Hybrid Rockets with Axial Injector: Port Diameter Effect on Fuel Regression Rate

Abstract

A numerical rebuilding of a series of test data obtained with static firings of a lab-scale hybrid rocket is carried out with a Reynolds-averaged Navier–Stokes solver including detailed gas–surface interaction modeling based on surface mass and energy balances. Two experimental campaigns are considered in which gaseous oxygen is fed into axisymmetric hydroxyl-terminated polybutadiene grains through an axial conical subsonic nozzle. A validation rebuilding of all of the firing tests has been performed first to highlight numerical prediction capabilities and modeling limits. Despite the several geometrical simplifications, which allows using a reduced number of cells in the computational domain and thus performing parametric analyses efficiently, the present computational fluid dynamics approach is able to capture the main features of the motor internal ballistics, fairly reproducing the average chamber pressure values and the fuel regression rate trends with oxidizer mass flux and port diameter. Computed flowfields show the establishment of a recirculation region at the motor head end, with a variable extension depending on the port diameter, which promotes propellant mixing and raises the fuel regression rate. Numerical simulations, supported by the experimental results, clarify the mechanism through which the port diameter has a direct influence on the fuel regression.