Abstract
This paper analyses the flow characteristics and oil-air distributions of oil flows in a tilting-pad journal bearing under different bearing loads. This titling-pad journal bearing is working at 3000 rpm rotation speed and its minimum film thicknesses have been measured under different loads from 180 kN to 299 kN. Based on the previous researches of this bearing under 180 kN, the gaseous cavitation and low-turbulence flow exists in this bearing flow. A suitable gaseous cavitation model and the SST model with low-Re correction are used in the film flow simulations. With the rotor and pads assumed to be rigid, the dynamic mesh and motion equations are applied to simulate the motions of the rotor and the rotations of the pads. Based on the simulation results under different bearing loads, the simulated minimum film thicknesses agrees well with the measured data. It indicates that the simulation results can catch the film geometries and flows correctly. With the load increasing, the rotor moves closer to the loaded pads and the minimum film thickness decreases. Taking the effect of boundary layers into consideration, the turbulence has a negative relationship with the film thickness and decreases in the loaded area under higher bearing load. It can be verified by the simulated lower turbulent viscosity ratio distributions in the loaded pads. In the unloaded area, both the film thickness and turbulence viscosity ratio are positively related to the bearing loads. Thus, the higher bearing load may lead the flow to be more different in the loaded and unloaded area, and the turbulence in the loaded pads may transfer to laminar in the end. As for the oil-air distributions, in the unloaded pads, with the bearing load increasing, the simulated air volume fraction increases in the unloaded pads with lower pressure. It should be caused by the higher film thickness of the unloaded pads under higher loads. In sum, the flow turbulence and cavitation process changes with the bearing load. With a higher load, the cavitation becomes more in the unloaded pads and the flow changes sharper from the high-turbulence unloaded area to the low-turbulence loaded area. As the simulation results is in good accordance with the experimental data, the SST model with low-Re correction and the gaseous cavitation model are verified to be suitable for bearing film simulations under different loads.
