS-FFD) method is introduced as the parametric method in the winglet design process. An improved particle swarm optimization (PSO) algorithm based on CVTs method is adopted serving as the optimization method for the winglet design. In order to verify the reduction effect on induced drag coefficient, a discrete vortex method is established based on Biot-Savart Law. The optimization results indicate that not only the induced drag coefficient is reduced obviously but also the total drag coefficient is decreased dramatically in the meantime under the situation of the equivalent lift coefficient.