Flapping and flexible wing aerodynamics of low reynolds number flight vehicles

For flight vehicles operated at the low Reynolds number regime, such as birds, bats, insects, as well as small man-made vehicles, flapping and fixed wings are employed in various ways to generate aerodynamic forces. For flapping wings, the unsteady fluid physics, interacting with wing kinematics and shapes determine the lift generation. For fixed wings, laminar-turbulent transition, three dimensional flows around low aspect ratio vehicles, and coupling between flexible wing structures and surrounding fluid flows are of major interest. In the present paper we discuss recent progress in understanding the low Reynolds number unsteady fluid dynamics associated with flapping wings, including leading-edge vortices, pitching-up rotation and wake-capturing mechanisms. For fixed wings, recent efforts in fluid-structure interaction and laminar-turbulent transition are highlighted.