Three-dimensional Lagrangian Voronoi analysis for clustering of particles and bubbles in turbulence

TL;DR

This paper uses 3D Voronoi analysis to quantify how inertial particles and bubbles cluster in turbulence, revealing that light particles tend to cluster in high-vorticity regions and maintain their clustering longer than heavy particles.

Contribution

It introduces a 3D Voronoi-based method to analyze particle clustering in turbulence, highlighting the behavior of light particles and their correlation with flow vorticity.

Findings

Light particles cluster most at Stokes numbers 1-2.

Clustering of light particles persists longer than that of heavy particles.

Light particles tend to cluster in high enstrophy regions.

Abstract

Three-dimensional Voronoi analysis is used to quantify the clustering of inertial particles in homogeneous isotropic turbulence using data from numerics and experiments. We study the clustering behavior at different density ratios and particle response times (i.e. Stokes numbers St). The Probability Density Functions (PDFs) of the Voronoi cell volumes of light and heavy particles show a different behavior from that of randomly distributed particles -i.e. fluid tracers-implying that clustering is present. The standard deviation of the PDF normalized by that of randomly distributed particles is used to quantify the clustering. Light particles show maximum clustering for St around 1-2. The results are consistent with previous investigations employing other approaches to quantify the clustering. We also present the joint PDFs of enstrophy and Voronoi volumes and their Lagrangian autocorrelations. The small Voronoi volumes of light particles correspond to regions of higher enstrophy than those of heavy particles, indicating that light particles cluster in higher vorticity regions. The Lagrangian temporal autocorrelation function of Voronoi volumes shows that the clustering of light particles lasts much longer than that of heavy or neutrally buoyant particles. Due to inertial effects, the Lagrangian autocorrelation time-scale of clustered light particles is even longer than that of the enstrophy of the flow itself.