Numerical investigation for characteristics and oil–air distributions of oil film in a tilting-pad journal bearing

Abstract

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.

A new gaseous cavitation model in a tilting-pad journal bearing

“…Under different static loads, the pads in the tilting-pad journal bearing tilt around the pivots because of moments. Taking the previous flow simulation results [28][29][30][31][32] into consideration, the moments normal to the rotational direction is negligible and the moment in the rotational direction is predominant. Thus, to simplify the simulation, only the moment and tilt in the rotational direction is taken into consideration.…”

“…Apart from the pad motions, the rotor motions should also be taken into consideration in various static loads. According to the previous simulation results, [28][29][30][31][32] the force on rotor is almost in the load direction and equals to the difference between the lubricant force on rotor and the rotor load. As the rotor motion is caused by the force on the rotor, only the rotor motion and force in the load direction are taken into consideration.…”

“…[22][23][24][25][26][27] Apart from these models, researchers also developed an equilibrium gaseous cavitation model for bearings. [28][29][30][31][32][33] However, the equilibrium model do not consider the non-equilibrium process between cavitation and dissolution in the real physical gaseous cavitation. What is more, the air backflow is also not considered in the original equilibrium model.…”

“…Based on the gaseous cavitation rate equation and Bunsen solubility, the present work develops a new gaseous cavitation model and applies it in a THD simulation of a tilting-pad journal bearing under a high 299 kN load. 13 According to the previous researches, 17,[31][32][33][34] the SST model with low-Re correction and air backflow from the bearing outlets is applied for simulations and comparisons between the equilibrium model and the new model. This work includes seven sections.…”

“… 22 – 27 Apart from these models, researchers also developed an equilibrium gaseous cavitation model for bearings. 28 – 33 …”