Numerical Model to Analyze Transient Behavior and Instabilities on Hybrid Rocket Motors

The study of hybrid rocket transient behavior is a very important issue in order to analyze instabilities and develop throttleable motors. In this paper, an unsteady numerical model is presented. The model is composed of three submodels linked together: 1) zero-dimensional model of the combustion chamber, 2) one-dimensional (1-D) radial model of the fuel grain, and 3) zero-dimensional model of the feeding system. The first model simulates combustion chamber dynamics. The one-dimensional radial model of the fuel grain includes both standard polymeric and liquefying propellants characterized by a melting layer. The fuel block models the heat exchange to the wall, the heat propagation through the solid/liquid phase, and the fuel surface evaporation/entrainment. Finally, the injection system block simulates the unsteady behavior of the feeding line and droplets break-up-evaporation dynamics. In this paper, all the blocks are presented together with their validation versus analytical test cases. For each block, an analysis of the effect of the influencing parameters on the transient thruster behavior is presented.