| Bubbly oil lubrication is a kind of lubrication with bubbly oil mixture as the lubrication medium.It has excellent lubricating properties such as large bearing capacity,low frictional power consumption and large working speed range,which has application prospects widely in the field of hydrodynamic journal bearings.Therefore,the application research on the performance of bubbly oil lubricated hydrodynamic journal bearings has significant engineering value.However,the shear rate of viscosity characteristics of bubbly oil mixtures is not high enough to satisfy the needs of lubrication calculation at large shear rates,and there is no consensus on the impact of bubbly oil lubrication on bearing performance.In this paper,the viscosity and density characteristics of bubbly oil are studied at large shear rates,and the viscosity and density model of bubbly oil mixtures are constructed.Taking stepped-groove and spiral-groove thrust bearings as the research objects,the lubrication modeling of high-speed bubbly oil lubricated thrust bearings is devoted,and the theoretical analysis and experimental investigation on the static characteristics of thrust bearings are carried out systematically.The main contents of this paper are as follows:1)The study on viscosity and density characteristics of bubbly oil mixtures at high shear rates.An experimental device is developed to test the viscosity characteristics of bubbly oil mixtures at large shear rates,and the relationship between the viscosity with aeration level,temperature and shear rates is analyzed experimentally.The viscosity model at different aeration levels is established based on the least square principle.Considering the effects of surface tension and temperature on bubble state,the density model of bubbly oil mixtures is derived.2)The establishment of lubrication model for the high-speed bubbly oil lubricated hydrodynamic thrust bearings.Based on the hydrodynamic lubrication theory,considering thermal effect and centrifugal effect,Reynolds equation and energy equation with bubbly oil lubricated are derived.Combined with the viscosity and density model of mixtures,the lubrication model of high-speed bubbly oil lubricated stepped-groove and spiral-groove thrust bearings are established,and the theoretical models are solved by numerical method to obtain the static characteristics of thrust bearings.3)A test device for high-speed hydrodynamic lubrication thrust bearing is developed.The static characteristics parameters of stepped-groove and spiral-groove thrust bearings at different aeration levels and speed are tested and compared with the theoretical results,the variation rules of aeration level and speed on static characteristics of thrust bearings are analyzed,and the influence of bubbly oil lubrication on bearing performance is revealed.The results of study suggest:1)The comparison between the theoretical calculation and experimental measurement results of static characteristics of high-speed bubby oil lubricated thrust bearings shows that the lubrication theoretical model established in this paper can be used to describe its static performance variation.2)Microbubbles can decrease the viscosity and density of mixtures,and bubbly oil lubrication can reduce the static characteristics of thrust bearings,including bearing capacity,friction torque,inlet and outlet temperature difference and side flow rate.With the increase of rotational speed and external load,the decrease of oil film thickness,friction torque,inlet and outlet temperature difference and side flow rate of thrust bearing increase with the increase of aeration level.3)Both thermal effect and centrifugal effect can reduce bearing capacity of stepped-groove and spiral-groove thrust bearings.Compared with the centrifugal effect,the thermal effect has a more obvious effect on the thrust bearing performance.4)Compared with stepped-groove,spiral-groove thrust bearing has greater bearing capacity,friction torque,inlet and outlet temperature difference,but the side flow rate is smaller. |
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