| Gas foil bearings(GFBs)have been applied to high speed rotational machine successfully,because they has many advantages,like high speed applicability,high efficiency,high temperature resistance and simple construction without maintenance.Except for the machines fixed firmly on the base,the application range extends to mobile platform,like aerospace and automobile fields.Therefore,the researches on rotor system supported by GFBs pursue higher speed and rotor stability,meanwhile,applicability problems should not be neglected.The GFBs use ambient air(or any process gas)as their working fluid or lubricant,which belongs to dynamic-pressure sliding bearing in theory.Because of the hydrodynamic effect,the gas film formed between rotor and bearing maintains rotor in suspension on hand,but on the other hand,it could results in instability problems similar to oil-lubricated bearing,such as fluid whirl and whip.The instabilities may restrict the development of GFBs seriously,so many scholars from domestic and overseas concentrate on solving these problems by theory and experimental methods.The research and summary of instabilities features and influence factors of rotordynamic supported by GFBs were studied in this thesis.Besides,research content also include application research on using gas foil bearing to mobile platform.Static load test and lift-off test had been conducted firstly on the original GFBs with one pad foil structure to measure the normal clearance,static structural stiffness and lift-off speed.Rotordynamic tests with different bearing clearance and rotor unbalance mass had been conducted,the recorded test data could be processed to get the waterfall plot and synchronous vibration amplitude.Basing on Jeffcott rotor model,test results had been analyzed to find the features and shortages of the rotordynamic system supported by original GFBs.For the purpose of improving the high speed stability of rotordynamic,two new GFBs,which are hybrid bump-metal mesh foil bearings(HB-MFBs)and three-pad bump foil bearing,were designed and manufactured based on the theories of increasing the damping of bearing and several pads of structure,respectively.Both static load test and lift-off test were conducted on these two new bearings to find the unique features compared to the original GFBs.Otherwise,rotordynamic experiments were also conducted with two types of bearings,benefits to rotordynamic stability of new bearing structures were studied.A test rig for changing the load of rotordynamic system by electromagnetic force were built on the base of existing rotor test rig.The electromagnetic force is considered to simulate the changing load when the rotordynamic system supported by GFBs is applied on mobile platform,which is in a deceleration or acceleration condition.Speed up-down tests with different applied loads were conducted on the rotor system supported by three types of bearings mentioned above to find the influences of loads.The variation of rotordynamic performance parameters under different conditions were studied based on the Jeffcott rotor model to find pros and cons of three types of bearings.A flexible platform were built using two pieces of sheet metal to fix and support the whole of existing rotor test rig.Impact force and exciting force with different frequencies and peak values could be applied on the whole of test rig to simulate the external effects from operating environment.Experiment results were studied to find the adaptive capacity of rotordynamic system supported by GFBs.This thesis mainly studied the rotordynamic performances supported by GFBs with many experiments,which includes stability on different speed,changing load of rotor system and external excitation from operating environment.The results can provide reference for the optimization and application of GFBs in the future. |
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