Experimental investigation on spiral-channel holes on turbine endwall

This study examines the cooling capacity of spiral-channel holes in the end wall using cascade wind tunnel experiments, and explores how the parameters of blowing ratio, film hole position, and compound angle affect the film cooling efficiency. The findings reveal that spiral-channel holes outperform cylindrical holes in cooling performance, primarily due to their ability to generate a more coherent cooling jet that extends over a broader surface area. Particularly, the cooling efficiency of the outlet and downstream regions of spiral-channel holes is found to be superior. When the mass flow ratio is 2.61% and 3.11%, the average efficiency of the case throughout the streamwise direction is 11.91% and 14.99% higher than that of the base, respectively. An examination of the mass flow ratio indicates that spiral-channel holes exhibit a higher initial value, which correlates with a significant improvement in film cooling performance at a critical mass-flow rate threshold of 2.33%. However, within the film cooling zone, the cooling efficiency decline is less severe compared to the unaffected areas as the temperature ratio rises. The study also notes that, when the expansion ratio increases, the overall cooling efficiency in regions influenced by film cooling declines further, with a more significant relative decrease observed at high Reynolds numbers. Additionally, as mainstream flow increases, the zone of high cooling efficiency at the outlet of film holes gradually diminishes. Notably, the zone of high cooling efficiency downstream of the fourth-row holes shifts from the pressure side toward the channel center, which, in turn, leads to a more evenly distributed cooling efficiency.