Numerical Investigation on Flow Field and Heat Transfer Phenomena in Multi-Hole Cooling Configurations

A transpiration cooled flat plate configuration is investigated numerically by application of a 3-D conjugate fluid flow and heat transfer solver, CHT-Flow. The geometrical setup and the fluid flow conditions are derived from modern gas turbine combustion chambers. The plate is composed of three layers, a substrate layer (CMSX-4) with a thickness of 2 mm, a bondcoat (MCrAlY) with a thickness 0,15 mm, and a thermal barrier coating (EB-PVD, Yttrium stabilized ZrO2) with a thickness 0,25 mm, respectively. The results of aerothermal calculations with adiabatic wall boundary conditions and the results of aerothermal calculation with fixed surface temperatures are compared to conjugate calculations that comprise both the fluid flow and the solid body. For conjugate calculations, there are no boundary conditions prescribed on the wall surfaces that are in contact with the fluid flow. The surface temperatures from the conjugate calculations are used as a boundary condition in the case of the aerothermal calculations with fixed surface temperatures. For the conjugate caluclations the numerical grid contains the cooling holes, the solid body, and the main flow area upon the plate. For the aerothermal investigations the grid contains the cooling holes and the main flow area. The transpiration cooling is realized by finest drilled holes with a diameter of 0,2 mm that are shaped in the region of the thermal barrier coating. The holes are inclined with an angle of 30°. Two different configurations are investigated that differ in the shaping of the holes in their outlet region. The numerical investigations focus on the deviation for the prediction of the thermal load of the solid body in the case of realistic cooling configuration that are induced by neglect of the heat transfer in the solid body. Due to a different prediction of the heat fluxes the structure of the cooling film deviates significantly between conjugate and aerothermal analysis. This investigations show that aerothermal investigation can only be a first step in a design process of cooling configurations.