Pressure surface separation / secondary flow interaction

Streamlines passing through the separation and into the secondary flow

The interaction between the pressure surface separation and the secondary flow has also been shown to be a significant loss producing mechanism. This has been studied in a steady inflow linear cascade using a datum thin, solid profile and varying the shape of its pressure surface near the endwalls. As the inlet boundary layer and the blade inlet and outlet angles were unchanged, the variation in secondary flow loss must be the result of loss creation inside the blade passage.

Endwall streamlines for datum and test profile

Endwall streamlines partly explain why the separation / secondary flow interaction can create significant loss (figure 4). When the separation becomes smaller or is removed completely, less fluid from the separation is entrained into the secondary flow and the secondary flow becomes weaker. Simulation has predicted this behaviour well, and is currently being used to identify the exact mechanism of loss creation.

Howard Hodson and Michael Brear

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