An investigation on film cooling with a coalition of forward and backward injection

Abstract

Full coverage film cooling, also known as effusion cooling, is used to protect combustor liner from high temperature gases in the gas turbine. Numerical analyses are carried out to investigate and compare cooling performance of two arrangements, namely mix and opposite injections composed of forward as well as backward injection holes. Mix injection arrangement consists of rows of cooling holes injecting in alternate backward and forward directions, while in opposite injection configuration holes inject just in the opposite directions. Computational study is carried out at various velocity ratios (VR) from 0.5 to 5.0. Forward and backward injecting cooling holes, in both the configurations, are inclined at 300 with respect to mainstream. Adiabatic film cooling effectiveness is estimated along stream wise as well as lateral directions. Except front few rows of cooling passages (holes), configuration with opposite injection shows superior cooling than mix injection at high velocity ratios. Developed effusion or diffusion film layer is seen for both mix and opposite injection configurations, at high velocity ratios, but it occurs bit early for opposite injection. In opposite injection, fluctuations in cooling effectiveness along stream wise direction are higher as compared to mix injection at all velocity ratios.