# Buoyancy-driven flow through a bed of solid particles produces a new form of Rayleigh-Taylor turbulence

## TL;DR

This study uses high-resolution simulations to explore how buoyancy-driven flow through a bed of solid particles alters Rayleigh-Taylor turbulence, revealing distinct mixing physics due to porosity.

## Contribution

It introduces a new understanding of RT turbulence in porous media and proposes an effective continuum model accounting for porosity effects.

## Key findings

- Mixing layer growth becomes linear in time for low porosity
- Velocity fluctuations saturate instead of growing linearly
- Porosity significantly alters classical RT turbulence behavior

## Abstract

Rayleigh--Taylor fluid turbulence through a bed of rigid, finite-size, spheres is investigated by means of high-resolution Direct Numerical Simulations (DNS), fully coupling the fluid and the solid phase via a state-of-the art Immersed Boundary Method (IBM). The porous character of the medium reveals a totally different physics for the mixing process when compared to the well-known phenomenology of classical RT mixing. For sufficiently small porosity, the growth-rate of the mixing layer is linear in time (instead of quadratical) and the velocity fluctuations tend to saturate to a constant value (instead of linearly growing). We propose an effective continuum model to fully explain these results where porosity originated by the finite-size spheres is parameterized by a friction coefficient.