浮环轴向长度对高速轻载涡轮增压器转子系统振动特性影响研究

浮环轴承内外轴向长度结构参数会影响油膜压力分布与偏心率,产生显著分频振动而引发高速轻载涡轮增压器转子非线性振动故障。基于流体润滑理论和浮环力矩平衡方程,推导了含浮环轴承的涡轮增压器转子系统动力学方程,揭示浮环轴承轴向长度与转子系统振动响应之间的关系。以某型汽油机用涡轮增压器转子系统为例,分析浮环内、外轴向长度对轴承油膜压力、偏心率等动力特性的影响,构建转子系统动力学有限元模型,通过三维振动瀑布图研究不同浮环轴向长度下转子系统频域瞬态振动响应,结果表明：浮环内轴向长度从2.6增加到4.6 mm,导致浮环转速升高,最大内油膜压力减小,轴颈偏心率降低,分频幅值增加且出现分频的轴颈转速由142 kr/min降至76 kr/min,更易产生明显的非线性涡动现象;浮环外轴向长度从3.6增加到6.15 mm,使浮环转速降低,最大外油膜压力变小,浮环偏心率及轴颈相对浮环的偏心率减小,低转速下分频幅值减少且出现分频的轴颈转速由10 kr/min升至22 kr/min,可抑制转子系统过早发生非线性涡动,为浮环轴承结构参数设计与试验提供理论支撑。     

轴承径向游隙对刚性转子不平衡响应的影响研究

针对某涡轮泵拟刚性转子振动较大的问题,在考虑轴承径向游隙的情况下,建立Jeffcott转子模型,对转子的不平衡响应进行分析,研究表明:随着轴承径向游隙增大,临界转速以下的不平衡响应幅值增大,在80%临界转速处,10倍偏心距的轴承径向游隙会产生15.5倍无轴承径向游隙的不平衡响应。因此,在亚临界转速下工作时,可采用预紧装置适当减小轴承径向游隙,降低转子-支承系统的振动。加装预紧装置的试验结果表明,施加2 000 N轴向预紧力时,转速8 000 r/min以下的转子振动幅值降低40.6%,验证了理论推导的正确性。     

弹性支承箔片动压气体径向轴承的实验研究

对新型结构弹性支承箔片动压气体径向轴承进行试验研究,在高速透平膨胀机(主轴轴径D=25.0mm、转子总长l=250.5mm、转子质量Gm=891g、额定工作转速10.64×104r/min)上达到了转子转速14.8×104r/min、超速40%的良好试验效果。对这种弹性支承箔片动压气体径向轴承的振动特性和稳定性进行试验研究。结果表明,该轴承具有优良的动态特性与稳定性,能有效抑制高速自激涡动的发展,在正确选择结构参数和表面处理方法后,有望替代目前在高速透平机械中广泛应用的静压气体轴承。     

波箔气体轴承支承的转子非线性振动的研究

为提高波箔气体轴承支承的微型透平机械转子在高速运转时的稳定性,需要对由波箔轴承气膜力和箔片摩擦力引起的非线性振动进行研究。建立在轴承气膜力和箔片摩擦力共同作用下的转子局部受力模型,运用4阶变步长Runge-Kutta法计算转子在不同转速下的振动响应,观察转子升速过程中的混沌运动成分,分析转速对转子非线性动力学性能的影响。结果表明,转速变化会引起响应形态的变化,非线性振动作用在临界转速区不明显,远离临界转速区时较明显。     

基于FLUENT的涡轮增压器推力轴承特性分析

轴向推力轴承,又称为止推轴承,被广泛应用于涡轮增压器中,增压器转子系统中产生的轴向力都是由轴向推力轴承承受。本文对涡轮增压器滑动轴承模型进行基于FLUENT的全三维数值仿真分析,得到轴向推力轴承三维油膜压力、流场、温度分布。通过分析,得到了稳态下轴向推力轴承油膜压力场、温度场、流场在不同转速下的分布特点:随着转速的上升,推力轴承内部流场的峰值压力随之上升,推力轴承承载能力与滑油流量也随之上升,并且峰值压力、轴向推力以及滑油流量和转速的关系是呈等比例上升;同时对比分析了转子转速、楔形深度、最小油膜厚度等一些关键参数对轴向推力轴承性能的影响。     

储能飞轮转子轴承系统动力学设计与试验研究

飞轮储能系统通过飞轮升速和降速来实现电能储存和释放,研究飞轮转子轴承系统固有频率预计、临界转速设计、动平衡等动力学问题。采用永磁轴承与螺旋槽动压轴承的混合支承方式,建立储能飞轮强度、动力学和充放电特性试验研究装置,进行了动平衡、阻尼支承调整、飞轮储能系统损耗和发电量测试等试验,试验飞轮达到设计转速42.0 kr/min,总储能497 W·h,从42.0 kr/min降速到13.8 kr/min,可用放电能达到290 W·h。     

涡轮减重前后增压器转子动力学分析及试验

以JP60C型车用增压器涡轮叶轮为研究对象,基于有限元分析的转子动力学分析软件DyRoBeS,对减重前后的增压器转子进行了临界转速分析;采用快速成型技术加工了蜡模,浇铸了减重优化的涡轮叶轮,对装配好的增压器进行了高速动平衡试验。分析及试验结果表明,由于涡轮重量的减轻降低了转子的柔性,减重优化后的轴承-转子系统的临界转速有所降低,但其工作转速仍工作在2阶临界转速和3阶临界转速之间,涡轮减重后增压器工作转速远离转子各阶临界转速,从而说明涡轮减重优化的合理性和有效性。     

支承方式对变循环发动机转子临界转速的影响

分析某双涵道变循环发动机转子系统结构特点,建立转子-支承系统三维有限元模型,计算、分析转子支承方式的改变对转子临界转速的影响.结果表明:以低压转子为主激励,转速在20 000 r/min内,4支点支承比5支点支承临界转速多一阶,其中第一、三阶临界转速降低,第二阶升高,第四阶基本不变.5支点方式能有效地减少柔性低压转子弯曲振动模态出现,但是会增加低压风扇盘的上下偏摆振动模态,较易发生风扇叶片与机匣的碰磨.4支点方式结构更简单,但是转子系统在高转速时需要多经过一阶临界转速,会增加转子及整机的振动.     

基于ANSYS的磁悬浮轴承转子系统的动力学特性研究

针对一个实际应用的磁悬浮支承柔性转子系统,进行多组参数条件下的有限元模态分析,分别得到系统的前8阶临界转速与模态振型。将有限元计算结果与试验结果进行对比分析,验证了有限元分析的正确性。通过对该磁悬浮转子系统的有限元分析表明:"轴承主导型"的低阶临界转速及振动模态是由轴承控制器各控制通道决定的;而"转子主导型"的高阶临界转速及振动模态符合传统的轴承转子系统动力学特性普遍规律。     

径向箔片空气轴承静态特性研究

以径向箔片空气轴承静态特性为研究对象,建立箔片空气轴承弹性支承结构的力学分析模型,采用有限元分析计算轴承形变特性,得到轴承承载力和结构刚度,然后利用设计的静态特性试验台对轴承进行静态测试,测试结果与仿真计算基本一致,说明仿真计算的正确性。并将计算得到的轴承静态刚度用于某高速转子的动力学计算,得到了转子的临界转速。     

Rotordynamic Analysis of an Oil-Free Turbocharger Supported on Lobed Gas Foil Bearings—Predictions versus Test Data

This article presents the predictions of the rotordynamic performance of oil-free turbochargers (TCs) for various lobed gas foil bearings (GFBs) with the first-generation bump-type configuration and compares these predictions to the measured test data reported earlier. The three-lobed GFBs used for the simulations have increased bearing clearances and mechanical preloads with a fixed minimum bearing clearance, thus yielding larger average bearing clearances and higher wedge effects at the same time. The engine-induced TC housing excitation is found to have no influence on the critical speeds and damping ratios of the rotor rigid modes. The synchronous and asynchronous GFB analyses imply decreases in destabilizing forces for the highly lobed GFBs. The predicted critical speed and damping ratio of the TC rotor supported on the lobed GFBs demonstrate increasing system natural frequency and enhanced rotordynamic stability with increasing mechanical preload. The rotordynamic and bearing analyses of the lobed GFBs validate the beneficial effects of the mechanical preload on the rotordynamic stability of GFBs even with an increased average bearing clearance, which leads to a decreased bearing friction torque as well.     

Effect of cooling flow on thermal performance of a gas foil bearing floating on a hot rotor

This paper presents the measurements of the thermal behavior of a gas foil bearing (GFB) floating on a hot rotor in a tangential air injection cooling scheme. The cooling air was tangentially injected against rotor spinning into the inlet mixing zone of the test GFB. The hollow rotor was heated by a cartridge heater. The GFB temperatures were measured at intervals of 30 deg along the circumference of the axial center except for at 45 deg, where the cooling flow is injected. The rotor temperatures were measured near the GFB side ends using an infrared thermometer, which was calibrated with a thermocouple. Load cells measure the static load and bearing torque. The baseline rotor temperature was measured without GFB over the axial length at rotor speeds up to 15 krpm and for increasing heater temperatures up to 400 °C. The results showed relatively uniform rotor temperatures at the test journal GFB section, and severe heat convections on the rotor surfaces. The GFB and rotor temperatures were measured under a static load of 80 N for increasing heater temperatures of 100 °C, 200 °C, 300 °C and 400 °C and with increasing cooling flow rates of 100 liter/min, 150 liter/min, and 200 liter/min. The circumferential GFB temperatures showed the maximum temperatures at the loaded zone and the minimum temperatures in the unloaded zone. The increasing cooling flow effectively reduced both the rotor and GFB temperatures, showing a dramatic decrease with the smallest amount of cooling flow. GFB friction torque was measured for two test cases for the static load of 80 N at a rotor speed of 10 krpm: 1) A lift-off and touch-down operating cycle for increasing heater temperatures without the cooling flow, and 2) a continuous operation for the heater temperature of 400 °C with increasing cooling flows. In test case 1, the GFB friction torque decreased for higher heater temperatures due to a larger thermal expansion of the bearing housing than the rotor’s. In test case 2, the GFB friction torque decreased with increasing cooling flows due to strong cooling effects on the rotor temperature. The results imply that the tangential air injection increased the GFB clearance by directly cooling the rotor and effectively alleviating the rotor expansion; hence, the scheme is capable of an effective cooling for high temperature GFB applications, such as micro gas turbines.     

Nonlinear Numerical Prediction of a Rotor–Bearing System Using Damped Flexure Pivot Tilting Pad Gas Bearings

Flexure pivot tilting pad gas bearings with pad radial compliance (FPTPGB-Cs) and metal mesh dampers (MMDs) in parallel (FPTPGB-C-MMDs) have been considered for application to high-speed and high-performance turbomachinery because of their advantages of high effective damping level and adequate compliance with variations in rotor geometry or misalignment. Although the dynamic coefficients of FPTPGB-C-MMDs have been predicted using the linear method, a nonlinear study is urgently needed for their high nonlinear behavior. A nonlinear numerical investigation on the rotor–bearing system supported by FPTPGB-C-MMDs is presented in this study by using the time domain orbit simulation method that couples rotor motion equations, the unsteady Reynolds equation, and pad motion (considering MMDs) equations. The nonlinear predictions are verified by the prediction and experimental results of a published paper.FPTPGB-C-MMDs can effectively suppress the subsynchronous vibrations compared with the rotor system supported by FPTPGB-Cs. The prediction results show that a high damper mesh density has a more positive effect on improving the stability of the rotor system by reducing the subsynchronous vibrations. Investigation shows that MMDs can improve the ability of the rotor system to sustain the effect of destabilizing forces. A high damper mesh density can sustain large destabilizing forces. The simulation results also indicate that low pad radial stiffness or preload leads to high amplitudes of subsynchronous vibrations. A small clearance results in an increase in critical speed and its synchronous amplitude. Moreover, large clearance results in a wide speed range that leads to the occurrence of subsynchronous vibrations with large amplitudes.     

Analysis of gas foil bearings integrating FE top foil models

Gas foil bearings (GFBs) find widespread usage in oil-free turbo expanders, APUs, and micro gas turbines for distributed power due to their low drag friction and ability to tolerate high-level vibrations. The performance of GFBs depends largely on the support elastic structure, i.e. a smooth foil on top of bump strips. Conventional models include only the bumps as equivalent stiffnesses uniformly distributed around the bearing circumference. More complex finite element (FE) models couple the elastic deformations of the 2D shell or 1D beam-like top foil to the bump deflections as well as to the gas film hydrodynamics. Predictions of journal attitude angle and minimum film thickness for increasing static loads and two journal speeds are obtained for a GFB tested decades ago. For the GFB studied, 2D FE model predictions overestimate the minimum film thickness at the bearing centerline, while underestimating it at the bearing edges. Predictions from the 1D FE model compare best to the limited tests data, reproducing closely the experimental circumferential wavy-like film thickness profile. Predicted stiffness and damping coefficients versus excitation frequency show that the two FE models result in slightly lower direct stiffness and damping coefficients than those from the simple elastic foundation model.     

Forced nonlinear response of gas foil bearing supported rotors

Microturbomachinery implements gas foil bearings (GFBs) in oil-free compact units with reduced maintenance and lower life cycle costs. Challenges for GFBs include intermittent contact and wear at startup and shutdown, and potential for large amplitude rotor whirl at high-speed operation. Subsynchronous motions are common in FBs, though hastily attributed to hydrodynamic bearing instability. In actuality, an FB load capacity depends mainly on its support structure, which shows a strong hardening effect. Presently, an FB force is modeled as a third-order structural element with nonlinear stiffnesses derived from measurements. Predictions of the performance of a rigid rotor supported on bump-type FBs and comparisons to rotor response measurements follow. The predictions evidence a Duffing oscillator dynamic behavior with multiple frequency responses, sub- and super-harmonic, within certain ranges of rotor speed. Predicted rotor amplitudes replicate accurately the measured responses, with a main whirl frequency locked at the system natural frequency. The predictions and measurements validate the simple FB model, i.e. a minute gas film with effective infinite stiffness, with applicability to large amplitude rotordynamic motions. For the first time in the open literature, a simple physical model reproduces the richness and complexity of measured rotor–GFB motions.     

高压离心泵滑动轴承稳定性分析

分析了高压离心泵轴承的动力学模型,通过径向滑动轴承的非定常运动雷诺方程计算出油膜的八个刚度系数和阻尼系数,并以此计算出转子的综合刚度和涡动比平方,得到油膜的失稳转速,最后以高压离心泵实际结构参数进行了轴承的稳定性分析,得出转子正常工作时是安全的结论.     

Modeling and Analysis of Novel Integrated Radial Hybrid Magnetic Bearing for Magnetic Bearing Reaction Wheel

Conventional ball bearing reaction wheel used to control the attitude of spacecraft can't absorb the centrifugal force caused by imbalance of the wheel rotor,and there will be a torque spike at zero speed,which seriously influences the accuracy and stability of spacecraft attitude control.Compared with traditional ball-bearing wheel,noncontact and no lubrication are the remarkable features of the magnetic bearing reaction wheel,and which can solve the high precision problems of wheel.In general,two radial magnetic bearings are needed in magnetic bearing wheel,and the design results in a relatively large axial dimension and smaller momentum-to-mass ratios.In this paper,a new type of magnetic bearing reaction wheel(MBRW) is introduced for satellite attitude control,and a novel integrated radial hybrid magnetic bearing(RHMB) with permanent magnet bias is designed to reduce the mass and minimize the size of the MBRW,etc.The equivalent magnetic circuit model for the RHMB is presented and a solution is found.The stiffness model is also presented,including current stiffness,position negative stiffness,as well as tilting current stiffness,tilting angular position negative stiffness,force and moment equilibrium equations.The design parameters of the RHMB are given according to the requirement of the MBRW with angular momentum of 30 N ? m ? s when the rotation speed of rotor reaches to 5 kr/min.The nonlinearity of the RHMB is shown by using the characteristic curves of force-control current-position,current stiffness,position stiffness,moment-control current-angular displacement,tilting current stiffness and tilting angular position stiffness considering all the rotor position within the clearance space and the control current.The proposed research ensures the performance of the radial magnetic bearing with permanent magnet bias,and provides theory basis for design of the magnetic bearing wheel.     

动压气体轴承-转子系统稳定性分析

本文建立了普通圆柱型动压气体轴承支承的单盘转子系统模型,写出了系统的运动方程,并引用气体轴承的动力特性数值分析所得到的8个动力特性系数,利用Routh-Hurwitz准则,研究了系统的稳定性,计算表明所设计的轴承-转子系统在设计转速范围内的运转是稳定的。讨论了气体轴承结构参数偏心率,长径比及平均径向间隙对稳定性的影响,得出了应当采用小偏心率,小长径比,大平均径向间隙提高轴承转子系统稳定性的结论。