# Turbulence statistics in a negatively buoyant multiphase plume

## TL;DR

This study examines turbulence in a negatively buoyant multiphase particle plume, revealing similarities and key differences with bubble plumes, including turbulence structure, energy budget, and spectral characteristics, advancing understanding of multiphase flow dynamics.

## Contribution

It provides detailed turbulence statistics of a heavy particle plume using advanced imaging, highlighting structural differences from bubble plumes and extending classical plume theories to multiphase flows.

## Key findings

- Turbulence exhibits self-similarity in the plume centerline.
- The particle plume shows a non-reversed skewness compared to bubble plumes.
- TKE budget includes significant shear production, unlike bubble plumes.

## Abstract

We investigate the turbulence statistics in a {multiphase plume made of heavy particles (particle Reynolds number at terminal velocity is 450)}. Using refractive-index-matched stereoscopic particle image velocimetry, we measure the locations of particles {whose buoyancy drives the formation of a multiphase plume,} {together with the local velocity of the induced flow in the ambient salt-water}. {Measurements in the plume centerplane exhibit self-similarity in mean flow characteristics consistent with classic integral plume theories.} The turbulence characteristics resemble those measured in a bubble plume, {including strong anisotropy in the normal Reynolds stresses. However, we observe structural differences between the two multiphase plumes. First, the skewness of the probability density function (PDF) of the axial velocity fluctuations is not that which would be predicted by simply reversing the direction of a bubble plume. Second, in contrast to a bubble plume, the particle plume has a non-negligible fluid-shear production term in the turbulent kinetic energy (TKE) budget. Third, the radial decay of all measured terms in the TKE budget is slower than those in a bubble plume.} Despite these dissimilarities, a bigger picture emerges that applies to both flows. The TKE production by particles (or bubbles) roughly balances the viscous dissipation, except near the plume centerline. The one-dimensional power-spectra of the velocity fluctuations show a -3 power-law that puts both the particle and bubble plume in a category different from single-phase shear-flow turbulence.