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Research Papers: Gas Turbines: Structures and Dynamics

Static and Dynamic Characteristics for a Pressure-Dam Bearing

[+] Author and Article Information
Bader Al-Jughaiman

 Saudi Aramco, Dhahran 31311, Saudi Arabiabader.jughaiman@aramco.com

Dara Childs

 Texas A&M University, College Station, TX 77843-3123dchilds@tamu.edu

J. Eng. Gas Turbines Power 130(5), 052501 (Jun 05, 2008) (7 pages) doi:10.1115/1.2906173 History: Received October 22, 2007; Revised November 06, 2007; Published June 05, 2008

Measured rotordynamic force coefficients (stiffness, damping, and added mass) and static characteristics (eccentricity and attitude angle) of a pressure-dam bearing are presented and compared to predictions from a Reynolds-equation model, using an isothermal and isoviscous laminar analysis. The bearing’s groove dimensions are close to the optimum predictions of Nicholas and Allaire (1980, “Analysis of Step Journal Bearings-Infinite Length and Stability  ,” ASLE Trans., 22, pp. 197–207) and are consistent with current field applications. Test conditions include four shaft speeds (4000rpm, 6000rpm, 8000rpm, and 10000rpm) and bearing unit loads from 0kPato1034kPa(150psi). Laminar flow was produced for all test conditions. A finite-element algorithm was used to generate solutions to the Reynolds-equation model. Excellent agreement was found between predictions and measurements for the eccentricity ratio and attitude angles. Predictions of stiffness and damping coefficients are in reasonable agreement with measurements. However, experimental results show that the bearing has significant added mass of about 60kg at no-load conditions, versus zero mass for predictions from the Reynolds-equation model and 40kg using Reinhardt and Lund’s (1975, “The Influence of Fluid Inertia on the Dynamic Properties of Journal Bearings  ,” ASME J. Lubr. Technol., 97, pp. 159–167) extended Reynolds-equation model for a plain journal bearing. The added mass quickly drops to zero as the load increases. Measured results also show a whirl frequency ratio near 0.36 at no-load conditions; however, a zero whirl frequency ratio was obtained at all loaded conditions, indicating an inherently stable bearing from a rotordynamics viewpoint.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic view of pressure-dam bearing after Ref. 3

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Figure 2

Test rig cross section

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Figure 3

Eccentricity ratio versus load

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Figure 4

Attitude angle versus load

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Figure 5

(a) Stiffness coefficients versus load; (b) stiffness coefficients versus load

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Figure 6

(a) Damping coefficients versus load; (b) damping coefficients versus load; (c) damping coefficients versus load; (d) damping coefficients versus load

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Figure 7

Added-mass coefficients versus load

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