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 coecients in comparison with the experimental results. Normally, the more flexible the pad pivot, the lower the dynamic coecients because the stiness of the pivot takes in series with the stiness and damping of the oil film. This paper investigates the influence of pivot stiness on the dynamic force coecients of two dierent 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 eect of the pivot stiness 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 stinesses 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 coecients of the two bearings obtained from the numerical simulation were compared with the experimental results. By the analysis it can be concluded that the eect of the pivot flexibility on the clearance profile, the shaft locus and on the dynamic coecients is very significant. More important, it is important to estimate the pivot stiness of each single pad using experimental measurements