Study On The Flow Pattern And Oil Scavenge Characteristics In An Aero-engine Bearing Chamber

Aero-engine bearing chamber,which is one of the important components of shaft supporting system,has an extremely complex two-phase flow status generated by the pressurized air used for sealing and the oil used for lubrication and cooling.The lubricating oil flow,heat transfer and oil scavenge of the bearing chamber have been significant to the lubricating system and even the whole aero-engine.In this paper,the corresponding basic research on the above problems is carried out to provide theoretical guidance for the lubrication and heat transfer design of bearing chamber.The transient simulation based on the VOF(volume of fluid)method of the oil/air two-phase flow was used to obtain the pressure fluctuation signal in the bearing chamber under specific working conditions.Then,the Hilbert-Huang transform was applied to analyze the spectrum characteristics of the signal and establish the correlation between the energy eigenvalue and the flow patterns.The results show that with the increase of shaft speed and air mass flow rate,the two-phase flow pattern changes from stratified flow to homogeneous flow,and the energy of pressure fluctuation transfers from low frequency band to high frequency band.Furthermore,the law changes opposite as the amount of oil increase.In order to solve the problem of oil scavenge in the bearing chamber,the amelioration of the existing scavenge sump structure was improved.The influence of the factors such as the width,depth and eccentricity of the sump on the two-phase flow and heat transfer characteristics in the bearing chamber was analyzed by taking the oil residence volume fraction,scavenge ratio and convection heat transfer coefficient of the wall as the evaluation parameters.The results indicate that as the shaft speed increases,the oil residence volume fraction and scavenge ratio decreases in general,while the wall heat exchange capacity increases.However,the oil residence volume increases in narrow sump(w=1 and w=1.5)and shallow sump(h=0.5 and h=1)at high shaft speed.When the sump width w=1.5 and depth h=2,the bearing chamber has better oil scavenge and heat transfer performance.And appropriate adjustment of the sump position can also improve the oil scavenge and heat transfer performance.Compared with the base shallow sump at high shaft speed,the bearing chamber with additional longitudinal grille has higher oil scavenge capacity,but the wall heat transfer effect is poorer than before.What‘s more,the problem of uneven distribution along the axial direction of the heat transfer can be improved by adding transverse grille.