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Research Papers

Control of Shroud Leakage Loss by Reducing Circumferential Mixing

[+] Author and Article Information
Budimir Rosic

Whittle Laboratory, Cambridge University, Cambridge, CB30DY, UKbr241@cam.ac.uk

John D. Denton

Whittle Laboratory, Cambridge University, Cambridge, CB30DY, UK

J. Turbomach 130(2), 021010 (Mar 21, 2008) (7 pages) doi:10.1115/1.2750682 History: Received July 14, 2006; Revised July 14, 2006; Published March 21, 2008

Shroud leakage flow undergoes little change in the tangential velocity as it passes over the shroud. Mixing due to the difference in tangential velocity between the main stream flow and the leakage flow creates a significant proportion of the total loss associated with shroud leakage flow. The unturned leakage flow also causes negative incidence and intensifies the secondary flows in the downstream blade row. This paper describes the experimental results of a concept to turn the rotor shroud leakage flow in the direction of the main blade passage flow in order to reduce the aerodynamic mixing losses. A three-stage air model turbine with low aspect ratio blading was used in this study. A series of different stationary turning vane geometries placed into the rotor shroud exit cavity downstream of each rotor blade row was tested. A significant improvement in flow angle and loss in the downstream stator blade rows was measured together with an increase in turbine brake efficiency of 0.4 %.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of model turbine

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Figure 2

Stage geometry with open shroud cavities

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Figure 3

Shroud leakage loss mechanism breakdown (CFD)

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Figure 4

Measured Cp0 distribution downstream of the stator 3, for the configurations with open (a) and closed (b) rotor shroud cavities, and predicted distribution for the case with the clean casing end wall (c)

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Figure 5

Schematic of shroud geometry and turning vanes in shroud exit cavity

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Figure 6

Turning vanes—geometry and details

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Figure 7

Turning vanes in the shroud exit cavity

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Figure 8

Cp0 contours downstream stator 3, for different number of turning vanes in shroud exit cavity

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Figure 9

Pitchwise-averaged yaw angle downstream stator 3, for different number of turning vanes in shroud exit cavity

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Figure 10

Absolute yaw angle distribution downstream of the rotor 2 in the case with eight turning vanes

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Figure 11

Change in overall turbine efficiency for different number of turning vanes

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Figure 12

L-shape turning vanes

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Figure 13

Cp0 contours downstream stator 3, for L-shape turning vanes

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Figure 14

Pitchwise-averaged yaw angle downstream stator 3, for L-shape turning vanes

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