Computational Fluid-dynamic Simulations of Hybrid Rocket Internal Flow Including Discharge Nozzle

A computational thermo-fluid-dynamic model of the hybrid rocket internal ballistics has been developed in the present work. Numerical simulations of the flowfield in two laboratory scales hybrid rocket motors, one in the 200-N class and the other in the 1 kN-class, operated with gaseous oxygen and high-density polyethylene have been carried out. The objective is twofold: first 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 as well as proper turbulence boundary conditions, along with chamber pressure and combustion efficiency. Second, the detailed study of the discharge nozzle flow and heat transfer. For the validation of the model, data retrieved from two firing tests are compared with the numerical results revealing good agreement of the average regression rates, fuel consumption axial profiles, and of the chamber pressure and combustion efficiency. The output of the motor ballistic simulations are then used for a detailed numerical study of the flow through the nozzle and of the unsteady thermal field inside the nozzle solid block showing different behaviors of graphite compared to ceramic material nozzle, highlighting the severe thermal gradient occurring in the ceramic material.