【作者】 徐超；

【导师】 冯凯；

【作者基本信息】 湖南大学 ， 机械工程， 2019， 硕士

【摘要】 气体箔片轴承在使用过程中能够提高系统效率和转速、降低系统污染,因此得到了广泛应用。随着旋转机械朝着高功率密度方向不断的发展,机器对于转速的要求也越来越高。然而,气体箔片轴承-转子系统在高转速下产生的次同步振动和转子过临界时产生的大幅同步振动是影响系统稳定性的两大因素,极大阻碍了轴承转子系统转速的进一步提升。为了有效抑制轴承转子系统的振动,提高系统的稳定性,本文创新性地提出PZT气体箔片主动轴承,通过在气体箔片轴承基底结构中引入PZT主动控制单元,改变轴承气膜形状来有效抑制轴承转子系统在高转速下的次同步振动与转子过临界时的大幅同步振动。此外,针对目前绝大部分气体箔片轴承实验台都无法为转子提供过临界运行状态的问题,设计搭建了柔性转子实验台,为该主动轴承在转子柔性状态下系统的稳定性研究提供实验台基础。本文主要工作如下:提出了PZT气体箔片主动轴承的概念并对其结构进行设计。PZT主动轴承在传统波箔型气体箔片轴承的基底结构中引入PZT主动控制单元,通过电压控制压电片的形变,并利用位移传递与放大机构将压电片的形变转化为气膜厚度的变化。该主动控制单元可以在轴承实际工作过程中对气膜厚度进行控制,可同时实现气体箔片轴承中连续气膜向三瓣式气膜的转变与气膜形状的改变,从而抑制转子次同步振动,提高系统的稳定性。为了得到最佳调控效果,针对PZT主动轴承中的位移传递与放大机构元件进行了铰链结构设计和静力学仿真、对PZT主动轴承的气膜压力分布进行计算,计算结果表明系统在40000rpm、载荷为100N的情况下,位移转换元件处的气膜抬起高度达到25微米左右能够使PZT主动轴承形成有效的三瓣式气膜。设计搭建了PZT气体箔片主动轴承-转子系统实验台并进行转子动力学特性实验。实验台主要由转子、PZT主动轴承、径向箔片轴承、推力轴承、电涡流位移传感器、热电偶温度传感器、信号采集系统、供气系统等组成,其中转子由涡轮驱动端、阶梯轴和自由端组成,为了防止转子的轴向窜动,在转子自由端设计了推力盘。实验台设计安装完成后对转子进行了多组40000rpm的降速实验,每组实验只改变压电片的输入电压值。之后对实验数据进行处理得到瀑布图,分析结果表明:在转速为40000rpm时,PZT主动轴承在150V的电压下工作能够形成明显的三瓣式气膜,有效地抑制次同步振动,大幅度提高系统的稳定性。设计搭建了可用于PZT气体箔片主动轴承转子系统过临界运行实验的柔性转子实验台。实验台设计主要包括:柔性转子实验台结构设计、实验台测试系统设计、径向气体箔片轴承设计、推力气体箔片轴承设计、驱动涡轮的参数设计。对设计之后的径向气体箔片轴承进行循环加载实验和起飞实验,循环加载实验结果显示轴承实际间隙偏大,通过垫shim的方式消除掉这一影响,起飞实验结果显示轴承的起飞转速约在8000rpm,并且起飞状况良好。之后,计算径向箔片轴承的刚度特性、阻尼特性,并将该参数代入轴承—转子系统中进行转子动力学分析,结果表明系统的一阶弯曲模态发生在30000rpm转速下。最后利用XL-ROTOR仿真分析转子的振动特性,并通过AF值来判断系统设计的合理性,计算结果显示AF值为2.38,符合设计要求。更多还原

【Abstract】 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.更多还原