Effects of Turbulence and Viscosity Variation on the Dynamic Coefficients of Fluid Film Journal Bearings

1985 ◽  
Vol 107 (2) ◽  
pp. 256-261 ◽  
Author(s):  
D. F. Wilcock ◽  
O. Pinkus
Keyword(s):  
High Speed ◽  
Dynamic Stiffness ◽  
Journal Bearings ◽  
Fluid Film ◽  
Turbulent Regime ◽  
Dynamic Coefficients ◽  
Damping Characteristics ◽  
Fluid Film Bearings ◽  
Viscosity Variation ◽  
Stiffness And Damping

Many high-speed or large fluid film bearings operate in the turbulent regime. However, relatively little consideration has been given to the effects of turbulence and of the variation in viscosity on the dynamic stiffness and damping characteristics of the bearings. Since the dynamic behavior of the rotor supported on such bearings is often closely tied to the bearing dynamic coefficients, knowledge of them may be critical to both the design and the in-place correction of rotor instabilities. These effects are here considered in some detail on the basis of computer calculated analytical results, both in general dimensionless terms and with regard to a specific numerical example.

Field Identification of Stiffness and Damping Characteristics of Fluid Film Bearings

2008 ◽  
Author(s):  
Sameh H. Tawfick ◽  
Aly El-Shafei ◽  
M. O. A. Mokhtar
Keyword(s):  
Journal Bearings ◽  
Fluid Film ◽  
Flexible Rotor ◽  
Test Rig ◽  
Vibration Data ◽  
Damping Characteristics ◽  
Fluid Film Bearings ◽  
Field Identification ◽  
Modal Mass ◽  
Stiffness And Damping

A method for field identification of stiffness and damping characteristics of fluid film bearings FFB is derived. The method relies on measuring both the shaft and the housing’s vibration response. Two independent unbalance runs are performed and the synchronous response is recorded. Using the housing vibration data, the amount of unbalance acting on the bearing, as well as the flexible shafts’ “modal mass” can be experimentally determined. Thus, with this method, field engineers can identify the bearings impedance in flexible rotor-bearing systems. A test rig comprising a flexible shaft supported on two cylindrical journal bearings is used to verify the proposed method. The amount of uncertainty in the derived coefficients is calculated.

Dynamic Identification of 280mm Diameter Tilting Pad Journal Bearings: Test Results and Measurement Uncertainties Assessment of Different Designs

2020 ◽  
Author(s):  
Riccardo Ferraro ◽  
Alice Innocenti ◽  
Mirko Libraschi ◽  
Michele Barsanti ◽  
Enrico Ciulli ◽  
...  
Keyword(s):  
High Performance ◽  
Dynamic Properties ◽  
Journal Bearings ◽  
Turbulent Regime ◽  
Dynamic Identification ◽  
Damping Characteristics ◽  
Flexible Rotors ◽  
Tilting Pad ◽  
Stiffness And Damping ◽  
Tilting Pad Journal Bearings

Abstract Tilting pad journal bearings (TPJBs) are crucial elements in turbomachinery applications providing stiffness and damping characteristics that determine rotor system dynamic behavior. Hence, a correct design and an accurate dynamic properties prediction is fundamental for the successful industrial operation of rotating machinery. Current design trends in turbomachinery aiming at higher efficiency and power through weight optimization and higher operating speeds determine the development of large flexible rotors that are particularly important from the rotordynamic standpoint. The dynamic feasibility of this type of machine relies on bearing stiffness and damping characteristics that must be predicted with a certain level of confidence in order to increase the accuracy of the expected rotordynamic behaviour and avoid unpredicted vibration issues when rotors are operated. Furthermore, large centrifugal compressors commonly used in Liquified Natural Gas (LNG) applications make the bearings operate at very high peripheral speed where the transition from laminar to turbulent regime occurs, increasing the necessity of predictions accuracy. In this paper a test campaign on different large TPJB solutions operating in turbulent lubrication regime has been performed on a dedicated test rig designed for investigations on large size high-performance oil bearings. In the present work both static performance and dynamic identification of the tested TPJB solutions are presented and compared to numerical model predictions. The results of an uncertainty quantification, performed to validate the experimental results, are also shown.

Thermohydrodynamic Analysis of Process-Liquid Hydrostatic Journal Bearings in Turbulent Regime, Part I: The Model and Perturbation Analysis

1995 ◽  
Vol 62 (3) ◽  
pp. 674-678 ◽  
Author(s):  
Zhou Yang ◽  
L. San Andres ◽  
D. W. Childs
Keyword(s):  
Energy Equation ◽  
Dynamic Performance ◽  
Journal Bearings ◽  
Fluid Film ◽  
Turbulent Regime ◽  
Fluid Inertia ◽  
Flow Process ◽  
Fluid Film Bearings ◽  
Friction Factors ◽  
Flow Turbulence

A bulk-flow thermohydrodynamic (THD) analysis is developed for prediction of the static and dynamic performance characteristics of turbulent-flow, process-liquid, hydrostatic journal bearings (HJBs). Pointwise evaluation of temperature and hence liquid properties is achieved through the solution of the energy equation in the fluid film with insulated boundaries, and justified for fluid film bearings with external pressurization. Fluid inertia within the film lands and at recess edges is preserved in the analysis. Flow turbulence is accounted through turbulence shear parameters based on friction factors derived from Moody’s formulae. The effects of fluid compressibility and temperature variation in the bearing recesses are included. Numerical solution and results are presented in the second part of this work and compared with some limited experimental data for a liquid hydrogen (LH2) bearing.

scholarly journals Alternation of the dynamic coefficients of short journal bearings due to wear

2015 ◽  
Vol 6 (5) ◽  
pp. 649-664
Author(s):  
Michael G. Papanikolaou ◽  
Michael G. Farmakopoulos ◽  
Chris A. Papadopoulos
Keyword(s):  
Dynamic Stiffness ◽  
Journal Bearings ◽  
Fe Analysis ◽  
Operating Conditions ◽  
Wear Depth ◽  
Content Type ◽  
Damping Coefficients ◽  
Dynamic Coefficients ◽  
Low Viscosity ◽  
Stiffness And Damping

Purpose – Wear in journal bearings occurs when the operating conditions (high load, high temperature, low angular velocity or low viscosity), downgrade the ability of the bearing to carry load. The wear depth increases because the rotor comes in contact with the bearing surface. Wear in journal bearings affects their characteristics because of its influence on the thickness of the fluid film. This influence can be detected in the dynamic behavior of the rotor and especially in the dynamic stiffness and damping coefficients. The paper aims to discuss these issues. Design/methodology/approach – In this paper, the effect of wear on the rotor dynamic stiffness and damping coefficients (K and C) of a short journal bearing is investigated. K and C in this work are estimated by using two methods a semi-analytical method and finite element (FE) analysis implemented in the ANSYS software. Findings – The main goal of this research is to make the identification of wear in journal bearings feasible by observing the alternation of their dynamic coefficients. Both of the methods implemented are proven to be useful, while FE analysis can provide more accurate results. Originality/value – This paper is original and has not been published elsewhere.

Influence of Fluid Film Boundary Migration on Dynamic Coefficients of Journal Bearings and Behavior of Rotor System

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Changmin Chen ◽  
Jianping Jing ◽  
Jiqing Cong ◽  
Zezeng Dai ◽  
Jianhua Cheng
Keyword(s):  
Journal Bearing ◽  
Boundary Migration ◽  
Dynamical Behavior ◽  
Journal Bearings ◽  
Rotor System ◽  
Fluid Film ◽  
Dynamic Coefficients ◽  
Film Boundary ◽  
Rotor Bearing ◽  
Stiffness And Damping

Abstract The position of fluid film in journal bearing will change while the journal moving in bearing, which can be named fluid film boundary migration (FFBM). It is usually ignored in the calculation of linear dynamic coefficients. While, the errors brought by this neglection was not ever investigated in detail. In this paper, the influence of FFBM on bearing dynamic coefficients and rotor system dynamic behaviors are investigated. A new perturbation-based model is proposed to take the FFBM into account by modifying the boundary conditions of governing equations. It is then verified by the experimental results and analytical results from previous research. Furthermore, the effects of FFBM on stiffness and damping in two typical journal bearings are investigated. The result indicates that the FFBM has a significant influence on dynamic coefficients of full circular journal bearing but little impact on journal bearing with axial grooves. Moreover, it affects the stiffness and damping more significantly in the cases of large length-to-diameter ratios or small eccentricity ratios in full circle bearing. Finally, the dynamical behavior of a rotor-bearing system with considering the FFBM is also investigated. The result shows that the FFBM of oil film has remarkable influences on the instability threshold and imbalance responses of the rotor system, which should not be ignored. The conclusions obtained in this research are expected to be helpful for the design of full circular journal bearings or rotor-bearing systems.

Self-Centering Film Dividers

1980 ◽  
Vol 102 (4) ◽  
pp. 490-494
Author(s):  
D. F. Wilcock
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Journal Bearings ◽  
The Self ◽  
Fluid Film ◽  
Turbulent Regime ◽  
Frictional Drag ◽  
Thrust Bearings ◽  
Average Shear ◽  
Effective Reynolds Number

One rather effective way to reduce the frictional drag of fluid film journal or thrust bearings, when operating in the turbulent regime, is to introduce a “floating” member dividing the fluid film into two roughly equal parts. The average shear rate is unchanged, but the effective Reynolds number is reduced, with a corresponding reduction in friction power. Such dividers have been widely used in floating sleeve journal bearings of the small high speed type. Use in thrust bearings is not known. In either application, it is essential that the self-centering divider center itself under all conditions after shaft rotation is initiated. This paper describes and analyzes a divider design that has such a property.

A Theoretical Estimation of the Performance of Journal Bearings Operating in the Turbulent Lubrication Regime

1975 ◽  
Vol 17 (2) ◽  
pp. 52-56 ◽  
Author(s):  
K. F. King ◽  
C. M. Taylor
Keyword(s):  
Kinematic Viscosity ◽  
Journal Bearings ◽  
Fluid Film ◽  
Turbulent Regime ◽  
Theoretical Estimation ◽  
Theoretical Evaluation ◽  
Fluid Film Bearings ◽  
Lubrication Regime

The use of process fluids of low kinematic viscosity as lubricants and the ever increasing surface speeds which are being encountered in fluid-film bearings have meant an increase in the number of bearings which operate in the turbulent regime. This paper describes a theoretical evaluation of the performance of 360-degree journal bearings operating turbulently, presents generalized data and discusses the results with comments upon the assumptions made and practical realities.

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