Effect of Surface Nonequilibrium Thermochemistry in Simulation of Carbon Based Ablators

Abstract

This study demonstrates that coupling of a material thermal response code and a flow solver using finite-rate gas/surface interaction model provides time-accurate solutions for multidimensional ablation of carbon based charring ablators. The material thermal response code used in this study is the Twodimensional Implicit Thermal Response and Ablation Program (TITAN), which predicts charring material thermal response and shape change on hypersonic space vehicles. Its governing equations include total energy balance, pyrolysis gas momentum conservation, and a three-component decomposition model. The flow code solves the reacting Navier-Stokes equations using Data Parallel Line Relaxation (DPLR) method. Loose coupling between material response and flow codes is performed by solving the surface mass balance in DPLR and the surface energy balance in TITAN. Thus, the material surface recession is predicted by finite-rate gas/surface interaction boundary conditions implemented in DPLR, and the surface temperature and pyrolysis gas injection rate are computed in TITAN. Two sets of gas/surface interaction chemistry between air and carbon surface developed by Park and Zhluktov, respectively, are studied. Coupled fluid-material response analyses of stagnation tests conducted in NASA Ames Research Center arc-jet facilities are considered. The ablating material used in these arc-jet tests was a Phenolic Impregnated Carbon Ablator (PICA). Computational predictions of in-depth material thermal response and surface recession are compared with the experimental measurements for stagnation cold wall heat flux ranging from 107 to 1100 W/cm 2 . Nomenclature

Chemical Erosion of Carbon-Phenolic Rocket Nozzles with Finite-Rate Surface Chemistry

“…In the present model, the pyrolysis gas itself is assumed to be in chemical equilibrium as it passes through the char and before injection into the nozzle flowfield. Under this reasonable assumption [22,23,28], its chemical composition can be calculated by a series of equilibrium chemistry solutions, provided that the elemental makeup of the gas is known. The equilibrium species concentrations of pyrolysis gas, as a function of pressure and temperature, are computed using a chemical equilibrium code [26] and stored in a database for computational efficiency.…”

“…The same kind of analysis, which is based on coupling a Navier-Stokes solution with surface ablation, cannot be found in open literature for erosion modeling of charring composite materials such as silica-and carbon-phenolics in SRM nozzles. However, extensive modeling has been performed for these materials, especially carbonphenolics, in the atmospheric reentry field [22][23][24].…”