Modeling of high density polyethylene regression rate in the simulation of hybrid rocket flowfields

Numerical simulations of the flowfield in a hybrid rocket engine are carried out with a Reynolds-averaged Navier-Stokes solver integrated with a customized gas-surface interaction wall boundary condition and loosely coupled with a radiation code based on the discrete transfer method. The fuel grain wall boundary condition is based on mass, species and energy conservation equations coupled with thermal radiation exchange and finite-rate Arrhenius kinetics for fuel pyrolysis modeling. Fuel pyrolysis is governed by the heat flux reaching the surface due to convection and radiation and by the energy required for the grain material to heat up and pyrolyze. Attention is focused here on a set of static firings performed with a lab-scale GOX/HDPE motor. A sensitivity analysis has been carried out on the literature pyrolysis models for HDPE, to evaluate the possible role of the uncertainty of such models on the actual prediction of regression rate. A reasonable agreement between measured and computed averaged regression rate and chamber pressure is obtained, with a noticeable improvement with respect to solutions without including radiative energy exchange.