Turbulence Locality and Granularlike Fluid Shear Viscosity in Collisional Suspensions

Berzi, Diego; Fraccarollo, Luigi

doi:10.1103/physrevlett.115.194501

Cited by 25 publications

(42 citation statements)

References 29 publications

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“…It indicates that kinetic theory is a good candidate as a continuum theory also for nonspherical particles. Experiments performed on gravity-driven collisional suspensions of plastic cylinders, of aspect ratio equal to 0.8, in water [24,25] show the same collapse, and are in good agreement with the present numerical simulations [ Fig. 3(b)] [26].…”

Section: Simulations and Theorysupporting

confidence: 88%

Stresses and orientational order in shearing flows of granular liquid crystals

et al. 2016

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We perform discrete element simulations of homogeneous shearing of frictionless cylinders and show that the particles are characterized by orientational order and form a granular liquid crystal. For elongated and flat cylinders, the alignment is in the plane of shearing, while cylinders having an aspect ratio equal to 1 and 0.8 show no orientational order. We show that the particle pressure is insensitive to the cylinder aspect ratio and well predicted by the kinetic theory of granular gases, with a singularity in the radial distribution function at contact different from that for frictionless spheres. The numerical results quantitatively agree with physical experiments on different geometries. The particle shear stress is affected by orientational anisotropy. We postulate that, for frictionless cylinders, the viscosity is roughly due to the motion of the orientationally disordered fraction of the particles, and show that it is proportional, through the order parameter, to the expression of kinetic theory. Finally, we suggest that the orientational order is the result of the competing effects of the shear rate, which induces alignment, and the granular temperature, which ramdomizes.

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Section: Simulations and Theorysupporting

confidence: 88%

Stresses and orientational order in shearing flows of granular liquid crystals

et al. 2016

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“…(b) Dimensionless granular shear stress

{\overset{τ}{true}}_{S}

likewise compared with the kinetic theory relation . (c) Dimensionless turbulent mixing length

{\overset{ℓ}{true}}_{m}

, compared with the constant approximation

{\overset{ℓ}{true}}_{m} \approx 0.2

(solid line) and the relation proposed by Berzi and Fraccarollo () (dashed line). (d) Dimensionless drag force

{\overset{f}{true}}_{D}

compared with relation (solid line) and fluidization cell data (triangles).…”

Section: Stress and Drag Relationsmentioning

confidence: 99%

“…First, we compare observed relationships for the granular pressure and shear stress with relations deduced from the kinetic theory of collisional granular flows (Berzi & Fraccarollo, ; Garzó & Dufty, ; Jenkins & Hanes, ), modified as in Armanini et al () to take into account added mass effects. The resulting equation of state for the granular pressure, or effective normal stress, can be written as

{\overset{p}{true}}_{S} = \frac{p_{S}}{ρ_{S} T} = ((), c_{S} + 4 c_{S}^{2} g_{0} false(c_{S} false) \frac{1 + e_{f}}{2}) ((), 1 + \frac{ρ_{L}}{ρ_{S}} a false(c_{s} false)),

where the dependence on granular concentration is expressed as the product of two factors.…”

Section: Stress and Drag Relationsmentioning

confidence: 99%

Stresses and Drag in Turbulent Bed Load From Refractive Index‐Matched Experiments

Capart

2018

Geophysical Research Letters

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We report steady open‐channel flow experiments that resolve the internal dynamics of turbulent bed load layers at subgrain diameter resolution. Optical access is gained by using materials of matched refractive index, and a laser light sheet is scanned across the medium to capture both the solid and liquid motions over a 3‐D volume. The imaging measurements yield vertical profiles of granular concentration, solid and liquid mean velocity, and velocity fluctuation statistics including the granular temperature and the Reynolds stress. This makes it possible to determine all principal contributions to the momentum balance of each phase. In particular, experimental profiles are obtained for the stresses and interphase drag force. They are used to test constitutive relationships derived from kinetic theory, turbulence theory, and fluidization cell experiments.

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“…It is worthwhile mentioning that, in purely collisional suspensions, the turbulent mixing length is local, i.e., it is only a function of the local value of the mean interparticle distance (a fraction of the particle diameter). 9 Here, given the influence of the turbulence on the particle motion, we take the turbulent mixing length to be nonlocal (proportional to the distance from the bed), as appropriated for turbulent fluids in absence of sediments. Further studies are necessary to understand the transition from local to nonlocal turbulence in suspensions.…”

Section: A Dense Layermentioning

confidence: 99%

“…7 In the collisional and turbulent-collisional suspensions, the large-scale fluid turbulence is suppressed, as experimentally revealed. 8,9 A further increase in the strength of the shearing fluid would cause the weight of the particles to be entirely balanced by the turbulent lift, in a portion of the domain where the turbulence is more intense. This turbulent lift mechanism to suspend the particles is considered important when 023302-2 D. Berzi and L. Fraccarollo Phys.…”

Section: Introductionmentioning

confidence: 99%

Intense sediment transport: Collisional to turbulent suspension

Berzi

Fraccarollo

2016

Physics of Fluids

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A recent simple analytical approach to the problem of steady, uniform transport of sediment by a turbulent shearing fluid dominated by interparticle collisions is extended to the case in which the mean turbulent lift may partially or totally support the weight of the sediment. We treat the granular–fluid mixture as a continuum and make use of constitutive relations of kinetic theory of granular gases to model the particle phase and a simple mixing-length approach for the fluid. We focus on pressure-driven flows over horizontal, erodible beds and divide the flow itself into layers, each dominated by different physical mechanisms. This permits a crude analytical integration of the governing equations and to obtain analytical expressions for the distribution of particle concentration and velocity. The predictions of the theory are compared with existing laboratory measurements on the flow of glass spheres and sand particles in water. We also show how to build a regime map to distinguish between collisional, turbulent-collisional, and fully turbulent suspensions.

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Turbulence Locality and Granularlike Fluid Shear Viscosity in Collisional Suspensions

Cited by 25 publications

References 29 publications

Stresses and orientational order in shearing flows of granular liquid crystals

Stresses and orientational order in shearing flows of granular liquid crystals

Stresses and Drag in Turbulent Bed Load From Refractive Index‐Matched Experiments

Intense sediment transport: Collisional to turbulent suspension

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