Numerical Study Of The Water-Lubricated Journal Bearings Considering The Effects Of Cavitation

Study on the theories and applications of water lubrication, provides theory base and reference for the designs of the environmental machine and friction pairs under water lubrication. The water lubrication technology can avoid environmental pollution which caused by the lubricant oil leak, protecting our existent space, serving the building of resource economy and friendly environments society.The tribological properties of water-lubricated bearings are effected significantly by the bush material, structure, working conditions. But it is no ideal way to choose or design the bush material and the bearing structure under various working condition to make bearing have high loading capacity and low friction coefficient. By contrast with oil lubrication, the water-lubricated bearings easily turn from laminar regime into turbulent one, and the film thickness of water-lubricated bearings is thin, so the computation of the numerical thermal elastohydrodynamic lubrication (TEHL) is hard to converge. Besides, the lubricant mechanism of water-lubricated bearings has not yet made significant progress and breakthrough for water is easy to cavitation and the water-lubricated bearings is difficult to model, especially some bearings with grooves.In this thesis, considering the effect of cavitation, the computation of a water-lubricated bearing is carried out by a model based on the numerical thermal elastohydrodynamic lubrication theory, and the hydrodynamic lubrication of a water-lubricated bearing was numerical simulated in turbulent regime, and the performance of journal bearing was analysed. A brief introduction to study and its main results are as follows: Based on the Reynolds's cavitation algorithm, the equations of the thermo-hydrodynamic lubrication of journal bearings are built up, and solve these equations by multi-grid method. The effects of mechanical properties, load or rotational speed to water lubricated bearing lubricating property are researched. The water film pressure distributions, film shapes, maximal surface temperature rise, temperature rise distributions are calculated under varied elastic modulus, load or rotational speed. The results show that the low elastic modulus material is preferred in the range of load-carrying ability etc., but the high elastic modulus material are preferred by heavier loads. Improving self-lubricating properties and enhancing coefficient of heat conduction are based on the modification point of materials with the high elastic modulus.Based on Fluent, the hydrodynamic lubrication of a water-lubricated journal bearing was numerical simulated and researched in turbulent regime, in order to quest for the best turbulence model, wall treatment and cavitation model to water-lubricated journal bearing in turbulent regime. The water-lubricated journal bearing with grooves is simulated and researched and the effects of operating conditions on bearings'turbulent performance are discussed. The results show that the pressure distributions, when Schnerr and Sauer cavitation model or Zwart-Gerber-Belamri cavitation model and k–εmodel with enhanced wall treatment are used, have good agreement with existing experimental measurements. As the quantity of straight grooves in water-lubricated journal bearing increase, the load decrease, friction factor increase. Besides the eddy as great as the grooves, the grooves have some other small eddies. There are one main pressure peak and some other small separate pressure peak on the shaft neck surface. The cavitation mostly occurs on the shaft neck surface.