Numerical simulations of a double-wall cooling with internal jet impingement and external hexagonal arrangement of film cooling holes

Abstract

Three-dimensional conjugate computations are conducted to investigate the flow and heat transfer characteristics of a double-wall cooling system with a novel hexagonal arrangement of film cooling holes. Under the same coolant flow rate, the heat transfer and cooling performance of angled holes in the hexagonal arrangement are investigated and compared with those in the counterparts with conventional linear arrangements of external film cooling holes. The boundary condition of numerical simulations maintains the fixed jet Reynolds numbers of 10,000, 20,000 and 30,000 and the corresponding blowing ratios of 0.5, 1.0 and 1.5. Different wall thermal conductivities are respectively used in the numerical computations in order to examine the effects of Biot number of the film cooling wall on the overall cooling performance. Polyhedral meshes and Shear-Stress Transport (SST) k−ω turbulence model have been adopted in the numerical computations to obtain the detailed heat transfer and flow field. The results indicate that the hexagonal arrangement of film cooling holes shows significant advantages for the double-wall cooling scheme to decrease the external surface temperature appreciably. As the Biot number increases the overall cooling effectiveness of the double-wall system shows a downward trend, which decreases by about up to 25% in the Biot number range of 0.3–1.2. With the engine-like turbine Biot number of Bi≈0.56 the hexagonal arrangement improves the total heat transfer quantity inside the film cooling holes by up to 3.8 times, and enhances the overall effectiveness by up to 24.5%, as compared with the linear arrangement of straight circular film cooling holes. The combinations of the increased convective heat transfer inside the film cooling holes and the improved external film coverage induced by the hexagonal arrangement are the main contributions to the improvement of overall cooling performance.