Abstract
Three dimensional deformations of roll vortices in a parabolic two dimensional jet were controlled by an acoustic bimodal excitation and tabs installed around the jet exhaust. The results confirm the possibility of the present technique to lock up the process of vortex pairing to chase the transition process of the two dimensional jet in detail through flow visualization and hotwire measurement. When the initial phase difference between the fundamental and its first subharmonic components was given to be 0 degree, vortex pairing occurred regularly. The vortex pairing occurs between a pair of three-dimensionally deformed roll vortices connected by the rib structures. The vortex pairing occurred only occasionally in the transition region when the initial phase difference was 120 degree. When the pairing didn't occur, the symmetric arrangement was maintained until far downstream of the nonlinear interaction region.
