Transport of spherical microparticles in a 3D vortex flow

TL;DR

This study explores how spherical particles of different sizes behave in a 3D vortex flow at moderate Reynolds numbers, revealing size-dependent exclusion from the vortex core and deviations from ideal motion.

Contribution

It provides new experimental and numerical insights into particle transport mechanisms in intermediate Reynolds number vortical flows, a less-explored regime.

Findings

Larger particles are excluded from the vortex core.

Small particles follow Burgers vortex-like motion.

Deviations occur for larger particles due to inertia and size effects.

Abstract

Particles are common in biological and environmental flows and are widely used in industrial and pharmaceutical applications. Their motion and flow dynamics are strongly affected by interactions with the surrounding flow structure. While particle-flow interactions have been extensively studied in low Reynolds number (Re) flows as well as in fully developed turbulence, the transport mechanisms of these particles in intermediate flow regimes remain less explored. Here, we investigate the response of neutrally buoyant spherical particles to a single vortex flow field. Using a microfluidic cross-slot geometry, we generate a well-characterized, stationary, three-dimensional streamwise vortex at moderate $\text{Re}$ ($\sim 50$). Our experimental results, supported by numerical simulations, show that with increasing particle diameter, they are progressively excluded from the vortex core. Initially, small particles follow a Burgers vortex-like self-similar motion, but for larger particle diameters, deviations from this trend emerge due to fluid inertia and finite-size effects. These findings enhance our understanding of particle dynamics in vortical flows and have implications for microfluidic applications involving particle sorting and separation.