Film cooling performance measurement over a flat plate for a single row of holes embedded in an inclined trench

Abstract

Film cooling heat transfer coefficient and effectiveness measurements downstream of a single row of holes embedded in an inclined trench injecting secondary fluid into the mainstream over a flat surface are reported here. The well-studied trench geometry is one where the walls of the trench are perpendicular and film injection holes are at an angle to the mainstream flow direction. In the current investigation, the trench is inclined at an angle to the mainstream and the injection holes are normal to the flow direction. Coolant injection in the form of a uniform stream at an angle to the mainstream is likely with this configuration. The trench inclination is kept constant at 35° and three hole pitch to diameter ratios equal to 3, 4.5 and 6 are studied for the blowing ratio varying between 0.3 and 2.5. The injection hole length to diameter ratios equal to 1.8 and 5.5 were studied and the influence on the net heat flux reduction ratio was found to be very small. The local effectiveness and the heat transfer coefficient values are presented and the variations in the cross-stream direction are observed to be very small. The effectiveness values for the current angular trench are higher whereas the heat transfer coefficients are smaller compared to the normal trench at higher blowing ratios. This results in increased Net Heat Flux Reduction ratio (NHFR) values for the current configuration which are observed to remain high at large downstream locations also.