Enhanced film cooling performance of a row of cylindrical holes embedded in the saw tooth slot

Abstract

The film cooling performance of a row of cylindrical holes embedded in the saw tooth slot on the flat plate was experimentally investigated using the transient thermochromic liquid crystal technique at blowing ratios of 1.0, 1.5 and 2.0 respectively. The density ratio of the coolant to the main stream was 0.92. An injection angle of 30° relative to the cooled surface in the streamwise direction and a length to diameter ratio of the hole of 6 were used. The saw tooth slot at the hole exit was used to enhance the spanwise spread of the coolant. The effects of the hole pitch, slot height and corner angle on film cooling performance were examined. The standard cylindrical hole was also tested for comparison. The emphasis of this study was on the analysis of the local and spanwise averaged values of the film effectiveness and heat transfer coefficient. Numerical simulation was also conducted to determine the velocity and thermal field to explain the enhanced mechanism of the film cooling by the saw tooth slot configuration. The results showed that the influence of the configurations on the film cooling was strongly dependent on the blowing ratio. A small hole pitch resulted in the significantly larger values of the film effectiveness. The opposite effect of the slot height on the film effectiveness was observed at low and high blowing ratios. A 60° corner provided the significantly larger values of the film effectiveness, especially at high blowing ratio. The heat transfer coefficients were similar for all configurations of the saw tooth slot at blowing ratio of 1.0. Increases in the hole pitch and the corner angle both resulted in a decrease in the heat transfer coefficient at blowing ratios of 1.5 and 2.0.