A local intermittency based Reynolds-averaged transition model for turbulent mixing induced by interfacial instabilities

TL;DR

This paper introduces a novel RANS-based mixing transition model that incorporates a local intermittency factor to better predict mixing induced by interfacial instabilities, addressing a longstanding challenge in turbulence modeling.

Contribution

It extends the intermittency concept to mixing problems by developing a transport equation for the intermittency factor and coupling it into existing turbulence models, enabling more accurate transition predictions.

Findings

Successfully predicts mixing transition in Richtmyer-Meshkov cases

Demonstrates good performance in capturing local transition effects

First to propose an intermittency transport equation for RANS mixing models

Abstract

Accurate prediction of mixing transition induced by interfacial instabilities is vital for engineering applications, but has remained a great challenge for decades. For engineering practices, Reynolds-averaged Navier-Stokes simulation (RANS) is the most viable method. However, existing RANS models for mixing problems are mostly designed for fully developed turbulence, failing to depict the locally spatio-temporal-dependent characteristic of transition. In the present study, the idea of the intermittent factor (denoted as $\gamma$), which has been widely used in boundary layer transition in aerospace engineering, is extended to the mixing problems. Specifically, a transport equation for $\gamma$ is built based on local flow variables, which is used to describe the locally spatio-temporal-dependent characteristic of transition. Furthermore, $\gamma$ is coupled into the widely used K-L turbulent mixing model to constrain the two key product sources terms that dominate the evolution of mixing, i.e. the Reynolds stress and the buoyancy effect. Subsequently, the simulations of two reshocked Richtmyer-Meshkov mixing cases with remarkable transition effects confirm that the proposed model has a good performance for predicting mixing transition. To the best of our knowledge, it is the first study that an extra transport equation for intermittent factor has been proposed for a RANS mixing transition model. More importantly, the present modeling framework is flexible and has the potential to be applied to other RANS models. It provides a promising strategy for more advanced modeling for mixing transition.