Journal of Fluid Mechanics


Active management of naturally separated flow over a solid surface. Part 1. The forced reattachment process

a1 Department of Aerospace Engineering, University of Arizona, Tucson, AZ 85721, USA

Article author query
darabi a   [Google Scholar] 
wygnanski i   [Google Scholar] 


The forced reattachment of flow to an inclined flat surface, simulating a simple flap, was investigated experimentally. The transition from a separated to an attached state of the flow was initiated by an abrupt change in the frequency and the amplitude of periodic perturbations emanating from a slot at the flap shoulder. The excitation parameters determined the total duration of the reattachment process. Minimum reattachment time occurred at an optimal excitation frequency of $F_{\hbox{\scriptsize{\it opt}}}^{+} \approx 1.5$, which was independent of amplitude and flap inclination. The control over the process was achieved by enhancing large spanwise vortices in the flow. Spatial amplification of consecutive vortices induces mean transport of fluid away from the flap surface which causes the main stream to reattach. The time scales of the excitation are at least an order of magnitude smaller than the typical reattachment times.

(Received April 20 2003)
(Revised February 24 2004)