Effects of simulated swirl purge flow and mid-passage gap leakage on turbine blade platform cooling and suction surface phantom cooling performance

Abstract

Effects of the coolant swirl ratio (SR) and density ratio (DR) of simulated upstream slot purge flow, which is used to simulate the rotation effect, and the mid-passage leakage blowing ratio M on the turbine blade platform cooling and suction side surface phantom cooling performance are numerically investigated using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model. Simulations with four slot injection swirl ratios (SR) of 0.4, 0.6, 0.8 and 1.0, three platform blowing ratios M of 0.5, 1.0, 1.5 and three coolant density ratios (DR) of 1.0, 1.5, 2.0 under four different mass flow ratios (MFR) that range from 0.5% to 1.25% are conducted. The calculated results indicate that at low mass flow ratio (MFR = 0.5% and 1.0%) the best and worst platform cooling performance appear at SR = 0.4 and 0.8, respectively. But at MFR = 1.25%, the swirl ratio has positive effect on the cooling effectiveness after eliminating the mainstream ingestion. In addition, the phantom cooling effectiveness also increases with the increase of the relative motion between coolant and blade with the movement of separation vortex toward suction side. With the increase of DR (changes simultaneously in slot and midpassage gap), the uncooled area near the leading edge, which is usually referred to as the hot ring, is enlarged at high swirl ratio and the platform cooling effectiveness decreases for the fore portion. Similarly, the density ratio has negative effect on the phantom cooling effectiveness for all the cases. As for the mid-passage gap, its coolant blowing ratio M has a significant impact on the downstream portion platform cooling by acting partly as an endwall fence. With the increase of blowing ratio M, the leakage coverage on the platform increases firstly and then decreases at low density ratio (DR = 1.0 and 1.5) but increases continuously at DR = 2.0. As a result, the platform cooling effectiveness reaches its highest at M = 1.0 and 1.5 for DR = 1.0 and 2.0, respectively. The phantom cooling effectiveness increases slightly when increasing M from 1.0 to 1.5, but has nearly no difference for further increasing M.