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Numerical simulations are important in bearing designs and should be in accordance with real working conditions. Two details are analyzed for the numerical simulations with a three-dimensional model of a large tilting-pad journal bearing included. The first detail is the flow model of the journal bearing simulations. The shear stress transport model with low-Reynolds number correction and the laminar model are used for the bearing simulations. In comparison with the laminar model, the pressure distribution of the shear stress transport model with low-Reynolds number correction is closer to and in good accordance with the experimental data. Thus, the shear stress transport model with low-Reynolds number correction is more suitable than the laminar model for the journal bearing simulations. The second detail is the backflow material of the bearing outlet boundary. Two backflow materials, air and oil, are simulated and compared with the experimental data. While the mechanical loss of the oil backflow is much higher than the experimental data, the simulated mechanical loss of the air backflow has an acceptable difference with the experimental mechanical loss. Therefore, air is a suitable backflow material for the journal bearing simulations. In summary, shear stress transport model with low-Reynolds number correction and air backflow should be used in the journal bearing simulations for accurate bearing predictions.

With rotating machineries working at high speeds, oil flow in bearings becomes superlaminar. Under superlaminar conditions, flow exhibits between laminar and fully developed turbulence. In this study, superlaminar oil flow in an oil-lubricated tilting-pad journal bearing is analyzed through computational fluid dynamics (CFD). A three-dimensional bearing model is established. CFD results from the laminar model and 14 turbulence models are compared with experimental findings. The laminar simulation results of padside pressure are inconsistent with the experimental data. Thus, the turbulence effects on superlaminar flow should be considered. The simulated temperature and pressure distributions from the classical fully developed turbulence models cannot correctly fit the experimental data. As such, turbulence models should be corrected for superlaminar flow. However, several corrections, such as transition correction, are unsuitable. Among all the flow models, the SST model with low-Re correction exhibits the best pressure distribution and turbulence viscosity ratio. Velocity profile analysis confirms that a buffer layer plays an important role in the superlaminar boundary layer. Classical fully developed turbulence models cannot accurately predict the buffer layer, but this problem can be resolved by initiating an appropriate low-Re correction. Therefore, the SST model with low-Re correction yields suitable results for superlaminar flows in bearings.

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This paper analyzes the effects of air in the oil film of a tilting-pad journal bearing on oil–air distributions and characteristics. With a gaseous cavitation model and shear stress transport model with low-Re correction included, the air backflow from the outlet boundary is analyzed in numerical simulations of a titling-pad journal bearing at 3000 r/min rotation speed and under 180 kN load. The simulated bearing load, pressure, and mechanical loss are in good accordance with the experimental data, indicating that the simulation results of the air backflow from the outlet boundary can catch the hydrodynamic characteristics accurately. Based on the turbulence viscosity ratio analysis, the turbulence effect cannot be ignored at the high rotational speed. With the comparison between the unloaded area and the loaded area, the boundary layer and turbulent flow develops with the film thickness increasing. Based on the analyses of simulated air volume fraction and pressure distribution, the gaseous cavitation occurs around the center part of the unloaded area, following the gaseous cavitation mechanisms. The backflow air flows into the low-pressure unloaded area from the outlet boundary and has a clear interval with the air from the gaseous cavitation. The air volume fraction increases with these two air sources and affects the mixture viscosity significantly, eventually influencing the shear stress on the rotor-side wall and bearing mechanical loss.