Parametric Analysis of Supersonic Film Cooling in Rocket Engine Nozzle Extensions

The nozzle extension is a critical component of liquid rocket engines for vacuum applications, ensuring the correct gas expansion needed to achieve both the thrust and the specific impulse required by the mission. Although, typically, in space applications rocket nozzles are cooled through regenerative cooling, in this case, due to the prohibitive dimensions of nozzle extensions, a more efficient alternative is employed: film cooling, a thin layer of refrigerant injected tangentially to the wall. This thesis, conducted for The Exploration Company, is focused on their LOX/LCH4 liquid bipropellant engine, Huracán, where supersonic gaseous film cooling is adopted to ensure acceptable temperature ranges in the nozzle extension's walls. In particular, the main task is to optimize the film cooling efficiency, by selecting the appropriate injection geometry which ensures the survival of the walls. To accomplish that, 2D and 3D simulations were conducted using STAR-CCM+ and Ansys Fluent, solving conjugate heat transfer problems and adopting proper reactant chemistry models to analyze flow expansion and its consequences. Thanks to this thesis, a general guideline on how nozzle extensions should be cooled is obtained, giving important insights into different outcomes between different injection geometries.