Computational investigation of film cooling and secondary flow on turbine endwall with coolant injection from upstream interrupted slot

High pressure turbine vane surface and endwall regions are extensively cooled through discrete holes and leakage flow from combustor-turbine interface gap. For making better use of the limited amount of the leakage flow, this paper describes numerical investigation of endwall film cooling performance of a two-dimensional cascade with upstream interrupted slot injection. The geometry of the vane, size of the slot and mainstream parameters are all taken from a real engine high pressure turbine. The effects of varying blowing ratio, location of the upstream slot and coolant incidence angle on cooling effectiveness are studied. The ranges of the studied parameters are: blowing ratio 1.0, 1.7, 1.86; slot location Z/Cax = −0.1, −0.2, −0.3; coolant incidence angle −10°, 10°, 20°. The calculations are completed by solving three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with shear stress transport (SST) k-ω turbulence model, meanwhile, the turbulence model was validated by comparing the calculated results with the experiment data. The calculated results show an important influence of blowing ratio and axial position of the interrupted slot on film cooling effectiveness. Cooling Effectiveness is increased with increasing blowing ratio and decreasing distance between the slot and leading edge of the vane. To compare with BR = 1.7 cooling effectiveness can be improved significantly in the condition of BR = 1.86. Slot location of Z/Cax = −0.1 provides much higher cooling effectiveness than the rest two locations. The physical mechanism of the improvement is that in the condition of high blowing ratio high momentum coolant flow helps to reduce the strength of horseshoe vortex and therefore to limit its negative effect on the cooling effectiveness. The high momentum coolant jet impinges on leading edge of the vane and climbs the surface of it. The coverage of the coolant at the leading edge endwall and pressure side endwall junction becomes better. The contours of effectiveness for different slot location are similar to those of different blowing ratio. The momentum of the coolant jet increases with the slot moving close to the leading edge of the vane and creates similar effectiveness contour patterns of raising blowing ratio. The effect of varying coolant incidence angle on the cooling effectiveness is weaker than blowing ratio and slot location. Average cooling effectiveness is increased about 14% when the angle changed from 10° to 20°.