Large spheres motion in a non homogeneous turbulent flow

TL;DR

This study explores how very large particles move within a turbulent von Karman flow, revealing their tendency to preferentially sample specific large-scale flow structures, unlike smaller neutrally buoyant particles.

Contribution

It provides new insights into the large-scale sampling behavior of large particles in turbulent flows, contrasting with prior findings on smaller particles.

Findings

Large particles explore the flow non-uniformly.

Particles tend to move near two tori near neutral lines.

Preferential sampling persists across various parameters.

Abstract

We investigate the dynamics of very large particles freely advected in a turbulent von Karman flow. Contrary to other experiments for which the particle dynamics is generally studied near the geometrical center of the flow, we track the particles in the whole experiment volume. We observe a strong influence of the mean structure of the flow that generates an unexpected large-scale sampling effect for the larger particles studied; contrary to neutrally buoyant particles of smaller yet finite sizes that exhibit no preferential concentration in homogeneous and isotropic turbulence (Fiabane et al., Phys. Rev. E 86(3), 2012). We find that particles whose diameter approaches the flow integral length scale explore the von Karman flow non-uniformly, with a higher probability to move in the vicinity of two tori situated near the poloidal neutral lines. This preferential sampling is quite robust with respect to changes of any varied parameters: Reynolds number, particle density and particle surface roughness.