Multiscale simulation of interacting turbulent and rarefied gas flows in the DSMC framework

• A deterministic-stochastic coupling method has been developed for unified investigation of turbulent and rarefied gas flow interactions. • The proposed method asymptotically converges to either k - ω SST turbulent model or DSMC results adaptively adjusting to different flow regimes. • The surface properties in opposing jet problems predicted by the proposed algorithm differ from original rarefied laminar solver due to significant turbulent effects. A multiscale stochastic-deterministic coupling method is proposed to investigate the complex interactions between turbulent and rarefied gas flows within a unified framework. This method intermittently integrates the general synthetic iterative scheme with the shear stress transport turbulence model into the direct simulation Monte Carlo (DSMC) approach, enabling the simulation of gas flows across the free-molecular, transition, slip, and turbulent regimes. First, the macroscopic synthetic equations, derived directly from DSMC, are coupled with the turbulence model to establish a constitutive relation that incorporates not only turbulent and laminar transport coefficients but also higher-order terms accounting for rarefaction effects. Second, the macroscopic properties, statistically sampled over specific time intervals in DSMC, along with the turbulent properties provided by the turbulence model, serve as initial conditions for solving the macroscopic synthetic equations. Finally, the simulation particles in DSMC are updated based on the macroscopic properties obtained from the synthetic equations. Numerical simulations demonstrate that the proposed method asymptotically converges to the turbulence model in the continuum regime and to the DSMC method in the rarefied regime, depending on the Knudsen number. This coupling method is then applied to simulate a turbulent opposing jet surrounded by hypersonic rarefied gas flows, revealing significant variations in surface properties due to the interplay of turbulent and rarefied effects.