Labyrinth seals are extensively used in turbomachinery to prevent high pressure gas from flowing into a region of low pressure. Because of thermal expansions and centrifugal forces, the actual seal clearance can vary based on engine conditions. Pressure ratio, Reynolds number, tip geometry, and seal clearance all affected the sealing performance. This paper deals with its influence on the leakage flow and heat transfer coefficient through a thirteen teeth straight through labyrinth seal. Three gaps were experimentally investigated using a stationary test rig. The experiments covered a range of Reynolds numbers between 5000 and 50000 and pressure ratios between 1.0 and 2.7. Cavity pressure measurements along the seal were also performed in order to characterize each constriction. In addition, 2D PIV measurements were made on the plane containing the seal teeth to obtain a high local resolution of the velocity distribution and the flow field within the seal. Experimental results show a strong influence of clearance on both leakage loss and heat transfer as well as on the development of the flow fields. A simplified model to calculate the leakage mass flow rate is presented and validated comparing its prediction capability with experimental data. In order to improve the agreement between numerical and experimental results a correction of published correlations is proposed.

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