CFD Simulations of Arcjet Experiments – A Survey of Recommended Practices and Lessons Learned

Arcjet test facilities can be used to evaluate the performance of thermal protection system (TPS) materials when exposed to re-entry type environments. The present work provides lessons learned from CFD analysis of arc-heated flow fields and recommends practices and models that could be used for similar flows. An overview of the NASA Ames arcjet facilities and the models tested in those arcjets is provided. Commonly-used model shapes used in arcjet experiments are discussed. The two different approaches to generating arcjet CFD solutions, predictive and reconstructive, are presented, and the differences between those CFD solution types in terms of assumptions and solution process 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. One of the keys to accurate arcjet CFD simulations is to properly model the inflow boundary condition at either the plenum or the nozzle throat. The procedure for estimating the CFD inflow procedure for different types of arcjet facilities is presented. Effects such as calorimeter surface catalycity and chamber blockage are discussed as well as the phenomena of enthalpy profiles and standing waves. 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 the arc-heater pressure and bulk enthalpy from specified mass flow rates and arc current are presented, and updated correlations are developed for the NASA Ames arcjet facilities. Insight is given into what the surface heating rate and pressure profiles should look like for the different model shapes.