Computational Fluid-Dynamic Simulations of the Internal Ballistics of Hybrid Rocket Burning Paraffin-based Fuel

A computational thermo-fluid-dynamic model for the simulation of the internal ballistics of hybrid rockets burning gaseous oxygen and paraffin-based fuel is presented in the present work. The main objective is the prediction of the solid fuel regression rate, which is calculated with an improved gas/surface interface treatment based on local mass, energy and mean mixture-fraction balances and an additional equation for modelling the liquid droplets entrainment contribution to the total fuel mass flow rate. Parametric analyses have been carried out to assess the effect of fuel physical properties on the results. Comparison between numerically calculated and experimentally measured regression rate axial profiles retrieved from three firing tests performed with two laboratory scales hybrid rocket motors are outlined to address preliminary validation of the model and identify possible future improvements.