Clustering and Turbophoresis in a Shear Flow without Walls

TL;DR

This study uses direct numerical simulations to analyze how inertial particles distribute in turbulent shear flows without walls, revealing the roles of turbophoresis and clustering across different particle inertias.

Contribution

It provides new insights into the mechanisms of particle inhomogeneity in wall-free turbulent flows, especially regarding turbophoresis and fractal clustering at various inertias.

Findings

Turbophoresis is strongest for particles with intermediate inertia.

Small-scale clustering and turbophoresis peak at different Stokes numbers.

The separation between clustering and turbophoresis peaks increases with Reynolds number.

Abstract

We investigate the spatial distribution of inertial particles suspended in the bulk of a turbulent inhomogeneous flow. By means of direct numerical simulations of particle trajectories transported by the turbulent Kolmogorov flow, we study large and small scale mechanisms inducing inhomogeneities in the distribution of heavy particles. We discuss turbophoresis both for large and weak inertia, providing heuristic arguments for the functional form of the particle density profile. In particular, we argue and numerically confirm that the turbophoretic effect is maximal for particles of intermediate inertia. Our results indicate that small-scale fractal clustering and turbophoresis peak in different ranges in the particles' Stokes number and the separation of the two peaks increases with the flow's Reynolds number.