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Research Papers

The Influence of Shroud and Cavity Geometry on Turbine Performance: An Experimental and Computational Study—Part I: Shroud Geometry

[+] Author and Article Information
Budimir Rosic

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

John D. Denton, Eric M. Curtis

Whittle Laboratory, Cambridge University, Cambridge CB30DY, UK

J. Turbomach 130(4), 041001 (Jun 17, 2008) (10 pages) doi:10.1115/1.2777201 History: Received June 18, 2007; Revised June 19, 2007; Published June 17, 2008

Imperfections in the turbine annulus geometry, caused by the presence of the shroud and associated cavity, have a significant influence on the aerodynamics of the main passage flow path. In this paper, the datum shroud geometry, representative of steam turbine industrial practice, was systematically varied and numerically tested. The study was carried out using a three-dimensional multiblock solver, which modeled the flow in a 1.5 stage turbine. The following geometry parameters were varied: inlet and exit cavity length, shroud overhang upstream of the rotor leading edge and downstream of the trailing edge, shroud thickness for fixed casing geometry and shroud cavity depth, and shroud cavity depth for the fixed shroud thickness. The aim of this study was to investigate the influence of the above geometric modifications on mainstream aerodynamics and to obtain a map of the possible turbine efficiency changes caused by different shroud geometries. The paper then focuses on the influence of different leakage flow fractions on the mainstream aerodynamics. This work highlighted the main mechanisms through which leakage flow affects the mainstream flow and how the two interact for different geometrical variations and leakage flow mass fractions.

Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Representation of the experimental turbine

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Figure 2

TBLOCK computational flow domain and grid details

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Figure 3

Comparison of experiment and CFD: (a) axial velocity and (b) relative yaw angle

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Figure 4

Radial velocity distribution in the exit cavity for different cavity lengths c

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Figure 5

Influence of the exit cavity length on (a) turbine performance and (b) leakage fraction

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Figure 6

Radial velocity distribution in the exit cavity for different shroud overhangs d

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Figure 7

Influence of the shroud overhang in the exit cavity on (a) turbine performance and (b) leakage fraction

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Figure 8

Radial velocity distribution in the inlet cavity for different cavity lengths ci

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Figure 9

Influence of the inlet cavity length on (a) turbine performance and (b) leakage fraction

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Figure 10

Pitchwise mass averaged relative yaw angle downstream of the rotor for different inlet cavity lengths ci

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Figure 11

Influence of the shroud overhang in the inlet cavity on (a) turbine performance and (b) leakage fraction

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Figure 12

Radial velocity distribution in the inlet and exit cavity for different shroud thicknesses s

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Figure 13

Influence of the shroud thickness s on (a) turbine performance and (b) leakage fraction

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Figure 14

Radial velocity distribution in the inlet and exit cavity for different shroud cavity depths g

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Figure 15

Influence of the shroud cavity depth g on (a) turbine performance and (b) leakage fraction

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Figure 16

Radial velocity distribution in the exit cavity for different leakage fractions

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Figure 17

Pitchwise mass averaged yaw angle upstream of Stator 2 for different leakage fractions

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Figure 18

Entropy function contours downstream of Stator 2 for different leakage fractions

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Figure 19

Pitchwise mass averaged yaw angle downstream of Stator 2 for different leakage fractions

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Figure 20

Entropy function contours downstream of the rotor for different leakage fractions

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Figure 21

Pitchwise mass averaged relative yaw angle downstream of the rotor for different leakage fractions

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Figure 22

Change in turbine efficiency with leakage fraction

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