Viscoelastic Effects on the Stability of Thin-Film Parallel Flow in Lubrication Applications

2000 ◽  
Author(s):  
Avraham Harnoy ◽  
Laksh. Shridhar ◽  
John Tavantzis
Keyword(s):  
Flow Instability ◽  
Hydrodynamic Lubrication ◽  
Fluid Model ◽  
Viscous Friction ◽  
Relaxation Effect ◽  
Parallel Flow ◽  
Fluid Viscosity ◽  
Fluid Films ◽  
Fluid Elasticity ◽  
The Stability

Abstract The analysis is concerned with the effect of fluid-elasticity on the stability of laminar parallel flow. The widely used multi-grade oils contain polymer additives that make them viscoelastic. These oils are widely used for high shear-rate laminar flow of hydrodynamic lubrication, where flow instability is undesirable because it significantly increases the viscous friction losses. A fluid model is applied where the stress-relaxation effect is considered in addition to the fluid viscosity. However, the normal stresses are disregarded. Extended Orr-Sommerfeld type analysis has been performed for elastic fluid films of lubrication. The conclusion is that the elasticity of the fluid has a destabilizing effect. For parallel flow, the transition to instability is at lower Reynolds number in comparison to Newtonian fluids.

scholarly journals The Effect of Slightly Upward and Downward Inclined Pipes on the Stability of Gas-Oil Two-Phase Flow

2014 ◽  
Vol 14 (1) ◽  
pp. 13
Author(s):  
Peyman Sabzi ◽  
Saheb Noroozi
Keyword(s):  
Two Phase Flow ◽  
Flow Instability ◽  
Fluid Model ◽  
Phase Flow ◽  
Momentum Exchange ◽  
Two Phase ◽  
Two Fluid Model ◽  
The Stability ◽  
Inclined Pipes ◽  
Two Fluid

Pipeline inclination has an important effect on the stability of two-phase flow and flow assurance in the pipeline. This inclination may be intentional; it may be inevitable in pipeline installation; or it may be due to an error in pipeline installation. In this situation, even the slight inclination of the pipe plays an important role in the growth or elimination of the instability of the two-phase flow. In this study using a code designed for the analysis of pipelines’ two-phase flow, the stability of the two-phase flow for Kerosene oil flow along with methane gas has been compared in downward inclined pipes, upward inclined pipes, and horizontal pipes. Using the mentioned computer code, it has been proved that the pipe’s upward inclination results in the increase of two-phase flow instability, while the pipe’s downward inclination is helpful in two-phase flow stability. In order to model two-phase flow in the pipe, two-fluid model has been used. This model considers each phase separately and the equations of mass conservation and momentum are written for each phase. The momentum exchange between the two phases and between each phase and the pipe wall has been considered. Conservation equations have been solved using SIMPLE algorithm in a numerical form with finite volume method.Keywords: Pipes, Two-Phase Flow, Inclined Stability, Two-Fluid Model

Influence of viscosity temperature dependence on the spectral characteristics of the thermoviscous liquids flow stability equation

2019 ◽  
Vol 14 (1) ◽  
pp. 52-58 ◽  
Author(s):  
A.D. Nizamova ◽  
V.N. Kireev ◽  
S.F. Urmancheev
Keyword(s):  
Reynolds Number ◽  
Spectral Characteristics ◽  
Wave Number ◽  
Critical Parameters ◽  
Fluid Viscosity ◽  
Flat Channel ◽  
Stability Equation ◽  
The Stability ◽  
Thermoviscous Fluid ◽  
Sommerfeld Equation

The flow of a viscous model fluid in a flat channel with a non-uniform temperature field is considered. The problem of the stability of a thermoviscous fluid is solved on the basis of the derived generalized Orr-Sommerfeld equation by the spectral decomposition method in Chebyshev polynomials. The effect of taking into account the linear and exponential dependences of the fluid viscosity on temperature on the spectral characteristics of the hydrodynamic stability equation for an incompressible fluid in a flat channel with given different wall temperatures is investigated. Analytically obtained profiles of the flow rate of a thermovisible fluid. The spectral pictures of the eigenvalues of the generalized Orr-Sommerfeld equation are constructed. It is shown that the structure of the spectra largely depends on the properties of the liquid, which are determined by the viscosity functional dependence index. It has been established that for small values of the thermoviscosity parameter the spectrum compares the spectrum for isothermal fluid flow, however, as it increases, the number of eigenvalues and their density increase, that is, there are more points at which the problem has a nontrivial solution. The stability of the flow of a thermoviscous fluid depends on the presence of an eigenvalue with a positive imaginary part among the entire set of eigenvalues found with fixed Reynolds number and wavenumber parameters. It is shown that with a fixed Reynolds number and a wave number with an increase in the thermoviscosity parameter, the flow becomes unstable. The spectral characteristics determine the structure of the eigenfunctions and the critical parameters of the flow of a thermally viscous fluid. The eigenfunctions constructed in the subsequent works show the behavior of transverse-velocity perturbations, their possible growth or decay over time.

The Effects of Vibrations on Particle Motion in a Viscous Fluid Cell

2008 ◽  
Vol 75 (3) ◽  
Author(s):  
Samer Hassan ◽  
Masahiro Kawaji
Keyword(s):  
Viscous Fluid ◽  
Drag Force ◽  
Particle Motion ◽  
Fluid Model ◽  
Resonance Phenomenon ◽  
Fluid Viscosity ◽  
Mass Force ◽  
Amplitude Data ◽  
Viscous Fluid Model ◽  
Fluid Cell

The effects of small vibrations on particle motion in a viscous fluid cell have been investigated experimentally and theoretically. A steel particle was suspended by a thin wire at the center of a fluid cell, and the cell was vibrated horizontally using an electromagnetic actuator and an air bearing stage. The vibration-induced particle amplitude measurements were performed for different fluid viscosities (58.0cP and 945cP), and cell vibration amplitudes and frequencies. A viscous fluid model was also developed to predict the vibration-induced particle motion. This model shows the effect of fluid viscosity compared to the inviscid model, which was presented earlier by Hassan et al. (2004, “The Effects of Vibrations on Particle Motion in an Infinite Fluid Cell,” ASME J. Appl. Mech., 73(1), pp. 72–78) and validated using data obtained for water. The viscous model with modified drag coefficients is shown to predict well the particle amplitude data for the fluid viscosities of 58.5cP and 945cP. While there is a resonance frequency corresponding to the particle peak amplitude for oil (58.0cP), this phenomenon disappeared for glycerol (945cP). This disappearance of resonance phenomenon is explained by referring to the theory of mechanical vibrations of a mass-spring-damper system. For the sinusoidal particle motion in a viscous fluid, the effective drag force has been obtained, which includes the virtual mass force, drag force proportional to the velocity, and the Basset or history force terms.

scholarly journals Shear models and parametric analysis of the PVC geomembrane-cushion interface in a high rock-fill dam

PLoS ONE ◽  
2021 ◽  
Vol 16 (1) ◽  
pp. e0245245
Author(s):  
Yun-Feng Liu ◽  
Ke Gu ◽  
Yi-Ming Shu ◽  
Xian-Lei Zhang ◽  
Xin-Xin Liu ◽  
...  
Keyword(s):  
Shear Stress ◽  
Friction Coefficient ◽  
Three Dimensional ◽  
Viscous Friction ◽  
Hydraulic Pressure ◽  
Viscous Shear Stress ◽  
Box Counting ◽  
Viscous Shear ◽  
The Stability ◽  
Hysteresis Friction

As a type of flexible impermeable material, a PVC geomembrane must be cooperatively used with cushion materials. The contact interface between a PVC geomembrane and cushion easily loses stability. In this present paper, we analyzed the shear models and parameters of the interface to study the stability. Two different cushion materials were used: the common extrusion sidewall and non-fines concrete. To simulate real working conditions, flexible silicone cushions were added under the loading plates to simulate hydraulic pressure loading, and the loading effect of flexible silicone cushions was demonstrated by measuring the actual contact areas under different normal pressures between the geomembrane and cushion using the thin-film pressure sensor. According to elastomer shear stress, there are two main types of shear stress between the PVC geomembrane and the cushion: viscous shear stress and hysteresis shear stress. The viscous shear stress between the geomembrane and the cement grout was measured using a dry, smooth concrete sample, then the precise formula parameters of the viscous shear stress and viscous friction coefficient were obtained. The hysteresis shear stress between the geomembrane and the cushion was calculated by subtracting the viscous shear stress from the total shear stress. The formula parameters of the hysteresis shear stress and hysteresis friction coefficient were calculated. The three-dimensional box-counting dimensions of the cushion surface were calculated, and the formula parameters of the hysteresis friction were positively correlated with the three-dimensional box dimensions.

Stability of parallel flow of a multi-component cylindrical plasma to electrostatic perturbations

1981 ◽  
Vol 26 (2) ◽  
pp. 369-383
Author(s):  
R. Lucas
Keyword(s):  
Normal Mode ◽  
Axial Velocity ◽  
Sufficient Conditions ◽  
Parallel Flow ◽  
Zeroth Order ◽  
Unperturbed State ◽  
Plasma Component ◽  
Cylindrical Plasma ◽  
The Stability ◽  
System Variables

Sufficient conditions for the stability of parallel flow of a warm N-component cylindrical plasma to electrostatic perturbations are obtained. In the unperturbed state the jth plasma component is assumed to have axial velocity Vj0(r), r being the radial co-ordinate, and the equilibrium quantities are permitted to be arbitrary functions of r consistent with the zeroth-order equations. The L2-norms of certain system variables are shown to be bounded uniformly in time. Circle theorems are obtained for the complex eigenfrequencies of any normal mode.

The Stability-Limiting Flow Mechanisms in a Subsonic Axial-Flow Compressor and Its Passive Control With Casing Treatment

2008 ◽  
Author(s):  
Xingen Lu ◽  
Junqiang Zhu ◽  
Chaoqun Nie ◽  
Weiguang Huang
Keyword(s):  
Flow Instability ◽  
State Of The Art ◽  
Axial Flow ◽  
Flow Mechanism ◽  
Blade Passage ◽  
Casing Treatment ◽  
Compressor Rotor ◽  
Flow Compressor ◽  
The Stability ◽  
End Wall

The phenomenon of flow instability in the compression system such as fan and compressor has been a long-standing “bottle-neck” problem for gas turbines/aircraft engines. With a vision of providing a state-of-the-art understanding of the flow field in axial-flow compressor in the perspective of enhancing their stability using passive means. Two topics are covered in this paper. The first topic is the stability-limiting flow mechanism close to stall, which is the basic knowledge needed to manipulate end-wall flow behavior for the stability improvement. The physical process occurring when approaching stall and the role of complex tip flow mechanism on flow instability in current high subsonic axial compressor rotor has been assessed using single blade passage computations. The second topic is flow instability manipulation with casing treatment. In order to advance the understanding of the fundamental mechanisms of casing treatment and determine the change in the flow field by which casing treatment improve compressor stability, systematic studies of the coupled flow through a subsonic compressor rotor and various end-wall treatments were carried out using a state-of-the-art multi-block flow solver. The numerically obtained flow fields were interrogated to identify complicated flow phenomenon around and within the end-wall treatments and describe the interaction between the rotor tip flow and end-wall treatments. Detailed analyses of the flow visualization at the rotor tip have exposed the different tip flow topologies between the cases with treatment casing and with untreated smooth wall. It was found that the primary stall margin enhancement afforded by end-wall treatments is a result of the tip flow manipulation. Compared to the smooth wall case, the treated casing significantly dampen or absorb the blockage near the upstream part of the blade passage caused by the upstream movement of tip clearance flow and weakens the roll-up of the core vortex. These mechanisms prevent an early spillage of low momentum fluid into the adjacent blade passage and delay the onset of flow instability.

A study of the stability of the Z pinch under fusion conditions using the Hall fluid model

1984 ◽  
Vol 27 (12) ◽  
pp. 2886 ◽  
Author(s):  
M. Coppins ◽  
D. J. Bond ◽  
M. G. Haines
Keyword(s):  
Fluid Model ◽  
The Stability ◽  
Z Pinch

On the Flow of a Polymer Melt Passing Over a Transverse Slot

1999 ◽  
Vol 19 (3) ◽  
pp. 175-196 ◽  
Author(s):  
G.H. Wu ◽  
C.K. Chen ◽  
S.H. Ju
Keyword(s):  
Fluid Model ◽  
Polymer Melt ◽  
Maxwell Fluid ◽  
Creeping Flow ◽  
Analytical Prediction ◽  
Hole Pressure ◽  
Fluid Elasticity ◽  
Conduit Wall ◽  
Liquid Flows ◽  
Transverse Slot

Abstract The phenomenon of hole pressure occurs whenever a polymeric or viscoelastic liquid flows over a depression in a conduit wall. Numerical simulations undertaken for the flow of an aqueous polyacrylamide melt passing over a transverse slot arc considered here. The fluid model used for this study is a White-Metzner constitutive equation describing the non-Newtonian behavior of the melt. The results were computed by an elastic-viscous split-stress finite clement method (EVSS-FEM). a mixed finite clement method incorporating the non-consistent streamline upwind scheme. For verification, the numerical algorithm was first applied to compute the corresponding flow of the upper-convected Maxwell fluid model, a special case of the Whitc-Metzner model characterized by constant viscosity and relation time. The resulting hole pressure (Ph) was evaluated for various Deborah numbers (De) and compared with the analytical prediction derived from the Higashitani-Pritchard (HP) theory. The agreement was found to be satisfactory for creeping flow in the low De range, for which the HP theory is valid. Subsequently, the hole pressure of this flow problem was predicted. The streamlines and pressure distribution along the channel walls arc also presented. Furthermore, the effects of fluid elasticity, shear thinning, the exponent in the viscosity function and the relaxation-time function, and slot geometry on the hole pressure were investigated.

Magneto-rheological fluid slot-entry journal bearing considering thermal effects

2019 ◽  
Vol 30 (18-19) ◽  
pp. 2831-2852 ◽  
Author(s):  
Krishnkant Sahu ◽  
Satish C Sharma
Keyword(s):  
Thermal Effects ◽  
Journal Bearing ◽  
Fluid Model ◽  
Viscous Friction ◽  
Fluid Film ◽  
Applied Current ◽  
Bingham Model ◽  
Geometric Imperfection ◽  
Fluid Film Bearings ◽  
Magneto Rheological

In recent times, controlling the performance of fluid film bearings smartly has become an important area for the fluid film bearing designers. This study deals with the numerical simulation of a magneto-rheological fluid–lubricated two-lobe hybrid slot-entry journal bearing. To make the operating condition more exact and realistic, the influence of geometric imperfection of the journal arising from manufacturing inaccuracies and thermal effect has been considered. Dave magneto-rheological fluid model, a constitutive relation of the Bingham model, and finite element method have been used in this article to simulate the behavior of the magneto-rheological fluid in a slot-entry bearing. The results indicate that the heat generated because of viscous friction rises the temperature of the magneto-rheological fluid, which changes the bearing performance significantly. Considering barrel-shaped journal and magneto-rheological fluid (applied current, Ic = 4 A), the performance of two-lobe slot-entry bearing is superior in terms of the value of [Formula: see text] approximately by a magnitude of 2%, 41%, 181%, 168%, 75%, and 41%, respectively, as compared to that of the base bearing (smooth [Formula: see text], two-lobe bearing, operating with a Newtonian fluid, Ic = 0 A).

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