Numerical Investigation of Conjugate Heat Transfer in an Effusion and Impingement Cooled Combustor Wall

In this paper, a numerical investigation of conjugate heat transfer in a double-wall combustor will be presented. The model replicates the cooling air duct, the double wall with impingement and effusion cooling, as well as the hot gas duct. For simplification, the walls are modeled planar, and the test parameters were adapted from an upcoming experiment at the Institute of Thermal Turbomachinery, Karlsruhe Institute of Technology. The geometry was scaled up by a factor of 8 through performing a similarity analysis. Aerodynamic and thermal boundary conditions were scaled to ambient pressure and low temperatures while maintaining dimensionless quantities from realistic operating conditions. The diameter of the cylindrical impingement cooling holes is D = 4mm. The effusion cooling holes are angled with α = 30° to the surface and have a cylindrical entrance diameter of E=2–√D ⁠. The outlet of the effusion cooling hole is fanshaped with an opening of 7° to each side as well as laidback by 7°. Both walls have a staggered pattern in which the rows of holes are repeated every 4th row. A range of blowing ratios from Meff = 0.5 to 3.0 was set as operating conditions for the calculations. Besides, the distance between the impingement wall and the effusion wall was varied from Hcav = 3D to 7D to investigate the influence on heat transfer and aerodynamic behavior of the setup. The results show an increase in the overall cooling effectiveness θ while reducing the cavity height Hcav. The overall cooling effectiveness θ increases with higher blowing ratios M but shows an absolute saturation above blowing ratios of approximately M > 2.0. Another significant finding is the aerodynamically unfavorable flow of the coolant into the effusion cooling holes and the identification of the flow path from the coolant.