No abstract

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.

In this study, an experimental investigation of the influence of the applied static load and rotational speed on the behaviour of a 160-mm diameter cylindrical journal bearing with two axial grooves was conducted. The rotational speed ranged from 66 rpm to 1440 rpm, and the applied static load varied from 0 kN to 350 kN in the vertical direction. The profiles of the pressure and the oil-film thickness during the shaft rotation have been measured by one proximity probe and one pressure probe installed in the rotating shaft. Measurements of the shaft centre position, dynamic coefficients, hydrodynamic pressure, temperature distributions on the bearing, film thickness, and bearing deformation under several operating conditions are presented and discussed