Flow Modulation and Force Control of Flapping Wings

Abstract : Flapping-wing offers unique force enhancement mechanisms over conventional flight methods for design of micro air vehicles (MAVs), especially in the low Reynolds number (Re) regime. The inherently unsteady nature of flapping kinematics is responsible for the primary force production, and also differentiates flapping-wing motion from conventional fixed and rotary wing configurations. From previous observation, the unsteady aerodynamic phenomena of flapping mechanism are not only sensitive to variations in the wing kinematics but also for the wing morphing. Results have shown that the dynamically changed wing surface, either actively or passively deformed, would potentially provide new aerodynamic mechanisms of force productions over completely rigid wings in flying. From morphing wing study in fixed or rotary wing aircrafts, the moving surface flow control concept can be achieved in three ways: 1) articulated flaps and/or slats; 2) surface flow control devices; and 3) continuously deforming surfaces. Among them, the dynamic flow control concept via trailing-edge flap (TEF) is presumed to be more applicable serving for novel MAVs wing designs, in terms of reduced size of control surface, complexity of moving surface control, weight of MAVs and so on. However, there is a lack of study of the effects of TEF on a flapping wing in computations and experiments, especially when the flap is in dynamic motion with respect to the leading-edge motion. In this funded work, we built up a team with experts from two institutes and hope to address the following basic questions about the aerodynamics of flapping flight: 1. What are the aerodynamic effects of dynamic trailing-edge flap motion when it moves through the flow? 2. What is the mutual interaction between fluid flow patterns and wing morphology patterns? 3. What is the proper way(s) to characterize wing flexibility from aerodynamics point of view? 4. What is the overall far field flow structure of flapping wings?