Dragonfly unsteady aerodynamics - The role of the wing phase relations in controlling the produced flows

Abstract

Daniel Saharon* and Marvin W. Luttges** #gf? 25'60 I ' Department of Aerospace Engineering Sciences University of Colorado Boulder, Colorado 80309-429 Visualizations of three-dimensional unsteady separated f low produced by a mechanically dr iven dragonfly wing kinematics model were collected and analyzed. Tandem wing effects were evaluated by comparison with effects produced by fore and aft wings tested individually. The effects of wing kinematics were studied with an emphasis on changes in the phase relations between fore and aft wings. Vortex structures produced by the mechanical model were quite similar to those elicited from tethered dragonflies in wind tunnel tests. The eight kinematic elements of the model wing beat were shortlived such that each yielded a specific transitional flow structure. Fore and aft wing phase differences produced flow structures that interacted, one with another, in d i f fer ing ways. Flow interactions were either constructive or destructive and yielded different wing flow interactions. Constructive flow interactions were evaluated in terms of integrating and fusing of vortex structures. Destructive flow interactions were evaluated in terms of vortex disruption, splitting and deflecting. The net results of these interactions were to enhance l i f t and thrust as seen in downwash and downstream flow structures.