Acoustic Control of Vortical Structure in a Plane Jet

Abstract

Characteristic features of coherent motions were experimentally analyzed in a transition region of a two-dimensional jet with parabolic velocity distribution. The symmetrical or the anti-symmetrical vortex arrangement was weakly emphasized in the jet through an acoustic method. Hotwire measurements through a conditional sampling method were conducted point by point throughout the entire transition region. The resultant figures of the flow fields were compared with the pictures given by flow visualization by a conditional multi-smokewire method. The velocity vector maps demonstrated the characteristic features of the streamwise development of the jet’s macroscopic structure; the intensity of the vortical fluid motion, the streamwise growth of the jet’s width, and the meandering motion of the jet. The vorticity contour maps illustrated the differences in behaviour between the two modes of coherent vortices in the transition region with respect to the streamwise changes in the scale, configuration, peak intensity, and convection velocity of the coherent vortices. The present results suggested good possibility of controlling the jet structure by the acoustic method.