FLOW THROUGH A STEAM TURBINE CASCADE WITH A SINGLE DAMAGED BLADE: EFFECT OF BLADE HEIGHT ON LOSS AND OUTFLOW ANGLE DISTRIBUTION

Flow measurements were made in a steam turbine cascade with a single blade of reduced height modeling a blade damage. In the experiments, the height of the single blade varied from full span (i.e., no tip clearance) up to totally removing the blade. The experimental investigation was supported by computational fluid dynamics (CFD) simulations which enabled further insight into local flow phenomena and mechanisms. It was found that the additional loss due to a gap increased strongly for the usual clearance level of a few percent of the blade chord but reached a relatively stable high loss plateau for higher clearances or rudimentary blades in the cascade flow channel. The tip-leakage vortex remained to be the dominant downstream flow feature and contains a high amount of loss, but for rudimentary blades, it transforms to the vortex pattern also observed for finite wings. Regarding the impact on the outflow angle distribution, the local downstream flow field can be interpreted by using the relations for cascades with high and low solidity.