Aerothermal Investigations on Mixing Flow Field of Film Cooling With Swirling Coolant Flow

This paper describes the experimental results of a new film cooling method blowing through circular and shaped film cooling holes with swirling coolant flow. The experiments have been conducted by using a scale-up model of a film cooling hole installed on the bottom surface of a low-speed wind tunnel. Swirling motion of film coolant was induced inside a hexagonal plenum by two slant impingement jets, which are inclined at α degree toward the vertical direction and installed in a staggered position. The two impingement jets generate swirling flows inside the plenum, and this swirling flow enters into a film cooling hole keeping the angular momentum until the exit of the film cooling hole. The slant angle of the impingement jets was changed as α = 0°, 10°, 20°, 30° in their wind tunnel tests. The film cooling effectiveness on the flat wall was measured by using pressure sensitive paint (PSP) technique. In addition, the spatial distribution of non-dimensional concentration (or temperature) and flow field were measured by laser induced fluorescence (LIF) and particle image velocimetry (PIV), respectively. In case of the circular film cooling hole, the coolant jet penetration into mainstream is suppressed by swirling motion of the coolant. As a result, though the coolant jet is deflected in the pitch direction, the film cooling effectiveness distribution on the wall keeps higher value behind the cooling hole over a long range. Additionally, kidney vortex structure disappeared. For the shaped cooling hole, the coolant jet spreads wider in spanwise direction at the downstream. Thus, the pitch averaged film cooling effectiveness at the downstream was 50% higher than that of the non-swirling case.