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Research Papers

Design Considerations for Axial Steam Turbine Rotor Inlet Cavity Volume and Length Scale

[+] Author and Article Information
Konstantinos G. Barmpalias1

 Laboratory for Energy Conversion, Department of Mechanical and Process Engineering, ETH Zurich, Zurich CH-8092, Switzerlandkonstantinos.barmpalias@power.alstom.com

Reza S. Abhari

 Laboratory for Energy Conversion, Department of Mechanical and Process Engineering, ETH Zurich, Zurich CH-8092, Switzerland

Anestis I. Kalfas

 Department of Mechanical Engineering, Aristotle University of Thessaloniki, GR-54124 Thessaloniki, Greece

Toshio Hirano, Naoki Shibukawa

 Power and Industrial Systems Research and Development Center, Toshiba Corporation, Yokohama 230-0045, Japan

Takashi Sasaki

 Turbine Design and Assembling Department Toshiba Corporation, Yokohama 230-0045, Japan

1

Corresponding author.

J. Turbomach 134(5), 051031 (May 31, 2012) (9 pages) doi:10.1115/1.4004827 History: Received July 12, 2011; Revised July 21, 2011; Published May 31, 2012

In this paper we examine the interaction between the cavity and main flows of three different rotor cavities. For each of the three rotor cavities, the cavity inlets differ in their axial cavity lengths, which are modified by extending the upper casing stator platform. The three cavity volumes are comprised of a baseline case, along with a 14% and a 28% volume reduction relative to the baseline case. Measurements show that there is an increase in efficiency of 0.3% for the 14% cavity volume reduction case (relative to the baseline case), whereas a further volume reduction of 28% (relative to the baseline case) decreases the efficiency. Computational analysis highlights the breakup of a toroidal vortex within the cavity as the primary factor explaining the changes in efficiency. The dominant cavity vortex originally present in the baseline case firstly broken up into two smaller vortices for the 14% cavity volume reduction case and secondly, completely replaced with a strong radial jet for the 28% volume reduction case. From a design perspective, reducing the cavity volume by extending the upper casing stator platform yields improvements in efficiency provided that the cavity vortex is still present. The design considerations, analysis and the associated aerodynamics are discussed in detail within this paper.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 16

CFD predicted tip passage vortex visualized with the use of streamlines at rotor exit for (a) baseline case, (b) 14% CVR case, and (c) 28% CVR case. The streamlines originate from three planes at rotor inlet: 99%, 95% and 90% of the blade span. Upstream view.

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Figure 1

Illustration of the inlet cavity (baseline case – configuration)

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Figure 2

Extension of the upper casing stator platform by (a) 17% and (b) 34% of the cavity’s axial length

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Figure 3

Schematic diagram of the two-stage axial turbine

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Figure 4

5HP and 2-sensor FRAP measurement probes

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Figure 5

The simulation domain is bordered by the measurement planes, solid lines at stage inlet and outlet. The center line sketches the simplified fluid path without the stator hub cavity. The domain interface is indicated by the dashed line.

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Figure 6

Comparison of experiment and CFD for (a) the pitchwise mass-averaged flow yaw angle distribution and (b) the pitchwise mass-averaged axial velocity distribution at stator exit

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Figure 7

Δeff for the baseline, 14% CVR and 28% CVR. Efficiency of the baseline case with the initial cavity volume used as a reference.

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Figure 8

Experimentally measured pitchwise mass-averaged total pressure coefficient at stator exit

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Figure 9

Experimentally measured pitchwise mass-averaged flow pitch angle at rotor exit

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Figure 10

CFD simulations of the inflow for the cases (a) baseline, (b) 14% CVR, and (c) 28% CVR; and the outflow for the cases (d) baseline, (e) 14% CVR, and (f) 28% CVR. The simulations show a meridional cut on the pressure for (a), (b) and (c), and on the suction side for (d), (e) and (f) of the rotor blade. The planes are colored with radial velocity and the secondary flow vectors are projected onto them. The flow path is denoted by solid lines.

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Figure 11

Schematic of vortex bifurcation during outflow and reconnection during inflow for the 14% CVR case

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Figure 12

CFD predicted instantaneous mass fluxes at cavity inlet for (a) baseline, (b) 14% CVR case, and (c) 28% CVR case

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Figure 13

CFD predicted mass inflow peak increase relative to the baseline case, solid line, axis on the left, and nondimensionalized axial position where the maximum inflow occurs, dashed line, axis on the right

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Figure 14

CFD predicted inflow and outflow at cavity entrance for (a) baseline case, (b) 14% CVR case and (c) 28% CVR case. The cavity inlet is colored to show the radial velocity. Positive radial velocity indicates fluid moving upwards into the cavity.

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Figure 15

CFD predicted tip passage vortex at rotor exit as seen from a downstream location for (a) baseline case, (b) 14% CVR case, and (c) 28% CVR case

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