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Research Papers: Gas Turbines: Industrial & Cogeneration

A Literature Review of Low Pressure Steam Turbine Exhaust Hood and Diffuser Studies

[+] Author and Article Information
Zoe Burton

e-mail: zoe.burton@durham.ac.uk

Grant L. Ingram

e-mail: g.l.ingram@durham.ac.uk

Simon Hogg

e-mail: simon.hogg@durham.ac.uk
School of Engineering and Computing Sciences,
Durham University,
South Road, Durham DH1 3LE, UK

1Corresponding author.

Contributed by the Industrial and Cogeneration Commitee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received October 26, 2012; final manuscript received January 8, 2013; published online May 22, 2013. Editor: David Wisler.

J. Eng. Gas Turbines Power 135(6), 062001 (May 22, 2013) (10 pages) Paper No: GTP-12-1424; doi: 10.1115/1.4023611 History: Received October 26, 2012; Revised January 08, 2013

This paper summarizes the findings from research studies carried out over the last 30 years, to better understand the flows in steam turbine low pressure exhaust hoods and diffusers. The work aims to highlight the areas where further study is still required. A detailed description of the flow structure is outlined and the influence of the last turbine stage and the hood geometry on loss coefficient is explored. At present, the key challenge faced is numerically modeling the three-dimensional, unsteady, transonic, wet steam exhaust hood flow given the impractically high computational power requirement. Multiple calculation simplifications to reduce the computational demand have been successfully verified with experimental data, but at present there is no ‘best-practice’ approach to reduce the computational time for routine design exercises. This paper highlights the importance of coupling the exhaust hood to the last stage steam turbine blades to capture the interaction; ensuring the total pressure and swirl angle profiles, along with the tip leakage jet are accurately applied to the diffuser inlet. The nonaxial symmetry of the exhaust hood means it is also important to model the full blade annulus. More studies have emerged modeling the wet steam and unsteady flow effects, but more work is required in this area to fully understand the impact on the flow structure.

Copyright © 2013 by ASME
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Figures

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Fig. 1

Definition of pressure recovery on the enthalpy entropy diagram

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Fig. 2

Labeled schematic of the flow structure in the exhaust hood

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Fig. 3

Important flow regions in the exhaust hood flow structure [2]

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Fig. 4

Separations within the diffuser and progression downstream (2) [2]

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Fig. 5

Separations in flow guide region, section A-A (2) [2]

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Fig. 6

Velocity contours at hood outlet [2]

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Fig. 7

Pressure contours at hood inlet [2]

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Fig. 8

Velocity vectors at section B-B (2) [21]

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Fig. 9

Diagram of the actuator disk model [4]

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Fig. 10

Diagram of the exhaust design system [21]

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Fig. 11

FFT of the unsteady total pressure on rotor pressure surface trailing edge [31]

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Fig. 12

Variation in stage efficiency with calculation methodology [28]

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Fig. 13

Comparison between calculated Cp and experimental at 2 locations [3]

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Fig. 14

Comparison of pressure distributions at rotor outlet [1,23]

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Fig. 15

Comparison of swirl angle distributions at rotor outlet [13,35]

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Fig. 16

Distribution and flow paths of moisture droplets in the exhaust hood [47]

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Fig. 17

Definition of influential geometric parameters

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Fig. 18

Area definitions in the exhaust hood [2,19]

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