Modeling Fluid Inertia Forces of Short Journal Bearings for Rotordynamic Applications

1995 ◽  
Vol 117 (4) ◽  
pp. 462-469 ◽  
Author(s):  
A. El-Shafei
Keyword(s):  
Momentum Equation ◽  
Journal Bearings ◽  
Fluid Inertia ◽  
Radial Acceleration ◽  
Damping Characteristics ◽  
Energy Approximation ◽  
Form Model ◽  
Fluid Inertia Effect ◽  
Stiffness And Damping ◽  
Inertia Forces

It has been recently suggested that fluid inertia may play an important role in the dynamic behavior of rotors supported on journal bearings. This paper presents a model for fluid inertia forces in short cylindrical journal bearings based on an energy approximation. The inertialess velocity profiles predicted by the solution of Reynolds’ equation are inserted in the axial momentum equation multiplied by the axial velocity profile and integrated across the film thickness, to obtain the pressure in short journal bearings including the fluid inertia effect. The pressure is then integrated to obtain the fluid inertia forces. It is shown that the inertia forces thus obtained are proportional to the usual radial, centripetal, tangential and coriolis accelerations of the journal, in addition to a nonlinear radial acceleration. Moreover, it is shown that the inertia forces contribute to the stiffness and damping characteristics of the journal bearings. The inertia coefficients of the bearings are obtained in cartesian and cylindrical coordinates, for both uncavitated and cavitated bearings, and are plotted versus the eccentricity ratio. The model thus obtained is an approximate analytical closed form model for fluid inertia forces in short journal bearings. Such a model is the most suitable for rotordynamic applications, particularly for time transient rotordynamic simulations.

Modelling Fluid Inertia Forces of Short Journal Bearings for Rotordynamic Applications

1993 ◽  
Author(s):  
A. El-Shafei
Keyword(s):  
Momentum Equation ◽  
Journal Bearings ◽  
Fluid Inertia ◽  
Radial Acceleration ◽  
Damping Characteristics ◽  
Energy Approximation ◽  
Form Model ◽  
Fluid Inertia Effect ◽  
Stiffness And Damping ◽  
Inertia Forces

Abstract It has been recently suggested that fluid inertia may play an important role in the dynamic behavior of rotors supported on journal bearings. This paper presents a model for fluid inertia forces in short cylindrical journal bearings based on an energy approximation. The inertialess velocity profiles predicted by the solution of Reynolds’ equation are inserted in the axial momentum equation multiplied by the axial velocity profile and integrated across the film thickness, to obtain the pressure in short journal bearings including the fluid inertia effect. The pressure is then integrated to obtain the fluid inertia forces. It is shown that the inertia forces thus obtained are proportional to the usual radial, centripetal, tangential and coriolis accelerations of the journal, in addition to a nonlinear radial acceleration. Moreover, it is shown that the inertia forces contribute to the stiffness and damping characteristics of the journal bearings. The inertia coefficients of the bearings are obtained in cartezian and cylindrical coordinates, for both uncavitated and cavitated bearings, and are plotted versus the eccentricity ratio. The model thus obtained is an analytical closed form model for fluid inertia forces in short journal bearings. Such a model is the most suitable for rotordynamic applications, particularly for time transient rotordynamic simulations.

Dynamic Stiffness and Damping Characteristics of Compensated Hydrostatic Thrust Bearings

1982 ◽  
Vol 104 (4) ◽  
pp. 491-496 ◽  
Author(s):  
M. K. Ghosh ◽  
B. C. Majumdar
Keyword(s):  
Load Capacity ◽  
Dynamic Stiffness ◽  
Fluid Inertia ◽  
Thrust Bearings ◽  
Continuity Equations ◽  
Damping Characteristics ◽  
Oil Flow ◽  
Stiffness And Damping ◽  
Compressibility Effects ◽  
Fluid Compressibility

This paper deals with an analysis of the dynamic behavior of compensated hydrostatic circular step thrust bearings taking into account fluid inertia and recess volume fluid compressibility effects. The Reynolds equation for fluid film and the recess flow continuity equations are linearized using perturbation methods. Results in terms of dimensionless load capacity, oil flow rate, stiffness, and damping are presented for capillary and orifice compensated bearings. Results show a marked influence of fluid inertia and recess volume fluid compressibility on the performance of the bearing.

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.

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.

The Effects of Fluid Inertia Forces in Parallel Circular Squeeze Film Bearings Lubricated With Pseudo-Plastic Fluids

1986 ◽  
Vol 108 (2) ◽  
pp. 282-287 ◽  
Author(s):  
Hiromu Hashimoto ◽  
Sanae Wada
Keyword(s):  
Numerical Solutions ◽  
Momentum Equation ◽  
Mean Value ◽  
Squeeze Film ◽  
Graphical Form ◽  
Shear Strain Rate ◽  
Fluid Inertia ◽  
Film Pressure ◽  
Inertia Forces ◽  
Plastic Fluids

The effects of fluid inertia forces in parallel circular squeeze film bearings lubricated with pseudo-plastic fluids are examined theoretically. In the derivation of lubrication equation, the cubic equation obtained from the empirical flow curves for pseudo-plastic fluids is used as the relation between shear stress and shear strain rate, and the inertia term in the momentum equation is approximated by the mean value averaged across the film thickness. Numerical solutions for the film pressure of circular bearings lubricated with Newtonian and pseudo-plastic fluids under the sinusoidal squeeze motion are presented in graphical form and the effects of inertia forces on the film pressure are determined.

Effect of Fluid Inertia on Stability of Oil Journal Bearings

1999 ◽  
Vol 122 (4) ◽  
pp. 741-745 ◽  
Author(s):  
S. K. Kakoty ◽  
B. C. Majumdar
Keyword(s):  
Reynolds Number ◽  
Steady State ◽  
Transient Analysis ◽  
Mass Parameter ◽  
Journal Bearings ◽  
Fluid Inertia ◽  
Viscous Forces ◽  
Fluid Inertia Effect ◽  
The Stability ◽  
Negligible Contribution

In the analysis of hydrodynamic journal bearings the effect of fluid inertia is generally neglected in view of its negligible contribution compared to viscous forces. However, the fluid inertia effect is to be taken in the analysis when modified Reynolds number is around one. Though there are a few attempts to analyze steady-state and dynamic characteristics of finite journal bearings, stability of the journal under the effect of fluid inertia is yet to be investigated. An attempt has been made to evaluate the mass parameter (a measure of stability) besides finding out the steady-state characteristics of finite journal bearings considering the effects of fluid inertia. The analysis is carried out for modified Reynolds number ∼O(1.), which is assumed to be laminar. A nonlinear time transient analysis is carried out for the stability analysis. [S0742-4787(00)00204-6]

Sign in / Sign up

Export Citation Format

Share Document