Fore‐and‐Aft Asymmetry in a Concentrated Suspension of Solid Spheres

Parsi, F.; Gadala-Maria, Francis

doi:10.1122/1.549944

Cited by 119 publications

(96 citation statements)

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“…15(b)). This fore-aft asymmetry is well-known to be responsible for the non-Newtonian behaviour of dense suspensions and has been observed in experiments Parsi & Gadala-Maria 1987). Our results in Fig.…”

Section: Microstructuresupporting

confidence: 78%

Rheology of sheared suspensions of rough frictional particles

et al. 2014

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This paper presents three-dimensional numerical simulations of non-Brownian concentrated suspensions in a Couette flow at zero Reynolds number using a fictitious domain method. Contacts between particles are modelled using a discrete element method (DEM)-like approach, which allows for a more physical description, including roughness and friction. This work emphasizes the effect of friction between particles and its role on rheological properties, especially on normal stress differences. Friction is shown to notably increase viscosity and second normal stress difference $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}|N_2|$ and decrease $|N_1|$, in better agreement with experiments. The hydrodynamic and contact contributions to the overall particle stress are particularly investigated. This shows that the effect of friction is mostly due to the additional contact stress since the hydrodynamic stress remains unaffected by friction. Simulation results are also compared with experiments, such as normal stresses or effective friction coefficient $\mu (I_v)$, and the agreement is improved when friction is accounted for. This suggests that friction is operative in actual suspensions.

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Section: Microstructuresupporting

confidence: 78%

Rheology of sheared suspensions of rough frictional particles

et al. 2014

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“…The boundary-layer is a prominent feature of the microstructure in strong shear flows observed in both computer simulations (Phung et al 1996;Foss & Brady 2000b) and experiments (Parsi & Gadala-Maria 1987). Figure 1 shows the microstructure in the plane of shear for hard spheres under neglect of hydrodynamic interactions in a simple shear flow; the formation of the boundary-layer is clearly evident and is accompanied by the growth of a wake downstream from the reference particle at the origin.…”

Section: Numerical Solutionmentioning

confidence: 90%

The non-Newtonian rheology of dilute colloidal suspensions

2002

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The non-Newtonian rheology is calculated numerically to second order in the volume fraction in steady simple shear flows for Brownian hard spheres in the presence of hydrodynamic and excluded volume interactions. Previous analytical and numerical results for the low-shear structure and rheology are confirmed, demonstrating that the viscosity shear thins proportional to P e 2 , where P e is the dimensionless shear rate or Péclet number, owing to the decreasing contribution of Brownian forces to the viscosity. In the large P e limit, remnants of Brownian diffusion balance convection in a boundary-layer in the compressive region of the flow. In consequence, the viscosity shear thickens when this boundary-layer coincides with the near-contact lubrication regime of the hydrodynamic interaction. Wakes are formed at large P e in the extensional zone downstream from the reference particle, leading to broken symmetry in the pair correlation function. As a result of this asymmetry and that in the boundary-layer, finite normal stress differences are obtained as well as positive departures in the generalized osmotic pressure from its equilibrium value. The first normal stress difference changes from positive to negative values as P e is increased when the hard-sphere limit is approached. This unusual effect is caused by the hydrodynamic lubrication forces that maintain particles in close proximity well into the extensional quadrant of the flow. The study demonstrates that many of the non-Newtonian effects observed in concentrated suspensions by experiments and by Stokesian dynamics simulations are present also in dilute suspensions. IntroductionThe rheology of colloidal suspensions, consisting of submicrometre size particles dispersed in a Newtonian fluid, is an active field of research. This activity stems from the wide variety of colloidal systems and the many settings in which fluid flow plays a key role. Our understanding of the rheological behaviour of colloidal suspensions has benefited from access to exact results on model systems, such as those on dilute suspensions of particles with well-defined interactions in weak flows. As these weakflow theories for concentrated systems are continually being improved (Brady 1996;Lionberger & Russel 2000), it is important to focus attention on the effect of stronger flows. By strong flows we mean flows in which the non-dimensional shear rate or Péclet number (P e) is large.Because of a number of developments, the effect on the bulk rheology of particle

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“…The anisotropy was attributed to the presence of pairs of spheres rotating around each other forming permanent doublets. On the other hand, in similar experiments, Parsi & Gadala-Maria (1987) showed that concentrated suspensions (φ = 40% − 50%) do exhibit fore-aft asymmetry, with a larger probability of finding pairs of spheres oriented on the approaching side of the reference particle, and attributed this asymmetric distribution to either the intrinsic roughness of the spheres or to the presence of a non-hydrodynamic repulsive force between particles. More recently, Rampall et al (1997) used a substantially improved flow-visualization technique to measure the pair distribution function of dilute suspensions (φ = 5% − 15%) undergoing simple shear flow in a shear tank apparatus, and showed that, contrary to the results of Husband & Gadala-Maria (1987), there is a depletion of permanent doublets moving in the region of closed streamlines, and that even for concentrations as small as 5% the distribution is fore-aft asymmetric.…”

Section: Introductionmentioning

confidence: 99%

Microstructure and velocity fluctuations in sheared suspensions

et al. 2004

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The velocity fluctuations present in macroscopically homogeneous suspensions of neutrally buoyant, non-Brownian spheres undergoing simple shear flow, and their dependence on the microstructure developed by the suspensions, are investigated in the limit of vanishingly small Reynolds numbers using Stokesian dynamics simulations. We show that, in the dilute limit, the standard deviation of the velocity fluctuations (the so-called suspension temperature) is proportional to the volume fraction, in both the transverse and the flow directions, and that a theoretical prediction, which considers only for the hydrodynamic interactions between isolated pairs of spheres, is in good agreement with the numerical results at low concentrations. Furthermore, we show that the whole velocity autocorrelation function can be predicted, in the dilute limit, based purely in two-particle encounters. We also simulate the velocity fluctuations that would result from a random hard-sphere distribution of spheres in simple shear flow, and thereby investigate the effects of the microstructure on the velocity fluctuations. Analogous results are discussed for the fluctuations in the angular velocity of the suspended spheres. In addition, we present the probability density functions for all the linear and angular velocity compo- The simulations include a non-hydrodynamic repulsive force between the spheres which, although extremely short ranged, leads to the development of fore-aft asymmetric distributions for large enough volume fractions, if the range of that force is kept unchanged.On the other hand, we show that, although the pair distribution function recovers its fore-aft symmetry in dilute suspensions, it remains anisotropic and that this anisotropy can be accurately described by assuming the complete absence of any permanent doublets of spheres.We also present a simple correction to the analysis of laser-Doppler velocimetry measurements, that only takes into account the mean angular rotation of the spheres in the vorticity direction, and which substantially improves the interpretation of these measurements at low volume fractions.

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Fore‐and‐Aft Asymmetry in a Concentrated Suspension of Solid Spheres

Cited by 119 publications

References 0 publications

Rheology of sheared suspensions of rough frictional particles

Rheology of sheared suspensions of rough frictional particles

The non-Newtonian rheology of dilute colloidal suspensions

Microstructure and velocity fluctuations in sheared suspensions

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