Tip leakage flows are important in compressors because of their strong influence on cascade performance and stability. Since there are separations and three-dimensional shear layers in tip leakage flows, the validity of RANS is not self-evident. The objective of this paper is to evaluate the influence of a RANS turbulence model in tip leakage flows. To achieve this, both fully resolved LES and RANS are conducted under the same design conditions and Reynolds stresses and flow structures are directly compared using the resolved LES as the high-fidelity reference result. Elicited results indicate that RANS can reproduce the bulk exit flow angle and Reynolds stresses distribution in a qualitative manner. However, quantitative comparision showed that the RANS underestimate Reynolds stresses at strong shear layers, so there are differences in the exit total pressure loss and the velocity distribution of the tip leakage vortex that may affect its prediction of the vortex breakdown and rotor stall performance in the case of simulations near the stall point.

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The leakage flow across the shroud of turbine blades causes substantial aerodynamic losses as it mixes with the freestream flow within the main annulus. The present paper shows the measurement results of two different rotor sealing designs in turbo machines in combination with tangential end wall contouring. Tests are conducted at 2-stage turbine integrated in an air cycle, located at the Institute of Power Plant Technology, Steam and Gas Turbines, RWTH Aachen University. Two operating points characterized by the stage loading coefficient at design and overload conditions are analyzed. Constant section shrouded airfoils are sealed by means of labyrinth seals as well as combined labyrinth- and brush seals. The investigations show the impact of the brush seal to the efficiency and respectively to the secondary flow. The pressure level within each cavity chamber is measured, which allows the analysis of the seal’s pressure drop and the corresponding mass flow that passes through the flow path above the shroud in detail. The flow profiles in several measurement planes are recorded along the radial height of the annulus thus the thermodynamic parameters as well as the flow direction are determined precisely. Therefore the impact of the different sealing types to the main flow can be visualized. Additionally the pressure distribution of one stator vane at the second stage is measured on two radial positions to detect changes of blade loading due to the brush seal application. The investigation turns out that the leakage flow is blocked for the configuration with brush seal thus mixing effects are inhibited however rotor – stator interaction is considered. It is also shown that the reduced leakage flow supports the impact of the end wall contouring which leads to significant benefits in off design operation.

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