Vortex Breakdown in Shear-Driven Flow Over a Rectangular Cavity

The vortex dynamics of flow past a rectangular cavity is investigated using numerical simulations and microfluidic experiments. The flow is inherently three-dimensional and is characterized by a large, dominant eddy filling most of the cavity with weak, yet significant flow in the axial direction along the vortex core and symmetrical about the center plane. Classical bubble-type vortex breakdown is observed in this rather simple geometry at sufficiently high Reynolds numbers (Re), depending on the channel width. The critical Re for the onset of vortex breakdown is identified as a function of channel width, and the evolution of the breakdown region is investigated as the channel width and Re increase. Results confirm the emergence and bifurcation of stagnation points that bound the breakdown bubble. The results also corroborate findings about vortex breakdown previously observed in other geometries, such as the transition from stagnation points to stable/unstable orbits resulting from the merging of breakdown zones and the correlation between vortex breakdown and critical wave phenomena.