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

Abstract

This paper describes the experimental results of a new film cooling method that utilizes swirling coolant flow through circular and shaped film cooling holes. The experiments were 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 the film coolant was induced inside a hexagonal plenum using two diagonal impingement jets, which were inclined at an angle of α toward the vertical direction and installed in staggered positions. These two impingement jets generated a swirling flow inside the plenum, which entered the film-cooling hole and maintained its angular momentum until exiting the film-cooling hole. The slant angle of the impingement jets was changed to α = 0 deg, 10 deg, 20 deg, and 30 deg in the wind tunnel tests. The film cooling effectiveness on a flat wall was measured by a pressure sensitive paint (PSP) technique. In addition, the spatial distributions of the nondimensional concentration (or temperature) and flow field were measured by laser-induced fluorescence (LIF) and particle image velocimetry (PIV), respectively. In the case of a circular film-cooling hole, the penetration of the coolant jet into the mainstream was suppressed by the swirling motion of the coolant. As a result, although the coolant jet was deflected in the pitch direction, the film cooling effectiveness on the wall maintained a higher value behind the cooling hole over a long range. Additionally, the kidney vortex structure disappeared. For the shaped cooling hole, the coolant jet spread wider in the spanwise direction downstream. Thus, the pitch-averaged film cooling effectiveness downstream was 50% higher than that in the nonswirling case.