Numerical simulations of fuel shape change in paraffin–oxygen hybrid rocket engines

Reynolds-averaged Navier-Stokes simulations with submodels of turbulence, chemistry, fluid-surface interaction, and radiation are performed in this work to rebuild the internal ballistics of an experimentally tested hybrid rocket engine with paraffin and gaseous oxygen as propellants. Firstly, the effects of the prechamber and postchamber cavities at the initial, average, and final diameter of a reference burn are assessed to be negligible. Then, numerical simulations modeling the fuel shape change in space and time are compared to simulations performed at uniform port radius. The latter provide reasonable regression rate, pressure, and final grain profile predictions with reduced computational cost. On the other hand, the more computationally expensive fuel shape change simulations improve the model prediction capabilities providing a more accurate comparison with experimental data. The fuel shape change approach is finally applied with success to simulations of a throttled burn.