Multi-Winglets: Multi-Objective Optimization of Aerodynamic Shapes

Various configurations of aircraft wing tip devices have been investigated by performing 3D aerodynamics analysis. The wing tip device in this study was derived from the wing tips of a soaring bird, featuring three smoothly blended elements. Each multi-winglet configuration was integrated into a complete wing-tail-body aircraft configuration. Geometry of each of the three elements in the multi-winglet was defined using 11 parameters, totaling 33 parameters defining a complete multi-winglet geometry. The current design methodology utilized a second order, 3D geometry generation algorithm based on locally analytical smoothly connected surface patches. This algorithm allows for creation of vastly diverse 3D geometries with minimal number of specified design parameters. A 3D, compressible, turbulent flow, steady state analysis was performed using a Navier-Stokes solver on each configuration to obtain the objective function values. Each configuration was analyzed at a free stream Mach number of 0.25 and at an angle of attack of 11 degrees to mimic the takeoff conditions of a passenger aircraft. Multi-objective optimization was carried out using modeFRONTIER utilizing a radial basis function response surface approximation coupled with a genetic algorithm. Maximizing coefficients of lift and lift-todrag ratio, while minimizing coefficients of drag and the magnitude of the coefficient of moment were the four simultaneous objectives. The multi-winglet concept was shown to have superior performance at subsonic and transonic speeds.