In recent years, due mainly to the use of very high surface speed and in some cases to the use of very low kinematic-viscosity lubricant, the occurrence of turbulence in the lubricating film has become of practical importance in lubrication problems. It is also important to investigate the thermal effects in the turbulent flow regime in case that the temperature variation in the bearing and lubricating films is significant. Moreover, the existence of cavitation region in the journal bearing requires careful specification of the boundary condition for accurate numerical analysis. This thesis proposes an algebraic Reynolds stress model for the analysis of the above turbulent lubrication problems, and carries out 3-dimensional isothermal and thermohydrodynamic(THD) analyses for finite journal bearings using various boundary conditions.
In the isothermal analysis, the static and dynamic characteristics of finite full journal bearings are analyzed with the boundary condition taking into account the occurrence of sub-cavity pressure loop immediately upstream of the cavitation region, and the influences of the boundary conditions on the bearing performances are investigated. In addition, experimental investigations are performed to measure film thickness and pressure distribution. A pressure probe and a gap sensor are embedded in the rotating shaft to obtain the continuous signal containing elastic or thermal distortions. The theoretical results are compared with the experimental data and theoretical solutions obtained by the previous studies and present experimental results. The analytical results using algebraic Reynolds stress model and vapor pressure boundary condition give best agreements with experimental data in the broad range of Reynolds number.
In the THD analysis, this thesis performs the three-dimensional analysis taking into account the variation of lubricant viscosity, heat transfer between the film and the bush, the lubricant recirculation and the flow in the cavitation zone of journal bearings. The results show that there is a significant influence of the temperature variation across and along the lubricating film on the bearing performances when the bearing is operated with high surface speeds and high viscosity lubricant, and the present analysis using algebraic Reynolds stress model is found to be most suitable to predict THD performances acculately.
The present turbulent lubrication theory can be usefully applied to the design of fluid film bearings operated in the turbulent regime.
