Study On Rotordynamic Characteristics And Experimental Verification Of Rotor System Of Oil-Free Turbocharger

Gas foil bearings(GFBs)are self-acting compliant-surface hydrodynamic bearings that using ambient air(or any process gas)as working fluid or lubricant.With GFBs,turbochargers would become oil-free,thus getting rid of the speed limitation and power loss imposed by oil lubrication,eliminating oil leakage entirely and reducing the complexity of the whole system.In this dissertation,GFBs were tried to be applied to a turbocharger,design principles and performance test procedure of oil free turbo machinery were also tried to be estabilshed.This paper presented comprehensive experimental studies on an oil-free turbocharger(TC)supported on two bump-type gas foil journal bearings(GFJBs)and a pair of bump-type gas foil thrust bearings(GFTBs).After choosing suitable GFBs and the rotordynamic performance analysis and calculation on the whole rotor system,oil-free TC bench had been built.The speed-up and coast-down tests demonstrated that the oil-free TC can operate at 68 krpm(not the top speed)stably.More importantly,this paper measured the real-time temperature of thrust bearing and radial bearing.During the period of steady speed,the temperature of thrust bearing and journal bearing fluctuated on a small scale,which means rotor-bearing system remains in a relatively stable state and also validates the feasibility of oil-free turbocharger design.In addition,the influence of different GFB types on the dynamic performance of supported rotor were also studied.Firstly,this paper compared the effects of three different types of GFJB on the rotor response.Comparing with the single top foil type GFJB,The experimental results showed that the shimmed GFJBs and the reversed double top foil GFJBs can effectively reduce the amplitude of the sub-synchronous vibration of the rotor and the onset speed of the sub-synchronous vibration.Moreover,the theoretical and experimental results of the response of different structural GFTBs to the rotor showed that the four-pad GFTB has higher bearing capacity than the six-pad GFTB and can inhibit the rotor vibration and improve the stability of the rotor system to a certain extent.Finally,experimental study on the response of the welded position of GFJBs to the rotor showed that when the welded position of GFJBs is relative to gravity direction clockwise 90° position,the synchronous and sub-synchronous amplitude of the rotor are the smallest,and the speed range of the sub-synchronous was also the smallest.