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

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.

The Effect of the Pivot Stiffness on the Performances of Five-Pad Tilting Pad Bearings

“…The dynamic stiffness and damping coefficients of fluid-film journal bearings in large turbine were experimentally evaluated very early [1]. Year by year, many research projects have focused on the prediction and measurement of static and dynamic behaviors of four-pad, five-pad TPJBs in load-on-pad and load-between-pad configuration [2][3][4][5][6]. In order to obtain accurate results for static and dynamic characteristics of TPJBs, the analytical model has been improved using the measured transfer functions between the rotor and the pad motion [7,8].…”

Measured and Predicted Operating Characteristics of a Tilting-Pad Journal Bearing with Jacking-Oil Device at Hydrostatic, Hybrid, and Hydrodynamic Operation

“…It is flexible to consider different boundary conditions, and comprehensively described in [11,13,14]. The numerical implementation is validated for different applications of hydrodynamic operation in [11][12][13][14][16][17][18]].…”

“…A significant decrease of main damping coefficients compared to the initial bearing configuration is detected. Hagemann et al [11] and Kukla et al [12] consider the geometrical influence of jacking-oil pockets in their analyses without determining their specific impact on their results. In their case, the jacking-oil pockets are machined into the white metal layer, however, without a bore communicating to an outer high pressure supply system or a check valve.…”

A Theoretical Study on Frequency Effects on Tilting-Pad Journal Bearing Dynamic Coefficients

“…The theoretical analysis is based on the code COMBROS R presented earlier in [10][11][12]. The code is based on the solution of a generalized Reynolds Equation and a three dimensional thermal bearing model including shaft, film and pads.…”