Improving turbine blade endwall cooling using air/mist mixtures and composite ramp-groove structures

Abstract

Serrated grooves enhance the film cooling performance of turbine blades through extended lateral diffusion when the air is mixed with mist. This work proposes a novel composite structure combining an upstream ramp and a serrated trench to fully exploit the cooling capability of the air/mist mixtures. The simulations show that the film coverage of the mixtures can be significantly improved because the composite structure has an advantage over the zigzag grooves without slopes, as the kidney vortices induced by the former is smaller than the latter. As a result, the amount of coolant entrained by the vortex pair is greater than that entrained by the mainstream. Also, the influence of the eddy current formed by the proposed cooling structure on the vaporization position of the droplet is analyzed for the first time, concluding that the composite structure can better utilize the latent heat of vaporization of the droplet. The benefits are clearly seen in the blow ratios studied and the improvement is more pronounced at high blow ratios. It is also found that the cooling effectiveness is not linearly related to the ramp angle, because it is obviously affected by the droplet size and concentration, and its high value can only be reached within a certain range of ramp angles. Even under high-temperature and high-pressure conditions, the composite structure can achieve ideal cooling effectiveness at the turbine blade endwall. This work explores the turbine blade endwall cooling structures, offering novel insights into designing endwall cooling structures in new directions.