Experimental Study On Influence Of Support Structure And Film Thickness On Performance Of Radial Gas Foil Bearings

Gas foil bearing(GFB)is one kind of active gas bearing which uses the ambient air as the lubrication medium.Compared with conventional oil bearing,GFB does not require the lubrication system,so the GFB's structure is much simpler than the oil bearing.Air foil bearing is not in direct contact with the rotor during operation,so GFB can have a higher speed and operate at higher temperatures.Researchers did a lot of research on GFB and applied GFB into air compressor,air cycle machine,micro gas turbine,turbo expander and micro turbojet engine and so on.The GFB consists of three parts: bearing sleeve,support structure and top foil.The support structure provides stiffness and damping coefficients for the bearing.The top foil is directly in contact with the rotor.So the clearance between the bearing and the rotor is also the clearance between the top foil and the rotor.In this thesis,in order to study the influence of the support structure on the bearing performance,experimental tests were performed on the GFB and the hybrid metal mesh bearing(HB-MFB).In order to study the influence of the clearance between the bearing and the rotor on the performance of the bearing,experimental tests were performed on the active bump-type foil bearing(ABFB).A high-speed motor spindle was used as the power source for the test rig.Push-pull load tests and impact load tests were conducted on both GFB and HB-MFB when the bearings are both on stationary and lift-off conditions.From the push-pull load tests,the hysteresis loop of the bearing and the clearance between the bearing and the rotor can be measured.From the impact load tests,the stiffness and damping coefficients of the bearing can be measured as a function of frequency.Push-pull load tests verifies the change of clearance value of ABFB.And conducting the lift-off tests under different bearing clearances to measure the bearing lift-off speed and lift-off torque.The stiffness and damping of GFB and HB-MFBs were compared to discuss the influence of support structure with different structures on bearing performance.The results of push-pull and impact load tests on HB-MFBs with different density of metal mesh blocks were compared at different speeds to discuss the influence of metal mesh blocks with different density on the bearing performance and the influence of rotor rotating speed on bearing performance.In addition,the lift-off speed and the lift-off torque of the ABFB with different bearing clearance were compared to discuss the influence of the clearance value between bearing and rotor on bearing performance.