Shape optimization of a membrane wing for micro air vehicle

Micro air vehicles with a maximal dimension of 15cm require original design concept due to their low Reynolds number flight regime. It has been empirically observed that a flexible membrane wing can improve the aerodynamic performance of the vehicles. To help advance our knowledge in this area, we investigate shape optimization of a membrane wing. A direct membrane wing optimization employing a coupled Navier-Stokes and flexible structure analysis is computationally expensive. Therefore, we use a rigid wing as a surrogate model. We employ a moving grid technique to facilitate automatic grid generation. Our objective is to maximize the lift-to-drag ratio under aerodynamic and geometry constraints. The optimized design exhibits reduced camber from root to tip. Overall, the aerodynamic improvement is primarily derived from the inner 70% of the wing. The optimized platform is checked for performance of the membrane wings and found to improve the performance by about the same margin. Furthermore, both optimized membrane and rigid wings improve the lift-to-drag ratios mainly by reducing the form drag. However, the membrane wing demonstrates less variation in lift-to-drag ratio as the angles of attack vary.