Optimization of Vane-Type Vortex Generators for Tiltrotor Wings using Computational Fluid Dynamics

Tiltrotor wings are thick and highly loaded airfoils, and are thus particularly susceptible to separation and early onset buffet and vortex generators are commonly used to alleviate these issues. Hence. the design of counter-rotating vortex generators on tiltrotor wings to control separation is considered. A representative tiltrotor wing airfoil (a modified NACA 64(4)-421) has been tested at a Reynolds number of 7.5 million (M = 0.24) and CL = 1.3 to demonstrate that a large separation is problematic in this flow case. Five parameters have been introduced to quantify the vortex generator design space (length, aspect ratio, angle, chord location and spacings ratio) and Latin Hypercube sampling of this design space has been undertaken using high fidelity CFD to construct a radial basis function based surrogate model. This model has been interrogated and refined using an efficient adaptive sampling method which incorporates both space-filling and local refinement properties in order to achieve an optimum solution. To determine this optimum, a global search algorithm based
on differential evolution was used for optimization of the model. The results obtained from the optimization eliminated the separation experienced by the clean geometry (from 11.1% to 0%), whilst reducing the drag obtained from the best Latin Hypercube sample by 7%.