Geometry Optimization of Hybrid Tilting-Pad Journal Bearings

Radial tilting-pad bearings under hybrid lubrication conditions are industrially used in heavy horizontal machines. One single orifice is normally designed and machined in the middle of the pad. Through such an orifice pressurized lubricant is injected and the rotor-bearing system is hydrostatically lubricated during start-up and run-up conditions. Nevertheless, at a pre-defined angular velocity the hydrostatic lubrication is turned-off and the rotor-bearing system operates under hydrodynamic condition. The main focus of the present work is to investigate the feasibility of using the hydrostatic lubrication as an auxiliary mechanism to improve rotor stability and increase damping reserve of rotor-bearing systems. The geometry of the bearing, namely number of orifices, their positioning over the pad surface and their diameters, are optimized using the damping factor of the rotor-bearing system as weighting functional. The dependency of the optimal parameters on the rotor angular velocity and injection pressure (operational conditions) is discussed and the limits of an increase in damping reserve via geometry optimization are elucidated.