THERMAL-FLUID AND MECHANICAL INVESTIGATIONS OF ADDITIVELY MANUFACTURED GEOMETRIES FOR TRANSPIRATION COOLING

Transpiration cooling has always been the dream of gas turbine high temperature component design. The uniform coolant coverage and enhanced heat transfer in porous wall provided by this cooling technique can significantly reduce the case metal temperature which is essential for improving forking efficiencies and operation life of gas turbine. Recently, with the capability of the innovative powder bed direct metal laser sintering (DMLS) additive manufacturing technology, the complex geometries of transpiration cooling part could be precisely fabricated and endued with improved mechanical strength. In the present study, five different schemes of transpiration cooling including (1) round holes with 1.5d in-line itch, (2) round holes with 2d in-line pitch, (3) round holes with in-line pitch, (4) round holes with 2d staggered pitch, (5) declined holes (20 inclination towards the main stream direction) with 2d in-line pitch in In718 superalloy plates were fabricated by direct metal laser sintering (DMLS) printer. temperature measurements of the hot side surfaces with coolant coverage were conducted to evaluate the cooling performances of those structures. Tensile bars containing the fame designed structure as the heat transfer test coupons in the gauge part were printed as well for the evaluation of the ultimate tensile strength. The test results showed that the coupons with smaller pore size had higher cooling effectiveness ut lower tensile strength. The smaller pitch value (P=1.5D) and the staggered pattern could enhance the cooling performance but decrease the mechanical strength as well. Taking both cooling efficiency and mechanical strength into consideration, the 0.3mm pore size coupon with 3d in-line pitch Fund holes is considered to be the optimal design with cooling effectiveness of 0.48 at the injection ratio of 2.5% and ultimate tensile strength of 775.9MPa. The present research work demonstrated the potential of additive manufacturing to design and fabricate the transpiration cooling structure with high cooling efficiencies and desired tensile strength.