Microscopic investigation of vortex breakdown in a dividing T-junction flow

Abstract

3D-printed microfluidic devices offer new ways to study fluid dynamics. We present the first clear visualization of vortex breakdown in a dividing T-junction flow. By individual control of the inflow and two outflows, we decouple the effects of swirl and rate of vorticity decay. We show that even slight outflow imbalances can greatly alter the structure of vortex breakdown, by creating a net pressure difference across the junction. Our results are summarized in a dimensionless phase diagram, which will guide the use of vortex breakdown in T-junctions to achieve specific flow manipulation.

Coupling of vortex breakdown and stability in a swirling flow

“…In aerodynamics systems, such as flow over a delta wing, depending on the angle of attack, breakdown can occur in the leading-edge vortices, which can drastically alter stability of the aircraft [14,15]. Recently, vortex breakdown has seen applications in microfluidics due to its ability to manipulate microparticles in a branching T-junction flow [16][17][18][19][20][21], in which one inflow splits into two opposite outflows.…”

“…This flow geometry was chosen for two main reasons. First, unlike the branching T-junction flow which has four Dean vortices [16][17][18][19][20][21], the vortex T-mixer flow has only one single dominant vortex, which greatly simplifies the interpretation of the numerical and experimental results. Second, it is easy to perform measurements for the vortex T-mixer flow.…”

Particle trapping in merging flow junctions by fluid-solute-colloid-boundary interactions

“…Driven by the interactions between the wall diffusioosmosis, particle diffusiophoresis, and the inlet fluid flow, the vortices enable robust trapping of colloidal particles near the junction. We emphasize that the reported particle trapping is a completely different mechanism from the trapping enabled by the inertial vortex breakdown [6][7][8][9][10][11] or the solute-mediated trapping enabled by the diffusiophoresis [14,15], as the current trapping is enabled by the combination of both the solute-mediated and the inertial effects. Since the particle trapping is driven by the presence of solute gradients, the trapping can happen in other flow geometries as well.…”

“…Three-dimensional (3D) particle visualization and numerical simulations are utilized to visualize the vortex so as to provide a rigorous understanding of the particle trapping phenomenon. The reported trapping mechanism is unique from the inertial trapping enabled by vortex breakdown [6][7][8][9][10][11], or the solute-mediated trapping enabled by diffusiophoresis [14,15], as the current trapping is facilitated by both the solute and the inertial effects, suggesting a new mechanism for particle trapping in flow networks.…”

“…While small suspended particles tend to passively follow fluid streamlines in laminar, modest Reynolds number flows, coupled nonlinear effects can result in unexpected particle dynamics in certain systems. For example, a spontaneous particle trapping mechanism was recently identified in branching flows through T-or angle-shaped junctions due to the coupling between inertial particle dynamics and the nonlinear vortex breakdown phenomena [6][7][8][9][10][11].…”