Effects Of non-Newtonian Rheology Research Articles

The Effect of Blood Rheology and Inlet Boundary Conditions on Realistic Abdominal Aortic Aneurysms under Pulsatile Flow Conditions.

The effects of non-Newtonian rheology and boundary conditions on various pathophysiologies have been studied quite extensively in the literature. The majority of results present qualitative and/or quantitative conclusions that are not thoroughly assessed from a statistical perspective. The finite volume method was employed for the numerical simulation of seven patient-specific abdominal aortic aneurysms. For each case, five rheological models and three inlet velocity boundary conditions were considered. Outlier- and heteroscedasticity-robust ANOVA tests assessed the simultaneous effect of rheological specifications and boundary conditions on fourteen variables that capture important characteristics of vascular flows. The selection of inlet velocity profiles appears as a more critical factor relative to rheological specifications, especially regarding differences in the oscillatory characteristics of computed flows. Response variables that relate to the average tangential force on the wall over the entire cycle do not differ significantly across alternative factor levels, as long as one focuses on non-Newtonian specifications. The two factors, namely blood rheological models and inlet velocity boundary condition, exert additive effects on variables that characterize vascular flows, with negligible interaction effects. Regarding thrombus-prone conditions, the Plug inlet profile offers an advantageous hemodynamic configuration with respect to the other two profiles.

Avaliação de formulações de taxa de deformação através de escoamentos permanentes e uniformes de fluidos não-Newtonianos no contexto de equações de águas rasas

ABSTRACT Non-Newtonian rheology effects, such as pseudoplasticity and viscoplasticity, are understood as shear stresses, incorporated to the energy slope term in the Shallow-Water Equations (SWE). However, non-Newtonian shear stresses are dependent of the shear rate, whose formulation is a function of the gradient of the velocity profile in the bottom. This study investigated two shear rate formulations that are commonly applied in the SWE literature: 1) a non-parameterized function; and 2) a function based on the Herschel-Bulkley rheological model. Their influence in steady uniform flows of non-Newtonian fluids was evaluated through numerical-theoretical comparisons. A Lax-Friedrichs scheme was implemented to solve the SWE system and allowed employing the shear rate formulations. Experimental tests were carried out and numerical simulations of hypothetical scenarios were performed. It was found that the non-parameterized formulation presented deviation in normal depth up to 14% in comparison with theoretical solution, while the formulation based on the Herschel-Bulkley model provided a good agreement, corroborated by punctual Computational Fluid Dynamics simulations (deviation less than 2%) and experimental data. The ratio of both shear rate formulations is strongly correlated to the deviation of normal depth, indicating that the non-parameterized shear rate function does not provide an acceptable result in the steady uniform flow.

The effects of non-Newtonian rheology in the upper mantle on relative sea level change and geodetic observables induced by glacial isostatic adjustment process

SUMMARY Studies of glacial isostatic adjustment (GIA) provide important constraints on the Earth's mantle viscosity. Most GIA models assume Newtonian viscosity through the mantle, but laboratory experimental studies of rock deformation, observational studies of seismic anisotropy, and modelling studies of mantle dynamics show that in the upper mantle non-Newtonian viscosity may be important. This study explores the non-Newtonian effects on the GIA induced variations in mantle stress and viscosity and on surface observables including vertical displacement, relative sea level (RSL) and gravity change. The recently updated and fully benchmarked software package CitcomSVE is used for GIA simulations. We adopt the ICE-6G ice deglaciation history, VM5a lower mantle and lithospheric viscosities, and a composite rheology that combines Newtonian and non-Newtonian viscosities for the upper mantle. Our results show that: (1) The mantle stress beneath glaciated regions increases significantly during deglaciation, leading to regionally reduced upper mantle viscosity by more than an order of magnitude. Such effects can be rather localized at the periphery of glaciated regions. However, non-Newtonian effects on far-field mantle viscosity are negligibly small. GIA induced stress is also significant in the lithosphere (∼30 MPa) and lower mantle (∼2 MPa). (2) The predicted RSL changes from non-Newtonian models display distinct features in comparison with the Newtonian model, including more rapid sea level falls associated with the rapid deglaciation at ∼14 000 yr ago followed by a more gradual sea level variation for sites near the centres of formerly glaciated regions, and an additional phase of sea level falls for the last ∼8000 yr for sites at the ice margins. Similar time-dependence associated with the deglaciation is also seen for rate of vertical displacement, suggesting a relatively slow present-day rates of vertical displacement and gravity change. These features can be explained by the non-Newtonian effects associated with a loading event which manifest a fast relaxation stage followed by a relative slow relaxation stage. Our results may provide GIA diagnoses for distinguishing non-Newtonian and Newtonian rheology.

Thermal Analysis of Journal bearing with controlled slip/no-slip boundary condition and Non-Newtonian Rheology of lubricant

This paper discusses the combined effect of Non-Newtonian rheology of lubricants and slip boundary condition on the static performance characteristics of finite hydrodynamic journal bearings. A modified JFO model with an adiabatic energy equation has been used for calculating the variation of performance parameters. It has been observed that shear-thinning lubricant with slip effect on partial circumferential region shows a significant percentage of improvement in load-carrying capacity and coefficient of friction. Further, For eccentricity ratio of less than 0.2, these lubricants give maximum tribological performance as compared to Newtonian lubricants under conventional boundary condition.

A Review of Russian Snow Avalanche Models—From Analytical Solutions to Novel 3D Models

The article is a review of mathematical models of snow avalanches that have been proposed since the middle of the 20th century and are still in use. The main attention is paid to the work of researchers from the Soviet Union and Russia, since many of their works were published only in Russian and are not widely available. Mathematical models of various levels of complexity for avalanches of various types—from dense to powder-snow avalanches—are discussed. Analytical solutions including formulas for the avalanche front speed are described. The results of simulations of the movement of avalanches are given that were used to create avalanche hazard maps. The last part of the article is devoted to constructing models of a new type, in which avalanches are considered as laminar or turbulent flows of non-Newtonian fluids, using the full (not depth-averaged) equations of continuum mechanics. The results of a numerical study of the effect of non-Newtonian rheology and mass entrainment on the avalanche dynamics are presented.

Convection-diffusion in unsteady non-Newtonian fluid flow in an annulus with wall absorption

The present study investigates the combined effects of non-Newtonian rheology and unsteady nature of the fluid on dispersion of a soluble substance between two coaxial cylinders having wall permeability at the outer wall with the flowing fluid is modelled as Casson fluid. Generalized dispersion method in combination with a finite difference scheme is used to study the dispersion phenomenon. Using the generalized dispersion model, the entire process of dispersion is expressed in terms of three transport coefficients viz., absorption, convection, and dispersion (effective diffusion) coefficients. These transport coefficients are evaluated numerically using Crank-Nicolson finite difference method. The mean concentration is expressed in terms of these transport coefficients. Effects of annular gap, yield stress, Womersley frequency parameter, amplitude of the pressure pulsation, and the absorption parameter on the transport coefficients and mean concentration are studied. Flow unsteadiness is observed influencing the dispersion coefficient both quantitatively and qualitatively. It is observed that, as Womersley number increases the fluctuation of the dispersion coefficient increases and the magnitude of dispersion coefficient decreases for small values of time (< 0.5) and increases for later values of time.

Numerical study on polymer nanofibers with electrically charged jet of viscoelastic fluid in electrospinning process

Electrospinning is a useful and efficient technique to produce polymeric nanofibers. Nanofibers of polymers are electrospun by creating an electrically charged jet of polymer solution. Numerical study on non-Newtonian and viscoelastic jets of polymer nanofibers in electrospinning process is presented in this work. In particular, the effect of non-Newtonian rheology on the jet profile during the electrospinning process is examined. The governing equations of the problem are solved numerically using the Keller-Box method. The effects of yield stress and power-law index on the elongation, velocity, stress and total force are presented and discussed in detail. The results show that by increasing the values of yield stress, the fluid elongation is reduced significantly.

Derivation of Non-Newtonian Magnetic Fluid Lubricated Rough Centrosymmetric Squeeze Film Reynolds Equation and its Application

AbstractBased upon the Shliomis ferromagnetic fluid model and the Stokes microcontinuum theory incorporating with the Christensen stochastic model, a modified Reynolds equation of centrosymmetric squeeze films has been derived in this paper. The Reynolds equation includes the combined effects of non-Newtonian rheology, magnetic fluids with applied magnetic fields, rotational inertia forces, and surface roughness. To guide the use of the derived equation, the squeeze film of rotational rough-surface circular disks lubricated with non-Newtonian magnetic fluids is illustrated. According to the results obtained, the effects of rotation inertia decrease the load capacity and the squeeze film time of smooth circular disks. By the use of non-Newtonian magnetic fluids with applied magnetic fields, the rotational circular disks predict better squeeze film performances. When the influences of circumferential roughness patterns are considered, the non-Newtonian magnetic-fluid lubricated rotational rough disks with applied magnetic fields provide further higher values of the load capacity and the squeeze film time as compared to those of the smooth case.

Effect of non-Newtonian rheology on electrified jets of polymer nanofibers in electrospinning process based on bead–spring model

In the recent decades, electrospinning was mainly concerned with the formation of nanofibers from synthetic polymers and natural polymers targeting predominantly technical applications areas such as textiles and filters. In this paper, the effect of nonlinear matter flow on the dynamics of electrified jets in electrospinning process is examined by analyzing the bead–spring model. The ordinary differential equation is derived from momentum equation which is solved numerically using the fourth-order Runge–Kutta method. The simulations show good agreement with the experimental data and provide a qualitative understanding of the role of viscoelasticity in the early stage of the electrospinning experiment. The results show that a non-Newtonian rheology can slow down the elongation dynamics, thereby reducing the stable jet length.

Non-newtonian Rabinowitsch Fluid Effects on the Lubrication Performances of Sine Film Thrust Bearings

Thrust bearings are generally developed to sustain axial load generated from rotating machinery. Predicting lubrication performances of thrust bearings plays an important role in engineering applications. Taking into account the effects of non-Newtonian rheology, the lubrication performances for a sine film thrust bearing are investigated in the present paper. By employing a small perturbation technique to the nonlinear non-Newtonian Reynolds equation, analytical solutions of the film pressure, the load-carrying capacity, the friction parameter and the required volume flow rate are derived. Comparing with the case lubricated with a Newtonian lubricant, the non-Newtonian Rabinowitsch fluids (including the pseudo-plastic fluids and the dilatant fluids) show significant influences on the lubrication performances of a sine film thrust bearing, especially for a larger value of the non-Newtonian parameter.

Rheology modulated non-equilibrium fluctuations in time-dependent diffusion processes

The effect of non-Newtonian rheology, manifested through a viscoelastic linearized Maxwell model, on the time-dependent non-equilibrium concentration fluctuations due to free diffusion as well as thermal diffusion of a species is analyzed theoretically. The non-equilibrium process is quantified through the concentration fluctuation auto-correlation function, also known as the dynamic structure factor. The analysis reveals that the effect of rheology is prominent for both the cases of free diffusion and thermal diffusion at long times where the rheology dictates not only the location of the peaks in concentration auto-correlations, but also the magnitudes; such peaks in the auto-correlation function are absent in the case of a Newtonian fluid. At smaller times, for the case of free diffusion presence of time-dependent peak(s) are observed, which are weakly dependent on the influence of rheology, a phenomenon which is absent in the case of thermal diffusion. Lastly, different regimes of the frequency dependent overall dynamic structure factor depending on the interplay of the fluid relaxation time and momentum diffusivity are evaluated.

Numerical analysis of non-Newtonian rheology effect on hydrocyclone flow field

Abstract In view of the limitations of the existing Newton fluid effects on the vortex flow mechanism study, numerical analysis of non Newton fluid effects was presented. Using Reynolds stress turbulence model (RSM) and mixed multiphase flow model (Mixture) of FLUENT (fluid calculation software) and combined with the constitutive equation of apparent viscosity of non-Newtonian fluid, the typical non-Newtonian fluid (drilling fluid, polymer flooding sewage and crude oil as medium) and Newton flow field (water as medium) were compared by quantitative analysis. Based on the research results of water, the effects of non-Newtonian rheology on the key parameters including the combined vortex motion index n and tangential velocity were analyzed. The study shows that: non-Newtonian rheology has a great effect on tangential velocity and n value, and tangential velocity decreases with non-Newtonian increasing. The three kinds of n values (constant segment) are: 0.564(water), 0.769(polymer flooding sewage), 0.708(drilling fluid) and their variation amplitudes are larger than Newtonian fluid. The same time, non-Newtonian rheology will lead to the phenomenon of turbulent drag reduction in the vortex flow field. Compared with the existing formula calculation results shown, the calculation result of non-Newtonian rheology is most consistent with the simulation result, and the original theory has large deviations. The study provides reference for theory research of non-Newtonian cyclone separation flow field.

Bubble migration in two-dimensional foam sheared in a wide-gap Couette device: Effects of non-Newtonian rheology

We report experiments on the migration of a large bubble in an otherwise monodisperse two-dimensional (2D) foam sheared in a wide-gap Couette device. The bubble migrates away from the walls toward an equilibrium position between the center of the gap and the inner cylinder. This differs from the situation in a narrow-gap Couette device, where the equilibrium position is at the center of the gap [Mohammadigoushki and Feng, Phys. Rev. Lett. 109, 084502 (2012)]. The shift in equilibrium position is attributed to the non-Newtonian rheology of the foam, which is brought out by the nonhomogeneous shearing in a wide-gap geometry. Two aspects of the rheology, shear-thinning and the first normal stress difference, are examined separately by comparing with bubble migration in a xanthan gum solution and a Boger fluid. Shear-thinning shifts the equilibrium position inward while the normal stress does the opposite. Bubble migration in the 2D foam is the outcome of the competition between the two effects.

Rheology effects on cross-stream diffusion in a Y-shaped micromixer

Micromixers are one of the essential components of modern bio-microfluidic devices. Since most bio-fluids are complex and their rheological behavior usually cannot be described by the Newton's law of viscosity, it is vital to take into account the non-linear behavior of the fluids being manipulated in these devices in the pertinent simulations. In this paper, the non-Newtonian rheology effects on mass transport in an electrokinetically driven Y-shaped micromixer of rectangular cross section are being investigated. The fluid rheological behavior is assumed to be efficiently described by the power-law viscosity model. The governing equations are solved in dimensionless form through a finite difference based numerical procedure for non-uniform grid. The results show that the deviations of the fluid rheological behavior from the predictions of the Newton's law of viscosity may result in significant alteration of the species concentration field, especially for thick EDLs. In this respect, a higher value of the flow behavior index gives rise to a thicker diffusion layer in the presence of a purely electroosmotic flow. Whereas the same is observed for a pressure assisted flow, the opposite is right in the presence of an adverse pressure gradient. Moreover, the diffusion layer extent is an increasing function of EDL thickness. The relevant functionality is pronounced by increasing the flow behavior index. In addition, the effect of decreasing both Péclet number and the rectangular geometry aspect ratio is to enhance the mixing efficiency.

The effects of non-Newtonian rheology in the dynamic coefficients of wide slider bearings with a secant-shaped film profile

Purpose – The purpose of this paper is to investigate the effects of non-Newtonian rheology on the dynamic characteristics of a secant-shaped couple-stress lubricated slider bearing. Design/methodology/approach – By applying the linear dynamic theory to the film force equation, a closed-form solution of the stiffness and damping coefficients is obtained for the secant-shaped bearing taking into account the non-Newtonian effects of Stokes couple stress fluids. Findings – Comparing with the secant-shaped Newtonian-lubricant bearing, the effects of non-Newtonian couple stresses provide an apparent improvement in the dynamic stiffness and damping characteristics, especially for the secant-shaped slider bearing operating at lower squeezing-film heights and with larger non-Newtonian couple stress parameters. Originality/value – Comparing with those of the inclined plane-shaped non-Newtonian slider bearings, better dynamic stiffness and damping performances are provided for the secant-shaped non-Newtonian slider bearing designed at larger values of the shoulder parameters. The advantages of secant-shaped slider-bearing types provide engineers useful information in bearing selection and engineering application.

Effects of non-Newtonian power law rheology on mass transport of a neutral solute for electro-osmotic flow in a porous microtube.

Mass transport of a neutral solute for a power law fluid in a porous microtube under electro-osmotic flow regime is characterized in this study. Combined electro-osmotic and pressure driven flow is conducted herein. An analytical solution of concentration profile within mass transfer boundary layer is derived from the first principle. The solute transport through the porous wall is also coupled with the electro-osmotic flow to predict the solute concentration in the permeate stream. The effects of non-Newtonian rheology and the operating conditions on the permeation rate and permeate solute concentration are analyzed in detail. Both cases of assisting (electro-osmotic and poiseulle flow are in same direction) and opposing flow (the individual flows are in opposite direction) cases are taken care of. Enhancement of Sherwood due to electro-osmotic flow for a non-porous conduit is also quantified. Effects if non-Newtonian rheology on Sherwood number enhancement are observed.

Effects of surface roughness and non-Newtonian micropolar fluids on dynamic characteristics of wide plane slider bearings

Based on the Eringen's microcontinuum theory and the Christensen's stochastic theory, the combined effects of non-Newtonian rheology and surface roughness on the dynamic characteristics of slider bearings have been investigated. According to the results, the effects of transverse roughness provide an increase in the load capacity and dynamic coefficients as compared to the smooth bearing lubricated with micropolar fluids, whereas the influences of longitudinal roughness yield a reversed trend. The quantitative effects of rough surfaces and non-Newtonian fluids on bearing performances are more pronounced for higher values of the roughness parameter, the coupling parameter and the interacting parameter.

Effects of Non-Newtonian Rheology on Curved Circular Squeeze Films: the Rabinowitsch Fluid Model

Effects of Non-Newtonian Rheology on Curved Circular Squeeze Films: the Rabinowitsch Fluid Model

Combined effects of non-Newtonian rheology and rotational inertia on the squeeze film characteristics of parallel circular discs

The combined effects of non-Newtonian couple stresses and rotational inertia on the squeeze film behaviours between parallel rotating circular discs have been analysed in this paper. On the basis of Stokes micro-continuum theory, the non-Newtonian Reynolds-type equation including the rotational inertial effects is derived, and applied to predict the squeeze film performance. According to the results obtained and discussed, the effects of rotational inertia yield a lower squeeze-film load-carrying capacity; however, the presence of non-Newtonian couple stresses provides an increase in the load-carrying capacity and the approaching time. Better squeeze film characteristics of rotating circular discs are achieved by the use of a non-Newtonian couple stress fluid.

Combined effects of non-Newtonian rheology and fluid inertia forces on the non-linear transient behaviour in circular squeeze films

On the basis of the momentum integral method and the microcontinuum theory, the combined effects of total fluid inertia forces and non-Newtonian couple stresses on the non-linear squeeze film characteristics between parallel circular discs are presented. The squeeze-film lubrication equation is derived from the Stokes couple-stress motion equation retaining total fluid inertia terms to take into account the effects of non-Newtonian couple stresses resulting from the base oil blended with various types of additives, and the effects of local fluid inertia and convective fluid inertia. The non-linear motion equation for the squeezing disc is then numerically solved by using fourth-order Runge-Kutta method. Comparing with the Newtonian-lubricant inertialess case, the combined effects of fluid inertia forces and non-Newtonian couple stresses provide a significant increment in the response time of the squeeze film. The operating life of squeeze film discs are therefore lengthened, especially for larger couple stress parameters, Reynolds numbers and body inertia parameters. A design example is provided to facilitate the engineers assessing the extent to design the non-linear squeezing film discs considering the combined effects of total fluid inertia forces and non-Newtonian couple stresses.