Oil Film Clearance Research Articles

Vibration response analysis of rotor system coupled with a novel 4-DOF SFD hydrodynamic model considering the influence of rotational displacement

As a damping structure, squeeze film dampers (SFDs) are commonly employed in turbomachinery. Aiming at the problem of hydrodynamic modeling and solution, this paper presents a four-degree-of-freedom (4-DOF) hydrodynamics model of SFD, which not only considers the influence of radial displacement on oil film clearance but also the influence of rotational displacement. The Reynolds equation of the SFD is solved utilizing the finite difference method (FDM). The oil film gap distribution and static properties of the SFD under different rotational displacements and journal eccentricity are analyzed. Then, the hydrodynamic model of the 4-DOF SFD is coupled with the rotor system, and the vibration characteristics of the SFD-rotor system are analyzed. Finally, the experimental verification is carried out. The analysis results reveal that the rotational displacement has little influence on the vibration response of the SFD-rotor system at the non-critical speed. However, near the critical speed, the occurrence of rotational displacement of the SFD is more beneficial to the vibration reduction effect. Moreover, the analysis results of the hydrodynamic characteristics of the SFD show that when the eccentricity is less than 0.4, the rotational displacement has little effect on the oil film gap distribution, load moment, and oil film reaction force. When the eccentricity exceeds 0.4, the rotational displacement has a great influence on the gap distribution, load moment, and oil film reaction force of SFD.

Study on the vibration control method of a turboshaft engine rotor based on piezoelectric squeeze film damper oil film clearance

Abstract. In the complex environment of the battlefield and dust weather, hard objects including birds, bullets, sand and others will inevitably cause impact damage to the compressor blades of turboshaft engines. The damage will further result in fatigue vibration of the gas generator rotor and catastrophic accidents such as excessive engine vibration and even crash. The relation between oil film clearance of dampers and damping of rotor systems as well as the damping and vibration amplitude of a rotor system are analyzed. The functional relation between oil film clearance and vibration amplitude is derived. Taking the gas generator rotor of a certain turboshaft engine as an example, the rotor dynamic model of a gas generator rotor with oil film bearing clearance is constructed, and the vibration response of the rotor system under different oil film clearances is analyzed. A new type of squeeze film damper (SFD) structure with piezoelectric-driven split pads is innovatively designed, and the vibration control system of the gas generator rotor is built. In addition, experimental research on rotor fault vibration control under different oil film clearances is carried out. The results show that, within a certain range, when oil film clearance decreases, amplitude will decrease. Under the experimental conditions, when the driving voltage of the piezoelectric actuator is adjusted from 0 to 70 V, the oil film clearance decreases from 156 to 118 µm. Then, the vibration amplitude decreases and gradually reaches stability after 0.036 s, and the vibration amplitude of the rotor system decreases by 12 %. When the driving voltage of the piezoelectric actuator is adjusted to 150 V, the oil film clearance decreases to 76 µm, and the vibration amplitude of the rotor system decreases by 28 %. When the new SFD adopts a piezoelectric-driven split-pad structure, the structure can adjust quickly the oil film clearance online so as to control the vibration of the rotor system. The research results can provide a technical reference for the vibration control of turboshaft engine rotor systems.

Analysis of Elastohydrodynamic Lubrication (EHL) Characteristics of Port Plate Pair of a Piston Pump

This article presents a steady-state elastohydrodynamic lubrication model for the contact and sliding interface of an axial piston pump’s port plate pair. The wedge-shaped oil film thickness, pressure, viscosity, and elastic deformation distribution of the port plate pair were investigated by using the finite difference method. The elastohydrodynamic lubrication characteristics for different operating parameters and two materials of the port plate pair were analyzed for comparison. Existing conditions for the EHL were calculated, and variations in leakage and friction coefficients were investigated. The results show that the elastic deformation of the interface greatly influences the oil film’s overall performance, which is related to the material, inlet pressure, velocity, viscosity, and the minimum oil film thickness that determines the EHL. The deformation caused by oil film pressure greatly influences the model leakage and friction coefficient, especially when the deformation is equal to the oil film clearance.

Nonlinear dynamic characteristics of a power-turbine rotor system with branching structure

The branching structure is commonly utilized in the rotor system due to several merits, such as enabling a more compact structure and achieving a higher power-weight ratio, and also usually omitted or concentrated on a disk in the form of lumped mass during modeling, resulting in an inability to achieve the desired modeling accuracy. The aim of this paper is to investigate the nonlinear dynamic characteristics of a power-turbine rotor system with branching structure in turbo-shaft engine. Considering the branching structure and the effect of nonlinear oil-film force due to the squeeze film damper (SFD), the dynamic model of the power-turbine rotor system with branching structure is developed by means of finite element method. Meanwhile the critical speeds and mode shapes of the power-turbine rotor system are achieved by numerical calculation, simulation and experiment. The results reveal that the calculation results of the critical speeds and mode shapes are in good agreement with the simulation and experimental results. Moreover, the detailed comparison of vibration responses of the power-turbine rotor system with and without SFD is conducted, and the effects of oil-film clearance, length and viscosity on vibration responses are further investigated, respectively. The numerical results reveal that when the oil-film clearance goes up, the vibration amplitude at resonance goes down and the opposite is also true, moreover, increasing the oil-film length or decreasing the oil-film viscosity will improve the vibration-reduction performance of SFD.

Dynamic modeling and response analysis of rub-impact rotor system with squeeze film damper under maneuvering load

With the development of the aero-engine rotor system towards accurate modeling, it is necessary to establish a general rotor system model considering many important strong nonlinear factors. In this paper, based on the finite element method, a 6-node rub-impact rotor system model including the newly-built blade-casing rub-impact force, climbing maneuvering load, nonlinear Hertz contact force of rolling bearing, rotor eccentric unbalance force, gravity field and squeeze film damper oil film force is established. The dynamic responses of the system under different rub-impact stiffness, different oil film clearance and different bearing clearance are analyzed in detail by means of bifurcation diagram, three-dimensional spectrum diagram and axis trajectory diagram. Through comparative analysis, it is found that the change of the oil film clearance has the greatest influence on the rub-impact response of the system, followed by the bearing clearance, and the change of the rub-impact stiffness has the least influence on the rub-impact response of the system. The study of this paper can provide a theoretical basis for the rub-impact response of the rub-impact rotor system with squeeze film damper under climbing maneuvering flight.

Acquisition Method for Micro-gap Oil Film Morphology of Hydrostatic Workbench Having Double Rectangular Cavities under Working Conditions of High-Speed and Heavy-Load

When the hydrostatic workbench is running under high-speed overload conditions, the friction by-product is partially placed, causing the micro-gap oil film to be smaller, and the tribology is exposed. The oil film morphology of hydrostatic workbench directly affects its lubrication performance, and the oil film morphology is determined by deformation of bearing friction pairs and the oil film morphology is extremely difficult to obtain. This study will provide an acquisition method for the oil film morphology through the deformation of the bearing friction pair, and the deformation prediction of hydrostatic workbench having double rectangular cavities in heavy type vertical lathe has studied based on ANSYS WORKBENCH, and these are helpful to further investigate oil film shape under the working conditions of high-speed and heavy-load. The oil film clearance test rig was established, and the simulation results were verified, which verified the effectiveness of the proposed numerical simulation method. It can be concluded that the rotational speed has a greater impact on the oil film thickness than that of load, and the oil film thickness of downstream side is smaller than that of upstream side, and oil film thickness changes more quickly inside of oil sealing edge than that of outside, and the friction behavior and failure mechanism of this kind of bearing are proved.

A comprehensive analysis of factors affecting the accuracy of the precision hydrostatic spindle with mid-thrust bearing layout

This paper investigates the influence of rotor coaxiality error on spindle accuracy under different operating conditions in the precision hydrostatic spindle with a mid-thrust bearing structure. Firstly, a linearized model of rotor dynamics equation with five degrees-of-freedom is established based on Newton’s law of motion and angular momentum principle. Then, by solving the Reynolds equation and the flow continuity equation using the mathematical perturbation method, the steady and transient pressure distribution functions of the hydrostatic bearings are obtained; subsequently, the stiffness and damping coefficient matrices of the spindle are determined. Furthermore, the linearized stiffness and damping coefficients are substituted into the rotor dynamics equation to obtain the instantaneous acceleration of the rotor, and the motion trajectory of the rotor is solved iteratively by the Euler method. Finally, the paper studies the influences of different rotor coaxiality, rotating speed, cutting load, oil supply pressure, and oil film clearance on dynamic characteristics, amplitude amplification factor, and radial runout of the spindle by computer simulation. The simulation results show that the spindle runout is more sensitive to rotor coaxiality error and oil film clearance.

Nonlinear vibration response characteristics of a dual-rotor-bearing system with squeeze film damper

Rolling bearing and Squeeze Film Damper (SFD) are used in rotor support structures, and most researches on the nonlinear rotor-bearing system are focused on the simple rotor-bearing systems. This work emphasizes the comparative analysis of the influence of SFD on the nonlinear dynamic behavior of the dual-rotor system supported by rolling bearings. Firstly, a reduced dynamic model is established by combining the Finite Element (FE) method and the free-interface method of component mode synthesis. The proposed model is verified by comparing the natural characteristics obtained from an FE model with those from the experiment. Then, the steady-state vibration responses of the system with or without SFD are solved by the numerical integration method. The influences of the ball bearing clearance, unbalance, centralizing spring stiffness and oil film clearance of SFD on the nonlinear steady-state vibration responses of the dual-rotor system are analyzed. Results show that SFD can effectively suppress the amplitude jump of the dual rotor system sustaining two rotors unbalance excitations. As the ball bearing clearance or unbalance increases, the amplitude jump phenomenon becomes more obvious, the resonance hysteresis phenomenon strengthens or weakens, the resonant peaks shift to the left or the right, respectively. SFD with unreasonable parameters will aggravate the system vibration, the smaller the oil film clearance, the better the damping performance of the SFD, the larger the centralizing spring stiffness is, the larger resonance amplitudes are.

Simulation and experimental investigations on water-lubricated squeeze film damping stern bearing

In order to solve the contradiction between high load-carrying capacity and low natural frequency in designing ship water-lubricated stern bearing, an idea of independent design of load carrying and vibration reduction functions was proposed, and the squeeze film damper technology was innovatively introduced into a conventional water-lubricated stern bearing (CWSB) to form a water-lubricated damping stern bearing (WDSB). Harmonic responses of two bearings were calculated, and a dynamic characteristic experiment was carried out. The results show that the maximum displacement response (MDR) decreases with the increase in oil film clearance. With the increase in inner flange height, MDR increases first and then decreases. MDR decreases first and then increases with the increase in distribution angle. As rotation rate speeds, the difference between two bearings’ Root Mean Square (RMS) vibration amplitude remains unchanged. As load increases, relative reductions of two bearings’ maximum amplitude and RMS decrease. Amid a load of 0.2 MPa and a rotational speed of 200r/min, compared with CWSB, the maximum amplitude of WDSB in the vertical direction is reduced by about 71.8%, and the relative reduction in RMS is about 47.8%, which verifies the damping effect of WDSB is remarkable.

Effect of flight/structural parameters and operating conditions on dynamic behavior of a squeeze-film damped rotor system during diving–climbing maneuver

During aircraft maneuvering flights, engine's rotor-bearing systems are subjected to parametric excitations and additional inertial forces, which may cause severe vibration and abnormal operation. Based on Lagrange's principle combined with finite element modeling, the differential equations of motion for a squeeze film damped rotor-bearing system mounted on an aircraft in maneuvering flight are derived. Using Newmark–Hilber–Hughes–Taylor integration method, dynamic characteristics of the nonlinear rotor system under maneuvering flight are investigated. The factors are considered, involving mass unbalance, oil–film force, gravity, parametric excitations and additional inertial forces, and instantaneous static eccentricity of journal induced by maneuvering loads. The effects of forward velocity, radius of curvature, rotating speed, mass unbalance, oil–film clearance, and elastic support stiffness on transient responses of rotor system are discussed during diving–climbing maneuver. The results indicate that when the aircraft performs a diving–climbing maneuver in the vertical plane, the journal deviates from the center of oil–film outer ring, and the excursion direction of whirl orbit is determined by centrifugal acceleration and additional gyroscopic moment. The journal whirls asynchronously around the instantaneous static eccentricity and its magnitude is related to the maneuvering loads and the supporting stiffness. Increasing forward velocity or decreasing pitching radius, the rotor vibration will enter earlier into or withdraw later from the relatively large eccentricity. Rotating near critical speeds or excessive mass unbalances should be prevented during maneuvering flights. For large maneuver, the oil–film radial clearance needs to be enlarged properly to avoid hard contact between journal and outer ring. In addition, the stiffness of elastic support needs to be appropriately determined for damping performance. Overall, it provides a flexible approach with good expandability to predict dynamic characteristics of on-board squeeze-film damped rotor system during maneuvering flights in the design process.

Analysis of the Hydrodynamic Lubrication Characteristics of the External Return Spherical Bearing Pair of an Axial Piston Pump/Motor

At present, the study on lubrication of return mechanism friction pair is only for the common axial piston pump, and the influence of kinematic characteristics of contact points between the retainer plate and the spherical hinge on lubrication of return mechanism friction pair is not considered. So, it is hard to directly apply the frictional lubrication characteristic of the bearing to design the external return mechanism. Based on the kinematic and operating characteristics of the external return mechanism and considering the lubrication situation of the friction pair under Newtonian fluid, a Reynolds equation in the spherical coordinate system was deduced, and then the lubrication of the external return spherical hinge under different structural parameters was analysed. The results show that different slant inclination of the external swash plate, pump shaft rotating speeds, and eccentricities all affect the lubrication characteristics of the friction pair, especially the slant inclination of the external swash plate and oil film clearance has great influence on axial leakage flow. Therefore, in the design of external return mechanism of the multirow axial piston pump, the lubrication performance of the external return spherical hinge under different slant inclinations of the external swash plate should be analysed and calculated.

Dynamic characteristics of high-speed gasoline engine turbocharger based on thermo-elasto-hydrodynamic lubrication bearing model and flexible multibody dynamics method.

A flexible multibody dynamic calculation model based on thermo-elasto-hydrodynamic lubrication bearing model was established. This numerical simulation method provided a more realistic turbocharger calculation model and a more reliable theoretical support for studying the dynamic vibration characteristics of the floating ring bearing turbocharger system. In order to fully consider the dynamic characteristics of each component, the behavior of the floating ring bearing was described by generalized incompressible Reynolds equation in thermo-elasto-hydrodynamic lubrication model. The flexible body substructure models were established by the modal synthesis method. Based on this model, the direct mathematical model of the relationship between the eccentricity of the rotor and the oil film clearance on the turbocharger's surface vibration was established. The influence of eccentricity and oil film thickness on the surface vibration of the turbocharger body was calculated by transient dynamics method. The results showed that the eccentricity of the rotor and the vibration of turbocharger housing were monotonic functions, but the interaction between the whirl of internal and external oil films made the mechanism of the influence of the oil film thickness on the turbocharger body's vibration complicated. The research provided a new idea for the structural vibration and synchronous noise control of the supercharger.

Effect of design parameters and operational conditions on the motion accuracy of hydrostatic thrust bearing

In this study, the effect of design parameters and operational conditions on motion accuracy of the closed configuration hydrostatic thrust bearing was researched. Key design parameters include land width, nominal oil film thickness, and perpendicularity error between mandrel and thrust plates. Oil supply pressure, external load, and rotation load are the considered operational conditions. Predictions of the induced effect are made by introducing oil film clearance function, governing equations, flow rate continuity equations, and dynamic equations of mandrel to model axial rotation error and angular motion error. The results show that the axial rotation accuracy increased, as land width (larger than 8 mm), nominal oil film thickness, and oil supply pressure increased, but there was little impact on angular motion error. The axial rotation error and angular motion error increased with the increase in the external load and rotation speed. Confirmation of the perpendicularity error has been achieved, in this study, by conducting experiments, using ultra-precision measuring machine. In addition, axial rotation error was tested on a hydrostatic rotary table and compared with the simulation results to check the validity of the proposed method. The results provide useful design guidelines and operation advice for hydrostatic thrust bearing in high-precision machine tools.

Matching the relationship between rotational speed and load-carrying capacity on high-speed and heavy-load hydrostatic thrust bearing

PurposeRotational speed and load-carrying capacity are two mutual coupling factors which affect high precision and stable operation of a hydrostatic thrust bearing. The purpose of this paper is to study reasonable matching relationship between the rotational speed and the load-carrying capacity.Design/methodology/approachA mathematical model of relationship between the rotational speed and the load-carrying capacity of the hydrostatic bearing with double-rectangle recess is set up on the basis of the tribology theory and the lubrication theory, and the load and rotational speed characteristics of an oil film temperature field and a pressure field in the hydrostatic bearing are analyzed, reasonable matching relationship between the rotational speed and the load-carrying capacity is deduced and a verification experiment is conducted.FindingsBy increasing the rotational speed, the oil film temperature increases, the average pressure decreases and the load-carrying capacity decreases. By increasing the load-carrying capacity, the oil film temperature and the average pressure increases and the rotational speed decreases; corresponding certain reasonable matching values are available.Originality/valueThe load-carrying capacity can be increased and the rotational speed improved by means of reducing the friction area of the oil recess by using low-viscosity lubricating oil and adding more oil film clearance; but, the stiffness of the hydrostatic bearing decreases.

Dynamic Characteristic Difference on Two Kinds of Broading Machine on the Similar Configuration

This paper focuses on the dynamics characteristic difference on the two kinds of broading machine, the workpiece moving and the cutting-tool moving. There is 0.002mm thickness of oil-film clearance between the mobile and immobile components of the broading machine. Hydraulic pressure derived from the driving oil cylinder drives the workpiece or cutting-tool moving, while the material on the workpiece is cutting. Cutting-tool of the machine is an external expand cutter with the groove for breaking the cutting waste, the manufacturing phase is a pulse impact cutting exciting applying on the broading machine correspondingly. On manufacturing, natural characteristic of the broading machine is approximately the pulse impulsion frequency of the machine;response amplitude of the lather is increasing manifesting. The study is focused on the dynamics characteristic of two kinds of broading machine, the difference is workpiece or cutter moving, to predict the manufacturing performance.

Finite Element Analysis of Static Characteristics of a Hydrostatic Guideway and its Effect Factors

Guide ways of ultra-precision machine tools always have sufficient stiffness and guiding precision. But guide way rails deformation caused by oil film pressure and slider offset lead to oil film clearance change which affects static stiffness and guiding precision. An inside-slider hydrostatic guide way is designed, and its static characteristics are analyzed. As a result, the effect of slider offset on stiffness and guiding precisions is obtained. A FE model of guide way is established. An elastomer of virtual material properties is used to simulate oil film, so that the relationship between oil film clearance and pressure can be represented in a certain range. Static stiffness and guiding precision are obtained considering deformation of rails.

Numerical Prediction of Manufacturing Error in Sliding Panel Structure

The present work focuses on the numerical prediction of the manufacture quality of a sliding panel structure, in which the mobile components are floating on the immobile components and the 0.002mm thickness oil-film clearance between the mobile and immobile components. The interaction between them is the interfacial coupling interaction. A single-point spring-damping supporting element is introduced to simulate this type of interaction traditionally, in which the torsion of the mobile components is increasing with the supporting element reduced. To analogy the interfacial coupling interaction, the finite centrality supporting method is introduced to study the thin oil-film effect between the mobile and immobile components. And the manufacturing quality is predicting through the numerical study. Compared with the results derived from the numerical and experiments, the manufacturing error is in accordance with each other.