In recent years, there has been major interest in the flow structure and loading on wings undergoing various unsteady maneuvers. The motivation for understanding biologically inspired flight at low Reynolds number comes from interest in small unmanned air vehicles. Flapping wings of insects and birds are characterized by large amplitude motions including rotation, pitching, and plunging. In contrast, to the case of a wing rotating in quiescent fluid, very little attention has been devoted to the flow structure along a low aspect ratio wing rotating in an incident steady flow, whereby the direction of flow is along the axis of rotation. This configuration corresponds to a 90° stroke plane; it is representative of fast forward and climbing flight. This investigation employs quantitative imaging to characterize the effect of advance ratio J on the development of the flow structure along, and in the wake of, a rotating wing maintained at a constant value of effective angle of attack.
Physics of Fluids Article: Bross, M., Ozen, C. a. & Rockwell, D. 2013 Flow structure on a rotating wing: Effect of steady incident flow. Phys. Fluids 25. LINK