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A Comparison of Quasi One-Dimensional and Two-Dimensional Ablation Models for Subliming Ablators

A method to couple a computational fluid dynamic analysis (CFD) with the material response code (ablation code) for a reentry vehicle is presented here. The geometry under consideration is a sphere cylinder geometry that resembles the YES-2 reentry capsule for which the Mach number is 23. The flow is considered to be steady and laminar, and the effect of radiation is ignored. To take into account the dissociative effect, a simplified model based on the use of a modified specific heat has been adopted following Stella et al. The aerothermodynamic analysis is done using Fluent 6.2. In the ablation analysis, both quasi one-dimensional and two-dimensional approaches have been considered. The heat fluxes determined using the CFD analysis are given as input to the ablation program to calculate the recession rate. The change of the flow field due to the geometry change caused by burn-off of the ablative material has been taken into account after every 500s, as the recession rate is seen to be of the order of micro-meters per second. The prime objective of this work is to bring out a methodology to combine CFD results with in-house codes and to give a comparison between quasi one-dimensional ablation model with two-dimensional ablation model for cylindrical geometries. The two-dimensional analysis gives results similar to those obtained by a quasi one-dimensional ablation, and hence the latter is adequate for problems of this kind.