LARGE-EDDY SIMULATION OF FILM COOLING IN AN ADVERSE PRESSURE GRADIENT FLOW

摘要

To analyze the interaction of multiple rows of film cooling holes in flows at adverse pressure gradients large-eddy simulations (LES) are performed. The considered three-row cooling configuration consists of inclined cooling holes at an angle of 30° with a lateral pitch p/D = 3 and a streamwise spacing l/D = 6. The cooling holes possess a fan-shaped exit geometry with lateral and streamwise expansions. For each cooling row the complete internal flow was computed. Air and CO_2 are injected to investigate the influence of an increased density ratio on the film cooling physics at adverse pressure gradients. CO_2 injected at the same blowing rate as air shows a higher magnitude of the Reynolds shear stress component and thus an enhanced mixing downstream of the cooling holes. The LES results of the air and CO_2 configurations are compared to the corresponding particle-image velocimetry (PIV) measurements and show a convincing agreement in terms of averaged streamwise velocity and streamwise velocity fluctuations. Furthermore the cooling effectiveness is investigated for a zero and an adverse pressure gradient configuration with a temperature ratio at gas turbine conditions. For the adverse pressure gradient case reduced temperature levels off the wall are observed. However, the cooling effectiveness shows only minor differences compared to the zero pressure gradient flow. The turbulent Schmidt number at CO_2 injection shows large variations. Just downstream of the injection it attains low values, whereas high values are detected in the upper mixing zone of the cooling flow and the freestream at each film cooling row.