Advanced cooling techniques are required to increase the Brayton cycle temperature ratio necessary for the increase of the overall cycle's efficiency. Current turbine components are cooled with an array of internal cooling channels in the midchord section of the blade, pin fin arrays at the trailing edge and impingement channels in the leading edge. Impingement channels provide the designer with high convective coefficients on the target surface. Increasing the heat transfer coefficient of these channels has been a subject of research for the past 20 years. In the current study, a triple row impingement channel is studied with a jet to target spacing of 6, 8 and 10. The effects of sidewalls are also analyzed. Temperature sensitive paint alongside thin foil heaters are used to obtain heat transfer distributions throughout the target and side walls of the three different channels. Thermal performances were also calculated for the two largest channels. It was found that the side walls provide a significant amount of cooling especially when the channels are mounted side by side so that their sidewalls behave as fins. Similar to literature it was found that an increase in Z/D decreases heat transfer coefficient and provides a more uniform profile. It was also found that the Z/D = 6 and 8 target wall heat transfer profiles are very similar, hinting to the fact that successful potential core impingement may have occurred at height of eight diameters. A Computational Fluid Dynamics, or CFD, study was also performed to provide better insight into the flow field that creates such characteristic heat transfer profiles. The Realizable k-µ solution with enhanced wall functions gave surface heat transfer coefficients 30% off from the experimental data.

The present work studies the relationship between target and sidewall surfaces of a multirow, narrow impingement channel at various jet heights with one impingement hole per row. Temperature sensitive paint and constant flux heaters are used to gather heat transfer data on the target and side walls. Jet-to-target distance is set to 1, 2, 3, 5, 7 and 9 jet diameters. The channel width is 4 jet diameters and the jet stream wise spacing is 5 jet diameters. All cases were run at Reynolds numbers ranging from 5,000 to 30,000. Pressure data is also gathered and used to calculate the channel mass flux profiles, used to better understand the flow characteristics of the impingement channel. While target plate heat transfer profiles have been thoroughly studied in the literature, side wall data has only recently begun to be studied. The present work shows the significant impact the side walls provide to the overall heat transfer capabilities of the impingement channel. It was shown that the side walls provide a significant amount of heat transfer to the channel. A channel height of three diameters was found to be the optimum height in order to achieve the largest heat transfer rates out of all channels.