0
Research Papers: Gas Turbines: Structures and Dynamics

The Impact of Pad Flexibility on the Rotordynamic Coefficients of Tilting-Pad Journal Bearings

[+] Author and Article Information
Jennifer E. Gaines

Sulzer Turbo Services,
La Porte, TX 77571
e-mail: gainesje@gmail.com

Dara W. Childs

Leland T. Jordan Professor of
Mechanical Engineering Department,
Texas A&M University,
College Station, TX 77840
e-mail: dchilds@turbo-lab.tamu.edu

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 4, 2015; final manuscript received October 23, 2015; published online February 23, 2016. Editor: David Wisler.

J. Eng. Gas Turbines Power 138(8), 082501 (Feb 23, 2016) (12 pages) Paper No: GTP-15-1394; doi: 10.1115/1.4032334 History: Received August 04, 2015; Revised October 23, 2015

Static and dynamic load tests were performed on a three-pad, rocker-pivot, tilting-pad journal bearing (TPJB) with three interchangeable pad configurations, each with measurably different pad flexibilities. Measured dynamic-stiffness data for the bearing were readily fitted by a frequency-independent, constant-coefficient [K][C][M] model. The test-bearing had a 101.74 mm diameter with L/D = 0.6. Tests were conducted over the speed range of 6–12 krpm, with unit loads varying from 0.172 to 1.724 MPa. An ISO VG 46 lubricant was used as the test fluid. Pad flexibility was characterized as the change in the pad's bending stiffness or the change in pad thickness. A finite-element model (FEM) was created to predict the structural bending stiffness of each pad configuration, showing a significant pad flexibility increase as pad thickness decreased. To examine the effect of pad flexibility on the rotordynamic coefficients, the measured results were compared across pad configurations and showed that the pad flexibility increase reduced the direct damping coefficients by 12–20%. As pad flexibility increased, the direct-stiffness coefficients could increase or decrease, depending on the unit load. They varied from an increase of 12% at low unit loads to a decrease of 3% at high unit loads. Results show that the pad's structural bending stiffness or flexibility is important when predicting the bearing’s dynamic performance. Damping is consistently overpredicted when neglecting pad flexibility. A nondimensional pad flexibility parameter αflex was developed. It related the average deflection across the pad surface to the pad's arc length and was to relate the pad flexibility of multiple bearings of different sizes. A bearing code was used to predict the percent change in direct damping coefficients for rigid-pad/flexible-pivot and flexible-pad/flexible-pivot models for a surface speed of 54 m/s and a unit load of 783 kPa for the three-pad configuration tested here plus five additional tested bearings from the literature. For the minimum pad thickness configuration tested here, the code predicted a 20% drop in predicted Cxx (off-load axis direct damping) when comparing a model that included pad flexibility with a model that neglected pad flexibility. In terms of αflex, the two thinnest pad configurations tested here are quite flexible compared to both TPJB's pads used in industry and previously tested TPJB pads.

Copyright © 2016 by ASME
Your Session has timed out. Please sign back in to continue.

References

Lund, J. W. , 1964, “ Spring and Damping Coefficients for the Tilting-Pad Journal Bearing,” ASLE Trans., 7(4), pp. 342–352. [CrossRef]
Nilsson, L. , 1978, “ The Influence of Bearing Flexibility on the Dynamic Performance of Radial Oil-Film Bearings,” 5th Leeds-Lyon Symposium on Tribology, Vol. 5, Lyon, France, pp. 311–319.
Hashimoto, H. , Wada, S. , and Marukawa, T. , 1985, “ Performance Characteristics of Large Scale Tilting-Pad Journal Bearings,” Bull. JSME, 28(242), pp. 1761–1767. [CrossRef]
Ettles, C. M. , 1980, “ The Analysis and Performance of Pivoted Pad Journal Bearings Considering Thermal and Elastic Effects,” ASME J. Lubr. Technol., 102(2), pp. 182–192. [CrossRef]
Malcher, L. , 1975, “ Die Federungs und Dampfungseigenschaften von Gleitlagern fur Turbomaschinen,” Dipl.-Ing. Thesis, Karlsruhe Technische Hochschule, Karlsruhe, Germany.
Klummp, R. , 1975, “ Beitrag zur Theoric von Kippsegment-Radiallagern,” Dissertation, Karlsruhe Technische Hochschule, Karlsruhe, Germany.
Lund, J. W. , and Pedersen, L. B. , 1987, “ The Influence of Pad Flexibility on the Dynamic Coefficients of a Tilting Pad Journal Bearing,” ASME J. Tribol., 109(1), pp. 65–70. [CrossRef]
Brugier, D. , and Pascal, M. , 1989, “ Influence of Elastic Deformations of Turbo-Generator Tilting Pad Bearings on the Static Behavior and on the Dynamic Coefficients in Different Designs,” ASME J. Tribol., 111(2), pp. 364–371. [CrossRef]
Earles, L. , Palazzolo, A. , and Armentrout, R. , 1990, “ A Finite Element Approach to Pad Flexibility Effects in Tilt Pad Journal Bearings: Part I—Single Pad Analysis,” ASME J. Tribol., 112(2), pp. 169–177. [CrossRef]
Earles, L. , Palazzolo, A. , and Armentrout, R. , 1990, “ A Finite Element Approach to Pad Flexibility Effects in Tilt Pad Journal Bearings: Part II—Assembled Bearing and System Analysis,” ASME J. Tribol., 112(2), pp. 178–182. [CrossRef]
Brockwell, K. , Kleinbub, D. , and Dmochowski, W. , 1990, “ Measurement and Calculation of the Dynamic Operating Characteristics of the Five Shoe, Tilting Pad Journal Bearing,” Tribol. Trans., 33(4), pp. 481–492. [CrossRef]
Kim, J. , Palazzolo, A. , and Gadangi, R. , 1995, “ Dynamic Characteristics of TEHD Tilt Pad Journal Bearing Simulation Including Multiple Mode Pad Flexibility Model,” ASME J. Vib. Acoust., 117(1), pp. 123–135. [CrossRef]
Cerda Varela, A. , and Santos, I. , 2011, “ Stability Analysis of an Industrial Gas Compressor Supported by Tilting-Pad Bearings Under Different Lubrication Regimes,” ASME J. Eng. Gas Turbines Power, 134(2), p. 022504. [CrossRef]
Cerda Varela, A. , and Santos, I. , 2012, “ Performance Improvement of Tilting-Pad Journal Bearing by Means of Controllable Lubrication,” Mech. Ind., 13(1), pp. 17–32. [CrossRef]
Cerda Varela, A. , Fillon, M. , and Santos, I. , 2012, “ On the Simplification for the Thermal Modeling of Tilting-Pad Journal Bearings Under Thermoelastohydrodynamic Regime,” ASME Paper No. GT2012-68329.
Wilkes, J. C. , 2012, “ Measured and Predicted Rotor-Pad Transfer Functions for a Rocker-Pivot Tilting-Pad Journal Bearing,” Ph.D. dissertation, Mechanical Engineering, Texas A&M University, College Station, TX.
Branagan, L. , and Barrett, L. , 1988, “ Thermal Analysis of Fixed and Tilting Pad Journal Bearings Including Cross-Film Viscosity Variations and Deformations,” ROMAC Report No. 276, UVa Report No. UVA/643092/MAE88/376.
Hagemann, T. , Kukla, S. , and Schwarze, H. , 2013, “ Measurement and Prediction of the Static Operating Conditions of a Large Turbine Tilting-Pad Bearing Under High Circumferential Speeds and Heavy Loads,” ASME Paper No. GT2013-95004.
Kukla, S. , Hagemann, T. , and Schwarze, H. , 2013, “ Measurement and Prediction of the Dynamic Characteristics of a Large Turbine Tilting-Pad Bearing Under High Circumferential Speeds,” ASME Paper No. GT2013-95074.
Kaul, A. , 1999, “ Design and Development of a Test Setup for the Experimental Determination of the Rotordynamic and Leakage Characteristics of Annular Bushing Oil Seals,” M.S. thesis, Mechanical Engineering, Texas A&M University, College Station, TX.
Glienicke, J. , 1966, “ Experimental Investigation of Stiffness and Damping Coefficients of Turbine Bearings and Their Application to Instability Predictions,” Proc. Inst. Mech. Eng., 181(2), pp. 116–129.
Kulhanek, C. , 2010, “ Dynamic and Static Characteristics of a Rocker-Pivot, Tilting-Pad Bearing With 50% and 60% Offsets,” M.S. thesis, Texas A&M University, College Station, TX.
Childs, D. , and Hale, K. , 1994, “ A Test Apparatus and Facility to Identify the Rotordynamic Coefficients of High-Speed Hydrostatic Bearings,” ASME J. Tribol., 116(2), pp. 337–344. [CrossRef]
Childs, D. , Vannini, G. , and Delgado, A. , 2011, “ Tilting-Pad Bearings: Measures Frequency Characteristics of Their Rotordynamic Coefficients,” 40th Turbomachinery Symposium, Turbomachinery Laboratory, Texas A&M University, College Station, TX, pp. 33–34.
Burrows, C. R. , Sayed-Esfahani, R. , and Stanway, R. , 1981, “ A Comparison of Multifrequency Techniques for Measuring the Dynamics of Squeeze-Film Bearings,” ASME J. Lubr. Technol., 103(1), pp. 137–143.
Tao, Y. , 2012, “ A Novel Computational Model for Tilting Pad Journal Bearings With Soft Pivot Stiffnesses,” Master's thesis, Mechanical Engineering, Texas A&M University, College Station, TX.
San Andrés, L. , and Li, Y. , 2015, “ On the Effect of Pad Flexibility on the Force Performance of Tilting Pad Journal Bearings: A Guide to Benchmarking a Predictive Model,” ASME Paper No. GT2015-42776.
Gaines, J. , 2014, “ Examining the Impact of Pad Flexibility on the Rotordynamic Coefficients of Rocker-Pivot-Pad Tilting-Pad Journal Bearings,” M.S. thesis, Texas A&M University, College Station, TX.
Tschoepe, D. , 2012, “ Measurements Versus Predictions for the Static and Dynamic Characteristics of a Four-Pad Rocker-Pivot, Tilting-Pad Journal Bearing,” M.S. thesis, Texas A&M University, College Station, TX.

Figures

Grahic Jump Location
Fig. 1

Change in pad curvature due to applied moments at the leading and trailing edge of the pad, see Wilkes [16]

Grahic Jump Location
Fig. 2

Main section of the oil bearing test rig [22]

Grahic Jump Location
Fig. 3

Stator shaker–stinger arrangement as viewed from the NDE

Grahic Jump Location
Fig. 4

Bearing configuration, instrumentation attachment, and raw coordinate system viewed from the DE

Grahic Jump Location
Fig. 5

Test-bearing pads with a thickness of 8.5 mm (1), 10 mm (2), and 11.5 mm (3)

Grahic Jump Location
Fig. 6

Measured CC and HC for the pad set with thickness tp = 8.5 mm

Grahic Jump Location
Fig. 7

Measured eccentricity and uncertainty in the loaded directions (y-axis) versus unit load for three-pad thickness

Grahic Jump Location
Fig. 8

Measured attitude angle and uncertainty for the three-pad configuration

Grahic Jump Location
Fig. 9

FEA static deflection predictions for tp = 11.5 mm with a uniform pressure distribution of 689 kPa (100 psi)

Grahic Jump Location
Fig. 10

Measured Kxx (dashed) and Kyy (solid) versus pad flexibility for three shaft speeds and unit loads with uncertainty bars for all shaft speed and unit load conditions

Grahic Jump Location
Fig. 11

Measured Kxy (dashed) and Kyx (solid) versus pad flexibility for three shaft speeds and unit loads with uncertainty bars for all shaft speed and unit load conditions

Grahic Jump Location
Fig. 12

Measured Cxx (dashed) and Cyy (solid) versus pad flexibility for three shaft speeds and unit loads with uncertainty bars for all shaft speed and unit load conditions

Grahic Jump Location
Fig. 13

Measured Cxy (dashed) and Cyx (solid) versus pad flexibility for three shaft speeds and unit loads with uncertainty bars for all shaft speed and unit load conditions

Grahic Jump Location
Fig. 14

Measured Mxx (dashed) and Myy (solid) versus pad flexibility for three shaft speeds and unit loads with uncertainty bars for all shaft speed and unit load conditions

Grahic Jump Location
Fig. 15

Measured Mxy (dashed) and Myx (solid) versus pad flexibility for three shaft speeds and unit loads with uncertainty bars for all shaft speed and unit load conditions

Grahic Jump Location
Fig. 16

Schematic of pad flexibility and parameters

Grahic Jump Location
Fig. 17

Percent change in predicted Cxx and Cyy versus the nondimensional pad flexibility parameter, αflex

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In