Effect of Hole Shape on Film Cooling Effectiveness Over a Flat Plate

Film cooling method of hot section components in the gas turbine engines is under continuous optimization for the enhanced cooling performance. In the present study, film cooling performance for a row of different shaped holes like triangular, circular and extended triangular have been considered. The adiabatic film effectiveness and the convective heat transfer coefficients are found experimentally on a flat plate. All the three test models are having holes of 5 mm diameter drilled at 20 mm pitch and inclined at an angle of 22 degrees. At the immediate downstream of these models, a flat plate is attached for finding the effect of these hole configurations. This flat plate is made with the low conductivity substrate and the stainless sheet of 0.2 mm thick is pasted over it in the flow path. The test model along with the flat plate is placed to the side wall of the rectangular duct where the mainstream air is supplied. The setup is made in such a way that the coolant air passed through the holes will create a film over the flat plate downstream. Infra Red camera is used to capture the thermal image of the entire test plate. The flat plate is connected with six thermocouples to have the reference surface temperature to correct the IR thermal image data. K-type thermocouples are used to measure the coolant and mainstream air temperatures. In both the heat transfer coefficient and adiabatic film cooling effectiveness experiments the blowing ratio is varied by 0.5 to 2.0, by keeping the constant mainstream air velocity of 20 m/s at ambient temperature. In the heat transfer coefficient experiments, the flat plate is heated with the constant heat flux conditions. In the adiabatic film cooling experiments, the coolant air is maintained at the temperature of −50°C with the help of liquid nitrogen heat exchanger bath. Results are plotted by taking the adiabatic film cooling effectiveness and convective heat transfer coefficient values from the centerline of holes downstream along the flow direction. From the results, the triangular and extended triangular hole models shown higher heat transfer coefficient and adiabatic film cooling effectiveness than the circular hole model.