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Research Papers: Flows in Complex Systems

On the Dynamic Properties of Pump Liquid Seals

[+] Author and Article Information
Alexandrina Untaroiu

Rotating Machinery and Controls
(ROMAC) Laboratory,
Mechanical and Aerospace Engineering
Department,
University of Virginia,
122 Engineer’s Way,
Charlottesville, VA 22904-4746
e-mail: au6d@virginia.edu

Vahe Hayrapetian

Division of Advanced Technology,
Pumps and Drives,
Flowserve Corporation,
2300 East Vernon Avenue,
Vernon, CA 90058

Costin D. Untaroiu

Rotating Machinery and Controls
(ROMAC) Laboratory,
Mechanical and Aerospace Engineering
Department,
University of Virginia,
122 Engineer’s Way,
Charlottesville, VA 22904-4746;
School of Biomedical Engineering and Sciences,
Virginia Polytechnic Institute and State University,
Blacksburg, VA 24060

Houston G. Wood

Rotating Machinery and Controls
(ROMAC) Laboratory,
Mechanical and Aerospace Engineering
Department,
University of Virginia,
122 Engineer's Way,
Charlottesville, VA 22904-4746

Bruno Schiavello

Division of Advanced Technology,
Pumps and Drives,
Flowserve Corporation,
1480 Valley Venter Parkway,
Bethlehem, PA 18017

James McGuire

Custom Engineered Pumps,
Flowserve Corporation,
2300 East Vernon Avenue,
Vernon, CA 90058

1Corresponding author.

Manuscript received December 13, 2011; final manuscript received December 17, 2012; published online April 8, 2013. Assoc. Editor: Edward M. Bennett.

J. Fluids Eng 135(5), 051104 (Apr 08, 2013) (10 pages) Paper No: FE-11-1492; doi: 10.1115/1.4023653 History: Received December 13, 2011; Revised December 17, 2012

Rotordynamic instability due to fluid flow in seals is a well known phenomenon that can occur in pumps as well as in steam turbines and air compressors. While analysis methods using bulk-flow equations are computationally efficient and can predict dynamic properties fairly well for short seals, they often lack accuracy in cases of seals with complex geometry or with large aspect ratios (L/D above 1.0). This paper presents the linearized rotordynamic coefficients for a liquid seal with large aspect ratio subjected to incompressible turbulent flow. The fluid-induced forces acting on the rotor are calculated by means of a three-dimensional computational fluid dynamics (3D-CFD) analysis, and are then expressed in terms of equivalent linearized stiffness, damping, and fluid inertia coefficients. For comparison, the seal dynamic coefficients were calculated using two other codes: one developed with the bulk flow method and one based on the finite difference method. The three sets of dynamic coefficients calculated in this study were used then to predict the rotor dynamic behavior of an industrial pump. These estimations were then compared to the vibration characteristic measured during the pump shop test, results indicating that the closest agreement was achieved utilizing the CFD generated coefficients. The results of rotor dynamic analysis using the coefficients derived from CFD approach, improved the prediction of both damped natural frequency and damping factor for the first mode, showing substantially smaller damping factor which is consistent with the experimentally observed instability of the rotor-bearing system. As result of continuously increasing computational power, it is believed that the CFD approach for calculating fluid excitation forces will become the standard in industry.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Schematic of a horizontal multistage pump: (a) inline and (b) back-to-back impeller configurations

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Fig. 2

2D sketch of balance drum leakage flow path including the upstream region (c = 0.305 mm, Sax= 9.95 mm)

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Fig. 3

Forces exerted on the whirling rotor in relative coordinate system

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Fig. 4

Radial fluid force components Fx and Fy monitored during simulation to ensure that convergence has been reached

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Fig. 10

Variation of fluid force components (estimated from CFD results for pressure distributions) normalized by eccentricity of rotor as function of assumed whirl speeds

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Fig. 9

Variation of (a) average pressure and (b) average fluid velocity function of axial location in the seal

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Fig. 14

Rotor normalized mode shape

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Fig. 8

Velocity distribution contour plot on axial cutplane—detail view

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Fig. 7

Pressure contour plot on axial cutplane—detail view

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Fig. 6

Contour plot of static pressure on stator surface

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Fig. 5

Balance drum CFD model

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Fig. 11

Leakage flow rate and rotordynamic coefficients function of seal aspect ratio

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Fig. 12

Campbell diagram: first and second mode frequencies

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Fig. 13

Damping versus damped natural frequency for 1× clearance condition

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Fig. 15

Rotor dynamic model: (a) undamped and (b) damped

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Fig. 16

Rotor dynamic results

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