EXPERIMENTAL AND NUMERICAL INVESTIGATION OF LIQUID FILM COOLING IN SMALL ROCKET ENGINES

Within the scope of a GSTP project, a Belgian-German research team performed experiments and simulations to characterise the behaviour of a liquid cooling film and to provide benchmark data for simulation models. The experiments were performed at DLR's M11.1 air vitiator test facility in Lampoldshausen, Germany. Ethanol was used as film coolant. Apart from being a potential renewable hydrocarbon fuel, ethanol is a suitable substitute fluid for monomethyl-hydrazine, which it is currently being used as propellant and film coolant in small liquid rocket engines. Compared to the situation in a real rocket engine, the experiment was designed to simplify the boundary conditions for the simulations by avoiding chemical reactions of the film with the hot gases as far as possible and to limit the phenomena subject to investigation to heat and mass transfer effects of a liquid cooling film subjected to heating and shear forces. The experimental setup used a planar film injector in a rectangular hot gas duct. Additionally to measurements of the pressure and temperature of the fluids at inlet and outlet of the test section, thermocouples were installed in the film cooled channel wall to provide information on the axial evolution of the film cooling efficiency. Furthermore, the channel provides optical access for nonintrusive measurement techniques. The von-Karman-Institute used this access to apply laser-based measurements of the temperature of the liquid film. DLR used a dedicated Background-Oriented Schlieren (BOS) technique to provide additional information on the evolution of the film thickness. Several tests have been performed in spring 2019. The test data have been analysed and are currently being used to benchmark simple engineering models as well as high-fidelity CFD models to predict the behaviour of liquid cooling films in rocket engines.