Effect of misalignment at 2nd vane endwall on heat transfer with purge flow

Abstract

Since the domestic power plants are typically operated at a partial load rather than the design point, the thermal expansion decreases, resulting in misalignment between first stage rotor and second stage stator. In this study, we investigate the heat transfer characteristics of a misalignment under purge flow at the second stage vane endwall through heat/mass transfer experiments using the naphthalene sublimation method and CFD simulations. Experiments are conducted at 4 vanes in a linear cascade with an inlet Reynolds number of 120,000, based on the vane axial chord length. In the absence of purge flow, a high heat transfer occurs in upstream of the vane endwall via horseshoe vortices. When a misalignment occurs, a more severe thermal load is observed as the mainstream attaches to the endwall due to recirculation flow upstream of the leading edge. Additionally, two high heat transfer regions are observed when a step-induced vortex occurs in the vane flow path. In case of the purge flow, the mixing of the mainstream and purge flow increases the intensity of the vortex, which increases heat transfer in the region upstream of the both flat and stepped endwall. In conclusion, we have found that the step difference has a crucial effect on thermal damage upstream of the second stage vane endwall as a little misalignment occurrence. The area-averaged heat transfer of the stepped endwall is increased by about 11.4% and 13.7% without and with purge flow, respectively, as compared to that of the flat endwall.