Multirow Film-Cooling Effectiveness of Vertically Oriented Slot Cross-Section Diffusion Holes on a Turbine Nozzle Guide Vane Suction Surface

Abstract In this article, a multirow film-cooling effectiveness experiment was conducted on a turbine nozzle guide vane suction surface using the pressure-sensitive paint (PSP) measurement technique. Five rows of film holes were designed at the suction side with a streamwise staggered arrangement and a 6D spanwise hole spacing. Two diffusion holes constructed based on a vertically oriented slot cross-section with 14-deg and 20-deg exit expansion angles were tested. A fan-shaped hole and a horizontally oriented slot cross-section diffusion hole were chosen as the baselines, and both had a 14-deg exit expansion angle. The experiment was carried out in a linear cascade with a mainstream Reynolds number of 62000, a mainstream turbulence intensity of 3.7%, and a coolant-to-mainstream density ratio of 1.5. The four averaged blowing ratios ranged from 0.5 to 2.0. The results showed that, regardless of the blowing ratio, under intense multirow film interactions, the vertically oriented slot cross-section diffusion holes can always produce uniform and consistent film coverage on the vane suction surface. The vertically oriented slot cross-section widens the distance between the up- and downstream walls and narrows the lateral width, thereby weakening the influence of the entrance “jetting effect.” The resulting flow pattern can adapt to a larger exit expansion angle. In addition to the smaller difference under a low blowing ratio, two vertically oriented slot cross-section diffusion holes yield prominently greater multirow effectiveness than do the horizontally oriented slot cross-section diffusion hole and conventional fan-shaped hole, in which the case with a 20-deg expansion angle performs better.