An experimental investigation of geometric effect of upstream converging slot-hole on end-wall film cooling and secondary vortex characteristics

A row of converging slot-holes is applied upstream of a linear GE-E3 high pressure turbine cascade to enhance film-cooling effect in end-wall leading edge region and weaken secondary vortices. Effects of geometric parameters of the converging hole-slot, including inclination angle and outlet-to-inlet area ratio, on time-mean characteristics of secondary vortices and adiabatic film-cooling effectiveness are respectively investigated with Time-Resolved Particle Image Velocimetry (TRPIV) and Planar Laser Induced Fluorescence (PLIF) techniques, at various coolant-to-mainstream blowing ratios. Three types of converging slot-holes with two different area ratios (ARs = 1.38 and 0.69) and inclination angles (α = 30° and 65°) are chosen, and a 30° cylindrical hole is compared as a reference. The comparison reveals that, the secondary vortices can be weakened by the coolant injection from the cylindrical hole only at higher blowing ratios; however, the 30° converging slot-holes has a potential to simultaneously improve end-wall cooling effect and weaken the secondary vortices, even at lower blowing ratios. For the two 30° converging slot-holes, the configuration with smaller AR = 0.69 is a better structure, because that can provide a better film-coverage performance, a higher film cooling effectiveness, and a stronger ability to weaken secondary vortices, compared to larger AR = 1.38. For the 65° converging slot-holes, the coolant lifts easily off the end-wall, and the secondary vortices are enhanced by the coolant injection. Therefore, this configuration is not suitable for weakening the secondary vortices.