Abstract
Effects of bimodal acoustic excitation on the behavior of coherent vortices were investigated in a two-dimensional parabolic jet exhausted from a nozzle of 10mm(=2h)×400mm through hot-wire measurement and multi-smokewire visualizations. The subharmonic velocity component increased remarkably in the streamwise direction when the phase difference was given as zero between the fundamental component, u_f, and its subharmonic component, u_s, measured at X/2h=3, Y/2h=0 where the velocity components could be detected most noticeably. In this case, vortex pairing occurred quite periodically at about X/2h≒7, 6.5 and 6 for u_s/u_f=1, 2 and 3, respectively and the vortex arrangement changed into antisymmetric one after the pairing. When the phase difference was given as 120°, the vortex pairing became to occur more occasionally with decreasing u_s/u_f. When the two vortices didn't paired, the symmetric arrangement was kept until far downstream.
