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Measurement and Prediction of the Dynamic Characteristics of a Large Turbine Tilting-Pad Bearing Under High Circumferential Speeds

[+] Author Affiliations
Sebastian Kukla

Ruhr University Bochum, Bochum, Germany

Thomas Hagemann, Hubert Schwarze

Technical University of Clausthal, Clausthal-Zellerfeld, Germany

Paper No. GT2013-95074, pp. V07BT30A020; 12 pages
doi:10.1115/GT2013-95074
From:
  • ASME Turbo Expo 2013: Turbine Technical Conference and Exposition
  • Volume 7B: Structures and Dynamics
  • San Antonio, Texas, USA, June 3–7, 2013
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-5527-0
  • Copyright © 2013 by ASME

abstract

The identification results for the linear dynamic coefficients of a K-C model for a large tilting-pad bearing in load between pad configuration are presented for specific bearing loads between 1.0 and 2.0 MPa and circumferential speeds of 39 m/s and 78 m/s. The bearing with a double tilting support is lubricated by spray-bars and can be described by the following specifications: Five pads, 0.23 nominal preload, 60% offset, 56° pad arc angle, 500 mm inner diameter, 350 mm pad length and 1.28 per mill relative bearing clearance. The test rig and the test procedure are described in detail. For the determination of the dynamic coefficients, a harmonic force is induced by two unbalance-vibration generators being attached to the frame of the rig. The relative movement between bearing and shaft is detected by proximity probes between bearing housing and shaft. The bearing forces are identified by measurements of the entire film pressure distribution in both circumferential and axial direction. In the post processing of the data, the dynamic force components are determined by a Fourier-analysis. This procedure is well-established for fixed-pad bearings. However, the uncertainties of its capabilities for tilting-pad bearings are investigated and discussed in this study. The theoretical analyses with the code COMBROS are based on a calculation of linear perturbations for the predicted static properties. The measurement and the calculation procedures show very good agreement for fixed-pad bearings. For a tilting-pad bearing the results differ with increasing frequency ratio and rotational speed. The experimental results show very poor frequency dependence in load direction and a very high one in the orthogonal direction. Theoretically, the influence of the frequency ratio is comparable in both planes and pretty low due to the pivot offset and the high effective preload. While good agreement for the measured and predicted K-C model can be observed at the lower rotational and vibrational frequency the correspondence becomes worse with the increase of both. The identification procedure uses the fluid film force to determine the dynamic coefficients and assumes that this is equal to the load on the bearing in every time step. The results indicate that the experimental identification is uncertain due to the elasticity of the double tilting bearing support and the initiated dynamic effects of it. An improvement of the measurement that also identifies the limitation of the current procedures as well as simplifications in the theoretical analyses are discussed.

Copyright © 2013 by ASME
Topics: Bearings , Turbines

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