Abstrakt

Water-lubricated hydrodynamic journal bearings are frequently applied as stern tube bearings due to their advantages over other bearing types. They are environmentally friendly, can operate without sealings and in conditions of low friction losses. The most popular are bearings with open axial grooves, which require, for proper operation, forced axial flow of the lubricating water. Correctly designed and operated stern tube bearings can successfully work in the fluid friction regime. The dynamic viscosity of water is relatively low compared to oil. This results in smaller minimum film thickness and lower ability to carry the load for water-lubricated bearings in comparison to oil-lubricated bearings under similar operating conditions. This is considered as a disadvantage of this bearings type. However, at the same time, the lower water viscosity limits the temperature rise in the lubricating film and reduces friction losses. For this reason, it is common practice to not include thermal effects in the theoretical analysis of water lubricated bearings and to assume an isothermal flow in the gap. On the other hand, it is known from such bearings exploitation that they can fail due to overheating, resulting in melting of polymer material of the bush. Experimental tests of water-lubricated bearings with polymeric bushes have shown that the gradual reduction of axial water flow often results in excessive temperature rise. However, this was not valid for all tested bearing materials. In this paper, an investigation of thermal effects accompanying operation of water-lubricated journal bearing is presented. For this purpose, numerical bearing model was developed using FSI (Fluid-Solid Interaction) simulation. It allowed to take into account complexity of the important phenomena for the hydrodynamic performance of the bearing, as for example: heat generation in the fluid film due to shearing, deformations of the bush or forced axial water flow. A water-lubricated bearing from theoretical investigation was also tested experimentally with the use of a full-scale test stand. Experimental investigations under limited axial water flow through the bearing revealed significant rise of the measured temperature of the bush. Measured amount of the heat generated in the bearing friction zone was much higher compared to calculated values. ture rise and enlarged heat generation.

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