Fluid Film Bearings Research Articles

Effect of Pad Material, Copper Versus Steel, on the Performance of a Tilting Pad Journal Bearing: Measurements and Predictions

Abstract High-temperature operation limits the life of fluid film bearings; hence the need to quantify the effect of pad material on the performance of tilting pad journal bearings (TPJBs). The paper presents measurements of performance conducted on a copper-pads bearing (C-PB) and a steel-pads bearing (S-PB). Both bearings have the same geometry and differ on the pads' backing material, copper versus steel, and slightly in the assembled cold clearance. The journal diameter D = 102 mm, and a bearing has five pads with length L = 0.4D, nominal radial clearance 0.064 mm, and pad preload of 0.42. The pads are 12.3 mm in thickness and have a 50% offset pivot, ball-in-socket type. The bearings operate at four shaft speeds ranging from 6 krpm (32 m/s surface speed) to 14 krpm (74 m/s) and under multiple specific loads ranging from 0.17 MPa to 2.1 MPa. ISO VG 32 oil, at a supply temperature of 49 °C, lubricates a test bearing configured with end seals (flooded bearing). At the highest load (on pad) and low shaft speed, the S-PB static eccentricity is up to 37% higher than that for the C-PB. The oil exit temperature rise is similar for both bearings, the maximum difference reaches 6 °C. For all operating conditions, the pads' peak temperature rise, having a maximum difference of 5 °C–16 °C, is larger for the S-PB. The S-PB produces a ∼5% lower drag power loss than that in the C-PB. Drag power in both bearings increases with shaft speed and is largely independent of the applied load. From dynamic load tests with multiple excitation frequencies to 250 Hz, the C-PB direct stiffness KYY (along the load direction) is up to 30% higher than the S-PB stiffness, while the difference in KXX between the C-PB and the S-PB ranges from 60% to 90%. Similar to the stiffness results, the C-PB produces larger direct damping coefficients; CYY and CXX are up to 25% and 40% larger than those for the S-PB. Both bearings, however, show symmetry in the damping coefficients, i.e., CXX ∼ CYY. Virtual mass coefficients (MXX, MYY) are significant in magnitude though having a large uncertainty. A computational physics model predicts the TPJB performance under identical conditions. The exhaustive comparison conducted with a sound dimensional characterization of parameters reveals that predictions agree well with measurements of journal eccentricity, oil exit temperature, pad surface temperatures, and stiffness and damping force coefficients. The differences amount to 20% or less. The model relies on specifying the material properties for pads and pivots and the operating (hot) clearance to produce accurate thermomechanically induced deformations that affect bearing performance at high loads and high surface speed operation.

Coupling analysis of tribological and dynamical behavior for a thermal turbulent fluid lubricated floating ring bearing-rotor system at ultra-high speeds

The floating-ring bearing supported turbocharger rotor system generally reaches the speeds exceeding 100,000 rpm in high-temperature environment, but the risky sub-synchronous whirl, oscillation, bifurcation, and chaos probably appear due to its unsteady hydrodynamic forces with the high shear rate and low viscosity lubricant. From this perspective of coupling tribology and dynamics, the transient acting pressures at the thermal double fluid-film bearing are computed by employing the turbulent lubrication theory, then a numerical model for the whole rotor-bearing system based on the transfer matrix method is developed to investigate its nonlinear vibration behavior. The results show that an “interval region” characterized by the synchronous unbalance vibration is available to avoid fluid-induced instability of this system at different high-speed requirements.

Design and Modeling of 2 MW AMB Rotor With Three Radial Bearing-Sensor Planes

Active magnetic bearings (AMBs) provide reliable solution for high-speed rotors, where oil-free and reliable operation are crucial. In high-power applications benefits of AMBs, compared to traditional rolling element bearings or fluid film bearings, are highly valued. Typical AMB rotors comprise two radial AMBs, which are designed with compressor or generator wheels integrated on the rotor. AMB dimensions and locations are carefully selected for each new application. The system design is being iterated such that the nodes of the lowest frequency rotor bending modes are sufficiently far away from the AMB and sensor nodes to ensure robust AMB control. The design is very challenging and cost sensitive. This work focuses on electromagnetic design, modeling, and control of fully levitated AMB-rotor with three radial AMBs. The additional bearing ensures that the same design can be reused with different applications and regardless of the changes in locations of nodes of the first bending mode. The control plant is modeled based on flexible rotor dynamics; while bearing inductances and forces are modeled with 2-D and 3-D finite element method (FEM) electromagnetic simulations. The presented multi-input multi-output (MIMO) model-based control is coupled and centralized with three actuator-sensor pairs for radial suspension. The control design is verified in simulations using nonlinear engineering models. Additionally, experimental identification results are included.

Influence of magnetorheological lubricant behavior on the performance of annular recessed orifice compensated non-textured/textured thrust pad bearing

Fluid film bearings operated with smart lubricants have been successfully used to enhance the lubricating performance. This article proposes a computational model to analyze the influence of magnetorheological lubricant on the performance of an annular recessed hybrid thrust bearing system. The governing modified Reynolds equation for circular thrust pad orifice compensated bearing is solved by finite element method. Further, for simulating the flow behavior of magnetorheological lubricant, a constitutive relation for the Bingham model Dave equation, has been used. The numerical results reveal that using magnetorheological lubricant improves the loading carrying capacity and damping coefficient of both annular and circular recess hybrid thrust bearings. Additionally, bearing lubricated with magnetorheological lubricant requires a lesser quantity of flow and hence less pumping power.

Performance of textured spherical thrust hybrid bearing operating with shear thinning and piezoviscous lubricants

Improving the lubricating performance of tribo-pairs using engineering textured surfaces has been the main focus of tribology research in recent years. The use of a suitably designed micro-texture on the bearing surface may have a beneficial effect on the performance of fluid film bearings. In the present paper, a mathematical model of a hybrid spherical thrust bearing is developed considering the effect of shear thinning and piezoviscous behaviour of a lubricant. The modified Reynolds equation for a hybrid spherical thrust bearing configuration together with a restrictor flow equation for a capillary restrictor is solved using a finite-element method. In this work, the effect of various micro-textures shapes (spherical, circular, conical and square) and non-Newtonian lubricant behaviour having shear thinning and piezoviscous effects are analysed. The numerically simulated result shows a strong dependence on the combined effect of shear thinning and piezoviscous lubricant behaviour and a chosen geometric shape of a texture. The frictional power loss is seen to reduce nearly by 24.05%, and the stiffness gets enhanced by 11.08%.

Ferrofluid Lubrication of Optimized Spiral-Grooved Conical Hybrid Journal Bearing Using Current-Carrying Wire Model

Abstract To systematically investigate the behavior of fluid film bearing, the determination of optimal parameters is of utmost importance. The core contributions of this article are as follows: (1) modeling of the conical bearing for spiral grooves with ferrofluid lubrication using current-carrying wire model for the fixed coordinate system, (2) deriving the expressions for the magnetic field model and frictional power loss other than Reynolds equation for ferrofluid lubrication, and (3) evaluation of optimal values of spiral-grooved bearing surface for different cross-sectional shapes and that of the current-carrying wire model for magnetic field generation in ferrofluid lubrication. The generalized minimum RESidual iterative solver and the Newton–Raphson method have facilitated the solution of complex nonlinear finite element (FE) formulated governing equations. Initially, the results have been obtained for determining the optimal values of spiral groove and ferrofluid model attributes. After that, using these optimal values, corresponding performance indicators are evaluated. It was found that there exists a optimum value of different geometric features for distinct cross-sectional shapes of spiral grooves.

Simply structured controllers for vibration suppression in long rotors

In this paper suppression of the transient flexural vibrational disturbances in long rotors, with fluid film bearings, is investigated. The rotor is described by a series of distributed shafts connected by the lumped discs, and the system is mounted on lumped fluid film bearings. Upon determination of the dynamic stiffness matrix of the system, the best approximate transfer function matrix description of the rotor, is determined. Initially vibration suppression by simple diagonal Proportional + Integral (PI) controllers is studied and via direct search optimisation techniques the PI parameters which exhibit fast vibration suppression is found. The resulted high integration rate, and low proportional gain PI controller, theoretically provided fast suppression time. However, it is shown that due to the strong coupling effect in the rotor system, and high rate of integration, the closed loop relative stability is weak, and feasibility of controller is questionable. Therefore, an alternative simple first order controller without integration action, that is named “attenuation filter “is suggested that can produce stronger stability and produces significant (not full) vibration suppression. The closed loop multivariable control of the rotor system comprising two vibration sensors and two magnetic actuators using such attenuation filter, is then simulated. The response to step disturbances, has provided 95% suppression with significantly fast response. It is concluded that although the attenuation filter may not provide 100% suppression, but it more reliable since the integration of the error, that results weak stability is avoided.

Enhanced hydrodynamic lubrication of lightly loaded fluid-film bearings due to the viscosity wedge effect

The paper is a theoretical and experimental research of the viscosity wedge effect in a thin incompressible fluid film. The goal of the theoretical part of the work is a new look on the solution of the Navier-Stokes equation, when the viscosity function is unknown, that allowed to solve an optimization problem and find the optimal viscosity distribution in a fluid-film bearing. The optimal distribution was partially implemented in a test rig with a lightly loaded fluid-film bearing lubricated with mixed hot and cold water. The experimental results correlate with simulation results and demonstrate that the viscosity wedge may have positive effect on decreasing the shaft vibrations and friction coefficient.

Evaluation of the Rotor Temperature Distribution of an Automotive Turbocharger Under Hot Gas Conditions Including Indirect Experimental Validation

Abstract While turbocharging is a key technology for improving the performance and efficiency of internal combustion engines, the operating behavior of the turbocharger is highly dependent on the rotor temperature distribution as it directly modifies viscosity and clearances of the fluid film bearings. Since a direct experimental identification of the rotor temperature of an automotive turbocharger is not feasible at an acceptable expense, a combination of numerical analysis and experimental identification is applied to investigate its temperature characteristic and level. On the one hand, a numerical conjugate heat transfer (CHT) model of the automotive turbocharger investigated is developed using a commercial CFD-tool and a bidirectional, thermal coupling of the CFD-model with thermohydrodynamic lubrication simulation codes is implemented. On the other hand, experimental investigations of the numerically modeled turbocharger are conducted on a hot gas turbocharger test rig for selected operating points. Here, rotor speeds range from 64.000 to 168.000 rpm. The turbine inlet temperature is set to 600 °C and the lubricant is supplied at a pressure of 300 kPa with 90 °C to ensure practically relevant boundary conditions. Comparisons of measured and numerically predicted local temperatures of the turbocharger components indicate a good agreement between the analyses. The calorimetrically determined frictional power loss of the bearings as well as the floating ring speed are used as additional validation parameters. Evaluation of heat flow of diabatic simulations indicates a high sensitivity of local temperatures to rotor speed and load. A cooling effect of the fluid film bearings is present. Consequently, results confirm the necessity of the diabatic approach to the heat flow analysis of turbocharger rotors.

Improvement of Tilting-Pad Journal Bearing Operating Characteristics by Application of Eddy Grooves

In high speed, high load fluid-film bearings, the laminar-turbulent flow transition can lead to a considerable reduction of the maximum bearing temperatures, due to a homogenization of the fluid-film temperature in radial direction. Since this phenomenon only occurs significantly in large bearings or at very high sliding speeds, means to achieve the effect at lower speeds have been investigated in the past. This paper shows an experimental investigation of this effect and how it can be used for smaller bearings by optimized eddy grooves, machined into the bearing surface. The investigations were carried out on a Miba journal bearing test rig with Ø120 mm shaft diameter at speeds between 50 m/s–110 m/s and at specific bearing loads up to 4.0 MPa. To investigate the potential of this technology, additional temperature probes were installed at the crucial position directly in the sliding surface of an up-to-date tilting pad journal bearing. The results show that the achieved surface temperature reduction with the optimized eddy grooves is significant and represents a considerable enhancement of bearing load capacity. This increase in performance opens new options for the design of bearings and related turbomachinery applications.

Data-driven system identification and optimal control of an active rotor-bearing system

Both diagnostics and control in any piece of rotating machinery is getting more and more attention as computational powers allow storage of big data sets, and we are able to perform approximation, feature extraction and classification of big data. Such transfer from traditional diagnostics and control to machine learning and decision making also makes new ways of system identification based on artificial neural network architectures more attractive as they are more flexible in representing non-linear dynamics. Data-driven linear system identification or non-linear system identification based on artificial neural networks when coupled with optimal control obtained using either traditional or machine learning approaches result in a powerful tool for rotor-bearing system modeling and control that allows using identified model for predictive analysis as well. In the present paper such approach is presented for a rotor system on two journal fluid-film bearings, one of the bearings is equipped with a set of two actuators for feeding pressure control that allows adjustments of rotor position in the bearing. Such adjustments are aimed at decreasing power loss due to friction, so the system is more energy efficient. The presented approach of system identification and modeling can be applied to any similar rotor system.

An Efficient Cavitation Model for Compressible Fluid Film Bearings

This article presents an efficient cavitation model for fluid film bearings, considering both gaseous and vaporous cavitation. This work presents a modification of Elrod’s cavitation algorithm, where the bulk fluid is similarly considered to be a mixture of liquid and bubbles, without the need for a switch function. By solving for properties of the bulk fluid in the film, the distribution of the gaseous, vapor, and liquid states is captured without detailed tracking of bubble dynamics, as well as the variable compressibility of the bulk fluid in both ruptured and full film regions. The model developed is implemented in a numerical algorithm to solve the compressible Reynolds equation. Finally, the approach developed is applied to test cases to demonstrate its potential, as well as for comparison with Elrod’s algorithm.

Load carrying capacity of a novel magnetic-liquid double suspension fixed pad thrust bearing

Purpose Proposing a new type of water-lubricated thrust bearing meets the load-bearing requirements of high-power shaft-less rim driven thrusters. Design/methodology/approach The designs were tested by establishing a bearing thermal-fluid-magnetic comprehensive simulation model and developing bearing fluid film force and magnetic simulation. Lubrication performance tests were carried out on the bearing test rig. Findings The Halbach array of magnet blocks is able to reach the maximum magnetic force. The material of sheath can help increase the magnetism. The magnetism is able to reduce wear during low-speed and the start-stop phase, while the eddy current loss at high speeds will lead to a decrease in magnetic force. The experiment found that the bearing was more stable at low speeds and would not demagnetize due to the temperature rise, but it is necessary to pay attention to the running stability at high speeds to prevent rubbing and impact. Originality/value An innovative combination of hydrodynamic pressure and permanent magnetic repulsion was observed to form a magnetic-liquid double suspension bearing with large bearing capacity. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2020-0295

Effect of rotating unbalance on nonlinear dynamic response of flexible rotors supported on tilting pad journal bearing

The effect of orientation of rotors and rotating unbalance at disc on the dynamic response of rotor supported by four pad tilting pad journal bearing (TPJB) is studied. The orientation of the rotor taken has a horizontal rotor (HR) and a vertical rotor (VR). The rotor element modeled as the Timoshenko beam element with four degrees of freedom per node. The disc is rigid and it is centrally mounted. The nonlinear forces by the fluid film in tilting pad journal bearing were determined by solving the Reynolds equation along with each pad. The infinite short bearing assumption has taken to find pressure distribution along with pads. Indigenous MATLAB® code has developed to solve the rotor-TPJB equation. The ODE-15s solver is used to find the related response data of journal and disc centers. Orbits, phase plots, and power spectrums used to analyze the behavior of the system. The sub-synchronous vibrations dominate at lower speeds and high rpm unbalance forces become much significant and overcome bearing fluid film forces causing catastrophically change in response of the system.

Tilting Pad Journal Bearing Misalignment Effect on Thermally Induced Synchronous Instability (Morton Effect)

Abstract This paper investigates the influence of misaligned journal bearing effects on the thermally induced rotor instability (Morton effect “ME”) problem. The Morton effect is caused by uneven viscous heating of the journal in a fluid film bearing, which causes thermal bending, especially in rotors with an overhung disc or coupling weight. The thermally induced bending in the shaft may cause a vibration instability, which results in an excessive level of synchronous vibration. Previous research focused on parametric studies of the rotor and bearing design parameters, including overhung mass, bearing radial clearance, and lubricant viscosity. The present study investigates the influence of journal misalignment on the Morton effect. A coupled fluid-thermal-structural, three-dimensional finite element model (FEM) is developed to simulate fluid film pressures and temperatures, and shaft temperatures and vibrations. Simulations were conducted with different ratios of journal misalignment, and different pad-pivot types to determine their effect on the phenomenon. The simulation results indicate that the amplitude of the misalignment angle affects the instability speed range (ISR) caused by the Morton effect under certain conditions.

Implication of Surface Texture and Slip on Hydrodynamic Fluid Film Bearings: A Comprehensive Survey

Implication of Surface Texture and Slip on Hydrodynamic Fluid Film Bearings: A Comprehensive Survey

A MEMS Turbopump for High-Temperature Rankine Micro Heat Engines—Part II: Experimental Demonstration

This paper presents the experimental demonstration and characterization of a MEMS turbopump with thermal insulation for high temperature operation. The fabrication and design were presented in the first part of this two-part paper. The device consists of a five-wafer stack enclosing a hybrid silicon-glass rotor supported by fluid film bearings, manufactured using MEMS fabrication methods. The rotor consists of a 4-mm diameter disk with microturbine blades on one side and a spiral groove viscous pump on the other side. First, the bearings, turbine and pump operation are characterised, up to a rotational speed of 100 kRPM. The turbine provided 0.16 W of mechanical power and the pump flow rate was above 2.55 mg/s. Then, the first demonstration of a MEMS turbopump operating at elevated temperatures was accomplished. Comparison was made with a non-insulated rotor to prove the effectiveness of the thermal insulation strategies. The insulated MEMS turbopump was demonstrated at 160°C on the turbine side without boiling water on the pump side. This work therefore enables the implementation of efficient and high-power density power plants-on-a-chip for a wide range of waste heat recovery applications. [2020-0051]

Machine learning for rotating machines: simulation, diagnosis and control

The goal of this work is association of several machine learning methods in a study of rotating machines with fluid-film bearings. A fitting method is applied to fit a non-linear reaction force in a bearing and solve a rotor dynamics problem. The solution in the form of a simulation model of a rotor machine has become a part of a control system based on reinforcement learning and the policy gradient method. Experimental part of the paper deals with a pattern recognition and fault diagnosis problem. All the methods are effective and accurate enough.

Imitation model of unbalanced rotor on fluid-film bearings

Diagnostics of rotating machines is taking a new step forward with the development of intellectual technologies based on predictive and machine learning tools. Despite having a range of advantages compared to humans in terms of big data processing powers, correlation and various feature extraction possibilities, and swiftness of operation, such systems are limited by measurement system elements in terms of their parameters: sensors and ADCs with their sensitivity properties and accuracy restrictions, microprocessors with limitation of processing powers, etc. Experimental data is used to recreate experimental environment in simulation of induced unbalance. The imitation model is based on rotor dynamics equations of rotor motion, Reynolds equation to estimate reaction forces of a fluid-film bearing and takes into account sensor parameters and position, gear coupling effect and other measurement system elements parameters. The results show that under certain conditions it becomes impossible to successfully track unbalance which in real conditions could lead to malfunction or failure of a rotor machine.

Effect of rotor misalignment on stability of journal bearings with finite width

The present work studies the dynamic response of fluid film bearing of finite length which is subjected to rotor misalignment. Vibration analysis of the rotor is used to obtain the limits of stability at different operating conditions. The lubricant flow in the bearing is considered laminar, incompressible and isoviscous. For a given small excitation of the bearing shaft, a time dependent Reynolds equation is introduced to investigate the dynamic response of the fluid film bearing. At a misalignment direction angle and misalignment degree, nonlinear perturbation dynamic equations are introduced and solved to determine the critical stability limit of motion for different values of eccentricity ratio. Vibration data is collected to obtain the transition from stable to unstable operating conditions (stability map). It is concluded here that increasing the value of misalignment degree yields to an increase in the value of critical bearing stability limit for a given value of misalignment direction angle. The critical stability number increases as the misalignment direction angle decreases and/or the steady state eccentricity ratio increases.