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.
A quasi-one-dimensional ablation analysis for a sharp-nosed, reusable, re-entry vehicle that could possibly be used in an unmanned space program, has been carried out by using an in-house code. The code is based on the boundary immobilization technique and the solution has been obtained using the tri-diagonal matrix algorithm (TDMA). The heat fluxes on the spherical nose cap that are used to determine the ablation rate of a thermal coating applied over the surface of the vehicle are obtained by performing a steady state aero-thermodynamic analysis. The aero-thermodynamic analysis for the viscous, compressible flow under consideration is carried out by using FLUENT 6.2. The computational fluid dynamics (CFD) simulations are performed at three locations on the trajectory that the vehicle follows, on re-entry. These simulations yield the temperature and heat flux distributions along the surface of the vehicle and the latter are given as input to the ablation code. The shell material of the vehicle is assumed to be zirconium boride (ZrB2). The code is validated with benchmark cases and the flow and heat transfer characteristics are also discussed. In brief, the present work presents a methodology for coupling an ablation code with CFD simulations from a commercial code, to study the effect of change of the nose region on the ablation process.
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