Simulation and surrogate-based design of rectangular vortex generators for tiltrotor aircraft wings

Design of counter-rotating rectangular vortex generators on a representative tiltrotor wing section is considered by surrogate-based optimization. Due to structural require- ments, tiltrotor wings are usually thick and highly loaded and are therefore susceptible to early onset buffet and separation. Boundary layer control is therefore essential and is commonly achieved by using vortex generators. A high fidelity CFD simulation framework has been developed that utilises a custom built mesh generator to produce high qual- ity structured meshes and viscous flow solutions obtained using the open-source library, OpenFOAM. A representative aerofoil and flow condition have been used (modified NACA 64(4)-421 at CL = 1.3) to demonstrate that a large separation region is problematic for this case. A vortex generator has therefore been added and its geometric properties designed to minimize the separation region on the aerofoil. Latin Hypercube sampling has been used to produce a number of high-fidelity flow solutions and a radial basis function interpolation used to create a surrogate model; these functions exactly preserve the simulation values at the know data points while simultaneously distributing that information through the re- mainder of the design space. Optimization of the surrogate using a global search algorithm based on differential evolution has produced results that virtually eliminate the separation on the aerofoil, while minimising the effect on the overall drag of the wing, demonstrating the quality of the method.