Effects of Coolant Feed Direction on Additively Manufactured Film Cooling Holes

Gas turbine components subjected to high temperatures can benefit from improved designs enabled by metal additive manufacturing (AM) with nickel alloys. Previous studies have shown that the impact on fluid flow and heat transfer resulting from surface roughness of additively manufactured parts is significant; these impacts must be understood to design turbine components successfully for AM. This study improves understanding of these impacts by examining the discharge coefficient and the effect of the coolant delivery direction on the performance of additively manufactured shaped film cooling holes. To accomplish this, five test coupons containing a row of baseline shaped film cooling holes were made from a high-temperature nickel alloy using a laser powder bed fusion (L-PBF) process. Flow and pressure drop measurements across the holes were collected to determine the discharge coefficient from the film cooling holes. Temperature measurements were collected to assess the overall effectiveness of the coupon surface as well as the cooling enhancement due to film cooling. The Biot number of the coupon wall was matched to a value one might find in a turbine engine to ensure this data is relevant. It was discovered that the flow experienced greater aerodynamic losses in film cooling holes with greater relative roughness, which resulted in a decreased discharge coefficient. The effectiveness measurements showed that the film cooling performance is better when coolant is fed in a co-flow configuration compared to a counter-flow configuration.