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Research Papers

Effects of Multiblocking and Axial Gap Distance on Performance of Partial Admission Turbines: A Numerical Analysis

[+] Author and Article Information
Narmin Baagherzadeh Hushmandi, Torsten H. Fransson

Department of Energy Technology, Royal Institute of Technology (KTH), SE 100 44, Stockholm, Sweden

J. Turbomach 133(3), 031028 (Feb 28, 2011) (9 pages) doi:10.1115/1.4002415 History: Received October 26, 2009; Revised June 03, 2010; Published February 28, 2011; Online February 28, 2011

In this paper, the effects of axial gap distance between the first stage stator and rotor blades and multiblocking on aerodynamics and performance of partial admission turbines are analyzed numerically. The selected test case is a two stage axial steam turbine with low reaction blades operating with compressed air. The multiblocking effect is studied by blocking the inlet annulus of the turbine in a single arc and in two opposing blocked arcs, each having the same admission degree. The effect of axial gap distance between the first stage stator and rotor blades is studied while varying the axial gap by 20% compared with the design gap distance. Finally, full admission turbine is modeled numerically for comparison. Performance of various computational cases showed that the first stage efficiency of the two stage partial admission turbine with double blockage was better than that of the single blockage turbine; however, the extra mixing losses of the double blockage turbine caused the efficiency to deteriorate in the downstream stage. It was shown that the two stage partial admission turbine with smaller axial gap than the design value had better efficiency of the first stage due to lower main flow and leakage flow interactions; however, the efficiency at the second stage decreased faster compared with the other cases. Numerical computations showed that the parameters, which increased the axial force of the first stage rotor wheel for the partial admission turbine, were longer blocked arc, single blocked arc, and reduced axial gap distance between the first stage stator and rotor blades.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 2

Geometry of the partial admission turbine (ε=0.524) single blocked arc (right) and two opposing blocked arcs (left)

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Figure 4

Efficiency of the two stage turbine at various partial admission configurations

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Figure 11

Static pressure contours and velocity vectors at a cross section passing the disk cavity and main flow between S1 and R1, design axial gap, ε=0.762, view upstream to downstream

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Figure 1

Axial section of the two stage turbine facility (7)

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Figure 12

Static pressure contours and velocity vectors at a cross section passing the disk cavity and main flow between S1 and R1, reduced axial gap, ε=0.762, view upstream to downstream

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Figure 3

Computational grid clipped with 45 deg angle

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Figure 13

Static pressure contours and velocity vectors at a cross section passing the disk cavity and main flow between S1 and R1, single blockage, ε=0.524, view upstream to downstream

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Figure 14

Static pressure contours and velocity vectors at a cross section passing the disk cavity and main flow between R1 and S2, single blockage, ε=0.524, view upstream to downstream

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Figure 15

Static pressure contours and velocity vectors at a cross section passing the disk cavity and main flow between S1 and R1, double blockage, ε=0.524, view upstream to downstream

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Figure 16

Static pressure contours and velocity vectors at a cross section passing the disk cavity and main flow between R1 and S2, double blockage, ε=0.524, view upstream to downstream

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Figure 17

Loss coefficient, ε=0.524 in two arcs, at a cross section downstream of R1, passing the disk cavity and main flow, view upstream to downstream

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Figure 18

Loss coefficient, ε=0.524 in one arc, at a cross section downstream of R1, passing the disk cavity and main flow, view upstream to downstream

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Figure 19

Loss coefficient, ε=0.524 in two arcs, at a cross section downstream of R2, passing the disk cavity and main flow, view upstream to downstream

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Figure 20

Loss coefficient, ε=0.524 in one arc, at a cross section downstream of R2, passing the disk cavity and main flow, view upstream to downstream

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Figure 21

Total and static pressures at cross sections 3, 4, 5, and 6 for full admission turbine

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Figure 6

Relative velocity vectors around a rotor blade at the midspan of a partial admission turbine with reduced axial gap (admitted channel)

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Figure 7

Relative velocity angles, right upstream and downstream of first stage rotor’s midspan, design axial gap

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Figure 8

Relative velocity angles, right upstream and downstream of first stage rotor’s midspan, reduced axial gap

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Figure 9

Relative velocity angles, right upstream and downstream of first stage rotor’s midspan, increased axial gap

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Figure 10

Axial force on rotor wheels in various partial admission configurations

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Figure 22

Total and static pressures at cross sections 3, 4, 5, and 6 partial admission turbine, ε=0.762, design gap

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Figure 23

Total and static pressures at cross sections 3, 4, 5, and 6, partial admission turbine

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Figure 24

Total pressure at cross sections 3, 4, 5, and 6, partial admission turbine, ε=0.524, double blocked arc

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Figure 5

Computed total to total efficiency of first stage from the two stage turbine at various admission configurations

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