Low Pressure Turbine Pressure Side Separation Bubbles

Linear cascade investigation

Smoke wire visualisation at cruise Reynolds number and negative incidence

The behaviour of these separations has been studied in detail in a steady inflow, linear cascade. This has revealed a number of interesting phenomena and suggests that these separations behave in a manner that is similar to leading edge separations on axial compressor blades (figure 2). In particular, the behaviour of the pressure surface separation is strongly dependent on incidence; as incidence is reduced the bubble size increases in size, tends to transition more violently and produces more loss. The instability mechanisms leading to transition also appear to vary with incidence. Press here to view an animation of the above figure.

An animation of the interaction of a wake with the separation bubble is also available

Current research is extending this study by including simulated wake passing. Preliminary results suggest that while wakes modulate the overall behaviour of the separation, the loss produced by the separation is not significantly altered.

Howard Hodson and Michael Brear

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