Haward, Simon J.Poole, R. J.Alves, M. A.Oliveira, Paulo J.Goldenfeld, NigelShen, Amy Q.2021-01-202021-01-202015-09-03http://hdl.handle.net/10400.6/11048Experimental measurements and numerical simulations are made on fluid flow through cross-slot devices with a range of aspect (depth:width) ratios, 0.4 < alpha < 3.87. For low Reynolds numbers Re, the flow is symmetric and a sharp boundary exists between fluid streams entering the cross-slot from opposite directions. Above an alpha-dependent critical value Re_c, the flow undergoes a symmetry-breaking bifurcation (though remains steady and laminar) and a spiral vortex structure develops about the central axis of the outflow channel. An order parameter characterizing the instability grows according to a sixth-order Landau potential, and shows a progression from second order to first order transitions as alpha increases. A tricritical point occurs for alpha ~ 0.55. The spiral vortex acts as a mixing region in the flow field and this phenomenon can be used to drive enhanced mixing in microfluidic devices.engSpiral vortex formationFlow instabilityCross-slotNewtonian flowjournal article10.1103/PhysRevE.93.031101