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A conjugate thermal analysis is performed for a charring ablative material by coupling an in-house direct simulation Monte Carlo flow solver with an in-house material thermal response solver at the fluid–solid interface. The coupling is achieved by exchanging and updating the interface properties (convective heat flux and wall temperature) between the flow and thermal solvers at certain anchor points along the reentry trajectory. Iterative and non-iterative coupling techniques are studied in this work and discussed. In-house flow-thermal code is validated by comparing surface heat flux and temperature variation with those obtained from an open-source code, Stochastic PArallel Rarefied-gas Time-accurate Analyzer, from Sandia National Laboratories, USA. The effect of introducing pyrolysis gas at the interface in the flow-thermal analysis is studied by applying a blowing correction function in an iterative manner. The effect of surface recession is also studied by enabling material degradation due to thermal ablation.

This paper presents the effect of blowing (transpiration flow) on hypersonic flow over a flat plate at different flow regimes. The investigation involves the study of the interaction between the free stream flow of argon gas at Mach 5 and transpiring gas introduced at the fluid–solid interface. The freestream Knudsen number considered for the present analysis are 0.002, 0.01, 0.05, and 0.25, extending from continuum to rarefied through transitional flow conditions. Flow simulations are performed using the open source particle-based direct simulation Monte Carlo (DSMC) solver called Stochastic PArallel Rarefied-gas Time-accurate Analyzer (SPARTA). In the DSMC framework, the transpiring gases are introduced as jets with specified velocity, number density, and temperature uniformly throughout the surface in the direction normal to the surface. The variation in flow field properties, such as density, temperature, and velocity with and without transpiration, is studied. The influence of rarefaction on surface heat flux distribution is studied at different flow Knudsen numbers. Furthermore, the effect of introducing the transpiring gas at different densities into the flow field is investigated and its impact on the surface heat flux is discussed. It is interesting to note that in certain cases, the heat flux actually increases locally as a result of the interaction between transpiring gas and freestream flow.

In the present work, nonreactive gas–surface interactions between nitrogen molecules and a [Formula: see text]-cristobalite surface are analyzed using the molecular dynamics framework. A sampling method is employed to perform trajectory calculations, and the tangential momentum accommodation coefficient is computed. The credibility of the reactive force field potential to model [Formula: see text] cristobalite is investigated, and the effect of the surface and gas temperatures on the tangential momentum accommodation coefficient is studied in detail. The obtained value of the tangential momentum accommodation coefficient (from molecular dynamics analysis) is used as an input parameter in the Maxwell gas–surface interaction model using the direct simulation Monte Carlo method to investigate the surface heat flux on the nose region of a model reentry vehicle. The computed heat-flux results obtained using a molecular-dynamics-derived accommodation coefficient are found to be in excellent agreement with the experimental data.