Computational Model of a Table Top Shock Tunnel for Hypersonic Environments

Atmospheric reentry events are subject to hypersonic conditions characterized by extreme velocities and temperatures. Thermal protection system (TPS) materials serve to protect the payload. Designing next-generation TPS requires recreating these conditions outside of actual reentry events which poses significant challenges, making current processes both time consuming and costly. A Table Top Shock Tunnel (TTST) facility offers researchers a new approach to replicating hypersonic conditions in a controlled lab setting. The compact size of the detonation-driven shock tunnel is both cost effective and easy to maintain. This facility is specifically focused on investigating the gas surface interactions between a sample material and the rarefied hypersonic flow. Investigating the exact conditions found in the shock tunnel will optimize the TTST facility’s workflow and allow for further investigation of hypersonic gas-surface interactions. In order to pre-determine the specific operating conditions, such as air species, incoming flow velocity, and material temperature of the shock tunnel, numerical simulations can be employed. Numerical simulations are fit for modeling this environment as they have the ability to accurately capture intricate gas dynamics and gas-surface chemical reactions. Current numerical simulations of the TTST environment lack the capability to comprehensively and efficiently capture the gas-surface interactions between the sample and incoming hypersonic flow. Therefore, a validated numerical model of the TTST with a robust framework for analyzing gas-surface interactions of novel materials is needed. As hypersonic flows typically encounter low-density regimes in the far field, but higher densities close to the body, it is crucial to select a modeling framework with the ability to capture the transition from highly rarefied to near-continuum flows. The Direct Simulation Monte Carlo (DSMC) method achieves this by stochastically assigning particle collisions and tracking individual particle movements. DSMC is particularly useful at capturing rarefied flows, which can be extended to pay close attention to the gas surface interactions of the sample. The Stochastic Parallel Rarefied-gas Time-accurate Analyzer (SPARTA), developed at Sandia National Laboratory (SNL), is a highly capable DSMC code. Known for its accuracy and versatility in modeling rarefied flows, it was chosen for designing the TTST model. To develop a validated TTST model in SPARTA it was essential to investigate existing numerical models of this experimental environment. Current models lack the ability to efficiently analyze different materials or investigate their gas-surface interactions, limiting its broader applicability. Therefore, it is necessary to create a simulation which includes a robust framework for implementing material samples and investigating gas-surface interactions. By matching input conditions of different models, we demonstrate SPARTA’s capability to accurately capture relevant flow fields. Our results show alignment between the SPARTA model and existing numerical models. With a validated simulation, we enable the investigation of new sample materials. Suitable test conditions can be determined and more complex behavior, such as gas-surface chemistry models, can be easily integrated. These materials could include ablatives used in TPS, fully leveraging the hypersonic capabilities of the TTST. Studying these materials is vital for gaining a comprehensive understanding of TPS and ensuring their success. The study of new materials with the use of computational models is essential to advancing our understanding of hypersonic flight technologies.