Effect of Slip Boundary Condition and Non-Newtonian Rheology of Lubricants on the Dynamic Characteristics of Finite Hydrodynamic Journal Bearing

2021 ◽  
Author(s):  
Mohammad Arif ◽  
Saurabh Kango ◽  
Dinesh Kumar Shukla
Keyword(s):  
Boundary Condition ◽  
Dynamic Stability ◽  
Journal Bearing ◽  
Mass Parameter ◽  
Critical Mass ◽  
Slip Boundary Condition ◽  
Slip Effect ◽  
Slip Boundary ◽  
Slip Region ◽  
Hydrodynamic Journal Bearing

Abstract In the present study, the influence of various slip zone locations on the dynamic stability of finite hydrodynamic journal bearing lubricated with non-Newtonian and Newtonian lubricants has been investigated. Linearized equation of motion with free vibration of rigid rotor has been used to find the optimum location of the slip region with maximum stability margin limit. It has been observed that bearing with interface of slip and no-slip region near the upstream side of minimum film-thickness location is effective in improving the direct and cross stiffness coefficient, critical mass parameter, and critical whirling speed. The magnitude of dynamic performance parameters with slip effect is highly dependent on the rheology of lubricant. Shear-thinning lubricants combined with slip boundary condition shows higher dynamic stability as compared to the Newtonian lubricants under the conventional boundary condition. For all considered rheology of lubricants, the dynamic stability of bearing with slip effect is improving by increasing the eccentricity ratio.

Numerical Analysis of a Journal Bearing With a Heterogeneous Slip/No-Slip Surface

2005 ◽  
Author(s):  
Alicia E. Fortier ◽  
Richard F. Salant
Keyword(s):  
Boundary Condition ◽  
Journal Bearing ◽  
Slip Surface ◽  
Slip Boundary Condition ◽  
Solid Boundary ◽  
Measured Velocity ◽  
Practical Applications ◽  
Slip Boundary ◽  
Fluid Behavior ◽  
Load Carrying

The no-slip boundary condition is part of the foundation of traditional lubrication theory. It states that fluid adjacent to a solid boundary has zero velocity relative to the solid surface. For most practical applications, the no-slip boundary condition is a good model for predicting fluid behavior. However, recent experimental research has found that for certain engineered surfaces the no-slip boundary condition is not valid. Measured velocity profiles show that slip occurs at the interface. In the present study, the effect of an engineered slip/no-slip surface on journal bearing performance is examined. A heterogeneous pattern, in which slip occurs in certain regions and is absent in others, is applied to the bearing surface. Fluid slip is assumed to occur according to the Navier relation. Analysis is performed numerically using a mass conserving algorithm for the solution of the Reynolds equation. Load carrying capacity and friction force are evaluated. It is found that judicious application of slip to a journal bearing’s surface can lead to improved bearing performance.

The Simulation of Liquid Flow in the Pore Network Model of Nanoporous Media

2020 ◽  
Vol 143 (3) ◽  
Author(s):  
Yaohao Guo ◽  
Lei Zhang ◽  
Hai Sun ◽  
Yongfei Yang ◽  
Zhi Xu ◽  
...  
Keyword(s):  
Boundary Condition ◽  
Liquid Flow ◽  
Effective Viscosity ◽  
Slip Length ◽  
Slip Boundary Condition ◽  
Slip Effect ◽  
Pore Throat ◽  
Slip Boundary ◽  
Nanoporous Media ◽  
Nanoscale Effect

Abstract The fluid–solid interaction force shows significant influence on liquid flow at nanoscale. Vast experimental observations in recent literatures have shown that Darcy's law cannot be applied to nanoporous media. In this study, the slip length and effective viscosity are adapted to characterize the nanoscale effect. First, the nanoscale effect is investigated in nanotubes through computational fluid dynamic (CFD) modeling analysis. Slip boundary condition has been studied as an important discrepancy between macroscopic flow and nanoscale liquid flow. The effect of viscosity change becomes more notable with the slip length increasing. Then, the flow equation for pore network modeling is developed to capture nanoscale effect. The results show that the apparent permeability of nanoscale systems is significantly underestimated when slip effect is neglected. The size of the pore throat determines whether the slip effect needs to be considered, and critical diameter of neglecting the slip effect for circular throat is 79.17 Ls. It is necessary to take the variation of effective viscosity into account under slip boundary condition. With the pore throat size decreasing, the nanoscale effect increases. The nanoscale effect is more sensitive to pore throat size under hydrophobic conditions than hydrophilic conditions.

An Analytic Model of Oil-Film Force on Hydrodynamic Journal Bearing of Finite Length

2008 ◽  
Author(s):  
JinFu Yang ◽  
Ce Chen ◽  
ShengBo Yang ◽  
DaRen Yu ◽  
Ying Cui ◽  
...  
Keyword(s):  
Finite Length ◽  
Journal Bearing ◽  
Slip Boundary Condition ◽  
Analytic Model ◽  
Clearance Ratio ◽  
Oil Film ◽  
Slip Boundary ◽  
Proposed Model ◽  
Speed Up ◽  
Hydrodynamic Journal Bearing

In order to more clearly express the interrelation between the oil-film force on hydrodynamic journal bearing of finite length and the wedging, whiling, and squeezing motions of journals, an analytic model with well-defined physical meaning is proposed in this paper by introducing the non-slip boundary condition for the oil-film velocity gradient without modifying the basic assumption for Reynolds equation to formulate the expression of oil-film pressure distribution, obtaining the analytic solution of oil-film force through integration of circumferential pressure, and defining the effect coefficients for wedging, whirling and squeezing motions, which are related to the clearance ratio and eccentricity ratio of bearings. The proposed model is compared with an existing model to show off its advantage. The proposed model was also applied to a 200MW steam turbine low-pressure rotor-bearing system to simulate the dynamic response of the rotor during the speed-up process. The analytic results of this application proved the validity of the proposed model.

Considerations on the moving contact-line singularity, with application to frictional drag on a slender drop

1988 ◽  
Vol 197 ◽  
pp. 157-169 ◽  
Author(s):  
P. A. Durbin
Keyword(s):  
Boundary Condition ◽  
Yield Stress ◽  
Contact Line ◽  
Slip Boundary Condition ◽  
Frictional Drag ◽  
Slip Boundary ◽  
Moving Contact Line ◽  
Moving Contact ◽  
Slip Region ◽  
Stress Boundary

It has previously been shown that the no-slip boundary condition leads to a singularity at a moving contact line and that this forces one to admit some form of slip. Present considerations on the energetics of slip due to shear stress lead to a yield stress boundary condition. A model for the distortion of the liquid state near solid boundaries gives a physical basis for this boundary condition. The yield stress condition is illustrated by an analysis of a slender drop rolling down an incline. That analysis provides a formula for the frictional drag resisting the drop movement. With the present boundary condition the length of the slip region becomes a property of the fluid flow.

Numerical Analysis of a Journal Bearing With a Heterogeneous Slip/No-Slip Surface

2005 ◽  
Vol 127 (4) ◽  
pp. 820-825 ◽  
Author(s):  
Alicia E. Fortier ◽  
Richard F. Salant
Keyword(s):  
Boundary Condition ◽  
Journal Bearing ◽  
Slip Surface ◽  
Slip Boundary Condition ◽  
Solid Boundary ◽  
Measured Velocity ◽  
Practical Applications ◽  
Slip Boundary ◽  
Fluid Behavior ◽  
Load Carrying

The no-slip boundary condition is part of the foundation of the traditional lubrication theory. It states that fluid adjacent to a solid boundary has zero velocity relative to the solid surface. For most practical applications, the no-slip boundary condition is a good model for predicting fluid behavior. However, recent experimental research has found that for certain engineered surfaces the no-slip boundary condition is not valid. Measured velocity profiles show that slip occurs at the interface. In the present study, the effect of an engineered slip/no-slip surface on journal bearing performance is examined. A heterogeneous pattern, in which slip occurs in certain regions and is absent in others, is applied to the bearing surface. Fluid slip is assumed to occur according to the Navier relation. Analysis is performed numerically using a mass conserving algorithm for the solution of the Reynolds equation. Load carrying capacity, side leakage rate, and friction force are evaluated. In addition, results are presented in the form of Raimondi and Boyd graphs. It is found that the judicious application of slip to a journal bearing’s surface can lead to improved bearing performance.

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