Effect of bleed hole on internal flow and heat transfer in matrix cooling channel

Abstract

Matrix is an internal cooling scheme which has advantages of stronger heat transfer and better structural strength than conventional serpentine ribbed channels in gas turbine blades. In some compound cooling designs, coolant is extracted from the internal channel to the outer chamber to realize impingement. This paper analyzes the effect of bleed extraction on the flow field and heat transfer in matrix cooling channel by numerical simulations. RANS method is employed to present detailed flow field and heat transfer distribution. The investigated matrix channel is comprised of eight sub-channels which form two layers, the rib angle is 45° and the sub-channel aspect ratio is 1:1. The results indicate that heat transfer augmentation is caused by the large-scale streamwise vortexes which dominate the sub-channel flow. Extraction can create extremely high heat transfer enhancement level around bleed holes and alter the flow structures in the sub-channel. Cases of different diameters, positions and arrangements of holes are compared and the result shows that the bleed position has the most significant effect on the internal flow and heat transfer. Bleed holes between the sub-channel centerline and rib-side wall can provide strong heat transfer and good thermal performance. The internal matrix cooling capacity can be maintained with 25% mass extraction. Although the thermal performance of matrix channel can be improved by bleed holes, it is lower than most of the conventional cooling methods unless the baseline matrix structure was modified.