Oscillation induced by vortex ring shedding in a cross-shaped channel

Abstract

Flow regimes in a cross-shaped channel are studied by Planar Laser Induced Fluorescence at 30 ≤ Re ≤ 350, and a segregated flow, a steady engulfment flow and an unsteady engulfment flow occur in turns with increasing Re. Specially, in the transition regime between steady and unsteady engulfment flow at 230 < Re < 300, an oscillation characterized by periodic shedding of the vortex ring is identified. Unlike the steady engulfment flow, the center vortex will break into two co-rotating vortices downstream for the vortex shedding oscillation. The fluid residence time in the cross-shaped channel is quantitively assessed. The formation of recirculation regions leads to the increase of the fluid residence time at Re≈110, while the fluid residence time is dramatically reduced at Re > 230 due to the shedding of vortex ring. Simulation results reveal that the oscillation is non-axisymmetric and the vortex ring is periodically generated from recirculation regions and propagated downstream, which is ascribed to vortex breakdown.