Computational Modeling of Gas-Surface Interactions for High-Enthalpy Reacting Flows

Abstract

The aerothermal heating of a Thermal Protection System (TPS) is significantly affected by the physical and chemical interactions that occur between the planetary entry vehicle surface and the hypersonic atmospheric gas. To study these processes, a gas-surface interaction model is used in the present numerical analysis that accounts for surface catalytic reactions and surface participating reactions. The study examines the effects of gas-surface interactions for graphite exposed to high enthalpy reacting nitrogen flow. The processes analyzed are the catalytic recombination of nitrogen atoms to molecules at the surface and the carbon nitridation reaction where nitrogen atoms react with the surface carbon to form gaseous CN. The results obtained using a computational fluid dynamic (CFD) code are assessed using data from experimental tests conducted in a 30 kW Inductively Coupled Plasma (ICP) Torch Facility at the University of Vermont. The species concentration gradient in the boundary layer and heat flux transferred to the surface are strongly affected by the surface reactions. The rate of carbon mass removal due to carbon nitridation is also calculated and compared to the measured value.

Real-Gas and Surface-Ablation Effects on Hypersonic Boundary-Layer Instability over a Blunt Cone

“…Likely, the nitridation coefficient is small, leading to a minimal impact on the simulation when nitridation is excluded. Recent results have also shown that the nitrogen-atom recombination reaction occurring at the surface of hot graphite is very fast [35,36]. For the tested cases, the nitrogen-atom concentration at the surface is only significant near the stagnation point, which is away from the flow instability studied.…”

“…If the derivative operators of Eqs. (33) and (35) are applied to a centered stencil in computational space, the standard central finite difference coefficients are obtained. In other words, the fourth-order method used by previous researchers for interior points can be obtained from the current method using a five-point stencil in computational space.…”