Experimental Characterization of Large Turbomachinery Tilting Pad Journal Bearings

The paper deals with the experimental characterization of different 280 mm diameter tilting pad journal bearings for turbomachines using a dedicated test rig. The test articles were a 5-pad Direct Lube Rocker Pivot bearing, a 5-pad Flooded Rocker Pivot bearing, and a 4-pad Flooded Ball and Socket Pivot bearing. The three bearings were tested in their specific design range of operating conditions. Their static and dynamic behavior was investigated as a function of different operating parameters. In particular, the assumed journal center eccentricity and pads temperature were measured, and the power loss determined as a function of angular speed for different static loads. Dynamic stiffness and damping coefficients were determined as a function of excitation frequency for different speeds and loads. The experimental results were compared showing the influence of the operating parameters, configuration, and oil supply.

Parametric Study of Flexure Pivot Bearing Induced Thermal Bow-Rotor Instability (Morton effect)

This paper investigates the journal asymmetric temperature induced thermal bow vibration of a rotor, as supported by a flexure pivot journal bearing (FPJB). Thermal bow induced vibration, known as Morton effect (ME) is caused by non-uniform viscous heating of the journal, and the resulting thermal bow often causes increasing vibration amplitudes with time-varying phase. Full FJPB's structural and thermal finite element models are developed and integrated into the flexible rotor model. The model is validated by comparing its predicted ME response with experimental results. A FPJB model, which uses predicted “equivalent” radial and tilting stiffness of the bearing is compared with the full FEM-based model. The impact of FPJB's design parameters such as web thickness, bearing material, and housing thicknesses are investigated with parametric studies. The results show that FPJB parameter values may have a major effect on the speed range of ME vibration, and its severity.

Evaluation of Stress and Fatigue of a Rail Vehicle Suspension Component

The article discusses the use of pivot bearing friction liners, made of selected materials, in railway freight wagons’ spherical centre bowls. Comparative studies on the effect of suspension dynamics on the equivalent stresses in the liner material were carried out using the finite element method and multibody simulation. The results show the magnitude and location of the highest stresses in the liner with varying input loads, friction coefficients and interacting materials. The analysis is a basis for a simulation method for predicting the fatigue life of the suspension friction liner placed in the centre bowl between the bogie frame and the vehicle body.

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

The role of the pivot flexibility in tilting-pad journal bearings (TPJBs) has become essential, particularly for bearings working at high applied load and relatively high rotor speeds. Predictions from a simple bearing model with rigid pivots show incorrect estimation of the dynamic coefficients in comparison with the experimental results. Normally, the more flexible the pad pivot, the lower the dynamic coefficients because the stiffness of the pivot takes in series with the stiffness and damping of the oil film. This paper investigates the influence of pivot stiffness on the dynamic force coefficients of two different five-pad TPJBs as a function of the applied static load and excitation frequency: rocker-backed pivot and spherical pivot bearings. In order to highlight the effect of the pivot stiffness in the spherical pivot bearing, displacement restriction components and elastic copper made shims have been used. Firstly, a thermo-elasto-hydrodynamic model for the static and dynamic characteristics of the two bearings is described. This model takes into account the flexibility of both pad and pivot. The pivot stiffnesses calculated by means of the Hertz theory and those obtained by experiments have been introduced and compared in the model. The clearance profiles of two tested bearing and the shaft center loci obtained by measurement and prediction are also shown. The dynamic coefficients of the two bearings obtained from the numerical simulation were compared with the experimental results. By the analysis it can be concluded that the effect of the pivot flexibility on the clearance profile, the shaft locus and on the dynamic coefficients is very significant. More important, it is important to estimate the pivot stiffness of each single pad using experimental measurements.

Analysis of Torsion Stiffness of Flexible Pivot Bearing with Radial Array Rectangular Section

Flexible pivot bearing, a kind of precision elastic components, can provide necessary angular displacement within limited range. The torsion stiffness of the bearing, as the most important performance specification, is studied in the paper. The analytical expression (for array numberNand) of the torsion stiffness of the flexible pivot bearing with rectangular section is deduced by using static equilibrium theory. The constituent parts and physical meaning of the expression are discussed. The accuracy and applicability of the deduced expression are investigated in comparison with other equations in references. A finite element model is built accurately. Simulation of the flexible bearing (N=4) is carried out to compare the FEM solution with that obtained by the derived expression. The results show that the deduced equation is applicable to allNradial array flexible pivot bearing with rectangular section, and the difference of the stiffness value is about 7% comparing with that calculated by simulation method.