Numerical Investigation for Characteristics and Oil-Air Distributions of a Tilting-Pad Journal Bearing Under Different Loads

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 smallest 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 turbulent flow exists in this bearing flow. A suitable gaseous cavitation model and the SST model with low-Re correction are suitable and used in the film flow simulations. With the rotor and pads assumed to be rigid, the dynamic mesh is applied to simulate the plane motions of the rotor and the rotations of the pads. The rotor force and pad moment are calculated in each step and used for calculating the motions of the rotor and pads in the next step. Based on the simulation results under different bearing loads, the differences between the simulated smallest film thicknesses and the measured data are not more than 20 μm. It indicates that the simulation results can catch the film geometries and flows correctly. With the load increasing, the location of the simulated smallest film thickness stays in the loaded pads and the smallest thickness decrease. It leads the boundary layers of the rotor-side wall and pad-side wall to interact more and decrease the turbulence in the loaded pads under higher loads. It can be verified by the simulated lower turbulence viscosity ratio distributions in the loaded pads. In the unloaded area, the film thickness is always thick enough for turbulence to develop and the flow regime stays the same with high turbulence viscosity ratio. Thus, in the loaded pads, while the film pressure become higher with load increasing, the turbulence decreases with the film thickness decreasing, which may eventually lead the flow to change from turbulent to laminar. As for the oil-air distributions, there exists no cavitation and air backflows in the high-pressure loaded area and the loaded pads are always filled with oil under different loads. 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 higher loads, the cavitation becomes more in the unloaded pads and the flow changes sharper from the high turbulence in the unloaded area to the low turbulence in the 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.