Reactive Rayleigh-Taylor Turbulence

TL;DR

This paper investigates how reactive transformations influence Rayleigh-Taylor turbulence using DNS, revealing a 'stirred flame' regime with intermittent temperature distribution and pure-fluid patches.

Contribution

It introduces a DNS-based analysis of reactive RT turbulence, highlighting the 'stirred flame' regime and the fractal nature of thin turbulent flames.

Findings

Reactions have minimal impact during early turbulent stages.

Pure-fluid patches form in the later stages of mixing.

Temperature distribution becomes highly intermittent in the stirred flame regime.

Abstract

The Rayleigh-Taylor (RT) instability develops and leads to turbulence when a heavy fluid falls under the action of gravity through a light one. We consider this phenomenon accompanied by a reactive transformation between the fluids, and study with Direct Numerical Simulations (DNS) how the reaction (flame) affects the turbulent mixing in the Boussinesq approximation. We discuss "slow" reactions where the characteristic reaction time exceeds the temporal scale of the RT instability. In the early turbulent stage, effects of the flame are distributed over a maturing mixing zone, whose development is weakly influenced by the reaction. At later times, the fully mixed zone transforms into a conglomerate of pure-fluid patches of sizes proportional to the mixing zone width. In this "stirred flame'' regime, temperature fluctuations are consumed by reactions in the regions separating the pure-fluid patches. This DNS-based qualitative description is followed by a phenomenology suggesting that thin turbulent flame is of a single-fractal character, and thus distribution of the temperature field is strongly intermittent.