Fluid film thickness in a compliant foil bearing is greatly influenced by the deflection of the bearing structure. Therefore, in order to properly model performance of a foil bearing, it is mandatory that the deflection of the compliant bearing structure due to the generated hydrodynamic pressure is determined accurately. This article proposes an easy-to-use two-dimensional model, which takes into account detailed geometry of the bump foil-top foil assembly and the interaction between bumps and which can predict the bearing deflection and stresses due to an arbitrary pressure load. The proposed model is first validated using a finite element analysis and the results available in the literature and then used to conduct a parametric study investigating the influence of bump foil geometry, the coefficient of friction between the bearing components, and the type of loading on the structural properties of the bearing. The most important parameters are also identified. The proposed analytical model is completely algebraic and can be easily implemented using any programming language, a spreadsheet, or even a calculator. The resulting solution can also be coupled with the appropriate hydrodynamic model to predict static performance of compliant foil bearings.
Fluid-structure interaction technique seems to be one of the most promising possibilities for theoretical analysis of lubrication problems. It allows coupling of different physical fields in one computational task, taking into account the interaction between them. In this article, two sets of fluid-structure interaction analyses focusing on the bearing performance evaluation are presented. One analysis was applied to a water-lubricated journal bearing and the other to a hydrodynamic thrust bearing lubricated with oil. Steady-state operation was considered in both cases. In the presented cases of fluid-structure interaction analyses, all important phenomena accompanying bearing operation are considered, e.g. lubricant flow, structure movements and their deformations as well as heat transfer in case of thrust bearing. The problems encountered during modelling are discussed in this article, as well as the results of calculations: hydrodynamic pressures, gap geometries or temperature profiles.
Hydropower industry increasingly frequently uses water lubricated bearings in turbines. This stems from the lack of negative impact of such solution on the environment. The paper presents an analysis of the influence of shaft misalignment in a turbine with water lubricated main shaft bearing on its hydrodynamic capacity. The theoretical analysis was based on the results of calculations for experimentally verified elastohydrodynamic lubrication (EHL) model. The obtained results showed impact of the stiffness of bush material and the degree of misalignment on bearing's hydrodynamic capacity.
First gas-lubricated compliant foil bearings (CFBs) were built in the 1950s. Due to their significant advantages, such as oil-free operation, good tolerance to bearing misalignment and very low maintenance, they have been penetrating the bearing applications for high speed compressors, air-cycle machines and gas turbines. The work presented here investigates a novel idea of water-lubricated compliant foil bearings, which could be used in applications where environmentally friendly lubrication is desired, for example in hydroelectric turbines or water pumps. Experimental results collected for three prototype water-lubricated foil journal bearings are presented. The tests were conducted under steady radial load and with the sliding speed varied incrementally. A sequence of design improvements is presented, with the best bearing demonstrating friction coefficient of about 0.01 at the sliding speed of about 4 m/s and the radial load of about 300 kPa. Encountered difficulties, research methodology and the testing equipment are also described.
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