Experimental and Numerical Analysis of Additively Manufactured Coupons With Parallel Channels and Inline Wall Jets

With the goal to realize gas turbine engine cycle efficiency of 65%, the turbine inlet temperature is predicted to rise to 1700° C. Additive manufacturing (AM) has opened new avenue to explore complex design spaces to enhance cooling in gas turbine blades. Present paper developed a series of additively manufactured parallel cooling channels with streamwise wall jets inside, which could be suitable for double wall and near wall cooling configurations in gas turbine hot section components. The tested coupons consisted of parallel channels, each channel further divided into small chambers using several spanwise separation walls. Height of these walls was kept less than channel height, thus forming a crossover slot jet with one of the end walls. Coolant entered from one side of channel and formed streamwise wall jet while crossing through the slot over to the downstream chamber. The test coupons were additively manufactured by Selective Laser Sintering technique using Inconel 718 alloy. Both experimental and numerical study has been conducted to analyze effect of pitch and blockage ratio on heat transfer. Pitch between subsequent slots was defined in terms of slot hydraulic diameter and was varied from 5D_j to 11D_j. Blockage ratio consisted of ratio of separation wall height to the channel height and varied from 0.5 to 0.75. Steady state heat transfer experiments with constant wall temperature boundary condition were performed for a channel Reynolds number range of 1800 to 5000. ANSYS CFX solver with the SST k-ω turbulence model was used to perform numerical simulation to obtain detailed understanding of existing flow field. Experimental results showed heat transfer enhancement of up to 6.5 times that of a smooth channel for the highest blockage ratio of 0.75. The blockage ratio exerted stronger effect both on pressure drop and heat transfer characteristics, as compared to pitch. The heat transfer as well as pressure drop were found to increase with a decrease in pitch and with an increase in blockage ratio. The numerical results revealed complex flow field which consisted of wall jets along with impingement, separation and recirculation zones in each chamber. It also revealed significant uniformity in heat transfer coefficient distribution on the slot side end wall. For all configurations, the gain in heat transfer was accompanied with high pressure drops. However, coupled with the high heat transfer, this design could lead to potential coolant savings.