Measurements of detailed heat transfer characteristics on a high-pressure turbine vane endwall with coolant injection

Detailed heat transfer characteristics over high-pressure turbine endwall surfaces with coolant injection were experimentally studied in this paper. Heat transfer experiments were conducted in a properly scaled-up endwall model for an engine-representative oncoming flow profile with a high freestream turbulence intensity of 9.8% at an exit Reynolds number of 0.76 x 10(6) and an exit Mach number of 0.37. Cooling for the endwall was accomplished by upstream purge flow from a slot and film coolant from three axial rows of discrete film-cooling holes within the vane passage on the endwall. An engine-like coolant-to-mainstream density ratio of 1.70 was achieved by using cooled foreign gas. High-resolution measurements of the endwall heat transfer coefficients were conducted by using a steady, high-resolution infrared thermography technique based on the superposition principle for purge flow blowing ratios of 0.1-0.45 and film coolant injection blowing ratios of 1.4-3.6, respectively. In particular, the effects of the cooling geometries without blowing were considered to simulate hole blockage due to deposition. Results showed that local heat transfer coefficients near the film-cooling hole exits were significantly enhanced due to strong interactions between film coolant injection and mainstream flows, but those downstream of the slot were inhibited, somewhat, by purge flow, resulting from the suppression of purge flow on horseshoe vortex at the vane leading edge. The inhibiting effects of purge flow on the endwall heat transfer are more prominent when purge flow and the film coolant are injected simultaneously. For the discrete holes, higher coolant injection rates generate increased heat transfer levels. Because ingestion and re-injection of mainstream flows through the slot or the film-cooling holes without blowing, the presence of both cooling geometries causes heat transfer enhancement, and the enhancement by the film-cooling holes is higher than that by the slot. The detailed heat transfer measurements in this paper can provide useful thermal boundaries for an optimized endwall film-cooling design that will be investigated in a follow-up study.