Linear Stability Analysis of Short Porous Journal Bearings—Use of the Brinkman Model

1995 ◽  
Vol 117 (1) ◽  
pp. 199-202 ◽  
Author(s):  
Jaw-Ren Lin ◽  
Chi-Chuan Hwang
Keyword(s):  
Linear Stability ◽  
Flow Model ◽  
Slip Flow ◽  
Journal Bearings ◽  
Shear Stresses ◽  
Brinkman Model ◽  
Stability Threshold ◽  
Viscous Shear ◽  
Shear Effects ◽  
The Stability

On the basis of a Brinkman model (BM), this paper predicts that the effects of viscous shear stresses on the linear stability of short porous journal bearings are apparent and not negligible. Compared with those of the slip-flow model (SFM) and the Darcy model (DM), the viscous shear effects provide a significant increase in the stability threshold speeds of short porous journal bearings.

Linear stability analysis of double-layered porous journal bearings under coupled-stress lubrication with slip flow and percolation effect of additives

2019 ◽  
Vol 71 (3) ◽  
pp. 447-458 ◽  
Author(s):  
Shitendu Some ◽  
Sisir Kumar Guha
Keyword(s):  
Linear Stability ◽  
Mass Parameter ◽  
Critical Mass ◽  
Slip Flow ◽  
Tangential Velocity ◽  
Journal Bearings ◽  
Content Type ◽  
Percolation Effect ◽  
The Stability ◽  
Coupled Stress

Purpose In the application of hydrostatic double-layered porous journal bearings, instability of bearing systems is a major problem. On the other hand, the use of non-Newtonian fluid as a lubricant is more practical in the present days. Furthermore, in case of porous bearing, neglecting slip effect and percolation effect of additives into the pores may lead to erroneous result. Hence, this paper aims to present the linear stability analysis of finite hydrostatic double-layered porous journal bearings lubricated with coupled-stress lubricant with tangential velocity slip and percolation effect. Design/methodology/approach First, considering the tangential velocity slip, the most general modified Reynolds-type equation has been derived for the film region and the governing equations for flow in the coarse and fine layers of porous medium incorporating the percolation effect. A linearized first-order perturbation method has been applied to obtain the threshold of stability in terms of critical mass parameter. The effect of various parameters on the stability is investigated and represented in the form of graphs. Furthermore, a comparison between the stability of double- and single-layered porous journal bearings has been exhibited. Findings In this paper, threshold of stability has been obtained in terms of critical mass parameter. The effect of slip coefficient, percolation factor, coupled-stress parameter, eccentricity ratio and bearing feeding parameter on the stability has been found. Originality/value There is no literature available so far that addresses the analysis of the linear stability of externally pressurized double-layered porous journal bearings with slip flow, including the percolation effect under coupled-stress lubrication. But in this paper, all these points are included which made this paper valuable in design purpose.

On the Lubrication of Short Porous Journal Bearings—Use of the Brinkman Model

1995 ◽  
Vol 117 (1) ◽  
pp. 196-199 ◽  
Author(s):  
Jaw-Ren Lin ◽  
Chi-Chuan Hwang
Keyword(s):  
Pressure Gradient ◽  
Journal Bearings ◽  
Shear Stresses ◽  
Brinkman Model ◽  
Eccentricity Ratio ◽  
Lubrication Performance ◽  
Viscous Shear ◽  
Permeability Parameter

Based on the Brinkman model (MB), this paper concerns the more realistic influence of viscous shear stresses on the lubrication performance of short porous journal bearings. Compared with those using the zero pressure gradient assumption (ZPGA), the effect of LPGA provides an improvement in the bearing performance, especially when the thick-walled bearing has higher permeability parameter or the journal operates at higher eccentricity ratio.

Non-linear stability analysis of micropolar fluid lubricated journal bearings with turbulent effect

2019 ◽  
Vol 71 (1) ◽  
pp. 31-39
Author(s):  
Subrata Das ◽  
Sisir Kumar Guha
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Micropolar Fluid ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Turbulent Regime ◽  
Content Type ◽  
Non Linear ◽  
The Stability ◽  
Bearing System

Purpose The purpose of this paper is to investigate the effect of turbulence on the stability characteristics of finite hydrodynamic journal bearing lubricated with micropolar fluid. Design/methodology/approach The non-dimensional transient Reynolds equation has been solved to obtain the non-dimensional pressure field which in turn used to obtain the load carrying capacity of the bearing. The second-order equations of motion applicable for journal bearing system have been solved using fourth-order Runge–Kutta method to obtain the stability characteristics. Findings It has been observed that turbulence has adverse effect on stability and the whirl ratio at laminar flow condition has the lowest value. Practical implications The paper provides the stability characteristics of the finite journal bearing lubricated with micropolar fluid operating in turbulent regime which is very common in practical applications. Originality/value Non-linear stability analysis of micropolar fluid lubricated journal bearing operating in turbulent regime has not been reported in literatures so far. This paper is an effort to address the problem of non-linear stability of journal bearings under micropolar lubrication with turbulent effect. The results obtained provide useful information for designing the journal bearing system for high speed applications.

On the linear stability analysis of finite-hydrodynamic porous journal bearings under coupled stress lubrication

2007 ◽  
Vol 221 (7) ◽  
pp. 831-840 ◽  
Author(s):  
S. K. Guha ◽  
A. K. Chattopadhyay
Keyword(s):  
Reynolds Equation ◽  
Dynamic Performance ◽  
Slip Flow ◽  
Tangential Velocity ◽  
Continuum Theory ◽  
Transient State ◽  
Velocity Slip ◽  
Journal Bearings ◽  
The Stability ◽  
Coupled Stress

The objective of the present investigation is to study theoretically, using the finite-difference techniques, the dynamic performance characteristics of finite-hydrodynamic porous journal bearings lubricated with coupled stress fluids. In the analysis based on the Stokes micro-continuum theory of the rheological effects of coupled stress fluids, a modified form of Reynolds equation governing the transient-state hydrodynamic film pressures in porous journal bearings with the effect of slip flow of coupled stress fluid as lubricant is obtained. Moreover, the tangential velocity slip at the surface of porous bush has been considered by using Beavers-Joseph criterion. Using the first-order perturbation of the modified Reynolds equation, the stability characteristics in terms of threshold stability parameter and whirl ratios are obtained for various parameters viz. permeability factor, slip coefficient, bearing feeding parameter, and eccentricity ratio. The results show that the coupled stress fluid exhibits better stability in comparison with Newtonian fluid.

Stability of Multirecess Hybrid-Operating Oil Journal Bearings

1985 ◽  
Vol 107 (1) ◽  
pp. 116-121 ◽  
Author(s):  
Y. S. Chen ◽  
H. Y. Wu ◽  
P. L. Xie
Keyword(s):  
Finite Difference Method ◽  
Dynamic Performance ◽  
Journal Bearings ◽  
Design Parameters ◽  
Stability Threshold ◽  
Damping Coefficients ◽  
Hybrid Bearing ◽  
The Stability ◽  
Stiffness And Damping ◽  
Bearing System

An analysis and a numerical solution using finite difference method to predict the dynamic performance of multirecess hybrid-operating oil journal bearings are presented. The linearized stiffness and damping coefficients of a typical capillary-compensated bearing with four recesses are computed for various design parameters. The corresponding stiffness and the stability threshold of the bearing are then obtained, and the opposite influences of the hydrodynamic action on them are demonstrated. The effect of rotor flexibility on the onset of self-excited whirl is discussed, and a method is given to determine the stability threshold of a rotor-hybrid bearing system.

Short Bearing Analysis Applied to Rotor Dynamics—Part 2: Results of Journal Bearing Response

1976 ◽  
Vol 98 (2) ◽  
pp. 319-329 ◽  
Author(s):  
R. G. Kirk ◽  
E. J. Gunter
Keyword(s):  
Transient Response ◽  
Journal Bearing ◽  
Rotor Dynamics ◽  
Journal Bearings ◽  
Radius Of Curvature ◽  
Extensive Investigation ◽  
Stability Threshold ◽  
Stability Maps ◽  
And Performance ◽  
The Stability

The results of an extensive investigation of the transient response of rotors supported in fluid-film journal bearings is presented in the form of computer generated orbits of rotor motion. The stability of the rotor-bearing system was determined by examination of the system characteristic equation in Part 1. Rotor transient response orbits demonstrate the rotor behavior below and above the stability threshold. The results show the effect of imbalance, steady loading, cyclic unidirectional and rotating loads upon the stability and performance of a short journal bearing. The results are compared to previous investigations and modified stability maps are deduced from the results obtained. The concept of whirl is examined and several plots presented of the instantaneous whirl ratio and radius of curvature versus cycles of motion (of the journal) for the various cases considered. Bearing forces are analyzed and the resulting plots of force versus cycles of motion are presented for selected cases.

scholarly journals Competition between the centrifugal and strato-rotational instabilities in the stratified Taylor–Couette flow

2018 ◽  
Vol 840 ◽  
pp. 5-24 ◽  
Author(s):  
Junho Park ◽  
Paul Billant ◽  
Jong-Jin Baik ◽  
Jaemyeong Mango Seo
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Couette Flow ◽  
Linear Stability Analysis ◽  
Reynolds Numbers ◽  
Axisymmetric Mode ◽  
Stability Threshold ◽  
Taylor Couette ◽  
The Stability ◽  
Taylor Couette Flow

The stably stratified Taylor–Couette flow is investigated experimentally and numerically through linear stability analysis. In the experiments, the stability threshold and flow regimes have been mapped over the ranges of outer and inner Reynolds numbers: $-2000<Re_{o}<2000$ and $0<Re_{i}<3000$, for the radius ratio $r_{i}/r_{o}=0.9$ and the Brunt–Väisälä frequency $N\approx 3.2~\text{rad}~\text{s}^{-1}$. The corresponding Froude numbers $F_{o}$ and $F_{i}$ are always much smaller than unity. Depending on $Re_{o}$ (or equivalently on the angular velocity ratio $\unicode[STIX]{x1D707}=\unicode[STIX]{x1D6FA}_{o}/\unicode[STIX]{x1D6FA}_{i}$), three different regimes have been identified above instability onset: a weakly non-axisymmetric mode with low azimuthal wavenumber $m=O(1)$ is observed for $Re_{o}<0$ ($\unicode[STIX]{x1D707}<0$), a highly non-axisymmetric mode with $m\sim 12$ occurs for $Re_{o}>840$ ($\unicode[STIX]{x1D707}>0.57$) while both modes are present simultaneously in the lower and upper parts of the flow for $0\leqslant Re_{o}\leqslant 840$ ($0\leqslant \unicode[STIX]{x1D707}\leqslant 0.57$). The destabilization of these primary modes and the transition to turbulence as $Re_{i}$ increases have been also studied. The linear stability analysis proves that the weakly non-axisymmetric mode is due to the centrifugal instability while the highly non-axisymmetric mode comes from the strato-rotational instability. These two instabilities can be clearly distinguished because of their distinct dominant azimuthal wavenumber and frequency, in agreement with the recent results of Park et al. (J. Fluid Mech., vol. 822, 2017, pp. 80–108). The stability threshold and the characteristics of the primary modes observed in the experiments are in very good agreement with the numerical predictions. Moreover, we show that the centrifugal and strato-rotational instabilities are observed simultaneously for $0\leqslant Re_{o}\leqslant 840$ in the lower and upper parts of the flow, respectively, because of the variations of the local Reynolds numbers along the vertical due to the salinity gradient.

Transient Unbalance Response of Four Multilobe Journal Bearings

1980 ◽  
Vol 102 (3) ◽  
pp. 300-306 ◽  
Author(s):  
P. E. Allaire ◽  
D. F. Li ◽  
K. C. Choy
Keyword(s):  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Transient Response ◽  
Journal Bearings ◽  
Stability Threshold ◽  
Unbalance Response ◽  
Fast Fourier Transform Analysis ◽  
Linearized Stability ◽  
The Stability

This work carries out an analysis of the transient response of four multilobe journal bearings (elliptical, offset, three-lobe, and four-lobe) subject to unbalance both below and above the linearized stability thresholds for the bearings. It extends the work of a previous paper on a balanced rotor in the same four bearing types. Transient orbits, bearing forces, and a numerical fast Fourier transform analysis of the orbits are presented. A comparison of bearing forces above the stability threshold for each bearing indicates that the elliptical bearing has the most violent whirl vibration amplitudes, while the offset bearing exhibits the least amount of subsynchronous vibration.

Stability and Transient Characteristics of Four Multilobe Journal Bearing Configurations

1980 ◽  
Vol 102 (3) ◽  
pp. 291-298 ◽  
Author(s):  
D. F. Li ◽  
K. C. Choy ◽  
P. E. Allaire
Keyword(s):  
Transient Analysis ◽  
Journal Bearing ◽  
Journal Bearings ◽  
Rigid Rotor ◽  
Frequency Content ◽  
Stability Threshold ◽  
Fast Fourier Transform Analysis ◽  
Linearized Stability ◽  
Nonlinear Transient ◽  
The Stability

Multilobe journal bearings are often used to improve the stability response of rotating machinery. Such machines operate near the stability threshold of the bearing-rotor system. This work determines the linearized stability threshold of four multilobe journal bearings: elliptical, offset elliptical, three lobe, and four lobe. A nonlinear transient analysis of a rigid rotor in each of these bearings is carried out above and below the threshold speed. Shaft orbits and bearing forces are calculated. A numerical fast Fourier transform analysis is used to obtain the frequency content of the nonlinear orbit.

Stability Analysis of Rotating Systems Supported by Textured Journal Bearings

2019 ◽  
Vol 142 (3) ◽  
Author(s):  
Douglas Jhon Ramos ◽  
Leandro Ito Ramos ◽  
Gregory Bregion Daniel
Keyword(s):  
Vibration Mode ◽  
Surface Texturing ◽  
Industrial Applications ◽  
Journal Bearings ◽  
Rotating System ◽  
Stability Threshold ◽  
Rotating Systems ◽  
Unstable Vibration ◽  
The Stability ◽  
Volume Method

Abstract Fluid-induced instability in rotating systems due to the presence of hydrodynamic journal bearings consists of an undesirable phenomenon with a considerable destructive potential. Surface texturing of journal bearings is currently investigated as a possible approach to improve the stability characteristics of rotating systems. Thereby, this work aims to evaluate the influence of textured journal bearings in the stability threshold and unstable vibration mode of rotating systems. The classical Reynolds equation is used to model the pressure distribution inside the bearing, being solved by the finite volume method (FVM). The rotating system evaluated in this work is a steam turbine that is modeled using the finite element method (FEM). Numerical results show that textured geometric parameters, i.e., shape, area density, and maximum depth, are capable of changing the stability threshold (for worse or better) as well as the corresponding unstable vibration mode. Moreover, the present study also indicates that a full texturing of journal bearings is desirable to achieve a better improvement in the stability threshold when compared with partial texturing. Based on the results obtained in this work, the textured journal bearings represent a promising and feasible tool to improve the stability conditions of rotating systems in industrial applications.

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