Study On Characteristics Of PZT Active Foil Bearing And Rig Of Flexible Rotor System

Gas foil bearings have been widely used due to their characteristic of,such as high speed,high efficiency,low loss and low pollution.They are considered to be ideal products to replace traditional rolling bearings and plain bearings.With the continuous development of the rotating machinery field,the requirements of the machine for the rotation speed are getting higher,but due to the existence of the continuous gas film,the bearing-rotor system is prone to sub-synchronous vibration at high speed,which reduces the stability of the system.The maximum speed of the system is largely limited.In addition,in the current rotating machinery field,most of the rotor systems work in the rigid mode of the rotor.Due to the limitation of the bending limit,the rotational speed of the rotor is difficult to further improve.Based on past experience.In order to increase the speed of the system,many test rigs use short and thick rotors,which results in a larger mass of the rotor and a higher take-off speed.The dry friction between the bearing and the rotor during the start-stop phase of the rotor will cause a larger bearing damage.In view of the above problems,this paper puts forward the concept of PZT gas foil active bearing and conducts related experimental research,and builds a flexible rotor test rig.Main tasks as follows:The concept of PZT gas foil active bearing is proposed and designed.On the basis of the foil-type gas foil bearing,the PZT active control mechanism is added to reduce the deformation of the piezoelectric piece by voltage,and the displacement of piezoelectric element is transformed by the displacement conversion element.The deformation of the sheet is transformed into the change of the film thickness,and the thickness of the film can be controlled during the experiment to realize the transition of the continuous film to the three-valve film in the gas foil bearing,thereby suppressing the subsynchronous vibration and improving the system stability.In order to obtain the optimal film thickness,the hinge structure had been designed and static simulation were carried out for the displacement conversion components in the PZT active bearing,and the film pressure distribution of the PZT active bearing was calculated.The calculation results show that when the system is at 40,000 rpm and the load is 100 N,the film lift height at the displacement conversion element of about 25 microns enables the PZT active bearing to form an effective three-lobed gas film.A PZT rotor test rig were designed and built and a series of experiments were conducted.The test rig is mainly composed of a rotor,a PZT active bearing,a radial foil bearing,a thrust bearing,an eddy current displacement sensor,a thermocouple temperature sensor,a signal acquisition system,a gas supply system,etc.,wherein the rotor is driven by a turbine,a stepped shaft,and a free end.In order to prevent axial turbulence of the rotor,a thrust plate is designed at the free end of the rotor.After the design and installation of the test rig,the rotor was subjected to multiple sets of 40000 rpm deceleration experiments,only the input voltage value of the piezoelectric piece were changed among each the experiments.After the experiment,the data is processed to obtain the waterfall chart,the analysis concludes that at the speed of 40,000 rpm,the PZT active bearing can work at 150 V to form a clear three-valve gas film,and it can effectively suppress subsynchronous vibration and greatly improve the system stability.A flexible rotor test rig equipped with gas foil bearings were designed,including: flexible rotor test rig structure design;test system design;radial gas foil bearing design;thrust gas foil bearing design;driving turbine parameter design.The cyclic loading test and the take-off test of the radial gas foil bearing are carried out.The cyclic loading test results show that the actual clearance of the bearing is too big,and the effect is eliminated by the way of the pad shim.The take-off test results show that the take-off speed of the bearing is about 8000 rpm and the process of taking-off is in good condition.After that,the stiffness characteristics and damping characteristics of the radial foil bearing are calculated,and the parameters are substituted into the bearing-rotor system for rotor dynamics analysis.The results show that the first-order bending mode of the system occurs at 30,000 rpm.Finally,the vibration characteristics of the rotor are analyzed by XL-ROTOR simulation,and the rationality of the system design is judged by the AF value.The calculation result shows that the AF value is 2.38,which meets the design requirements.