Numerical investigation of charring thermal protection pyrolysis and ablation in solid rocket motors

The solid rocket propulsion is a simple and reliable system, it is less complex than liquid propulsion because it does not require tanks, pumps and the propellant is already stored into the combustion chamber. The main issues are the lower propulsive performance and the lack of controllability. The solid rocket motor thrust can be controlled only moving the nozzle direction of few degrees while its magnitude can not be controlled, therefore it is very important to well know the thrust profile because there is no possibility to control its magnitude during the flight. The thrust shape can be obtained experimentally or performing simulations. The first way is quite expensive therefore the second one is preferable. The tool ROBOOST (ROcket BOOst Simulation Tool), developed by the university of Bologna propulsion laboratory in collaboration with Avio S.p.A., already achieves the goal to predict the thrust profile during the ignition phase and the combustion one. But it fails to follow the experimental curve in the tail-off, underestimating the residual thrust. This discrepancy can be due to different phenomena that are not considered in the this simulation: heat coming from the nozzle, heat coming from slugs and the mass flow rate due to the thermal protection pyrolysis and ablation. This thesis focuses on simulate thermal protection pyrolysis and ablation obtaining their behavior when they are exposed to the hot gases of the combustion chamber.