Conjugate Analyses of Ablation in Rocket Nozzles

Abstract

A methodology coupling the LeMANS flow solver to the MOPAR-MD material response solver is presented, enabling fully coupled, conjugate, two-dimensional simulations of ablation of pyrolyzing materials in rocket nozzle applications. Five different treatments of the surface energy balance are presented, with increasing levels of fidelity. One of these methods eliminates transfer coefficient approximations and the need for precomputed ${\mathit{B}}^{\prime }$ tables by directly using species diffusion at the ablating wall to compute char mass flux. Equilibrium surface chemistry is assumed; these calculations are performed using the Mutation++ library. Ablation of the High Internal Pressure–Producing Orifice nozzle test case is investigated using decoupled and conjugate analysis methods, exploring the influence of surface energy balance treatment, turbulence model, and radiation on the predicted ablation response. The Integrated Equilibrium Surface Chemistry approach can fully capture the effects of ablation product species injection into the nozzle flowfield, in addition to the effects of recession, wall temperature, and blowing, and provides the best agreement with experimental recession measurements. The choice of turbulence model is found to have a weak influence on the predicted ablation response, whereas the impact of radiative heat transfer on recession predictions is found to be highly dependent on the selected surface energy balance treatment. By rigorously capturing the strong interactions and dependencies that exist between the reacting flowfield and the ablating material, improved analysis accuracy is demonstrated.