Oscillating rectangular and octagonal profiles: Interaction of leading- and trailing-edge vortex formation

Force measurements and how visualization for transversely oscillating rectangular and octagonal profiles are presented. Flow fields are analysed, classified and related to the fluid forces and to the type of excitation of eventual fluid-elastic oscillations. The interaction of instability-induced and movement-induced excitation is shown, as well as the interaction of impinging leading-edge and trailing-edge vortices. The mechanisms leading to an energy transfer from the fluid to the body are associated with the phase shift of the fluctuating lift forces relative to the body oscillation. The abrupt change of phasing, observed within the range of synchronization of body motion and vortex shedding, is explained by an alteration of the timing in the formation of the synchronized vortices at the trailing-edge. Aspects of resonance and annihilation of lift forces are discussed with respect to the formation of vertical structures at the leading- and trailing-edge. (C) 1997 Academic Press Limited.