Review and implementation of engineering models of rocket film cooling and nozzle erosion

The present work, reviews the improvements which have been implemented in the European Space Propulsion System Simulation (ESPSS) libraries v3.6, regarding the chamber film cooling and the nozzle erosion. In particular, attention is focused on the adopted mathematical modeling of the phenomenology, on models implementation into the ESPSS libraries, and lastly on the validation procedure. Active chamber cooling and nozzle erosion are two important and common design choices regarding liquid and solid/hybrid rocket engines, respectively. Dealing with liquid engines, active cooling systems are often required to extract heat from the hot-gas flow and specifically, the film cooling represents a valid design solution in support of the regenerative cooling system, capable of providing a significant protection to the chamber at the cost of a performance loss. On the other hand, the use o an ablative thermal protection system (TPS) represents a widespread solution to protect the nozzle structure from the chamber harsh thermochemical environment if other kind of cooling techniques are not feasible, as in the case of solid and hybrid rockets. As a drawback, ablative materials are subjected to a thermochemical erosion process, leading to a nozzle throat enlargement and thus to a specific impulse loss and to a modified thrust curve. During the design process, reliable numerical models are necessary to reduce the number of expensive hot-firing tests. In this sense, the European Space Propulsion System Simulation (ESPSS) framework has been historically conceived developed by ESA to simulate complex systems steady-state and transient analyses. The inclusion of film cooling and nozzle erosion low-order models might represent an useful asset during the engine development phase, allowing for quick evaluations of complex phenomena in an inter- dependent system-wide representation. Reliability of the results is assessed by comparing the numerical results with experimental test cases and CFD simulations.