Simulation study of particle clouds in oscillating shear flow

2018 ◽  
Vol 852 ◽  
pp. 484-506
Author(s):  
Amanda A. Howard ◽  
Martin R. Maxey
Keyword(s):  
Strain Amplitude ◽  
Volume Fraction ◽  
Normal Direction ◽  
Streamwise Direction ◽  
Large Role ◽  
Single Body ◽  
Brownian Particles ◽  
Force Coupling ◽  
Induced Flow ◽  
Neutrally Buoyant

Simulations of cylindrical clouds of concentrated, neutrally buoyant, suspended particles are used to investigate the dispersion of the particles in an oscillating Couette flow. In experiments by Metzger & Butler (Phys. Fluids, vol. 24 (2), 2012, 021703) with spherical clouds of non-Brownian particles, the clouds are shown to elongate at volume fraction $\unicode[STIX]{x1D719}=0.4$ but form ‘galaxies’ where the cloud rotates as a single body with extended arms when $\unicode[STIX]{x1D719}>0.4$ and the ratio of the cloud radius to particle radius, $R/a$, is sufficiently large. The simulations, which use the force coupling method, are completed for $\unicode[STIX]{x1D719}=0.4$ and $\unicode[STIX]{x1D719}=0.55$, with $R/a$ between $5$ and $20$. The cloud shape for $\unicode[STIX]{x1D719}=0.4$ is shown to be reversible at low strain amplitude, and extend in the streamwise direction along the centre of the cloud at moderate strain amplitude. For higher strain amplitude the clouds extend near the channel walls to form a parallelogram. The results demonstrate that the particle contact force determines the transition between these states and plays a large role in the irreversibility of the parallelograms. Rotating galaxies form at $\unicode[STIX]{x1D719}=0.55$ with $R/a\geqslant 15$, and are characterized by a particle-induced flow in the wall-normal direction.

scholarly journals Tunable fall velocity of a dense ball in oscillatory cross-sheared concentrated suspensions

2014 ◽  
Vol 746 ◽  
Author(s):  
Frédéric Blanc ◽  
Elisabeth Lemaire ◽  
François Peters
Keyword(s):  
Strain Amplitude ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Small Strain ◽  
Concentrated Suspensions ◽  
Particle Volume ◽  
Fall Velocity ◽  
Brownian Particles ◽  
Ball Velocity ◽  
Neutrally Buoyant

AbstractThe fall velocity of a dense large ball in a suspension of neutrally buoyant non-Brownian particles subjected to horizontal oscillatory shear is studied. As the strain amplitude is increased, the velocity increases up to a maximum value before decreasing to the value that it would have in a resting suspension. The higher the frequency is, the stronger the effect is. The falling ball velocity can be largely increased in the presence of the oscillatory cross-shear flow. For instance, for a particle volume fraction of $\varPhi =0.47$ it reaches four times the value it has in the unsheared suspension. At small strain amplitudes, it turns out that the velocity of the falling ball is determined by a balance between the steady drag flow, which drives the apparent suspension viscosity toward a high value, and the oscillatory cross-shear, which lessens it. A simple model is proposed to explain the experimental observations at small strain amplitude. The velocity decrease observed at larger amplitude is not completely understood yet.

Suspensions with a tunable effective viscosity: a numerical study

2012 ◽  
Vol 693 ◽  
pp. 345-366 ◽  
Author(s):  
L. Jibuti ◽  
S. Rafaï ◽  
P. Peyla
Keyword(s):  
Effective Viscosity ◽  
Volume Fraction ◽  
Numerical Study ◽  
Spherical Particles ◽  
Dimensionless Number ◽  
Particle Rotation ◽  
Concentrated Suspensions ◽  
Sheared Suspensions ◽  
Neutrally Buoyant ◽  
Universal Behaviour

AbstractIn this paper, we conduct a numerical investigation of sheared suspensions of non-colloidal spherical particles on which a torque is applied. Particles are mono-dispersed and neutrally buoyant. Since the torque modifies particle rotation, we show that it can indeed strongly change the effective viscosity of semi-dilute or even more concentrated suspensions. We perform our calculations up to a volume fraction of 28 %. And we compare our results to data obtained at 40 % by Yeo and Maxey (Phys. Rev. E, vol. 81, 2010, p. 62501) with a totally different numerical method. Depending on the torque orientation, one can increase (decrease) the rotation of the particles. This results in a strong enhancement (reduction) of the effective shear viscosity of the suspension. We construct a dimensionless number $\Theta $ which represents the average relative angular velocity of the particles divided by the vorticity of the fluid generated by the shear flow. We show that the contribution of the particles to the effective viscosity can be suppressed for a given and unique value of $\Theta $ independently of the volume fraction. In addition, we obtain a universal behaviour (i.e. independent of the volume fraction) when we plot the relative effective viscosity divided by the relative effective viscosity without torque as a function of $\Theta $. Finally, we show that a modified Faxén law can be equivalently established for large concentrations.

scholarly journals Confined flow of suspensions modelled by a frictional rheology

2014 ◽  
Vol 759 ◽  
pp. 197-235 ◽  
Author(s):  
Brice Lecampion ◽  
Dmitry I. Garagash
Keyword(s):  
Shear Stress ◽  
Friction Coefficient ◽  
Normal Stress ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Numerical Predictions ◽  
Dry Granular Flow ◽  
Neutrally Buoyant ◽  
Constitutive Parameters ◽  
Axial Development

AbstractWe investigate in detail the problem of confined pressure-driven laminar flow of neutrally buoyant non-Brownian suspensions using a frictional rheology based on the recent proposal of Boyer et al. (Phys. Rev. Lett., vol. 107 (18), 2011, 188301). The friction coefficient (shear stress over particle normal stress) and solid volume fraction are taken as functions of the dimensionless viscous number $I$ defined as the ratio between the fluid shear stress and the particle normal stress. We clarify the contributions of the contact and hydrodynamic interactions on the evolution of the friction coefficient between the dilute and dense regimes reducing the phenomenological constitutive description to three physical parameters. We also propose an extension of this constitutive framework from the flowing regime (bounded by the maximum flowing solid volume fraction) to the fully jammed state (the random close packing limit). We obtain an analytical solution of the fully developed flow in channel and pipe for the frictional suspension rheology. The result can be transposed to dry granular flow upon appropriate redefinition of the dimensionless number $I$. The predictions are in excellent agreement with available experimental results for neutrally buoyant suspensions, when using the values of the constitutive parameters obtained independently from stress-controlled rheological measurements. In particular, the frictional rheology correctly predicts the transition from Poiseuille to plug flow and the associated particles migration with the increase of the entrance solid volume fraction. We also numerically solve for the axial development of the flow from the inlet of the channel/pipe toward the fully developed state. The available experimental data are in good agreement with our numerical predictions, when using an accepted phenomenological description of the relative phase slip obtained independently from batch-settlement experiments. The solution of the axial development of the flow notably provides a quantitative estimation of the entrance length effect in a pipe for suspensions when the continuum assumption is valid. Practically, the latter requires that the predicted width of the central (jammed) plug is wider than one particle diameter. A simple analytical expression for development length, inversely proportional to the gap-averaged diffusivity of a frictional suspension, is shown to encapsulate the numerical solution in the entire range of flow conditions from dilute to dense.

A Numerical Approach in Predicting Flow Field Induced by Randomly Moving Nano Particles

2013 ◽  
Author(s):  
Way Lee Cheng ◽  
Reza Sadr
Keyword(s):  
Flow Field ◽  
Underlying Mechanism ◽  
Numerical Approach ◽  
Small Time ◽  
Nano Particles ◽  
Navier Stokes ◽  
Time Step ◽  
Navier Stokes Equation ◽  
Brownian Particles ◽  
Induced Flow

There have been several reports that suspending nano-particles in a fluid, or nanofluids, can enhance heat transfer properties such as conductivity. However, the extend of the reported enhancement is inconsistent in the literature and the exact mechanisms that govern these observations (or phenomena) are not fully understood. Although the interaction between the fluid and suspended particles is suspected to be the main contributor to this phenomenon, literature shows contradicting conclusions in the underlying mechanism responsible for these effects. This highlights the need for development of computational tools in this area. In this study, a computational approach is developed for simulating the induced flow field by randomly moving particles suspended in a quiescent fluid. Brownian displacement is used to describe the random walk of the particles in the fluid. The steady state movement is described with simplified Navier-Stokes equation to solve for the induced fluid flow around the moving particles with constant velocity at small time steps. The unsteady behavior of the induced flow field is approximated using the velocity profiles obtained from FLUENT. Initial results show that random movements of Brownian particles suspended in the fluid induce a random flow disturbance in the flow field. It is observed that the flow statistics converge asymptotically as time-step reduces. Moreover, inclusion of the transitional movement of the particles significantly affects the results.

The motion of Brownian particles and sediment on an inclined plate

1997 ◽  
Vol 337 ◽  
pp. 25-47 ◽  
Author(s):  
A. A. DAHLKILD
Keyword(s):  
Volume Fraction ◽  
Particle Density ◽  
Particle Volume Fraction ◽  
Present Theory ◽  
Brownian Diffusion ◽  
Inclined Plate ◽  
Particle Volume ◽  
Hindered Settling ◽  
Brownian Particles ◽  
And Migration

The gravitational settling of a homogeneous suspension of Brownian particles on an inclined plate is considered. The hindered settling towards the wall and the viscous, buoyancy-driven bulk motion of the sediment are considered assuming steady conditions and accounting for the effects of Brownian diffusion, shear-induced diffusion and migration of particles due to a gradient in shear stress. Generally, the results show the development of a sediment boundary layer where the settling towards the wall is balanced by Brownian diffusion at the beginning of the plate and by shear-induced diffusion further downstream. Compared to previous results in the literature, the present theory allows steady-state solutions for extended values of the plate inclination and particle volume fraction above the sediment; upon reconsidering the case with non-Brownian particles, a new similarity solution, with a stable shock in particle density, is developed.

Binder/Filler Interaction and the Nonlinear Behavior of Highly-Filled Elastomers

1990 ◽  
Vol 63 (4) ◽  
pp. 488-502 ◽  
Author(s):  
R. G. Stacer ◽  
C. Hübner ◽  
D. M. Husband
Keyword(s):  
Surface Area ◽  
Strain Amplitude ◽  
Nonlinear Response ◽  
Volume Fraction ◽  
Viscoelastic Behavior ◽  
Interaction Model ◽  
Nonlinear Behavior ◽  
Small Deformation ◽  
Amplitude Dependence ◽  
Filled Rubbers

Abstract 1. The small-deformation-viscoelastic response of elastomers containing nonreinforcing filler has been investigated. Nonlinear viscoelastic behavior was observed as a pronounced strain-amplitude dependence. The degree of this dependence was quantified using a power-law representation as a single nonlinear parameter, m. 2. The magnitude of m was a function of formulation variables. It was found that m increased with the volume fraction and particle size of filler material, as well as the volume fraction of plasticizer. Reduced values of m were observed in the presence of bonding agent and with greater degrees of apparent crosslinking. The latter was controlled in this study through imbalanced urethane cures. 3. Nonlinear behavior of elastomers containing nonreinforcing filler has been compared and contrasted with the data base for carbon-black-reinforced elastomers. The major difference is in the effect of the surface area of filler particles. Nonlinear response in black-filled rubbers increases with surface area, while the opposite is reported in this study. Additionally, the relationship between viscoelastic dissipation and the magnitude of nonlinear response, well established for black-filled rubbers, was not observed. These results indicate that the response of elastomers containing nonreinforcing filler, although nearly identical in appearance to that seen with reinforcing filler, is not driven by the same mechanism. 4. A binder/filler interaction model is proposed for materials containing nonreinforcing filler. This model is based on the ideal adhesive strength of the binder/filler interface. In this model, greater attraction between polymer and particle surfaces reduces molecular slippage during deformation, leading to a decreased dependence of the modulus on strain amplitude, or decreased nonlinearity. It is shown that the model provides reasonable predictions for the observed phenomena.

Dispersion of a ball settling through a quiescent neutrally buoyant suspension

1998 ◽  
Vol 361 ◽  
pp. 309-331 ◽  
Author(s):  
JAMES R. ABBOTT ◽  
ALAN L. GRAHAM ◽  
LISA A. MONDY ◽  
HOWARD BRENNER
Keyword(s):  
Settling Velocity ◽  
Volume Fraction ◽  
Functional Dependence ◽  
Vertical Component ◽  
Transversely Isotropic ◽  
Suspended Particles ◽  
Three Dimensions ◽  
Ball Diameter ◽  
The Mean ◽  
Neutrally Buoyant

Individual falling balls were allowed to settle through otherwise quiescent well-mixed suspensions of non-colloidal neutrally buoyant spheres dispersed in a Newtonian liquid. Balls were tracked in three dimensions to determine the variances in their positions about a mean uniform vertical settling path. The primary experimental parameters investigated were the size of the falling ball and the volume fraction and size of the suspended particles. Unlike the horizontal variances, the vertical variances were found to be affected by short-time deterministic behaviour relating to the instantaneous local configurational arrangement of the suspended particles. For sufficiently long intervals between successive observations, the trajectories of the balls were observed to disperse about their mean settling paths in a random manner. This points to the existence of a Gaussian hydrodynamic dispersivity that characterizes the linear temporal growth of the variance in the position of a falling ball. The functional dependence of these horizontal and vertical dispersivities upon the parameters investigated was established.The dispersivity dyadic was observed to be transversely isotropic with respect to the direction of gravity, with the vertical component at least 25 times larger than the horizontal component. The vertical dispersivity Dˆv (made dimensionless with the diameter of the suspended spheres and the mean settling velocity) was observed to decrease with increasing falling ball diameter, but to decrease less rapidly with concentration than theoretically predicted for very dilute suspensions; moreover, for falling balls equal in size to the suspended spheres, Dˆv increased linearly with increasing volume fraction ϕ of suspended solids.In addition to the above experiments performed on suspensions of spheres, previously published settling-velocity data on the fall of balls through neutrally buoyant suspensions of rods possessing an aspect ratio of 20 were re-analysed, and vertical dispersivities calculated therefrom. (These data, taken by several of the present investigators in conjunction with other researchers, had only been grossly analysed in prior publications to extract the mean settling velocity of the ball, no attempt having been made at the time to extract dispersivity data too.) The resulting vertical dispersivities, when rendered dimensionless with the rod length and mean settling velocity, showed no statistically significant dependence upon the falling-ball diameter; moreover, all other things being equal, these dispersivities were observed to increase with increasing rod concentration.

Suspensions in a tilted trough: second normal stress difference

2011 ◽  
Vol 686 ◽  
pp. 26-39 ◽  
Author(s):  
Étienne Couturier ◽  
François Boyer ◽  
Olivier Pouliquen ◽  
Élisabeth Guazzelli
Keyword(s):  
Shear Stress ◽  
Normal Stress ◽  
Volume Fraction ◽  
Behavioural Change ◽  
Normal Stress Difference ◽  
Stress Difference ◽  
Rigid Spheres ◽  
First Normal Stress Difference ◽  
Second Normal Stress Difference ◽  
Neutrally Buoyant

AbstractWe measure the second normal-stress difference in suspensions of non-Brownian neutrally buoyant rigid spheres dispersed in a Newtonian fluid. We use a method inspired by Wineman & Pipkin (Acta Mechanica, vol. 2, 1966, pp. 104–115) and Tanner (Trans. Soc. Rheol., vol. 14, 1970, pp. 483–507), which relies on the examination of the shape of the suspension free surface in a tilted trough flow. The second normal-stress difference is found to be negative and linear in shear stress. The ratio of the second normal-stress difference to shear stress increases with increasing volume fraction. A clear behavioural change exhibiting a strong (approximately linear) growth in the magnitude of this ratio with volume fraction is seen above a volume fraction of 0.22. By comparing our results with previous data obtained for the same batch of spheres by Boyer, Pouliquen & Guazzeli (J. Fluid Mech., 2011, doi:10.1017/jfm.2011.272), the ratio of the first normal-stress difference to the shear stress is estimated and its magnitude is found to be very small.

scholarly journals A rational method for determining intermittency in the transitional boundary layer

2019 ◽  
Vol 61 (1) ◽  
Author(s):  
Dhamotharan Veerasamy ◽  
Chris Atkin
Keyword(s):  
Boundary Layer ◽  
Plate Boundary ◽  
Threshold Value ◽  
Normal Direction ◽  
Transitional Flow ◽  
Streamwise Direction ◽  
Transitional Boundary Layer ◽  
Rational Procedure ◽  
Selection Of ◽  
Flat Plate Boundary Layer

Abstract A new rational procedure is proposed for determining the intermittency in the streamwise direction. One of the key parameters for the intermittency determination is the selection of a threshold value, which often involves a certain level of subjectivity. Here, a reliable way of choosing the threshold value in a more objective manner is proposed. The proposed approach involves a single threshold value, equal to the magnitude of the maximum laminar perturbation in the transitional flow. The results obtained are validated with the widely used dual-slope method. In this paper, the measurements are carried out on an experimental arrangement, involving the interaction of an upstream aerofoil wake with a downstream flat plate boundary layer. As a by-product of the study, a scaling parameter has been identified which captures the length of the transition zone as the proximity of the aerofoil in the wall-normal direction is varied. Graphic abstract

Effect of microstructural constituents and morphological characteristics on low cycle fatigue behaviour of inter-critically annealed 20MnMoNi55 steel

2021 ◽  
pp. 146442072110387
Author(s):  
Parichay Basu ◽  
Sanjib K Acharyya ◽  
Prasanta Sahoo
Keyword(s):  
Finite Element ◽  
Strain Amplitude ◽  
Crystal Plasticity ◽  
Volume Fraction ◽  
Low Cycle Fatigue ◽  
Stress Triaxiality ◽  
Morphological Characteristics ◽  
Strain Curve ◽  
Cycle Fatigue ◽  
Microstructural Parameters

The effect of varying microstructural parameters on the cyclic behaviour of dual-phase steels was studied on the basis of experimental and micromechanical finite-element simulated results. The initial bainitic morphology of as-received 20MnMoNi55 steel was transformed into ferrite and martensite through proper inter-critical heat treatment procedures. Strain-controlled low cycle fatigue tests were conducted at room temperature with different strain amplitudes at a specific strain rate of 10−3/s. The cyclic stress–strain curve, obtained through joining the peak stresses of hysteresis loops corresponding to different strain amplitude, shows an increase in strain hardening with an increase in volume fraction of martensite. Whereas the rate of cyclic softening, considering the decrease in stress amplitude with respect to elapsed cycles, increases with increasing strain amplitude. Inclusive of all affecting microstructural parameters, an original microstructure-based representative volume element associated with a crystal plasticity-based material model was adopted for conducting micromechanical finite-element simulation. In addition to several parameters associated with a crystal plasticity model, consideration of initial geometrically necessary dislocation density in constituent phases resulted in the accurate prediction of a hysteresis loop at low strain amplitude as compared with the experimental results. A variation of stress triaxiality built up in ferrite matrix with martensite fraction along with deformation inhomogeneity between ferrite and martensite was also observed through a strain partitioning phenomenon obtained from finite-element simulated results.

Sign in / Sign up

Export Citation Format

Share Document