基于有限元法的离心泵转子系统动力学特性研究

本文应用基于有限元法的Workbench软件对离心泵"干态"和"湿态"条件下的转子系统进行模态分析,得到两种条件下的临界转速。应用计算流体力学(CFD)中的准静态法得到了密封口环处的流体激振力并将其添加到"湿态"模态分析中。结果发现,"湿态"条件下,转子的临界转速远大于"干态"条件下的临界转速,这说明密封口环间隙处的流体激振力对转子起到一定的支撑作用。     

基于有限元法的锅炉给水泵转子系统分析

为了研究多级锅炉给水泵转子系统应力应变以及干态和湿态下临界转速,通过ANSYS软件中的Workbench组件对给水泵转子系统进行应力应变分析,同时采用APDL组件对给水泵的转子系统分别进行干态和湿态的对比计算。通过上述数值计算,获得了转子系统的应力应变以及干态和湿态下的临界转速,可以看出,在转子系统装配中叶轮的装配位置上径向变化较大,对比显示湿态下转子系统的临界转速比干态下临界转速大幅提高,更符合真实状态;预估了在湿态下临界转速数值结果。所采用的针对某型锅炉给水泵的应力应变及临界转速的研究方法,可为同类的给水泵产品转子系统的研究提供参考。     

基于Workbench平台的超超临界锅炉给水泵转子动力学有限元分析

超超临界(百万千瓦机组)锅炉给水泵转子的临界转速计算是锅炉给水泵转子设计中一个重要的步骤。通过ANSYS 12.0 Workbench平台,求得转子在刚性支承、弹性支承以及"湿态"工况下的临界转速,以对比密封水膜和轴承油膜等因素对转子动力学分析的影响,为锅炉给水泵安全平稳运行提供依据。     

迷宫密封对立式安注泵转子动力特性的影响研究

本文针对某型立式低压安注泵机组的转子-轴承系统的动力学特性展开研究,分别建立了干态(不考虑密封)和湿态(考虑密封)两种分析模型,且对每种分析模型分别进行了无阻尼固有频率分析和复模态分析。根据API 610标准的要求,湿态模型中考虑密封1倍间隙和2倍间隙两种工况。无阻尼固有频率分析得到了干态和湿态两种间隙下的前六阶固有频率,分析结果表明,密封能提高转子系统的临界转速,密封间隙的变化对临界转速的影响较小。复模态分析得到了干态和湿态两种间隙下的前六阶阻尼固有频率及相应的对数衰减率。分析结果表明,该转子为柔性转子,考虑密封后对数衰减率变化较大,稳定性满足设计要求。     

密封间隙力对泵临界转速的影响

基于泵产品临界转速的实际计算和国外泵行业研究报告,阐述了密封间隙力对计算泵临界转速的重要作用,提出要以湿态临界转速计算结果作为安全裕度的判据。     

基于减缩法的离心泵转子动力学分析

以多级离心泵三维转子为研究对象,采用等效圆环法建立了叶轮高保真动力学模型并进行了验证。针对三维模型自由度多等特点,基于旋转子结构方法,采用ANSYS程序对离心泵转子干态和湿态下因模型边界条件的不同分别进行减缩,该方法考虑了旋转陀螺效应的影响。干态情况下,模型减缩了30%自由度,计算得到的前三阶临界转速最大误差为0.5%,振型基本一致。湿态情况下,模型减缩了68%自由度,临界转速最大误差为0.17%,稳态不平衡响应计算结果与原模型基本相同。该方法可以用于多级离心泵转子干态和湿态转子动力学设计。     

间隙环流对十一柱塞航空液压泵转子系统临界转速的影响分析

以十一柱塞航空轴向泵转子系统为研究对象,基于转子动力学理论,构建转子系统的离散模型;然后根据流体连续定理及动量定理建立间隙环流运动的偏微分方程组;采用线性摄动法求解得到间隙环流激振力,并以矩阵的形式施加于干转子动力学方程上,组建湿转子系统动力学方程;在MATLAB软件中编写求解程序,计算干/湿转子的临界转速;最后搭建航空泵转子系统实验平台,完成干/湿转子系统临界转速对比实验研究工作。对比分析结果表明,间隙环流产生的动态流体激振力会影响转子系统的动力学特性,一定程度上会降低系统的临界转速,且随间隙比W的增大,降低趋势更显著。     

离心多级泵转子临界转速的计算

对锅炉给水泵(离心式多级泵)转子的干临界和湿临界转速进行了计算.计算中考虑了两端滑动轴承及诸密封环动力特性的影响.在对密封环动力特性计算分析的基础上给出了改进设计后的临界转速计算结果.     

船舶脱硫泵转子系统临界转速计算及不平衡响应分析

为提高船用脱硫泵运行可靠性,利用有限元分析软件对脱硫泵转子系统进行了临界转速计算与不平衡响应分析,得到转子系统"干态"和"湿态"两种工况下的临界转速与不平衡响应曲线.分析泵轴材料密度以及水动力刚度对转子系统临界转速的影响;对比转子系统"干态"和"湿态"两种工况下的不平衡响应幅值,分析转子系统阻尼系数对不平衡响应幅值的影...     

多级离心泵-电机轴系转子动力学分析

采用MADYN2000分析软件对离心泵密封刚度和阻尼进行了分析,得到了刚度和阻尼变化曲线。以水泵-电机转子轴系为研究对象,采用ANSYS软件建立了轴系三维转子有限元模型,分别对轴系在干态和湿态情况下的临界转速和转子应变能分布进行了分析。相比在干态情况下,湿态情况下第一阶临界转速有所增高,前四阶轴系转子的应变能均有所下降,但还是具有偏大的特点。第二阶振型以电机转子弯曲为主,在高转速情况下应加强对电机转子的振动监测。     

Numerical simulation of rotordynamic coefficients for eccentric annular-type-plain-pump seal using CFD analysis

Annular seals are primarily used to control the leakage in turbomachinery, such as pumps. Consequently, annular seals substantially affect the stability of turbomachinery. Designing the annular seals of high performance pumps require the accurate prediction of the seal’s leakage flow rate and rotordynamic coefficients. The bulk-flow model is the traditional means for leakage flow rate analysis and predictions. Bulk-flow analysis is based on the Hirs’ lubrication equation, which simplifies the Navier-Stokes equation. However, the analysis of the bulk-flow model requires a great amount of time to develop an analysis code. Furthermore, the code possesses many constraints for analyzing seals with complicated shapes. 3D CFD simulations provide faster and less expensive estimates of the flow field for a wide variety of operating parameters and flow conditions. In this study, the flow field and the rotordynamic coefficients of a plain-eccentricannular seal were simulated with circular whirl orbits using 3D CFD code. A relative coordinate system was defined to calculate the 3D velocity profile and the dynamic pressure distribution of the seal clearance for each rotor whirling speed. The rotordynamic coefficients were determined by reaction forces of seal fluid, which were calculated by integrating the dynamic pressures to the whole area of seal. The results from our analyses were compared to existing theoretical calculations as well as compared to results acquired from experiments. The present 3D CFD results of leakage and rotordynamic coefficients of K and C showed better improvement in prediction.     

Fluid-structure interaction analysis of annular seals and rotor systems in multi-stage pumps

Annular seals play an important role in determining the vibrational behavior of rotors in multi-stage pumps. To determine the critical speeds and unbalanced responses of rotor systems which consider annular seals, a fluid-structure interaction (FSI) method was developed, and the numerical method was verified by experiments conducted on a model rotor. In a typical FSI process, rotor systems are modeled based on a node-element method, and the motion equations are expressed in a type of matrix. To consider the influence of annular seals, dynamic coefficients of annular seals were introduced into the motion equations through matrix transformation. The test results of the model rotor showed good agreement with the calculated results. Based on the FSI method proposed here, the governing equations of annular seals were solved in two different ways. The results showed that the Childs method is more accurate in predicting a rotor’s critical speed. The critical speeds of the model rotor were calculated at different clearance sizes and length/diameter ratios. Tilting coefficients of long seals were added to the dynamic coefficients to consider the influence of tilting. The critical speeds reached their maximum value when the L/D ratio was around 1.25, and tilting enhanced the rotor’s stability when long annular seals were located in either end of the shaft.     

迷宫密封对转子系统稳定性影响研究

透平机械中汽流激振力主要产生于各种形式的密封处,其对转子系统的稳定性有不良影响。因迷宫密封的存在而引起汽流激振,其各有关结构和工况参数对转子动力特性均存在影响。本文主要分析转子转速、入口预旋比、密封间隙、压差、齿数变化等一系列因素对转子系统稳定性的影响,为迷宫密封汽流激振的防治和迷宫密封设计中各参数的最优确定提供参考依据。     

A Transient Dynamic Analysis of Mechanical Seals Including Asperity Contact and Face Deformation

Face seals are typically designed to be in contact at standstill. However, as speed and pressure build up, the seal faces deform from their factory flat conditions because of viscous and dry friction heating, as well as mechanical and centrifugal effects. It is imperative that such deformations form a converging gap for radial flow to ensure stable operation and to promote favorable dynamic tracking between stator and rotor. A numerical simulation is presented for the transient response of a face seal that is subjected to forcing misalignments while speeds and pressures are ramped up and down. Asperity contact forces and transient face deformation caused by viscous heating are included. A new closed-form solution is obtained for the elastoplastic contact model, which allows seamless transition between contacting and noncontacting modes of operation. The model is then used to calculate face contact forces that occur predominantly during startup and shutdown. The viscous heating model shows that the time-dependent deformation (coning) is hereditary and that it lags behind the instantaneous heat generation. The dynamic analysis provides a numerical solution for the seal motion in axial and angular modes. The eventual build up of hydrostatic pressure and coning during startup generates opening forces and moments that separate the seal faces, resulting in noncontacting operation. The reverse occurs during shutdown; however, because of the thermal time constant a seal may continue to leak even after it returns to standstill. The analysis and simulation results compare very well with a closed-form solution that predicts a critical speed of separation of contacting seals.     

Numerical techniques for computing nonlinear dynamic characteristic of rotor-seal system

A transient CFD procedure to compute the nonlinear dynamic characteristic of the coupled rotor-seal system was presented in this study. In each time step, the displacement diffusion model was implemented to govern the mesh deformation, and the URANS (Unsteady Reynolds averaged Navier-Stokes) equations were solved to obtain the transient fluid force on the rotor surface for the free vibrations. With the obtained fluid force from the CFD solver, the nonlinear equations of motion for a simplified rotor-seal system were numerically solved on the basis of external user defined routines. During each transient time step, the computed fluid force from the CFD solver and the rotor motion from the user defined routines were transferred to each other timely. The rotor center trajectories, frequency spectrum and projection of Poincaré section were calculated to investigate the nonlinear dynamic performance of the single disk rotor-seal system. The effects of the rotational speed and pressure ratio on the vibration characteristic of the rotor-seal system were analyzed by the bifurcation theorem. The results show that the coupled rotor-seal system experiences a period-one motion, resonance, periodic-doubling motion, quasi-periodic motion, and finally possible chaotic motion as the rotor speed increases. The pressure ratio has pronounced effect on the frequency response of the first-order critical speed; however, it has little influence on the motion state as well as the frequency response of the rotating speed. Although a constant-clearance annular smooth stator seal was selected as the research object in the current paper, the presented transient CFD method is still available for other complex annular seals, such as labyrinth seal, honeycomb seal, pocket damper seal, etc.     

The reduction of the vibration level in high-speed rotor systems by means of floating seal rings

The dynamics of high-speed rotor systems is studied during the rotation of the rotor in floating seal rings considering the effects of the hydrodynamic interaction forces between the rotor and the seal rings. A dynamic analysis of the “flexible-rotor-hydrodynamic-medium-floating-rings” system shows that the floating seal ring becomes a broad-band hydrodynamic oscillation damper when the rotor speed coincides with the partial frequency of the ring. Under transient conditions, it is practical to vary the speed slowly during the speedup/shutdown. The effect of the hydrodynamic forces also leads to the disappearance of the rotor critical speed since the rotor’s stiffness increases on the hydrodynamic layer more rapidly than the speed. The parameters of the seal rings of a multi-mass rotor system of turbo-driven pump assemblies for liquid-propellant rocket engines, such as the pressure drop and the masses, that ensure the damping of the oscillations are found.     

Influence of the Mechanical Seals on the Dynamic Performance of Rotor–Bearing Systems

In this paper, to consider the effects of mechanical seals, a lumped-mass model and the transfer matrix method are used to establish the equations for the dynamics performance of rotor bearing system. The general inverted iteration method is also used to solve the eigenvalue problem of these equations. To check the response of the rotor bearing system under unbalance motivation, the Gauss method is used to calculate the dynamic response of the constrained vibration. The results, based on the dynamic properties calculation of a typical mechanical spiral seal, such as stiffness coefficients and damping coefficients, exert the influence of the mechanical seal on the rotor bearing system of the high-speed machinery. Meanwhile, some structure parameters that may affect the dynamic performance and forced vibration under unbalance motivation of the rotor bearing system considering mechanical seals are analyzed in the paper. The analysis results show that the mechanical seal more or less has effects on the rotor bearing system. The mechanical seal has much more effects on the flexible rotor bearing system than on the rigid one. For instance, in a certain case, if the effects of the mechanical seal were taken into account, the system s critical speed may increase by 70 80%.     

CFD Study on Stepped and Drum Balance Labyrinth Seal

The stability of rotors in turbomachines is affected by the labyrinth seal where driving forces are generated. Recent research results have shown that the preswirl has a significant influence on the rotordynamic characteristics of the straight labyrinth seal including both tooth-on-stator and tooth-on-rotor configurations. However, modern turbomachines require higher and higher pressure drop for the seal so that the eye seal is usually designed as stepped labyrinth, whereas the balance drum usually employs a tooth-interlocking labyrinth and a larger number of teeth. Both designs could generate greater forces on the rotor than the straight labyrinth seal. Therefore, it is necessary to further study the influence of preswirl on stepped and tooth-interlocking labyrinth seals. This article employed 3D calculational fluid dynamics (CFD) to solve the flow in those seals. Then the rotordynamic coefficients of the two seals at different preswirl rates were calculated based on the CFD results. The results were compared with test data and bulk flow results. A rotor stability analysis was conducted considering the balance drum seal with the coefficients predicted by the numerical method.     

A new transient CFD method for determining the dynamic coefficients of liquid annular seals

Currently, the dynamic characteristics of annular seals are numerically investigated mainly by solving the bulk flow equations using perturbation method, or by simulating the perturbed flow field of annular seal using CFD method. The adopted disturbance way is generally the circular whirling motion of rotor around seal centre with constant speed. Relative to the transient CFD simulation, the quasisteady CFD simulation introducing Moving reference frame (MRF) has been widely used by researchers. Both the dynamic mesh problem and the time-consuming problem suppress the use of transient CFD simulation in annular seal research. In the paper, a new transient CFD method based on rotor’s variable-speed whirl is presented to improve the time-consuming problem and all the (total 20) dynamic coefficients of concentric liquid seal can be obtained by only two transient CFD simulations, one for the variable-speed cylindrical whirl and the other for the variable-speed conical whirl. The results are compared with those from the experiment, the quasi-steady CFD method and the traditional transient CFD method based on constant-speed whirl. The comparisons show that the new transient method can keep the good accuracy of traditional transient method and meantime largely save the computational time.     

A modeling of pump impeller shroud and wear-ring seal as a whole, and its application to the pump rotordynamics

A modeling methodology of pump impeller shroud and wear-ring seal as a whole has been developed to give its rotordynamic coefficients. In this work the governing equations are derived for the continuous flow path of the impeller shroud and wear-ring seal. Pressure loss at the discontinuity of the connecting point between the impeller shroud and the wear-ring seal is defined by utilizing a pressure loss coefficient obtained from experimental measurements. The governing equations are solved directly by using the known conditions at the inlet of the impeller shroud and the outlet of the wear-ring seal. A detailed rotordynamic analysis has been carried out on a 750 m-head fourteen-stage centrifugal pump system with the effects of the hydrodynamic forces of such as impeller shroud and wear-ring seals, balance piston, and interstage seals. Results have shown that the first critical speed obtained with all the seal effects is much higher than that obtained without those effects, and moreover that the system under consideration is unstable. Large cross coupled stiffness (k) of the impeller shroud and wear-ring seal has been suspected as the source of the problem. Design modifications of the impeller shroud and wear-ring seal geometry have been performed to decrease k and increase the direct damping(C). Finally, the design modifications have yielded a stable and well damped system.