Rotor Bearing Research Articles

Effect of radial clearance on the dynamic behavior of adjustable journal bearings in turbulent and laminar flow regimes

Radial clearance critically affects journal bearing performance, specifically the lubrication performance. This study investigates the lubrication characteristics of a journal bearing with adjustable radial clearance and compares the dynamic behavior of the bearing under laminar and turbulent flow regimes. The adjustable bearing exhibits two states of oil film pressure at different radial clearances. When the radial clearance is reduced from 100%cr to 80%cr, the oil film pressure is present only on the lower bearing bush; after being reduced to 70%cr, the upper bearing bush achieves effective lubrication; and after reduction from 70%cr to 30%cr, the oil film pressure increases more than six-fold. The turbulent flow model of the clearance adjustable bearing is then established considering the lubricant flow state, and the turbulence correction factors for different flow states are calculated. The journal bearing exhibits better lubrication characteristics under laminar than under turbulent flow conditions, and in some operating conditions, the stable velocity range calculated according to laminar flow theory may become unstable in turbulent flow conditions. Therefore, applying turbulence assumptions to design the operating speed range of rotating machinery under such conditions yields a greater safety threshold, which can reduce the risk of instability. The stability of the rotor bearing system is closely related to the radial clearance, and reducing the radial clearance will improve the stability of the system. In the turbulent flow state, the oil film pressure changes drastically, thus reducing the system stability. Moreover, the larger the radial clearance of the bearing, the more prominent the turbulence effect. Thus, reducing the bearing clearance prevents drastic changes in oil film pressure and improves the stability of the system.

Improved Wear and Corrosion Resistance in TiC-Reinforced SUS304 Stainless Steel

Herein, the vacuum arc-melting process is applied to incorporate various amounts of Ti and C into SUS304 austenitic stainless steel based on the high-entropy alloy concept to obtain wear- and corrosion-resistant alloys with in situ carbide reinforcements. Five compositions containing the equivalent of 5, 10, 15, 20, and 25 volume percentages of TiC in SUS304 stainless steel, named A1, A2, A3, A4, and A5, respectively, were designed, melted, and solidified by the arc-melting method. Microstructural analyses, hardness measurements, immersion tests in four corrosive solutions, electrochemical measurements in a 3.5 wt % NaCl(aq) solution, and tribological tests were conducted to determine the properties and explain the relevant mechanisms. A1 exhibited a eutectic structure between FCC dendrites, while A2, A3, A4, and A5 possessed proeutectic dendritic TiC, FCC dendrites enveloping the TiC dendrites, and a eutectic structure. A5 represents the optimal composition. Its hardness, wear resistance, and corrosion resistance are 2, 14, and 4 times higher than those of SUS304, respectively. Additionally, its wear resistance is 2.5 times that of high-chromium cast iron. Consequently, A5 could have a 2.5-fold longer lifetime in wear operation. Therefore, A5 could be potentially applied in corrosive and abrasive environments, such as rotary shafts, rotors, bearings, and structural parts in food, chemical, and optoelectronic industries.

The annulling of the sudden appearance of an unbalance in rotary machines by using active magnetic bearings

The application of magnetic bearings has become more frequent during the last 20 years and represents a significant aspect of improvements in the construction of machines with rotary motion. With the advancement of technology, the number of applications in which magnetic bearings have found their application is increasing. In this paper, it is shown how the effect of magnetic forces can annul the negative influence of unbalance, which suddenly appeared in a rotor supported in active magnetic bearings. Such cases may occur in operation due to breakage and rotor parts falling off (e.g., fan blades), which will lead to a sudden change in the mass balance of the rotor system and dislocation of the centre of mass in relation to the geometric centre of the rotor. In the paper, a mathematical model of the dynamic behaviour of a rigid rotor in active magnetic bearings was developed. The model is nonlinear and has five degrees of freedom and can only be solved numerically. The Newmark beta method and the Newton-Raphson method were used to solve the system of nonlinear differential equations. The results of the simulation showed the advantages of using active magnetic bearings for annulling sudden occurrences of unbalance in rotary machines.

Effect of loaded-pad thickness on the static behaviors of five-pad hydrodynamic journal bearings

The use of tilting pad journal bearings (TPJBs) has increased in the recent past due to their stabilizing effects on the rotor bearing system. Most of the studies about steady state and dynamic behaviors of TPJBs are usually evaluated by means of thermohydrodynamic models assuming nominal dimensions for the bearing. However, machining errors could lead to actual bearing geometry and dimensions different from the nominal ones. In particular, for TPJB the asymmetry of the bearing geometry leads to unexpected behavior of the bearing. In this paper, effects of non-uniform clearance on TPJBs’ performances such as clearance profile, shaft locus, power loss, pad tilt angle, and pressure distribution are evaluated using an analytical model. The results show that effects of non-uniform clearance on static characteristics of TPJBs are considerable when evaluating the efficiency of the bearing in particular and system in general.

STRESS-STRAIN STATE AND CRITICAL ROTATIONAL VELOCITIES OF AIR BLOWER ROTOR PART OF A HIGH BOOST ENGINE

The stress-strain state and critical rotation speeds of the air blower rotor part of highly forced engine are investigated. For this purpose, their parametric geometric and finite-element models are built. Due to the high speeds of rotation, the impeller disk acquires an umbrella-shaped deformed shape. This deformation can cause a gap to be selected between the impellers and the stator of the supercharger. In areas of abrupt change of shape on the impeller there is a concentration of stresses. In addition, the supercharger impeller is located cantilevered. This causes low critical speeds. These frequencies may fall within the operating range of angular velocities of the supercharger rotor. All these factors in the complex within a single calculation model were not previously taken into account. Instead, taking into account the dependences of stress, strain and critical velocity levels on the design parameters is of interest in the development of supercharger designs. In particular, the stiffness characteristics of the elastic rotor bearings were varied. The influence of these parameters on the critical rotation speeds of the rotor part of the air supercharger is determined. Recommendations have been developed for debugging from hazardous supercharger modes. In particular, it is proposed to reduce the radial stiffness of the shaft bearings by using elastic flexible rings. This can reduce critical rotor velocities beyond the operating range. In addition, a lighter material can be used to increase the strength of the impeller. It is also possible to limit the operating range of the angular rotational velocities of the rotor part of the investigated air blower. Analysis of the stress-strain state and the critical rotational velocities of the rotor were carried out on the basis of a unified generalized mathematical and numerical model. Keywords: rotor system, air blower, impeller, stress-strain state, critical rotation speed

Studying the Temperature Characteristics of Oil at the Outlet From the K27-145 Turbocharger Rotor Bearing

Studying the Temperature Characteristics of Oil at the Outlet From the K27-145 Turbocharger Rotor Bearing

Fractional-order model and nonlinear vibration analyses of hybrid gas journal bearing–rotor system

It is important to propose a reasonable nonlinear dynamic model of gas dynamic bearing–rotor system for the stable operation of turbocharger. This paper presents a hybrid gas journal bearing (HGJBs)–rotor system with flexible supporting structure. A fractional-order dynamic model of the symmetrical flexible HGJB–rotor system is established. A tracking–alarming method is proposed to obtain the rotational speed ratio at the bifurcation point. The stable and unstable regions of the rotational speed ratio Ωω for both the rigid bearing–rotor system and flexible HGJB–rotor system are analyzed. The nonlinear dynamic behaviors of HGJB–rotor system versus the fractional order αd and rotational speed ratio Ωω are studied. Results show the fractional-order dynamic model can realize the reasonable prediction of nonlinear dynamic behaviors. An increase in the rotational speed ratio Ωω and the decrease of fractional order αd result in a growth of the vibration amplitude. The adoption of flexible supporting structure is a good strategy to increase the size of stable region.

Computational fluid dynamics-based investigation of the static and dynamic characteristic of hydrostatic bearing with nanolubricant: A theoretical method

The objective of this work is to study the characteristics of the hydrostatic bearing with nanolubricant. To investigate the effect of nanoparticle additives on the performance of hydrostatic bearings, a coupled heat transfer finite-element model of the hydrostatic bearing is developed, and the results of the static and dynamic performance of the hydrostatic bearing with lubricant and nanolubricant are evaluated based on computational fluid dynamics methods at different eccentricity ratios. The results show that the rotation error of the bearing–rotor system is reduced by using nanolubricant at a high eccentricity ratio.

Early Detection of Faults in Induction Motors—A Review

There is an increasing interest in improving energy efficiency and reducing operational costs of induction motors in the industry. These costs can be significantly reduced, and the efficiency of the motor can be improved if the condition of the machine is monitored regularly and if monitoring techniques are able to detect failures at an incipient stage. An early fault detection makes the elimination of costly standstills, unscheduled downtime, unplanned breakdowns, and industrial injuries possible. Furthermore, maintaining a proper motor operation by reducing incipient failures can reduce motor losses and extend its operating life. There are many review papers in which analyses of fault detection techniques in induction motors can be found. However, all these reviewed techniques can detect failures only at developed or advanced stages. To our knowledge, no review exists that assesses works able to detect failures at incipient stages. This paper presents a review of techniques and methodologies that can detect faults at early stages. The review presents an analysis of the existing techniques focusing on the following principal motor components: stator, rotor, and rolling bearings. For steady-state and transient operating modes of the motor, the methodologies are discussed and recommendations for future research in this area are also presented.

Multi-sensor optimal placement of rotor-bearing system based on fault diagnosability

In view of the current situation that there are few studies on whether the fault signals that may occur in the rotor bearing system can be identified and analyzed in the sensor arrangement, fault diagnosability is applied to the optimal arrangement of the sensors in the rotor bearing system. The preliminary layout of the multi-sensor is carried out by analyzing the transmission path of the vibration signals in the rotor bearing system and based on the minimum path. Secondly, the nonparametric kernel density estimation method calculates the state information’s probability density function. The K-L divergence value is further used to measure fault detectability, fault separability, and fault diagnosability. Then, the correlation function method is used to fuse the multi-sensor information, and the optimal sensor layout is given with the fault diagnosability as an index. Finally, the validity of the method is proved by the experimental laboratory data and the correlation coefficient.

Dynamic and Thermal Investigations of the Forward Dry-Friction Whirl/Whip of a Vertical Rotor-AMB System during Touchdowns

When an active magnetic bearing (AMB) rotor drops, it impacts the touchdown bearing (TDB) and produces friction on its surface. The vertical AMB rotor has no stable support in the radial direction, and the rotor exhibits a violent whirl motion in the gap of the TDB. In this study, a complete dynamic and thermal model of the AMB-rotor-TDB system was established, and the complete drop process was simulated. When the rotor dropped, it obtained stable support after several bounces on the thrust surface of the TDB inner ring in the axial direction. In the radial direction, the rotor entered whirl motion after the initial collisions. There is a natural whirl frequency so that the drop forward whirl is divided into the dry-friction whirl and whip states. The contact force and heat generation of the TDB were monitored in the simulation and had different performancs in the two states. Both the initial collisions and the stabilized whirl motions were studied to evaluate the reliability of the TDB. Finally, a series of drop tests were performed, and the experimental results were in good agreement with the simulation.

Frictional analysis on stiffness and damping characteristics of bump foil gas bearings

Gas foil bearing has been used in high-speed turbomachinery for its high speed, high adaptability, and eco-friendly. The stability of the rotor bearing system is greatly enhanced due to the flexible foil support structure. In the foil supporting structure, vibration energy of the rotor bearing system can be absorbed by the Coulomb friction dissipation. In order to evaluate the frictional dissipation on bearing performance, a quasi-2-dimensional mechanical model is proposed considering the Coulomb friction. The Coulomb damping dissipation characteristics of the bearing in operating conditions are analyzed by coupling gas film. Frictional analysis is conducted on the bump foil bearing with different structural parameters, such as bump height, foil thickness, friction coefficient and number of bump foil strips. The stiffness of the foil bump is less affected by the base load. In the process of foil bearing design, the optimal friction coefficient, bump height should be properly selected in favor of either foil bearing stiffness or damping characteristics. In addition, the overall performance of bump foil bearing is strongly affected by the number of bump foil strips.

Определение теплового состояния элементов турбокомпрессора поршневого двигателя

The power boost of heat engines is conditioned by the increase in the load on all its elements and related units. The turbocharger is one of the most common units that provide the power boost of a heat engine. The reliability of the turbocharger and its tribo-couplings guarantees the stable operation of not only it, but also the machine as a whole. An increase in the rotor speed leads to an increase in the thermal loading of the turbocharger elements. In this regard, timely assessment of the thermal state of the tribocoupling components, temperature distribution over the shaft, housing and other elements of the turbocharger is an urgent task. An algorithm for calculating heat transfer between the elements of a turbocharger has been developed, and an assessment of the heat load of radial multilayer plain bearings of a flexible asymmetric rotor has been made. The simulation was carried out in the ANSYS Fluent software package. The experimental data of the manufacturing plant were used as boundary conditions. The results of the calculation are given: the distribution of thermal fields in the turbocharger housing and the temperature in the area of ??the turbine and compressor plain bearings. Dependences of temperatures in the bearing area on the rotor speed are obtained. The calculation results were verified by comparing the temperatures in the turbine and compressor plain bearings with the data given in the publications of other authors. The temperature values in the outer and inner layers of the bearing were the initial data for calculating the dynamics of the turbocharger rotor, taking into account the thermal deformations of the tribocouple elements. The results of the research will be used to assess the stability of the movement of the rotor, the failure-free operation of the bearing assembly, as well as the reliability and durability of the turbocharger as a whole.

Dynamic Response Analysis of the Rotor Using the Jeffcott Method and Performance Improvement Using Active Magnetic Bearing

The most common component of mechanical systems today is rotating machines. In these systems, vibration is caused by rotating components. As a result, to decrease the amplitude of vibrations created by rotating equipment, it’s required to understand the behavior of the system. In this work, the problem of vibrations in conventional bearing systems and the effect of adding active magnetic bearings to rotating machines to reduce the amplitude of vibrations are discussed. In this paper, the vibrations in the rotary bearing system were studied theoretically and analytically by using simulation programs to calculate the natural frequencies and parameters affecting the performance. In the theoretical part, the shaft of the rotating bearing was analyzed by the Jeffcott method depending on several parameters changed with the frequency value to observe the amplitude of the vibrations in the shaft. In an analytical aspect by simulation, a representative model of active magnetic bearings was built using the COMSOL 2020 program, and the effect of adding these bearings on capacitance, vibration reduction, and frequency behavior was examined. SolidWorks 2018 software was used to analyze the magnetic field and its distribution in the magnetic bearing coil. The results indicate that when magnetic active bearings were introduced to the rotating bearing shafts, the vibration amplitude was reduced by approximately 60%. From this work, it can be concluded that the system becomes more stable when the active magnetic bearing is added to the rotating bearing shaft, giving it a more stable and firm nature.

Study of Rotational Stability in HTS Magnetic Bearing Rotor Incorporated the Secondary of the Induction Motor

This paper proposes the study of rotational stability in HTS magnetic bearing rotor using the pinning force of the high temperature superconductor (HTS) incorporated the secondary of the induction motor. In this study, the designed rotor is rotated by the rotating magnetic field of the secondary of the induction motor (IM). The magnetic bearing rotor has the function of the secondary side of the IM. In order to verify whether this instability affects the levitation characteristics by the pinning force, the horizontal angle of the rotor during the rotation is measured. At that time, the rotational characteristics are measured. Vibration suddenly occurred at a low rotational speed after the power supply started. After that, the rotor rotated stably. The inclination of the rotor is suppressed by 37.4% when the levitation gap <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</i> decreases. The pinning force increases as the levitation gap decreases. Therefore, the vibration suppressing effect of the rotor is obtained and the average angle is decreased. From the rotational experiments, it was confirmed the rotor with secondary of the IM function does not affect the levitation characteristics by the pinning force.

Numerical modeling and design decisions for aerostatic bearings with relatively large nozzle sizes in Magic-Angle Spinning (MAS) systems

Numerical stability analysis for aerostatic bearings was performed to obtain optimized design parameters for small submillimeter to millimeter range diameter cylindrical rotors. Such rotors are used in nuclear magnetic resonance (NMR) application to rotate sample around an axis inclined by magic angle (54.74o) relative to the magnetic field direction at rotational frequencies of about 100 kHz (magic-angle spinning, MAS). The governing Reynolds equation for the fluid film between rotor and bearing was modified for small size aerostatic bearings with relatively large nozzle diameters. The modified Reynolds equation was solved using a finite-volume method to obtain pressure and film thickness around the rotor. This led to the solution of the maximum stable inertial force as a function of rotational frequency and design parameters. The comparison with aerostatic bearings with infinitesimal nozzle sizes was obtained for supported rotor weight and critical vibrational frequency of the rotor. The stable inertial force was found to correspond to a specific nozzle diameter and a specific rotor–bearing clearance. Numerical investigation also shows an enhancement of stable inertial force with decreasing nozzle number or increasing molecular mass of the impinging gas for a specific range of nozzle parameters. Experimental observations further confirmed the role of nozzle diameter, nozzle number and molecular weight of the gas in enhancing the rotor spinning frequency. Further, design decisions were made based on such analysis and were tested for varying rotor size and bearing properties. Using design optimization based on numerical simulation, the maximum frequency of rotation for a home-built 0.4mm MAS rotor could be enhanced from 25 kHz up to 110 kHz, still below the extrapolation from large rotors.

Design of a Herringbone-Grooved Bearing for Application in an Electrically Driven Air Compressor

A turbo compressor was investigated to ensure the operational reliability of the charging of fuel cell systems. This study investigated air-lubricated herringbone bearings to support the high-speed rotating shaft. For reliable operation of the rotor bearing system, stable operation in the whole speed range (up to 120 krpm), as well as low lift-off speed, is an important issue. Some publications containing guidelines for an optimized design in terms of stability and lift-off behavior date back to the 1970s, with some simplifying assumptions (such as narrow groove theory and small eccentricity analysis). Many publications have addressed the calculations, as well as the optimization of herringbone-grooved bearings; however, general design guidelines are still missing in the view of the authors. Although the investigations related to bearings for the support of a lightweight rotor for a special compressor of a fuel cell unit, this study could also indicate favorable bearing designs for other high-speed applications. Here, the compressible Reynolds equation was solved in the whole solution domain using a conservative finite difference scheme, and the corresponding bearing characteristics were determined. In a perturbation analysis, the linearized dynamic coefficients of the herringbone bearing are calculated. To compare the suitability and performance of the various herringbone-grooved bearing designs, especially at high speed, the simple model of a Jeffcott rotor airborne with two identical herringbone-grooved journal bearings (HGJBs) was used. The geometrical parameters of the HGJBs were varied, and their effects on bearing characteristics and stability were evaluated. Recommendations concerning favorable geometrical bearing parameters for a sufficiently high stability threshold speed and reasonable low lift-off speed were the result of the parameter study.

Modeling and Simulation Study for Failure Prevention of Shredder Rotor Bearing System Used for Synthetic Elastic Material Applications

Modeling and Simulation Study for Failure Prevention of Shredder Rotor Bearing System Used for Synthetic Elastic Material Applications

Analysis of Nonlinear Characteristics and the Factors Affecting the Operation of the Active Magnetic Bearings Rotor System Considering Alford Force

Based on a test rig supported by active magnetic bearings (AMBs), this paper focuses on the study of the nonlinear dynamic characteristics and the factors affecting the operation of a rotor system under the coupling of magnetic bearing force and Alford force. In order to solve the nonlinear dynamic response of rotor system, a dynamic equation of the rotor which introduces Alford force and the electromagnetic force of the AMBs controlled by PID is established. By changing the control parameters (kPP and kDD), operation parameters (rotational speed), and structural parameters (clearance between impeller and volute), the equation is solved by using Runge−-Kutta method. The results show that the rotor system exhibits complex nonlinear dynamic characteristics under the coupling action of Alford force and magnetic bearing force. The rotor system appears different dynamic behaviors such as single period, multi multi-period, and quasi quasi-period when changing the control parameters. Among all the control parameters, adjusting kDD is more effective to ensure system stability. The amplitude of rotor increases from 8.2 μμm to 11.9 μμm with the increase of speed from 6000 rpm to 10,000 rpm, while that decreases from 9.6 μμm to 8.2 μμm with the increase of clearance between impeller and volute from 1mm to 4 mm. Therefore, under the influence of Alford force, apart from the control parameters, the operation parameters and structural parameters of magnetic bearings also affect the operation of the rotor system supported by the AMBs.

Influence of pad geometry and method of oil supply on the thermal state of GTE rotor tilting-pad journal bearing

High heat generation in the hydrodynamic wedge is one of the main factors limiting application of pad journal bearings as bearings for rotors of aircraft gas turbine engines. The goal of the research is to study the influence of the oil supply method on the bearing thermal state and to determine the design factors reducing the bearing temperature. The study was carried out with the use of bearings with diameters of 100320 mm with different design of the oil supply: through oil dispensing grooves in the pads, through oil nozzles in the inter-pad space, using lead-in chamfers for the pads, with oil bypass channels. The tasks posed were solved by using volumetric geometric models with the tools of computational fluid dynamics in the ANSYS CFX package in which differential equations describing the model are solved by the finite element method. The patterns of temperature and pressure distribution over the surface of the lower, most loaded bearing pad were obtained for various options of oil supply and different geometry of bearing pads; values of the bearing load carrying capacity, maximum pressure in the working gap, the oil mass flow through the elements of the oil supply; dependences of the bearing static performance on the distance between the shaft and nozzles. Oil supply through oil dispensing grooves made in pads is a factor that negatively affects the bearing thermal state, which is associated with so-called locking of the working gap. It is shown that implementation of oil supply through the space between the pads is more efficient. The use of a lead-in chamfer with plain inserts simplifies oil supply to the working gap. The design solutions described make it possible to reduce the maximum oil temperature in the bearing by 36 degrees Celsius.