AIAA 2003-0634 Optimization of Controlled Jets in Crossflow

This experimental study focused on the controlled acoustical excitation of a round gas jet injected transversely into crossflow. Use of an open loop, “feed forward” controller or compensator in the experiments 1 allowed for straightforward comparisons to be made among jet responses to different conditions of acoustic excitation of jet fluid. It was found that, for a variety of excitation frequencies, optimal temporal pulse widths during square wave excitation produced clear and distinctly rolled up vortical structures as well as increased jet penetration into the crossflow. In many cases, application of forcing frequencies corresponding to subharmonics of the natural vortex rollup mode for the unforced transverse jet also produced increased jet penetration coincident with deeply penetrating, distinct vortical structures in the jet. Yet in other instances, merely exciting at the “optimal” pulse width and a low excitation frequency (in comparison to the natural rollup frequency) yielded the best jet penetration and spread. These results on optimization were interpreted in terms of a universal time scale associated with vortex ring formation and propagation.