Outer Oil Films Research Articles

Analysis of Dynamic Characteristics of Small-Scale and Low-Stiffness Ring Squeeze Film Damper-Rotor System

Rotor machinery supports are susceptible to fracture arising from multi-period or irregular transient vibration and even the inconspicuous fatigue phenomenon. The novel dynamic model of a rotor mounted on the floating ring squeeze film damper (SFD) was developed. The proposed SFD implements low stiffness and small scale to overcome the deficiency. Based on the theory of hydrodynamic lubrication, the Reynolds equations on the working principle of the floating ring are established. Then, the dynamic characteristics of the rotor system during maneuvers, with the floating ring SFD supports, are subsequently examined by adopting the finite difference method. In addition, the oil film whirl mechanism of the floating ring SFD is demonstrated according to the transient analysis of the fluid–structure interaction model. The results of the SFD simulation reveal that, with increasing eccentricity ratio, both the inner and outer oil film pressure tend to be larger due to the shrinkage of the effective coverage of oil film. The maximum oil film pressure and bearing capacity increase nonlinearly within a certain eccentricity ratio range. Through the comparisons of the results, the vibration suppression effects of the proposed SFD are analyzed. This work will provide the practical reference for the dynamic design of the rotor support system.

An investigation on the lubrication characteristics of floating ring bearing with consideration of multi-coupling factors

The paper investigates the static and dynamic lubrication parameters of the floating ring bearing (FRB). Modified lubrication models considering the effects of various coupling factors are proposed. Multiscale methods are exploited to enhance the accuracy and efficiency of the calculation. The simulation procedures are developed to analyze the lubrication performances. Theoretical results agree well with the references. Influences of clearance ratio, vertical load and rotating speed on the static lubrication parameters and the dynamic lubrication parameters of the inner oil film and the outer oil film are investigated systematically. Changing rules of the lubrication parameters are summarized and concluded. The clearance ratio has influences on the lubrication performances of the inner film while has no influences on the outer film. The vertical load has influences on the lubrication performances of the bearing. The conclusions are applicable to such floating ring bearing with the similar structures.

Effect of the inlet oil temperature on vibration characteristics of the high-speed turbocharger rotor system

The inlet oil temperature of the rotor system with high-speed and light-load turbocharger will change during operation, which will change the vibration characteristics of the rotor system and even cause vibration accidents. Taking a certain type of high-speed and light-load turbocharger rotor system as the research object, the changes in oil film viscosity, friction power consumption, oil film temperature rise, and ring speed ratio with the inlet oil temperature of floating ring bearings are analyzed. A dynamic finite-element model of the turbocharger rotor–floating-ring-bearing system is constructed, and the finite-element model is verified through the critical speed and colormap spectrogram. The Newmark integral method is used to analyze the nonlinear transient response of the rotor system, and the influence of the inlet oil temperature on the vibration response characteristics of the rotor system is studied. The results show that an increase in the inlet oil temperature leads to a decrease in the internal and external oil film viscosities, frictional power consumption, temperature rise, and an increase in the ring speed ratio. When the inlet oil temperature increases from 50 °C to 130 °C, the amplitude of the inner oil film oscillation will gradually decrease, but the amplitude of the outer oil film vortex will gradually increase, and the journal speed point where the inner oil film oscillation and the outer oil film vortex will appear about 30% in advance. In summary, the rotor vibration is better when the inlet oil temperature is about 90 °C. The conclusion of this paper can provide a theoretical reference for selecting the operating parameters of the rotor system with the least vibration for high-speed light-load turbochargers.

Wire Mesh Dampers for Semi-Floating Ring Bearings in Automotive Turbochargers: Measurements of Structural Stiffness and Damping Parameters

The current work introduces a new semi-floating ring bearing (SFRB) system developed for improving the rotordynamic and vibration performance of automotive turbochargers (TCs) at extreme operation conditions, such as high temperature, severe external force excitation, and large rotor imbalance. The new bearing design replaces outer oil films, i.e., squeeze film dampers (SFDs), in TC SFRBs with wire mesh dampers (WMDs). This SFRB configuration integrating WMDs aims to implement reliable mechanical components, as an inexpensive and simple alternative to SFDs, with consistent and superior damping capability, as well as predictable forced performance. Since WMDs are in series with the inner oil films of SFRBs, experimentally determined force coefficients of WMDs are of great importance in the design process of TC rotor-bearing systems (RBSs). Presently, the measurements of applied static load and ensuing deflection determine the structural stiffnesses of the WMDs. The WMD damping parameters, including dissipated energy, loss factor, and dry friction coefficient, are estimated from the area of the distinctive local hysteresis loop of the load versus WMD displacement data recorded during consecutive loading-unloading cycles as a function of applied preload with a constant amplitude of motion. The changes in WMD loss factor and dry friction coefficient due to increases in preload are more significant for the WMDs with lower density. The present work shows, to date, the most comprehensive measurements of static load characteristics on the WMDs for application into small automotive TCs. More importantly, the extensive test measurements of WMD deflection versus increasing static loads will aid to anchor predictions of future computation model.

Numerical Continuation Applied to Nonlinear Rotor Dynamics

Besides the synchronous oscillations due to unbalance, high-speed rotors in oil film bearings are known to show whirl/whip instabilities which exhibit various types of subsynchronous oscillations. Here, the methods of numerical continuation are applied to study the subsynchronous oscillations in detail. The main scope is to analyze the stability and bifurcation behavior of the unbalanced Laval/Jeffcott rotor supported in semi-floating ring bearings. Characteristic bifurcation scenarios prove the existence of two different types of Hopf bifurcations which represent whirl/whip instabilities due to the inner or the outer oil films. Furthermore, it is shown that the critical limit cycle of non-tolerable amplitude is born at a saddle-node bifurcation. Finally, the influence of unbalance on the subsynchronous oscillations is investigated by tracing the occurring bifurcations in the parameter plane of the unbalance load and the rotor speed. The obtained bifurcation curves provide extended stability charts which illustrate the global solution behavior of the considered rotor bearing systems.

Effects of floating ring bearing manufacturing tolerance clearances on the dynamic characteristics for turbocharger

The inner and outer oil film dynamic characteristic coefficients of floating ring bearings(FRBs) change due to the manufacturing tolerance of the floating ring, journal and intermediate, which leads to high-speed turbocharger’s vibration too large and even causes nonlinear vibration accident. However, the investigation of floating ring bearing manufacturing tolerance clearance on the rotordynamic characteristics is less at present. In order to study the influence law of inner and outer clearance on turbocharger vibration, the rotor dynamic motion equations of turbocharger supported in FRBs are derived by analyzing the size relations between floating ring, journal and intermediate for the inner and outer oil film clearances, the time transient response analysis for combination of FRBs clearance are developed. A realistic turbocharger is taken as a research object, the FE model of the turbocharger with FRBs is modeled. Under the conditions of four kinds of limit state bearing clearances for inner and outer oil film, the nonlinear transient analyses are performed based on the established FE dynamic models of the nonlinear rotor-FRBs system applied incentive combinations of gravity and unbalance force, respectively. From the waterfall, the simulation results show that the speed for the appearance of fractional frequency is not identical and the amplitude magnitude is different under the four kinds of bearing manufacturing tolerance limit clearances, and fractional frequency does not appear in the turbocharger and the amplitude is minimum under the ODMin/IDMax bearing manufacturing tolerance clearances. The turbocharger vibration is reduced by controlling the manufacturing tolerance clearance combinations of FRBs, which is helpful for the dynamic design and production-manufacturing of high-speed turbocharger.

Elastic ring deformation and pedestal contact status analysis of elastic ring squeeze film damper

This paper investigates the dynamic parametric characteristic of the elastic ring squeeze film damper (ERSFD). Firstly, the coupled oil film Reynolds equations and dynamic equations of an ERSFD supported rotor system are established. The finite differential method and numerical simulation are used to analyze the oil film pressure distribution, bearing capacity of ERSFD, oil film stiffness and damping characteristics during a vibration period. Then, based on the oil film pressure results, the deformation of elastic ring is revealed by the finite element method. Finally, pedestal contact status is analyzed according to the change of oil film thickness during a vibration period. The results reveal that the oil film pressure is sectionally continuous, the deformation of elastic ring is complex under the compression of inner and outer oil film, and different pedestal contacts occur in a vibration period. The level of nonlinearity of the bearing capacity, oil film stiffness and damping can be effectively lightened by application of the elastic ring.

Stability and bifurcation phenomena of Laval/Jeffcott rotors in semi-floating ring bearings

Within this contribution, a linear-elastic Laval/Jeffcott rotor is considered, which is symmetrically supported in two identical semi-floating ring bearings. Run-up simulations and bifurcation analyses are carried out to investigate the stability and bifurcation phenomena of the rotor-bearing system. In particular, the methods of numerical continuation are applied to identify the nonlinear phenomena (jump phenomena, coexistence of solutions, etc.) and the corresponding bifurcations. The occurrence of subsynchronous oscillations is examined, which is caused by an oil whirl/whip instability due to the inner oil films. In this case, the main damping is provided by the outer oil films so that the oscillation amplitudes usually remain moderate. Besides these well-known subsynchronous oscillations with moderate amplitudes (oil whirl/whip instability due to the inner oil films), it is shown that self-excited oscillations with very high amplitudes also exist. This effect resembles Total Instability known from rotors in full-floating ring bearings. A detailed bifurcation analysis proves the coexistence of a so-called critical limit cycle with high amplitudes in the case of the perfectly balanced rotor which represents Total Instability. Finally, a variation of rotor and bearing parameters shows the influence on both the subsynchronous oscillations of tolerable amplitudes and the critical limit cycle oscillations.

The verification of adiabatic model of a lateral sliding bearing with a floating ring bearing

This research work describes the adiabatic model of a lateral slide bearing with a floating ring bearing. In order to support recommended assumptions for a designed model and for an evaluation accuracy of achieved results, the author developed a verification method which let comparing results received in a numerical way with that of the ones received in experimental tests. The evaluation criteria of a theoretical model were presented in regard to results from empirical studies. These criteria were divided into three groups. As the basic criteria, the author accepted the position of a bearing journal centre towards a fixed bearing bush, also for these positions pressure and temperature distributions in the outer oil film were chosen. In the conclusion, suggestions were made about the comparison of pressure and temperature distributions, frictional moments on a fixed bush surface, and angular velocities of a floating ring bearing towards a fixed bearing bush. The reasons of differences between measured and calculated values were also discussed.

Oil whirl, oil whip and whirl/whip synchronization occurring in rotor systems with full-floating ring bearings

High-speed rotors are often supported in floating ring bearings because of their good damping behavior. In contrast to conventional hydrodynamic bearings with a single oil film, full-floating ring bearings consist of two oil films: An inner and an outer oil film. As single oil-film bearings, full-floating ring bearings also show the typical fluid-film-induced instabilities (self-excited vibrations). Both inner and outer oil films can become unstable and exhibit oil whirl/whip instabilities.

Dynamic Modeling of a Dual Clearance Squeeze Film Damper. Part II

Squeeze film dampers (SFD) have been used for many years to control the vibrations of the shafts in high-speed rotating machinery. Dual squeeze film dampers are essentially a combination of two SFDs separated by a sleeve. Normal operation utilizes only one oil film, as in a conventional damper, and the sleeve is fixed in place. However, under high load conditions, the sleeve is released and both oil films become operational. An experimental facility was designed and built to study both single and dual SFD behavior within mechanically controlled orbits. The first part of this paper presents a description of this test rig and provides a dynamic model of a single SFD. In this portion of the paper, we present results obtained while the inner sleeve is released and both oil films are operational. Here the inner sleeve is not supported by any mechanical device; the anti-rotational effect is provided by the opposed actions of the inner oil film and of the outer oil film. The modeling covers the inner and the outer oil films, the elastic fixtures, the unbalanced shaft, and the sleeve. Numerical results are compared with the experimental data. Presented at the ASME/STLE Tribology Conference, in Long Beach, California October 24-27, 2004 Review led by Luis San Andres

EFFECTS OF CHARACTERISTICS OF FLOATING BUSH BEARINGS ON THE STABILITY OF TURBOCHARGERS

The effect of the spring and damping characteristics of a floating bush bearing on the stability is investigated numerically. The characteristics of the bearing's inner and outer oil film are calculated separately. In this calculation, the configuration of the bearing's surfaces, namely, the oil paths, and the increase of the temperature due to the bearing loss are taken into account. The rotor dynamics are then calculated and the characteristics of the unstable vibration of the rotor investigated. This kind of shaft-bearing system has four rigid vibration modes : two in which the bushes move in phase with the shaft and two in which the bushes move out of phase with the shaft. The spring constant of the outer oil film mostly affects the former two modes, whereas the damping characteristics of the outer oil film affects all modes. By taking the advantage of these effects, we can control the unstable vibration and eliminate the mode we need to avoid.