Multiscale simulation of coexisting turbulent and rarefied gas flows

TL;DR

This paper introduces a multiscale simulation method that effectively models the interaction between turbulent and rarefied gas flows, validated against experimental data and applied to hypersonic jet problems.

Contribution

The authors develop a novel multiscale approach combining the Boltzmann equation with turbulence modeling, enabling accurate simulation across flow regimes without undue influence of turbulence models.

Findings

Turbulence significantly impacts surface heat flux in hypersonic flows.

The method accurately captures both turbulent and rarefied flow behaviors.

Turbulence models do not adversely affect rarefied flow simulations.

Abstract

Simulating complex gas flows from turbulent to rarefied regimes is a long-standing challenge, since turbulence and rarefied flow represent contrasting extremes of computational aerodynamics. We propose a multiscale method to bridge this gap. Our method builds upon the general synthetic iterative scheme for the mesoscopic Boltzmann equation, and integrates the $k$-$\omega$ model in the macroscopic synthetic equation to address turbulent effects. We have not only validated this approach using the experimental data of turbulent flows, but also confirmed that the turbulence model exerts no undue influence on highly rarefied flows. Our method is then applied to opposing jet problems in hypersonic flight surrounding by rarefied gas flows, showing that the turbulence could cause significant impacts on the surface heat flux, which cannot be captured by the turbulent model nor the laminar Boltzmann solution alone. This study provides a viable framework for advancing our understanding of the interaction between turbulent and rarefied gas flows.