Investigation of cooled pads for tilting-pad bearings

Several rotating machines are nowadays equipped with both thrust and journal tilting-pad bearings. The maximum temperature in the pads is critical for applications running at high speeds and loads, where significant temperatures can originate, due to shear stresses in the oil-film or by the surroundings. In these cases, the minimum oil-film thickness and the pad thermal crowning must be considered. Leading edge groove bearings can partially solve the problem by controlling the oil inlet temperature in the shoes. Other attempts to reduce the bearing temperature can be found in several industrial bearings and are mainly focused on the nozzles of the oil inlet. Another approach for the reduction of the heat generated in the lubricant fluid, is based on the use of suitable cooling circuits inside the pads, where the pads are cooled by an external cooling fluid. This method can be applied both to the pads of tilting-pad thrust bearings (axial load) and tilting-pad journal bearings (radial load). The cooling circuit among consecutive pads of the bearing can be also optimized considering for the temperature distribution in the bearing. Furthermore, the same oil used for the lubrication process can be used as cooling fluid. Because rotating machines are already equipped with an external cooling system for the lubricant fluid, negligible modifications in the machine layout can be required for the installation of this kind of pads, if the same lubricating oil is used as cooling fluid. Conversely, a more suitable and efficient cooling fluid can be adopted. The manufacturing issues of the cooling channels inside the pad, can be solved with the additive manufacturing technology. In the paper, the results of numerical simulations for a cooled pad bearing will be described. Several paths and cross sections of the cooling circuit will be investigated by means of computational fluid dynamics (CFD) simulation allowing the maximum temperature reduction to be obtained.