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Research Papers

Unsteady Forces of Rotor Blades in Full and Partial Admission Turbines

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

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

J. Turbomach 133(4), 041017 (Apr 25, 2011) (12 pages) doi:10.1115/1.4002408 History: Received May 27, 2009; Revised February 10, 2010; Published April 25, 2011; Online April 25, 2011

A numerical and experimental study of partial admission in a low reaction two-stage axial air test turbine is performed in this paper. In order to model one part load configuration, corresponding to zero flow in one of the admission arcs, the inlet was blocked at one segmental arc, at the leading edge of the first stage guide vanes. Due to the unsymmetrical geometry, the full annulus of the turbine was modeled numerically. The computational domain contained the shroud and disk cavities. The full admission turbine configuration was also modeled for reference comparisons. Computed unsteady forces of the first stage rotor blades showed cyclic change both in magnitude and direction while moving around the circumference. Unsteady forces of first stage rotor blades were plotted in the frequency domain using Fourier analysis. The largest amplitudes caused by partial admission were at first and second multiples of rotational frequency due to the existence of single blockage and change in the force direction. Unsteady forces of rotating blades in a partial admission turbine could cause unexpected failures in operation; therefore, knowledge about the frequency content of the unsteady force vector and the related amplitudes is vital to the design process of partial admission turbine blades. The pressure plots showed that the nonuniformity in the static pressure field decreases considerably downstream of the second stage’s stator row, while the nonuniformity in the dynamic pressure field is still large. The numerical results between the first stage’s stator and rotor rows showed that the leakage flow leaves the blade path down into the disk cavity in the admitted sector and re-enters downstream of the blocked channel. This process compensates for the sudden pressure drop downstream of the blockage but reduces the momentum of the main flow.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Axial section of the two-stage turbine (5)

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Figure 2

Schematic diagram of rotor blade profile

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Figure 3

Computational grid for the partial admission turbine simulations (extended inlet)

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Figure 4

Computational grid: (a) around the blades, (b) disk cavity between S1 and R1, (c) first stage shroud, and (d) complete grid clipped with 45 deg arc (short inlet)

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Figure 5

Computed tangential forces of first stage rotor blades in full admission

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Figure 6

Tangential forces of first stage rotor blades at full admission in frequency domain

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Figure 7

Computed axial forces of first stage rotor blades at full admission

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Figure 8

Axial forces of first stage rotor blades at full admission in frequency domain

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Figure 9

Computed tangential forces of first stage rotor blades at partial admission

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Figure 10

Tangential forces of first stage rotor blades in partial admission in frequency domain

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Figure 11

Computed axial forces of first stage rotor blades at partial admission

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Figure 12

Axial forces of first stage rotor blades in partial admission in frequency domain

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Figure 13

Computed and measured torque on the rotor shaft of the partial admission turbine

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Figure 14

Static pressure at cross section 3

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Figure 15

Computed total pressure at section 3

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Figure 16

Total pressure at first stage stator trailing edge

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Figure 17

Static pressure at cross section 4

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Figure 18

Total pressure at cross section 4

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Figure 19

Static pressure contours and velocity vectors at a cross section passing the cavity between S1 and R1 (view: upstream to downstream)

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Figure 20

Static pressure contours and velocity vectors at a cross section passing the cavity between R1 and S2 (view: upstream to downstream)

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Figure 21

Static pressure at cross section 5

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Figure 22

Total pressure at cross section 5

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Figure 23

Static pressure contours and velocity vectors at a cross section passing the cavity between S2 and R2 (view: upstream to downstream)

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Figure 24

Static pressure contours and velocity vectors at a cross section passing the cavity between R2 and Ex (view: upstream to downstream)

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Figure 25

Static pressure at cross section 6

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Figure 26

Total pressure at cross section 6

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Figure 27

Computational grid of the two-stage partial admission turbine without leakage flow modeling

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Figure 28

Static pressure at cross section 3 (simple-3D model and experimental data)

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Figure 29

Static pressure at cross section 4 (simple-3D model and experimental data)

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Figure 30

Static pressure at cross section 2

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Figure 31

Total pressure at cross section 2

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Figure 32

Static pressure at casing of cross section 4

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Figure 33

Static pressure at hub of cross section 4

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