Simulation of Tilting-pad Journal Bearing Equipped with Cooled Pads

Abstract

Tilting-pad journal bearings (TPJB) are widely installed in rotating machines owing to their higher stability given by negligible values of the cross-terms of dynamic coefficients if compared to full circular or elliptical oil-film journal bearings. TPJBs have also some drawbacks, like hot oil carry over, the risk of flutter in the unloaded pads and higher cost. The former leads to the increase in the temperature of the pads due to the shear stresses in the oil-film and can be reduced by adopting suitable oil nozzles and higher oil inlet flow-rates. The increase in the oil-film temperature leads to the reduction in the lubricant viscosity and, therefore, to the reduction in the oil-film thickness. Moreover, the increase in the pad temperature leads to high thermal deformations of the pad that correspond to changes in the oil-film thickness due to the change in the geometry of the pads. In general, the lower the temperature in the oil-film and pads, the higher the load that can be applied. Therefore, the reduction in the temperature of the lubricant is a key aspect for oil-film bearings. For high speed machines the adoption of a cooling system for the pads can reduce the temperature issues in the bearing. The case of a TPJB with pads having internal channels for a forced circulation of an external cooling fluid will be considered and investigated in this paper and the effectiveness of the system proved by means of numerical simulations.