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Mar 2013

Volume 25, Issue 3, Articles (03xxxx)

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Phys. Fluids 25, 031302 (2013); http://dx.doi.org/10.1063/1.4793543 (13 pages)

Gretar Tryggvason, Sadegh Dabiri, Bahman Aboulhasanzadeh, and Jiacai Lu
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back to top Particulate, Multiphase, and Granular Flows

Granular suspension avalanches. I. Macro-viscous behavior

Christophe Ancey, Nicolas Andreini, and Gaël Epely-Chauvin

Phys. Fluids 25, 033301 (2013); http://dx.doi.org/10.1063/1.4793719 (21 pages) | Cited 2 times

Online Publication Date: 6 March 2013

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We experimentally studied the flow behavior of a fixed volume of granular suspension, initially contained in a reservoir and released down an inclined flume. Here “granular suspension” refers to a suspension of non-Brownian particles in a viscous fluid. Depending on the solids fraction, density mismatch, and particle size distribution, a wealth of behaviors can be observed. Here we report and interpret results obtained with granular suspensions, which consisted of neutrally buoyant particles with a solids fraction (ϕ = 0.575–0.595) close to the maximum random packing fraction (estimated at ϕm = 0.625). The particles had the same refractive index as the fluid, which made it possible to measure the velocity profiles inside the moving bulk and far from the sidewalls. Additional information such as the front position and the flow depth was also recorded. Three regimes were observed. At early times, the flow features were reminiscent of homogeneous Newtonian fluids (e.g., the same dependence of the front position on time). At later times, the free surface became more and more bumpy as fractures developed within the bulk. This fracture process ultimately gave rise to a stick-slip regime, in which the suspension moved intermittently. In this paper, we focus on the first regime referred to as the macro-viscous regime. Although the bulk flow properties looked like those of Newtonian fluids, the internal dynamics were much richer.
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47.57.E- Suspensions
83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.50.Ha Flow in channels
47.20.Gv Viscous and viscoelastic instabilities
47.45.Gx Slip flows and accommodation
47.60.Dx Flows in ducts and channels

Granular suspension avalanches. II. Plastic regime

Nicolas Andreini, Christophe Ancey, and Gaël Epely-Chauvin

Phys. Fluids 25, 033302 (2013); http://dx.doi.org/10.1063/1.4793720 (23 pages) | Cited 2 times

Online Publication Date: 6 March 2013

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We present flume experiments showing plastic behavior for perfectly density-matched suspensions of non-Brownian particles within a Newtonian fluid. In contrast with most earlier experimental investigations (carried out using coaxial cylinder rheometers), we obtained our rheological information by studying thin films of suspension flowing down an inclined flume. Using particles with the same refractive index as the interstitial fluid made it possible to measure the velocity field far from the wall using a laser-optical system. At long times, a stick-slip regime occurred as soon as the fluid pressure dropped sufficiently for the particle pressure to become compressive. Our explanation was that the drop in fluid pressure combined with the surface tension caused the flow to come to rest by significantly increasing flow resistance. However, the reason why the fluid pressure diffused through the pores during the stick phases escaped our understanding of suspension rheology.
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83.80.Hj Suspensions, dispersions, pastes, slurries, colloids
83.60.La Viscoplasticity; yield stress
47.57.E- Suspensions
47.57.Qk Rheological aspects
83.50.Ha Flow in channels
47.60.Dx Flows in ducts and channels

Decaying versus stationary turbulence in particle-laden isotropic turbulence: Heavy particle statistics modifications

Abouelmagd H. Abdelsamie and Changhoon Lee

Phys. Fluids 25, 033303 (2013); http://dx.doi.org/10.1063/1.4795333 (18 pages)

Online Publication Date: 18 March 2013

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The current paper examines the heavy particle statistics modification by two-way interaction in particle-laden isotropic turbulence in an attempt to interpret their statistics modification using the information of modulated turbulence. Moreover, we clarify the distinctions of this modification between decaying and stationary turbulence as an extension of our previous work [A. H. Abdelsamie and C. Lee, “Decaying versus stationary turbulence in particle-laden isotropic turbulence: Turbulence modulation mechanism,” Phys. Fluids 24, 015106 (2012)10.1063/1.3678332]. Direct Numerical Simulation (DNS) was carried out using 1283 grid points at a Taylor micro-scale Reynolds number of Rλ ∼ 70. The effect of O(106) solid particles with a different Stokes number (St) was implemented as a point-force approximation in the Navier-Stokes equation. Various statistics associated with particle dispersion are investigated, and the auto-correlations models which was provided by Jung et al. [“Behavior of heavy particles in isotropic turbulence,” Phys. Rev. E 77, 016307 (2008)10.1103/PhysRevE.77.016307] are extended in the current paper. DNS results reveal that the two-way coupling interaction enhances the fluid and heavy particle auto-correlation functions and the alignment between their velocity vectors for all Stokes numbers in decaying and stationary turbulence, but for different reasons. The modification mechanisms of particle dispersion statistics in stationary turbulence are different from those in decaying turbulence depending on the Stokes number, particularly for St <1.
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47.55.Kf Particle-laden flows
02.30.Jr Partial differential equations
02.30.Mv Approximations and expansions
47.10.ad Navier-Stokes equations
47.27.ek Direct numerical simulations
47.27.Gs Isotropic turbulence; homogeneous turbulence

Radial distribution and axial dispersion of suspended particles inside a narrow cylinder due to mildly inertial flow

S. Bhattacharya, D. K. Gurung, and S. Navardi

Phys. Fluids 25, 033304 (2013); http://dx.doi.org/10.1063/1.4791794 (9 pages)

Online Publication Date: 25 March 2013

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The combined effects of radial drift due to flow inertia and diffusion due to Brownian motion significantly modify the radial probability distribution and the axial dispersion of conduit-bound suspended bodies. This interplay depends on the product of Peclet Pe and Reynolds Re numbers so that even apparently non-Brownian systems with high Pe exhibit the changes if Re is small. This article describes the probability distribution and the Taylor dispersion coefficient under such conditions for systems with low vessel-to-particle size-ratios where the effect is especially pronounced, but the flow-simulation is considerably difficult. We also identify the parametric regimes and the physical conditions required to see a substantial manifestation of the effect.
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47.55.Kf Particle-laden flows
47.57.eb Diffusion and aggregation
47.60.-i Flow phenomena in quasi-one-dimensional systems
47.11.-j Computational methods in fluid dynamics
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