Experimental investigation on gaseous film cooling for a GCH4/GOX rocket combustion chamber

Film cooling is a widely used technique to reduce the heat transferred to the wall in highly loaded rocket combustion chambers. Its analysis for the methane/oxygen bipropellant combination, one of the most promising solutions nowadays for the future of space propulsion is of strong interest. Methane is classified as a green propellant when comparing to solutions like solid motors, and it shows better volumetric performance and lower handling costs than the cryogenic couple hydrogen/oxygen. This thesis constitutes an experimental investigation on gaseous film cooling in a subscale methane/oxygen rocket chamber using different fluids as coolants (nitrogen, argon, methane and hydrogen), as well as two different geometries for the applicator, always using tangential injection at the faceplate of the chamber. The testing campaigns are designed, executed and studied. The data is then analysed, mainly through the non-adiabatic effectiveness, which has been slightly modified to take into account specific phenomena correlated to the use of a capacitive hardware. Careful attention is put on the influence of the blowing parameter as the main driver for film cooling. Finally, the numerical implementation of some film cooling models in the engineering in-house tool is performed to be confronted with the experimental data. The results confirm the strong influence of the blowing ratio on the effectiveness. The increase of this parameter enhances the cooling, but the existence of a threshold on this positive influence is observed. Downstream, the injection of film can induce a higher heat flux to the wall due to mixing enhancement, modification of the chemical reactions and pressure rising. A certain part of the chamber is then protected by the film, while a region with a negative effectiveness can exist. The size of this region is also influenced by the blowing parameter, increasing with it. About fluid influence, lower density and higher specific heat show better cooling performance. The work has been developed at the Institute for Flight Propulsion (LFA, Lehrstuhl für Flugantriebe) of the Technical University of Munich (TUM, Technische Universität München).