The leakage flow in a 2-D stationary stepped labyrinth seal is investigated by means of flow visualization, pressure field measurements, and Particle Image Velocimetry. The basis of investigation is a generic stepped labyrinth seal currently used by the industry in steam turbine generators. Geometric and flow parameters were varied in order to examine their influence on leakage through seals. Flow visualization results revealed inter-related mechanisms of energy loss in labyrinth seals to include turbulence induced viscous losses, chamber vortex generation, flow stagnation, and increased flow streamline curvature. A five times scale model was constructed and tested over a range of seal pressure ratios from 1:1 to 10:1. Model configurations included a baseline and six variants of the basic design that were conceptually devised to be superior and by varying step height and knife angle. Detail pressure and velocity measurements were carried out. Results show that with relatively minor changes in geometry, determined based on our understanding of the physics of the flow, leakage reductions of up to 17% were accomplished.

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