Experimental and Numerical Analysis of Transient Erosion in Hybrid Rockets

A crucial component of space transportation systems is the propulsive nozzle assembly. Here, due to the high temperature and velocity of the exhaust gases, harsh conditions in terms of heat fluxes are faced, leading to the requirement of a proper thermal protection system (TPS). Regarding HRE, a common solution is to use a carbon-based TPS. However, carbon surface recedes because of its chemical interaction with the combustion products, increasing the nozzle throat area and resulting in a performance loss. In the present work, the transient heating and erosion processes of a graphitic nozzle are numerically analyzed by means of coupled computational fluid dynamics (CFD) and material response (MR) simulations. The CFD solver is integrated with a validated gas-surface interaction model which takes into account finite-rate heterogeneous chemical reactions at the nozzle surface. The material response software is the Porous material Analysis Toolbox based on Open-FOAM (PATO), which is able to solve the transient three- dimensional heat conduction problem in solid media. Finite-rate thermochemical ablation tables are provided to the material response software in order to compute nozzle transient erosion by means of CFD-provided boundaries. The CFD-MR coupling strategy adopted has been validated by comparison with experimental data from a group of 2kN-thrust class CAMUI-type hybrid rocket firing tests performed at the Hokkaido University. The capabilities of the CFD-MR coupled approach in predicting the erosion onset time and the in-depth heating are stressed by comparing the obtained results with the state-of-art steady-state CFD ones.