Experimental investigation on the cooling performance of multi-row film holes of a serpentine nozzle

There are significant technical challenges in measuring the film cooling effectiveness (η) of the serpentine nozzle using pressure-sensitive paint (PSP) technology in a confined curved space, and the complex pressure gradients make the cooling performance complicated. This study investigates the cooling performance of multi-row holes of a serpentine nozzle, experimentally and numerically. The results show that the cooling performance of the upstream region is better than that of the downstream region for a small relative mass flow ratio (MFR_r), while the opposite is true for large MFR_rs. The area-averaged film cooling effectiveness (η‾_area) at MFR_r = 0.75, 1.0, and 1.5 is 8.1 %, 2.9 %, and 1.6 % lower than that at MFR_r = 1.25, respectively. The use of multi-row film holes with a staggered arrangement demonstrates clear advantages over inline arrangements, with the η‾_area for staggered arrangements being 30.4 % higher than that for inline arrangements. A smaller inclination angle shows better film cooling performance, with the η‾_area for inclination angles of 45° and 60° being 8.9 % and 20.5 % lower than that for an angle of 30°, respectively. Fan-shaped holes exhibit the highest η‾_area at all MFR_rs, while other diffuser-shaped holes only perform well at certain MFR_rs. Cylindrical, laidback, and laidback fan-shaped holes exhibit η‾_area values that are 12.2 %, 7.1 %, and 8.7 % lower than that of fan-shaped holes, respectively. Therefore, a staggered arrangement should be applied for the multi-row film hole design of a serpentine nozzle, in addition to using film holes with smaller inclination angles and a fan-shaped exit.