Film Cooling With Swirling Coolant Flow Controlled by Impingement Cooling in a Closed Cavity

A new film cooling concept has been developed by managing the swirled film coolant 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 on the plenum chamber wall. Film cooling tests have been conducted by using a circular film cooling hole model mounted on a low speed wind tunnel. Heat transfer coefficient distributions of inclined jet impingements in a closed cavity was measured by naphthalene sublimation method and the film cooling effectiveness on the surface of the wind tunnel was measured by pressure sensitive paint (PSP). It appeared from experimental results that the swirled film coolant flow deteriorated the film cooling effectiveness at low swirl number but improved it at high swirl number. To investigate the mechanism of the improved film cooling effectiveness by the swirled coolant, the spatial distribution of the film cooling effectiveness and flow field were measured by laser induced fluorescence (LIF) and particle image velocimetry (PIV), respectively. The coolant jet penetration into mainstream is suppressed by the strong swirling motion of the coolant. As a result the film cooling effectiveness distribution on the wall keeps higher value behind the cooling hole over a long range. Additionally, kidney vortex structure was disappeared at high swirl number.