ANALYSIS OF COOLING EFFECTIVENESS AND HEAT TRANSFER VARIATIONS ON THE END WALL OF A NOZZLE GUIDE VANE CAUSED BY TURBINE LEAKAGE FLOWS

Abstract

Extensive thermodynamic measurements were carried out on a vane endwall to investigate the interaction with the upstream rotor leakage flow. The experiments were performed at the low speed cascade wind tunnel (NGG) of the German Aerospace Centre (DLR), Göttingen. The investigated cascade consists of three large nozzle guide vanes. The effect of tip leakage flow was simulated by blow-off air. This was ejected through a leakage gap in the side wall closely upstream of the cascade. To investigate the different, possible constructive solutions of tip clearances, at least two different blowing directions were investigated: tangential and perpendicular to the mainstream at three different mass flow ratios. The influence of inlet turbulence was investigated too, applying an active turbulence grid in the intake. To get a realistic temperature gradient the leakage air was cooled down by a heat exchanger to adjust a distinctive temperature difference to the mainstream. The surface temperatures were detected by an infrared camera. Heat flux measurements assisted the interpretation of the resulting distributions of film-cooling effectiveness. It appeared that even for perpendicular injection a large amount of leakage air is distributed to the front area of the end wall although the secondary flow structure is amplified. The leakage air for mass flow ratios until 1.0% is visible between the 3D-separation lines of the horseshow vortices. With tangential ejection an adiabatic effectiveness of haw=0.2 at the cascade outlet was detectable. For both investigated injection directions it was possible to weaken the three dimensional vortex structures. For a further increase in resolution of the adiabatic effectiveness some examinations applying the so-called superposition method were performed.