Computational Fluid Dynamics Simulations of Arcjet Experiments: Recommended Practices and Lessons Learned

Arcjet test facilities can be used to evaluate the performance of thermal protection system materials when exposed to reentry environments. An overview of the NASA Ames arcjet facilities and the models tested in those arcjets is provided. Commonly used model shapes in arcjet experiments are discussed. Two different approaches to generating arcjet computational fluid dynamics (CFD) solutions, predictive and reconstructive, are presented, and the differences between those CFD solution types in terms of assumptions and solution processes are discussed. The different options for defining the CFD domain for the combined plenum-nozzle-free jet model are explored. The physical modeling assumptions and modeling choices for the gas chemistry, transport properties, and surface boundary conditions are presented. The process of determining the inflow conditions required for CFD simulations using the 1-D isentropic equations is discussed. Effects such as calorimeter surface catalycity, chamber blockage, enthalpy profiles, and standing waves are discussed. Two thermodynamic quantities that are important for accurate arcjet CFD simulations are the arc-heater pressure and bulk enthalpy of the test gas. Correlations to estimate these quantities from specified mass flow rates and arc currents are presented. Insight is given into what the surface heating rate and pressure profiles should look like for the different model shapes.