This paper describes the structure of the tip clearance flow in a low speed isolated compressor rotor. Pneumatic cobra probes are radially traversed upstream and downstream of the blade row and the time averaged total pressure losses across the blade row calculated. The increase in pressure losses due to the tip clearance flow is clearly seen.

The nature of the tip losses is investigated further using a unique 3D laser transit anemometer to measure velocities and turbulence levels. A 3D representation of the resulting flow field is then constructed using the experimentally measured velocity vectors. With the aid of ‘stream particles’ released into this flow field a vortex structure is then visualised. A section through the path of this vortex assists in showing its development through the blade row.

Due to the co-location of this vortex and the total pressure losses in the passage, it is this vortex which is believed to be responsible for the excess total pressure losses in the tip region.

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