Ph.D. Thesis Defense by Andrew Honohan
Friday, April 4, 2003

(Dr. Ari Glezer, advisor)

"The Interaction of Synthetic Jets with Cross-flow and the Modification of Aerodynamic Surfaces"

Abstract

Unsteady flow control methods for the modification of lift and drag on aerodynamic surfaces have primarily focused on delay of separation or inducement of reattachment by introducing small disturbances into the upstream wall boundary layer. These methods have typically depended upon the receptivity of the flow to excitation within a relatively narrow bandwidth. An ongoing research program at Georgia Tech has led to the development of a new approach to the manipulation and control of shear flows using synthetic jet actuators, which are typically operated at a frequency an order of magnitude higher than the characteristic frequency of the flow.

The interaction of synthetic jets with a cross flow, and the effect of this interaction on the aerodynamic characteristics of a circular cylinder is investigated experimentally using particle image velocimetry (PIV). Depending upon a local dimensionless frequency, either a closed recirculating region or a finite train of discrete vortices is formed in the vicinity of the jet orifice. These flow structures locally modify the streamwise pressure gradient and lead to the establishment of a thinner, more stable, boundary layer. When synthetic jets are properly placed on a lifting body, higher than normal adverse pressure gradients can be overcome, resulting in the delay or suppression of boundary layer separation and thus augmented aerodynamic performance. Since the dynamics of the interaction are typically coupled to the modified global aerodynamics including the alteration of the separated flow region, the interaction is also investigated in the within a flat plate boundary layer.