Analysis of oil shedding and ligaments formation on bearing rotary elements

For designing efficient lubrication system of an aeroengine bearing chamber,sufficient knowledge on oil/air two-phase flow characteristics is required.When analyzing bearing chamber two-phase flow,the essential prerequisite is quantifying the oil ligaments,which are detached from bearing rotary elements and shed into the bearing chamber.Related investigations are mainly targeted at liquid shedding on the rotating disk as opposed to the bearing rotary elements.Moreover,the research based on bearing rotary elements is conducted by experiment.Due to the limited operating conditions,experimental studies cannot guide engineering applications.To overcome these limitations,a theoretical model is established in this paper,for revealing the mechanism of oil shedding from bearing rotary elements and quantifying the shedding ligaments.The theoretical model is validated against experimental results from classical studies.In addition,the correlation for shedding ligaments number based on aeroengine bearing structural and operational parameters is obtained via theoretical analysis.The analytical results demonstrate that oil shedding and ligaments formation appear at the edge of bearing inner race outer-periphery.The number of shedding ligaments increases with the rise of shaft rotational speed while decreases with the growth of oil viscosity.

A 3D CFD simulation of oil spray-collection and delivery process in an aeroengine inter-shaft bearing

Under-race lubrication applied to the inter-shaft bearing of aeroengine is characterized by spray oil collection and oil delivery to the bearing via flow-path structure. Droplet splashing induced by the collision between spray oil and the scoop as well as oil flowing characteristics in the flow-path influence bearing lubrication efficiency. In previous investigations, the spray oil collection and oil delivery analysis were separated, and the effect of droplet splashing on bearing lubrication efficiency was not considered. Moreover, time-varying characteristics of oil delivered to the bearing were not accounted for. This is caused by time variations of the circumferential position of rollers and under-race feed holes. To overcome these limitations, a numerical model which integrates the spray oil collection and oil delivery analysis is proposed in this paper. The model is embedded with the function of calculating the flow rate of splashing droplets and analyzing time-varying characteristics of the oil fed to the bearing. Furthermore, the numerical model is validated by experimental investigation. The proposed numerical model facilitates the accurate calculation of bearing lubrication efficiency as well as the design of an efficient lubrication structure.