Numerical analysis of carbon-based nozzle erosion including transient heating and shape change

Nozzle erosion during solid rocket motors and hybrid rocket engines firings needs to be accurately predicted in order to get reliable performance predictions. Moreover, the accurate sizing of the ablative thermal protection system (TPS), ensuring lightweight (i.e., minimum thickness) structures and preventing excessive heating, is of fundamental importance. In this context, reliable numerical models are required to accurately predict the thermochemical and thermophysical behavior of ablative TPS. The aim of the present work is to perform a numerical investigation on the coupled effects of nozzle ablation and of its thermophysical material response. This is achieved by performing axisymmetric computational fluid dynamics (CFD) simulations including finite-rate ablative boundary conditions and simulations obtained with the recently developed Porous material Analysis Toolbox based on Open-FOAM (PATO). Finite-rate thermochemical ablation tables for propulsive nozzle applications are firstly generated and then provided to PATO. The main advantages of employing these finite-rate tables are highlighted by comparison with the classical chemical equilibrium approach. The results obtained by loosely coupling CFD and material response simulations (using both finite-rate and equilibrium ablation tables) are validated by comparison with firing tests data of a sub-scale Space Shuttle solid propellant booster employing a carbon-phenolic nozzle.