Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session D36: Suspensions: RheologyNon-Newtonian Particles
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Chair: Jonas Einarsson, Stanford University Room: 302 |
Sunday, November 19, 2017 2:15PM - 2:28PM |
D36.00001: The Einstein viscosity with fluid elasticity Jonas Einarsson, Mengfei Yang, Eric S. G. Shaqfeh We give the first correction to the suspension viscosity due to fluid elasticity for a dilute suspension of spheres in a viscoelastic medium. Our perturbation theory is valid to $O(\textrm{Wi}^2)$ in the Weissenberg number $\textrm{Wi}=\dot\gamma \lambda$, where $\dot\gamma$ is the typical magnitude of the suspension velocity gradient, and $\lambda$ is the relaxation time of the viscoelastic fluid. For shear flow we find that the suspension shear-thickens due to elastic stretching in strain {\lq}hot spots{\rq} near the particle, despite the fact that the stress inside the particles decreases relative to the Newtonian case. We thus argue that it is crucial to correctly model the extensional rheology of the suspending medium to predict the shear rheology of the suspension. For uniaxial extensional flow we correct existing results at $O(\textrm{Wi})$, and find dramatic strain-rate thickening at $O(\textrm{Wi}^2)$. We validate our theory with fully resolved numerical simulations. [Preview Abstract] |
Sunday, November 19, 2017 2:28PM - 2:41PM |
D36.00002: Mixture of thickening and non-thickening particles. Yasaman Madraki, Guillaume Ovarlez, Sarah Hormozi We study suspensions of non-colloidal particles (non-thickening particles) in a cornstarch solution (thickening particles in an aqueous solution). ~We show how polydispersity influences the shear thickening, particularly how a Continuous Shear Thickening (CST) behavior transitions to a Discontinuous Shear Thickening (DST) behavior. In addition, we present our results on the role of confinement effects on the general thickening behaviors. [Preview Abstract] |
Sunday, November 19, 2017 2:41PM - 2:54PM |
D36.00003: Simulations of shear-thinning frictional non-Brownian suspensions. Elisabeth Lemaire, Laurent Lobry, Frederic Blanc, Francois Peters Most non-Brownian suspensions exhibit non-Newtonian behaviours such as anisotropic normal stresses, shear-thickening or shear-thinning. The later is still largely an open question. Acrivos et al. (JoR 1994) proposed that particle resuspension is responsible for the apparent shear-thinning behavior in a cylindrical Couette rheometer. Another explanation has been suggested by Vasquez-Quesada et al. (PRL 2017), who noticed that some polymeric suspending liquids themselves are shear-thinning for the high shear-rate values involved in the narrow gaps between particles. Here we propose that the shear-thinning behaviour is directly connected to the solid contact between particles that has been shown to play a crucial role in the rheological behaviour of concentrated non-Brownian suspensions. In particular, it has been recently shown that frictional contact between particles greatly enhances the viscosity. Even though the friction coefficient between macroscopic surfaces does not depend on the load, it may be not the case at the scale of the low load contact between particles in suspensions. Here, we present discrete numerical simulations where the friction coefficient decreases with the interparticle forces. The obtained shear-thinning behaviour is in good agreement with our experiments. [Preview Abstract] |
Sunday, November 19, 2017 2:54PM - 3:07PM |
D36.00004: On the effects of long-range hydrodynamic interactions in dense suspensions Stany Gallier, Laurent Lobry, Francois Peters This work intends to evaluate the role of many-body long-range hydrodynamic interactions (LRHI) on dense suspensions. Three-dimensional simulations of sheared suspensions are conducted with and without LRHI for volume fractions between 0.1 and 0.62 (frictionless) and 0.1 and 0.54 (frictional). Discarding LRHI leads to an overestimation of viscosity by a factor of 1.5-2 for intermediate volume fractions. However, near jamming, viscosities are much closer and diverge with similar scaling laws; the critical fraction is found to be about 0.65 (frictionless) and 0.58 (frictional). LRHI are found to have a marked impact on diffusion coefficients. Particle velocities are correlated on a much longer range when LRHI are included, meaning that long-range hydrodynamics may not be significantly screened by crowding. Assuming only short-range lubrication interactions is therefore suitable only for qualitative simulations of rheology near jamming but becomes questionable for more dilute suspensions. [Preview Abstract] |
Sunday, November 19, 2017 3:07PM - 3:20PM |
D36.00005: Towards establishing the rheology of a sediment bed Edward Biegert, Bernhard Vowinckel, Eckart Meiburg In order to gain a better understanding of erosion, we have conducted numerical simulations of particle-resolved flows similar to the experiments of Aussillous et al. (2013), which involve laminar pressure-driven flows over erodible sediment beds. These simulations allow us to resolve velocity profiles and stresses of the fluid-particle mixtures within and above the sediment bed, which can be difficult or impossible to measure experimentally. Thus, we can begin investigating the rheology of the fluid-particle mixtures. In particular, we compare the effective viscosity as a function of volume fraction to existing models, such as those of Eilers (1943), Morris and Boulay (1999), and Boyer et al. (2011). [Preview Abstract] |
Sunday, November 19, 2017 3:20PM - 3:33PM |
D36.00006: Instabilities, rheology and spontaneous flows in magnetotactic bacterial suspensions. Roberto Alonso-Matilla, David Saintillan Magnetotactic bacteria are motile prokaryotes, mostly present in marine habitats, that synthesize intracellular magnetic membrane-bounded crystals known as magnetosomes. They behave as self-propelled permanent magnetic dipoles that orient and migrate along the geomagnetic field lines of the Earth. In this work, we analyze the macroscopic transport properties of suspensions of such bacteria in microfluidic devices. When placed in an external magnetic field, these microorganisms feel a net magnetic torque which is transmitted to the surrounding fluid, and can give rise to a net unidirectional fluid flow in a planar channel, with a flow rate and direction that can be controlled by adjusting both the magnitude and orientation of the external field. Using a continuum kinetic model, we provide a physical explanation for the onset of these spontaneous flows. We also study the rheological properties and stability of these suspensions in both an applied shear flow and a pressure-driven flow. [Preview Abstract] |
Sunday, November 19, 2017 3:33PM - 3:46PM |
D36.00007: Structural and rheological relaxation upon flow cessation in colloidal dispersions: Transient, nonlinear microrheology Ritesh P. Mohanty, Roseanna N. Zia We theoretically study the impact of particle roughness, Brownian motion, and hydrodynamic interactions on the relaxation of colloidal dispersions by examining the structural and rheological relaxation after microrheological flow cessation. In particular, we focus on the disparity in timescales over which hydrodynamic and entropic forces act and influence colloidal relaxation. To do this, we employ the active microrheology framework, in which a colloidal probe, driven by an arbitrarily strong external force, interacts with many surrounding particle configurations before reaching steady-state motion. We utilize the steady-state structure around the probe as the initial condition in a Smoluchowski equation that we solve to obtain the structural evolution upon flow cessation. We systematically tune the strength of hydrodynamic and entropic forces, and study their influence on structural and rheological relaxation. Upon cessation, the non-Newtonian behavior arising directly from hydrodynamic forces dissipates instantaneously, while the entropic contributions decay over longer times. We find that increasing pre-cessation external flow strength enhances the relaxation rate, while hydrodynamic interactions slow down the relaxation. [Preview Abstract] |
Sunday, November 19, 2017 3:46PM - 3:59PM |
D36.00008: Numerical study of inertial effects on the rheology of filament suspensions. Arash Alizad Banaei, Marco Edoardo Rosti, Luca Brandt Significant work has been devoted to modeling fiber suspensions as they occur in many applications such as paper and food industries. Most of the works are limited to the motion of rigid cylindrical rods in low Stokes flows. Here, we investigate the rheological properties of flexible filament suspensions by means of numerical simulations. We considered the filaments as one-dimensional inextensible slender bodies obeying the Euler-Bernoulli equations and study the effect of flexibility, flow inertia and volume fraction on the rheology of the suspensions. The numerical simulations are performed using the Immersed Boundary Method to model the fluid/structure interaction. The results indicate that the inertia has significant effect on the relative viscosity of the suspensions. The effect is larger for less deformable filaments. The filament suspensions exhibit viscoelastic behavior and the first normal stress has a maximum for moderate flexibilities. The relative viscosity increases with volume fraction of the filaments and it is more sensitive to the volume fraction for larger Reynolds numbers. For a constant flexibility, the mean end-to-end distance of the filaments decreases with Reynolds number and the mean velocity fluctuations of the fluid increases with the Reynolds number. [Preview Abstract] |
Sunday, November 19, 2017 3:59PM - 4:12PM |
D36.00009: Rheology of concentrated suspensions of non-colloidal rigid fibers Elisabeth Guazzelli, Franco Tapia, Saif Shaikh, Jason E. Butler, Olivier Pouliquen Pressure and volume-imposed rheology is used to study suspensions of non-colloidal, rigid fibers in the concentrated regime for aspect ratios ranging from 3 to 15. The suspensions exhibit yield-stresses. Subtracting these apparent yield-stresses reveals a viscous scaling for both the shear and normal stresses. The variation in aspect ratio does not affect the friction coefficient (ratio of shear and normal stresses), but increasing the aspect ratio lowers the maximum volume fraction at which the suspension flows. Constitutive laws are proposed for the viscosities and the friction coefficient close to this maximum flowable fraction. The scaling of the stresses near this jamming transition are found to differ substantially from that of a suspension of spheres. [Preview Abstract] |
Sunday, November 19, 2017 4:12PM - 4:25PM |
D36.00010: High-pressure high-temperature rheological studies of colloidal suspensions with carbon nanotube Anoop Baby, Reza Sadr, Rommel Yarc, Mahmood Amani Selection of the drilling fluid, drilling mud, is vital in minimizing the cost and time required for the drilling in oil fields. Drilling mud aids in cooling, lubricating drilling bit, removing the debries from the drill bore and maintaining the wellbore stability. Owing to the enhanced thermo-physical properties and stable nature, suspensions of nanoparticles have been suggested for drilling fluids. High-pressure and high-temperature rheology of a nanomud suspension (nano particles suspended in a mud solution) is studied here. The nanomud is prepared by dispersing a water-based drilling mud suspension (water with 1{\%} Bentonite and 7{\%}Barite particles) with multi-walled carbon nanotubes, MWCNT. The effect of pressure, temperature, and shear rate are independently studied for the various particle loading of the nanoparticles. Viscosity values are measured at a maximum pressure of 170MPa with temperatures ranging from ambient to 180oC. The effect of MWCNT concentration and variation in shear rate are also investigated A shear thinning non-Newtonian behavior is observed for the basemud and the nanomud samples for all cases. The basemud showed an increase in viscosity with an increase in pressure. However, with MWCNT particle addition, this trend is observed to have reversed. [Preview Abstract] |
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