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Research Papers: Gas Turbines: Turbomachinery

Vibration Modeling and Experimental Results of Two-Phase Twin-Screw Pump

[+] Author and Article Information
Ameen Muhammed

Artificial Lift Systems,
Baker Hughes, Inc.,
Claremore, OK 74017
e-mail: ameen.muhammed@bakerhughes.com

Dara W. Childs

Leland T. Jordan Professor of Mechanical
Engineering Turbomachinery Laboratory,
Texas A&M University,
College Station, TX 77843-3123
e-mail: dchilds@tamu.edu

1Corresponding author.

Contributed by the Turbomachinery Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 13, 2015; final manuscript received January 13, 2016; published online March 22, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(9), 092601 (Mar 22, 2016) (17 pages) Paper No: GTP-15-1448; doi: 10.1115/1.4032662 History: Received September 13, 2015; Revised January 13, 2016

In turbomachines, the transfer of energy between the rotor and the fluid does not—in theory—result in lateral forces on the rotor. In positive displacement machines, on the other hand, the transfer of energy between the moving components and the working fluid usually results in unbalanced pressure fields and forces. Muhammed and Childs (2013, “Rotordynamics of a Two-Phase Flow Twin Screw Pump,” ASME J. Eng. Gas Turbines Power, 135(6), p. 062502) developed a model to predict the dynamic forces in twin-screw pumps, showing that the helical screw shape generates hydraulic forces that oscillate at multiples of running speed. The work presented here attempts to validate the model of Muhammed and Childs (2013, “Rotordynamics of a Two-Phase Flow Twin Screw Pump,” ASME J. Eng. Gas Turbines Power, 135(6), p. 062502) using a clear-casing twin-screw pump. The pump runs in both single and multiphase conditions with exit pressure up to 300 kPa and a flow rate 0.6 l/s. The pump was instrumented with dynamic pressure probes across the axial length of the screw in two perpendicular directions to validate the dynamic model. Two proximity probes measured the dynamic rotor displacement at the outlet to validate the rotordynamics model and the hydrodynamic cyclic forces predicted by Muhammed and Childs (2013, “Rotordynamics of a Two-Phase Flow Twin Screw Pump,” ASME J. Eng. Gas Turbines Power, 135(6), p. 062502). The predictions were found to be in good agreement with the measurements. The amplitude of the dynamic pressure measurements in two perpendicular plans supported the main assumptions of the model (constant pressure inside the chambers and linear pressure drop across the screw lands). The predicted rotor orbits at the pump outlet in the middle of the rotor matched the experimental orbits closely. The spectrum of the response showed harmonics of the running speed as predicted by the model. The pump rotor's calculated critical speed was at 24.8 krpm, roughly 14 times the rotor's running speed of 1750 rpm. The measured and observed excitation frequencies extended out to nine times running speed, still well below the first critical speed. However, for longer twin-screw pumps running at higher speed, the coincidence of a higher-harmonic excitation frequency with the lightly damped first critical speed should be considered.

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References

Muhammed, A. R. A. , and Childs, D. W. , 2013, “ Rotordynamics of a Two-Phase Flow Twin Screw Pump,” ASME J. Eng. Gas Turbines Power, 135(6), p. 062502. [CrossRef]
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Figures

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Fig. 1

Twin-screw pump cut away section [2]

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Fig. 2

Clearances in twin-screw pump [3]

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Fig. 4

Screw thread terminal angle definition

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Fig. 5

Helical screw section

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Fig. 6

Circumferential and radial clearances regions and screws mating

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Fig. 7

One-dimensional axial pressure buildup

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Fig. 8

Radial clearance flow region

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Fig. 9

Radial clearance flow region (δrc exaggerated)

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Fig. 10

Opening of discharge chamber to pump outlet

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Fig. 11

Meshing line projection on the unwrapped screw geometry

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Fig. 12

Bornemann clear-casing pump

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Fig. 13

Sensors arrangement

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Fig. 14

Rotor structural model (dim. in mm)

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Fig. 15

UCS map for clear-casing pump rotor

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Fig. 16

Vertical force versus deflection from dead-weight test

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Fig. 17

Axial locations of the applied predicted dynamic forces

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Fig. 18

Single-phase measured dynamic axial pressure distribution in the horizontal ZX plane

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Fig. 19

Single-phase measured dynamic axial pressure distribution in the vertical ZY plane

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Fig. 20

Dynamic events of the horizontal discharge pressure sensor

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Fig. 21

Horizontal versus vertical measured dynamic pressure at middle sensors

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Fig. 22

Measured versus predicted single-phase dynamic pressure

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Fig. 23

Predicted dynamic force components at four axial locations of the screw section

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Fig. 24

Predicted dynamic vertical force magnitude and phase angle spectrum at axial location Z4 = 49 mm

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Fig. 25

Measured versus predicted vertical dynamic response at midspan

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Fig. 26

Measured versus predicted horizontal dynamic response at midspan

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Fig. 27

Measured versus predicted orbit at the midspan

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Fig. 28

Measured versus predicted dynamic-response spectrum at the midspan

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Fig. 29

Waterfall plot of the measured vertical response spectrum at the midspan

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Fig. 30

Measured dynamic pressure axial distribution

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Fig. 31

Horizontal dynamic pressure measurements versus predictions

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Fig. 32

Vertical dynamic pressure measurements versus predictions

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Fig. 33

Predicted vertical static force axial distribution

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Fig. 34

Vertical midspan static-deflection measurements versus predictions

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Fig. 35

Measured versus predicted response at the rotor midspan (high GVF)

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Fig. 36

Measured versus predicted orbit at the rotor midspan (high GVF)

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