Vortex structure in the stagnation region of an excited plane impinging jet

Vortex structure in the stagnation region of an excited plane impinging jet has been experimentally investigated by digital particle image velocity (DPIV). Jet excitation was utilized to lock the phase of the vortex motion and all the component of phase averaged vorticity were obtained. Selective amplification of the wall jet stream component of RMS vorticity on the stagnation stream-line was recognized. Phase-averaged vorticity isosurfaces revealed that the rib vortices in the braid region and vortex potato just downstream of the spanwise rollers merge into the counter-rotating vortex pairs in the vicinity of the wall. The vorticity of the vortex pairs was augmented by the continuous stretching in the stagnation region. Production terms in the transport equation of the phase-averaged vorticity and principal axis of the strain rate tensor were evaluated to understand the transport mechanism of seeds of the counter-rotating vortices.