Combined Effect of Slot Injection, Effusion Array and Dilution Hole on the Heat Transfer Coefficient of a Real Combustor Liner: Part 2: Numerical Analysis

Due to the higher cooling requirements of novel combustor liners a comprehensive understanding of the phenomena concerning the interaction of hot gases with different coolant flows plays a major role in the definition of a well performing liner. A numerical study of a real engine cooling scheme was performed on a test article replicating a slot injection and an effusion array with a central large dilution hole. Geometry consists of a rectangular cross-section duct with a flat plate comprised 272 holes arranged in 29 staggered rows (d = 1.65 mm, Sx/d = 7.6, Sy/d = 6, L/d = 5.5, = 30 deg); a dilution hole (D = 18.75 mm) is located at the 14th row. A detailed experimental survey has been performed on this test article making possible to compare both predicted adiabatic effectiveness and heat transfer coefficient. The study has a twofold objective. On one hand it aims to assess the accuracy of standard industrial CFD analysis in the prediction of heat transfer on the hot side of realistic effusion cooled plates, and, on the other hand, it allows to better understand the structure of flow field, not investigated with experiments. Steady state RANS calculations have been performed on 3D computational domain with a full explicit discretization of effusion holes, with a sensitivity to standard two-equation turbulence models. Numerical results have pointed out a large dependence on effusion velocity ratio and, despite the well known deficiency of eddy viscosity models in the prediction of film effectiveness, CFD results have shown an excellent agreement with experiments in the prediction of hot side heat transfer coefficient. The entity of local heat transfer augmentation due to gas-jets interaction and its dependence on jets velocity ratio were predicted with very satisfactory agreement. The increase of heat transfer is usually located very close to jet exits and it is mainly due to local flow acceleration and vortices whose calculation is not affected by the inaccurate jet mixing prediction of first order turbulence models. Besides the comparison with experimental data of the companion paper, an additional numerical investigation was performed to assess the effect of a variable density ratio. Obtained results point out the opportunity to scale the increase in heat transfer coefficient with effusion jets velocity ratio.