On the development of a film cooling layer

Different aerodynamic aspects of the flow field generated when a single jet or a row of jets are ejected into a mainstream are experimentally investigated. The similarity parameters are taken such as to match those of the three-dimensional film cooling. The objective is to deepen the understanding of the complex phenomena associated with these flows, and to provide a comprehensible and detailed data base for validation of numerical codes. To be able to obtain high resolution measurements, the study is made on large scale models. The scale enlargement obliges to use moderate velocities, so that the Reynolds number can be kept within realistic limits and the similarity preserved. The use of low air speeds prevents the analysis of compressibility effects. This restriction is not as severe as one can think because, according to the related bibliography, these effects start to be noticeable at Mach numbers higher than 0.8, while the designers avoid to inject the coolant in the vicinity of shock waves to avoid boundary layer separation. The study is made on three different models installed in a low speed wind tunnel. A first model consists of a flat plate with a single inclined circular hole. The isolated jet/mainstream interaction is investigated by means of this first test plate. The other two models present the same configuration as the first but having now a row of holes with different pitch to diameter ratios in each case. These models are useful to understand the interaction between jets and to analyze the formation and development of the coolant layer.