Dilute suspension of neutrally buoyant particles in viscoelastic turbulent channel flow

2019 ◽  
Vol 875 ◽  
pp. 286-320 ◽  
Author(s):  
Amir Esteghamatian ◽  
Tamer A. Zaki
Keyword(s):  
Channel Flow ◽  
Volume Fraction ◽  
Qualitative Difference ◽  
Turbulent Channel Flow ◽  
Polymer Chains ◽  
Spherical Particles ◽  
Lower Probability ◽  
Fluid Field ◽  
The Individual ◽  
Neutrally Buoyant

Direct numerical simulations of viscoelastic turbulent channel flow laden with neutrally buoyant spherical particles are performed. Two FENE-P viscoelastic and one Newtonian fluid are examined, and for each the particle-laden configuration is contrasted to a reference condition without seeding. The size of the particles is larger than the dissipation length scale, and their presence enhances drag in a manner that is intrinsically different in the viscoelastic and Newtonian flows. While the particles effectively suppress the turbulence activity, they significantly enhance the polymer stresses. The polymer chains are markedly stretched in the vicinity of the particles, altering the correlation between the turbulence and polymer work that is commonly observed in single-phase viscoelastic turbulence. At the lower elasticity, the particles enhance the cycle of hibernating and active turbulence and, in turn, their migration and volume-fraction profiles are qualitatively altered by the intermittency of the turbulence. Particle–fluid momentum transfer is investigated by estimating the local fluid field on a trimmed spherical shell around the individual particles. And by comparing the particle microstructures, a lower probability of particle alignment in the streamwise direction is observed in the viscoelastic configuration. This effect is attributed to a qualitative difference in the conditionally averaged velocity fields in the vicinity of the particles in the Newtonian and viscoelastic flows.

scholarly journals Flow Modulation by Finite-Size Neutrally Buoyant Particles in a Turbulent Channel Flow

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Lian-Ping Wang ◽  
Cheng Peng ◽  
Zhaoli Guo ◽  
Zhaosheng Yu
Keyword(s):  
Particle Size ◽  
Solid Particle ◽  
Channel Flow ◽  
Volume Fraction ◽  
Finite Size ◽  
Turbulent Channel Flow ◽  
Solid Particles ◽  
Momentum Exchange ◽  
Flow Modulation ◽  
Neutrally Buoyant

A fully mesoscopic, multiple-relaxation-time (MRT) lattice Boltzmann method (LBM) is developed to perform particle-resolved direct numerical simulation (DNS) of wall-bounded turbulent particle-laden flows. The fluid–solid particle interfaces are treated as sharp interfaces with no-slip and no-penetration conditions. The force and torque acting on a solid particle are computed by a local Galilean-invariant momentum exchange method. The first objective of the paper is to demonstrate that the approach yields accurate results for both single-phase and particle-laden turbulent channel flows, by comparing the LBM results to the published benchmark results and a full-macroscopic finite-difference direct-forcing (FDDF) approach. The second objective is to study turbulence modulations by finite-size solid particles in a turbulent channel flow and to demonstrate the effects of particle size. Neutrally buoyant particles with diameters 10% and 5% the channel width and a volume fraction of about 7% are considered. We found that the mean flow speed was reduced due to the presence of the solid particles, but the local phase-averaged flow dissipation was increased. The effects of finite particle size are reflected in the level and location of flow modulation, as well as in the volume fraction distribution and particle slip velocity near the wall.

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.

The Role of Polymer-particle Interactions on the Viscoelastic Properties of Polymer Nanocomposites

2007 ◽  
Vol 1056 ◽  
Author(s):  
Alireza Sarvestani ◽  
Esmaiel Jabbari
Keyword(s):  
Polymer Nanocomposites ◽  
Volume Fraction ◽  
Molecular Model ◽  
Low Frequency ◽  
Maxwell Model ◽  
Equilibrium Structure ◽  
Polymer Chains ◽  
Spherical Particles ◽  
Filler Concentration ◽  
Adsorbed Polymer

ABSTRACTA molecular model is proposed for the dynamics of polymer chains in dilute polymer solutions containing well-dispersed spherical particles. In the presence of short range energetic affinity between the monomers and filler surface, the equilibrium structure of the adsorbed polymer layer is determined by a scaling theory. The viscoelastic response of the suspension is studied by a Maxwell model. It is shown that the solid-like properties of polymer nanocomposites in low frequency regimes could be attributed to the slowdown of the relaxation process of polymer chains. This process is controlled by the monomer-particle frictional interactions, density of the adsorbed polymer chains on the particles surface (controlled by monomer-particle adsorption energy), and volume fraction of the interfacial layer which can be enhanced by reduction of filler size or increasing the filler concentration.

A direct numerical investigation of two-way interactions in a particle-laden turbulent channel flow

2019 ◽  
Vol 875 ◽  
pp. 1096-1144 ◽  
Author(s):  
Cheng Peng ◽  
Orlando M. Ayala ◽  
Lian-Ping Wang
Keyword(s):  
Channel Flow ◽  
Finite Size ◽  
Turbulent Channel Flow ◽  
Spherical Particles ◽  
Homogeneous Distribution ◽  
Particle Sizes ◽  
Small Particles ◽  
Particle Rotation ◽  
Turbulence Modulation ◽  
Budget Analysis

Understanding the two-way interactions between finite-size solid particles and a wall-bounded turbulent flow is crucial in a variety of natural and engineering applications. Previous experimental measurements and particle-resolved direct numerical simulations revealed some interesting phenomena related to particle distribution and turbulence modulation, but their in-depth analyses are largely missing. In this study, turbulent channel flows laden with neutrally buoyant finite-size spherical particles are simulated using the lattice Boltzmann method. Two particle sizes are considered, with diameters equal to 14.45 and 28.9 wall units. To understand the roles played by the particle rotation, two additional simulations with the same particle sizes but no particle rotation are also presented for comparison. Particles of both sizes are found to form clusters. Under the Stokes lubrication corrections, small particles are found to have a stronger preference to form clusters, and their clusters orientate more in the streamwise direction. As a result, small particles reduce the mean flow velocity less than large particles. Particles are also found to result in a more homogeneous distribution of turbulent kinetic energy (TKE) in the wall-normal direction, as well as a more isotropic distribution of TKE among different spatial directions. To understand these turbulence modulation phenomena, we analyse in detail the total and component-wise volume-averaged budget equations of TKE with the simulation data. This budget analysis reveals several mechanisms through which the particles modulate local and global TKE in the particle-laden turbulent channel flow.

scholarly journals Turbulent channel flow of a dense binary mixture of rigid particles

2017 ◽  
Vol 818 ◽  
pp. 623-645 ◽  
Author(s):  
Iman Lashgari ◽  
Francesco Picano ◽  
Pedro Costa ◽  
Wim-Paul Breugem ◽  
Luca Brandt
Keyword(s):  
Binary Mixture ◽  
Channel Flow ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Turbulent Channel Flow ◽  
Channel Height ◽  
Wall Region ◽  
Small Particles ◽  
Rigid Particles ◽  
Large Particles

We study turbulent channel flow of a binary mixture of finite-sized neutrally buoyant rigid particles by means of interface-resolved direct numerical simulations. We fix the bulk Reynolds number and total solid volume fraction, $Re_{b}=5600$ and $\unicode[STIX]{x1D6F7}=20\,\%$, and vary the relative fraction of small and large particles. The binary mixture consists of particles of two different sizes, $2h/d_{l}=20$ and $2h/d_{s}=30$ where $h$ is the half-channel height and $d_{l}$ and $d_{s}$ the diameters of the large and small particles. While the particulate flow statistics exhibit a significant alteration of the mean velocity profile and turbulent fluctuations with respect to the unladen flow, the differences between the mono-disperse and bi-disperse cases are small. However, we observe a clear segregation of small particles at the wall in binary mixtures, which affects the dynamics of the near-wall region and thus the overall drag. This results in a higher drag in suspensions with a larger number of large particles. As regards bi-disperse effects on the particle dynamics, a non-monotonic variation of the particle dispersion in the spanwise (homogeneous) direction is observed when increasing the percentage of small/large particles. Finally, we note that particles of the same size tend to cluster more at contact whereas the dynamics of the large particles gives the highest collision kernels due to a higher approaching speed.

scholarly journals Life and death by boundary conditions

2015 ◽  
Vol 768 ◽  
pp. 1-4 ◽  
Author(s):  
Andrea Prosperetti
Keyword(s):  
Boundary Conditions ◽  
Numerical Simulations ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Spherical Particles ◽  
Life And Death

Picano et al. (J. Fluid Mech., vol. 764, 2015, pp. 463–487) have conducted fully resolved numerical simulations of many thousands of spherical particles in a turbulent channel flow with $\mathit{Re}=5600$. Their results give a tantalizing demonstration of the vastness of the vistas that this line of research is about to open.

The influence of inertia on the rheology of a periodic suspension of neutrally buoyant rigid ellipsoids

2015 ◽  
Vol 781 ◽  
pp. 506-549 ◽  
Author(s):  
Mohsen Daghooghi ◽  
Iman Borazjani
Keyword(s):  
Normal Stress ◽  
Reynolds Stress ◽  
Intrinsic Viscosity ◽  
Volume Fraction ◽  
Normal Stress Difference ◽  
Numerical Results ◽  
Spherical Particles ◽  
Stress Difference ◽  
Neutrally Buoyant ◽  
Normal Difference

We investigate the rheological properties of a suspension of neutrally buoyant rigid ellipsoids by fluid–structure interaction simulations of a particle in a periodic domain under simple shear using the curvilinear immersed-boundary (CURVIB) method along with a quaternion–angular velocity technique to calculate the dynamics of the particle’s motion. We calculate all the different terms of particle stress for the first time for non-spherical particles, i.e. in addition to the stresslet, we calculate the acceleration and Reynolds stress, which are typically ignored in previous similar works. Furthermore, we derive analytical expressions for all these terms to verify the numerical results and deduce the effect of inertia by comparing our numerical results with the analytical solution. The effect of particle Reynolds number ($\mathit{Re}$), volume fraction (${\it\phi}$), and the shape of particles has been studied on all mechanisms of stress generation, the intrinsic viscosity, and normal stress differences of the suspension for the range$0.008\leqslant {\it\phi}\leqslant 0.112$and$0.01\leqslant \mathit{Re}\leqslant 10.0$. We found that inertia increases the shear and the second normal difference of the stresslet (dominant term of the particle stress), and decreases the first normal difference that is generated due to the strain field. The contribution of acceleration stress to the total stress is found to be important in the second normal stress difference, with a cycle-average comparable to the stresslet component. We also discovered that the contribution of Reynolds stress in the first normal stress difference becomes important even when inertia is as low as$\mathit{Re}\sim O(0.1)$, and its value can be even greater than the stresslet when inertia increases, i.e. Reynolds stresses cannot be ignored for non-spherical particles. For concentrations in the range from dilute to semi-dilute, the effect of inertia on the intrinsic viscosity of a suspension is found to be comparable to the volume fraction. Furthermore, our calculations show that for a dilute concentration and the low-inertia regime ($\mathit{Re}<1.0$), the intrinsic viscosity of a suspension consisting of ellipsoids with an aspect ratio of five can be 20 % higher than its Stokesian analytical value.

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