Asymmetry and bifurcations in three-dimensional sudden-contraction channel flows

Abstract

This study reports the presence of two different stable modes of bifurcation in the near field of a three-dimensional sudden contraction. To be precise, flow downstream of a symmetric sudden contraction undergoes a transition from a symmetric state to an asymmetric state through a symmetry-breaking pitchfork bifurcation following an increase in the channel aspect ratio or the Reynolds number. In addition, the oncoming (upstream) symmetry-plane flow exhibits spanwise bifurcations along the topological core lines of each of the salient roof and floor eddies. Small aspect-ratio (contraction) channels are noted to facilitate interesting splitting of the salient roof and floor eddies into multicore forms with accompanying spanwise flow bifurcations along the respective vortical core lines. Herein extensive three-dimensional simulations performed with various aspect and contraction ratios and Reynolds numbers clearly suggest that flow transition in the sudden-contraction channels should indeed occur primarily through these two generically distinct modes of bifurcation.