Reentry aerothermodynamic analysis of a high-speed vehicle with coupled ablating surface interface effects at rarefied conditions

Abstract

This study presents a conjugate flow-thermal analysis of a hypersonic reentry vehicle in rarefied flow conditions, along with a stability analysis for the coupled ablation problem, highlighting additional time-step stability criteria. A novel coupling of an in-house Direct Simulation Monte Carlo (DSMC) solver with a material thermal response (MTR) solver is used. The DSMC solver is extended to simulate the physical injection of transpiring pyrolysis gas into the gas-surface interface, modeled as surface jets. The MTR code solves heat conduction in a two-dimensional/axisymmetric geometry, accounting for complex thermochemical processes, including endothermic pyrolysis, transpiration cooling and surface recession due to thermal ablation. The DSMC and MTR solvers are loosely coupled at selected time intervals (anchor points) along the reentry trajectory, exchanging boundary conditions at the fluid–solid interface. A code-to-code comparison with the well-established open-source DSMC solver, SPARTA, shows good agreement with the in-house mass-injecting DSMC framework. The results highlight the importance of the coupled DSMC-MTR framework for accurately modeling the interaction between flow and thermal domains, which is crucial in rarefied flows and for curved geometries, areas where empirical models, such as blowing effect correlation, show large deviations. Unlike the traditional empirical correlation, the DSMC framework captures the physical transpiring boundary, significantly improving flow simulations. The study also reveals that while the iterative coupling method provides accurate results, it becomes prohibitively expensive at lower altitudes, while the non-iterative method becomes unstable below 90 km. This limitation underscores the need for more sophisticated models at the gas-surface interface, particularly for transpiring boundaries, to better capture the complex interactions in hypersonic flows.