Laminar And Turbulent Lubrication Characteristics Of Journal Bearings

With the development of economy and technology, China witnesses a rapid increase in electricity demand. Nowadays, the main sources of electric power consist of the thermal power generation and the hydroelectric generation. Hydroelectric generation has received many helps from the government, while thermal power can’t meet the requirements of the strategy of sustainable development. So far there have been many researches on the lubrication performance of journal bearings in the water turbo generator which is the core device for hydroelectric generation. As for the journal bearings in water turbo generator, water contamination into lubricants is inevitable, so it is of great significance to study oil-water mixture in lubrication. And the active design of surface textures is a new technique to improve the load capacity and stability of bearings, which is of importance to improve the performance of bearings in water turbo generator.In part 1, the industrial background on the design of journal bearings in water turbo generator were introduced, and the significance of the effects of oil-water mixture and surface texture on the lubrication of journal bearing were highlighted. The mixed viscosity models of two liquids, effects of surface texture on the lubrication and the turbulent lubrication models were reviewed and compared. The brief introduction for the main research content was given.In part 2, the relationships of viscosity, mass concentration of water and temperatures in lubricants with oil-water mixture were experimentally investigated. A mathematical model of multi-tilting-pad journal bearings in the transient thermal elastohydrodynamic lubrication (TEHD) was established. The lubrication properties of journal bearings in the lubrication with oil-water mixture were calculated by the development of the corresponding Fortran application programs. The orbit of shaft center, film thickness, film pressure and temperature in equilibrium position were analyzed respectively.In part 3. how the initial conditions, including initial load, initial rotate speed and initial temperature, influence on the transient lubrication characteristics of journal bearings from start-up to stable stage were investigated. And the effects of impact load on the film pressure, thickness and temperature were revealed. The fault causes in the start-up were also analyzed.In part 4, the active design of surface textures was used to improve the load capacity of bearings. Based on the turbulence theory, a method was developed to study the lubrication characteristics of journal bearings, and by the turbulent model, RNG κ-ε model, the corresponding Fluent application programs was developed to investigate the influences of surface texture in the bearing pads of water-lubricated journal bearings on the film pressure, load capacity and turbulent characteristics. Furthermore, effects of shape, location, multi-scale and size of surface textures on the turbulent lubrication characteristics of bearing were studied.In part 5, a new emulsion of oil-water mixture was established by UDF in Fluent. The physical properties of this new emulsion were based on the water-in-oil emulsion in part 1, and they were applied in the turbulent model proposed in part 4. The effects of the shape of surface texture, the speed of journal bearing and the mass fraction of water in the emulsion on the carrying capacity and turbulence characteristics of journal bearings were analyzed respectively.The final part summarized this thesis and proposed other important contents and aspects in the future.