Research Papers: Gas Turbines: Structures and Dynamics

Rotordynamic Force Prediction of Centrifugal Compressor Impellers Using Computational Fluid Dynamics

[+] Author and Article Information
J. Jeffrey Moore

Mechanical and Materials Engineering Division, Southwest Research Institute®, Post Office Drawer 28510, San Antonio, TX 78228-0510jeff.moore@swri.org

David L. Ransom

Mechanical and Materials Engineering Division, Southwest Research Institute®, Post Office Drawer 28510, San Antonio, TX 78228-0510david.ransom@swri.org

Flavia Viana

Mechanical and Materials Engineering Division, Southwest Research Institute®, Post Office Drawer 28510, San Antonio, TX 78228-0510flavia.viana@swri.org

J. Eng. Gas Turbines Power 133(4), 042504 (Nov 19, 2010) (10 pages) doi:10.1115/1.2900958 History: Received May 11, 2007; Revised January 03, 2008; Published November 19, 2010; Online November 19, 2010

The energy industry depends on centrifugal compressors to produce, process, reinject, and transport many different gases. Centrifugal compressors use one or more impellers to impart momentum to the flowing gas and, thereby, produce an increase in pressure through diffusion. As the operating pressure in a compressor increases, the fluid-rotor interaction at the seals and impellers become more important. Also, the new generation of megascale liquefied natural gas compressors is dependent on accurate assessment of these forces. The aerodynamic forces and cross-coupled stiffness from the impellers cannot be accurately predicted with traditional methods and must be estimated with semiempirical formulations. The result of these inaccuracies is a potential for compressor designs that can experience unexpected, dangerous, and damaging instabilities and subsynchronous vibrations. The current investigation is intended to advance the state of the art to achieve an improved, physics-based method of predicted aerodynamic destabilizing cross-coupling forces on centrifugal compressor impellers using computational fluid dynamics (CFD). CFD was employed in this study to predict the impeller-fluid interaction forces, which gives rise to the aerodynamic cross coupling. The procedure utilized in this study was developed by Moore and Palazzolo (2002, “Rotordynamic Force Prediction of Centrifugal Impeller Shroud Passages Using Computational Fluid Dynamic Techniques With Combined Primary Secondary Flow Model  ,” ASME J. Eng. Gas Turbines Power, 123, pp. 910–918), which applied the method to liquid pump impellers. Their results showed good correlation to test data. Unfortunately, no such data exist for centrifugal compressors. Therefore, in order to validate the present model, comparisons will be made to predict the instability of an industrial centrifugal compressor. A parametric CFD study is then presented leading to a new analytical expression for predicting the cross-coupled stiffness for centrifugal impellers.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Compressor impeller mesh showing sliding interfaces

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Figure 2

Unstructured grid showing prism layer

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Figure 3

Rotating reference frame transformation (ω=rotational angular velocity; Ω=whirl angular velocity; ε=eccentricity)

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Figure 4

Eccentric shroud geometry for impeller

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Figure 5

Schematic of four-stage compressor rotor

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Figure 6

Waterfall plot of compressor during factory testing

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Figure 7

Streamlines in meridional plane

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Figure 8

Impedance versus whirling frequency for Stage 3 impeller at Instability point 1

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Figure 9

Rotor beam model

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Figure 10

Unstable mode of vibration of compressor rotor

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Figure 11

Aerocross-coupling sensitivity of compressor rotor



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