Particle clusters within inertial vortical flows in micro-cross-shaped channels

Inertial vortical flows can be used as a tool to capture and manipulate microparticles, vesicles, or cells. Current work follows our previous report [Zhang et al., Int. J. Multiphase Flow 150, 104030 (2022)] to study the flow of diluted particle suspension in micro-cross-shaped channels at 20 < Re < 500 by micro-laser-induced fluorescence and high-speed photography. Effects of inlet aspect ratio (α) and Reynolds numbers (Re) on flow regimes and particle capture were studied. Numerical simulation was adopted to reveal vortex breakdown dynamics associated with particle capture. For each α, as Re increases, segregated flows, steady engulfment flows, vortex shedding flows, and unsteady engulfment flows appear in turns. Experimental results demonstrate a flow-induced, Re and α-dependent particle cluster within steady engulfment and vortex shedding flows, and an increase in α decreases the onset Re of the cluster. With increasing Re, an interesting oscillation of the cluster is established, which triggers the escape of captured particles. Simulation results show that the oscillation frequencies of the cluster and fluid are comparable. Although isolated particles display brief recirculating paths under unsteady engulfment flows, the particle cluster disappears.