Experimental evaluation of cooling effectiveness from novel film holes over turbine endwalls with inlet swirl

In this paper, cooling characteristics of a novel film hole are experimentally evaluated over a linear turbine endwall for enhancing the endwall film cooling. The novel hole features a bean-shaped exit and cooling effectiveness over the endwall cooled by the bean-shaped holes is measured by using the pressure-sensitive paint technique for a wide range of coolant flow rates that cover typical engine conditions. For direct comparisons, measurements are also undertaken on the same endwall film-protected by traditional cylindrical holes with the equal hole distribution pattern at the same coolant consumption. Particularly, residual swirl from upstream combustors is considered in this study for increasing the adaptability of the novel holes in complex approaching flow conditions that are typically seen in today's advanced aircraft engines. Results reveal that the bean-shaped holes present superior cooling effectiveness to the cylindrical holes and the outperformance of the shaped holes becomes more prominent at higher coolant flow rates. The superiority is diminished when the shaped holes are positioned close to the passage suction side. Overall, effectiveness can be generally augmented more than two times by the novel holes. The inclusion of the swirl has adverse effects on both the bean-shaped and cylindrical holes. Despite this, the bean-shaped holes still outperform the cylindrical holes. An important finding is that inlet negative swirl is much more detrimental to the cooling over the endwall than the inlet positive swirl, regardless of the hole shapes. This is expected to provide guidelines for the arrangement of swirlers within the combustors.