Membrane Micro Air Vehicles with Adaptive Aerodynamic Twist: Numerical Modeling

Abstract

Micro air vehicles are typically characterized by a low aspect ratio wing operating at low Reynolds numbers (104): aerodynamics involve a three-dimensional flow field with numerous regions of separated flow. Furthermore, aerodynamic twist can be built into the wing through the use of a thin membrane skin, to adaptively increase the wing camber. This work formulates a static aeroelastic model of such a wing, by coupling a linear membrane model to a well-validated steady laminar Navier–Stokes solver. The membrane deformation causes a significant pressure redistribution which increases lift and longitudinal static stability, though a drag penalty also develops. The efficiency of a rigid wing increases with Reynolds number, but decreases for a membrane wing, as the deformation generally provides a nonoptimal airfoil shape. Membrane deformation leads to larger separation bubbles, and acts as a barrier to the tip vortex formation. At high angles of attack, the aerodynamic twist causes a direct interaction between the recirculating flow and the tip vortices, indicating potential roll instabilities.