Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session Q04: Suspension : Rheology 
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Chair: Elisabeth Guazzelli, CNRS Room: 203 
Tuesday, November 26, 2019 7:45AM  7:58AM 
Q04.00001: Constitutive model for timedependent flows of shearthickening suspensions Jurriaan Gillissen, Christopher Ness, Joseph Peterson, Helen Wilson, Michael Cates We develop a tensorial constitutive model for dense, shearthickening particle suspensions subjected to timedependent flow. Our model combines a recently proposed evolution equation for the suspension microstructure in rateindependent materials with ideas developed previously to explain the steady flow of shearthickening ones, whereby friction proliferates among compressive contacts at large particle stresses. We apply our model to shear reversal, and find good qualitative agreement with particlelevel, discreteelement simulations whose results we also present. [Preview Abstract] 
Tuesday, November 26, 2019 7:58AM  8:11AM 
Q04.00002: The influence of surface roughness on the rheology of immersed and dry frictional spheres Elisabeth Guazzelli, Franco Tapia, Olivier Pouliquen Pressureimposed rheometry is used to examine the influence of surface roughness on the rheology of immersed and dry frictional spheres in the dense regime. The quasistatic value of the effective friction coefficient is not significantly affected by particle roughness while the critical volume fraction at jamming decreases with increasing roughness. These values are found to be similar in immersed and dry conditions. Rescaling the volume fraction by the maximum volume fraction leads to collapses of rheological data on master curves. The asymptotic behaviors are examined close to the jamming transition. [Preview Abstract] 
Tuesday, November 26, 2019 8:11AM  8:24AM 
Q04.00003: Mechanism of contact network formation leading to discontinuous shear thickening in dense suspensions. Prabhu Nott, Tabish Khan The phenomenon of discontinuous shear thickening (DST) of dense particleliquid suspensions has received considerable attention in recent years, and it is now generally believed that the formation of a Coulomb frictionmediated particle contact network causes the dramatic rise in viscosity at a critical shear stress. A common feature of most experimental studies is that the suspension is 'prepared' by preshearing for a long time before conducting the shear rate or stress sweep. The implicit assumption in this protocol is that in the prepared state, the stress responds to the applies shear rate/stress within small strain. Here we present experimental evidence that paints a contrasting picture. By following three different shear protocols, we show that substantial strain is required to build up the contact network that culminates in shear thickening. Our study indicates that the contact network results from a cooperative arrangement of smaller clusters of particles. We show that over the period of shear, the suspension goes through continuous shear thickening (CST), then DST, followed by jamming, and finally frictional plastic deformation. [Preview Abstract] 
Tuesday, November 26, 2019 8:24AM  8:37AM 
Q04.00004: Shearthickening of a noncolloidal suspension with a viscoelastic matrix Marco Ellero, Adolfo VazquezQuesada, Pep EspaĆ±ol, Roger Tanner In this work we study the rheology of a noncolloidal suspension of rigid spherical particles interacting with a viscoelastic matrix. Threedimensional numerical simulations under shear flow are performed using the smoothed particle hydrodynamics method and compared with experimental data using different elastic Boger fluids. The rheological properties of the Boger matrices are matched in simulation under viscometric flow conditions. Suspension rheology under dilute to semiconcentrated conditions is explored. It is found that at small Deborah numbers De, relative suspension viscosities $\eta_{\mathrm{r}}$exhibit a plateau at every concentration. By increasing De shearthickening is observed. Under dilute conditions ($\varphi =$0.05) numerical results for $\eta_{\mathrm{r}}$agree quantitatively with experimental data. By increasing the solid volume fraction towards $\varphi =$0.3, despite the fact that the trend is well captured, the agreement remains qualitative. With regard to the specific mechanism of elastic thickening, the microstructural analysis shows that it correlates well with the averaged viscoelastic dissipation function, requiring a scaling as De$^{\mathrm{\alpha }}$with an exponent $\alpha $ greater than 2 to take place. Locally, flow regions responsible of the elastic thickening are well correlated to areas with significant extensional component. [Preview Abstract] 
Tuesday, November 26, 2019 8:37AM  8:50AM 
Q04.00005: A new dimensionless number governing dethickening in orthogonally perturbed shear thickened suspensions Meera Ramaswamy, Abhishek Shetty, Itai Cohen When concentrated colloidal suspensions are under stress, their viscosity can increase by over an order of magnitude. Previous work has shown that this shear thickened viscosity can be tuned by applying fast oscillatory perturbations orthogonal to the primary shear flows in the system. In this talk, I show that dethickening in the regime where the primary shear flow has fully thickened the suspension, is governed by a single dimensionless parameter  the ratio of the orthogonal shear rate amplitude to that of the primary shear rate. In contrast, a second parameter is required to describe the data in the primary shear flow regime where the suspension is thickening. Understanding these parameters will enable better strategies to tune the properties of shear thickening suspensions for applications ranging from 3D printing to the processing of cement. [Preview Abstract] 

Q04.00006: ABSTRACT WITHDRAWN 
Tuesday, November 26, 2019 9:03AM  9:16AM 
Q04.00007: Dynamical behavior of electrorheological suspensions. Suchandra Das, Sriram Pillapakkam, Naga Musunuri, Islam Benouaguef, Edison Amah, Ian Fischer, Pushpendra Singh Electrorheological suspensions are formed by suspending dielectric solid particles in a dielectric liquid. The size of the particles varies between nano and micro meters, depending on the requirements of the intended application. When an electric field is applied, the particles become polarized and form chains and columns which align in the direction of the field, and this increases the viscosity of the electrorheological suspension. This change in the suspension microstructure and viscosity happens within a few milliseconds after the electric field is applied, and when the electric field is removed the viscosity goes back to the original value, which makes the suspension suitable for the applications where a quick response time is desired. The aim of this work is to employ the experimental and direct numerical simulation techniques to study the electrorheological response and the role of parameters such as the particle size and polarizabilities in the process. [Preview Abstract] 
Tuesday, November 26, 2019 9:16AM  9:29AM 
Q04.00008: Oscillatory shear response of the rigidrod model in nematic regime Giovanniantonio Natale, Marco De Corato Nematic phase of rigidrod molecules presents rheological complexities given the intrinsic anisotropy of the molecules and spatial variation of an average molecular orientation (director) in the bulk. This microscopic model has been investigated in simple shear flow showing complex dynamics (logrolling, wagging and tumbling regimes). Oscillatory shear flow is a model transient flow field which introduces a transient and periodic perturbation to the system. Recently, large amplitude oscillatory shear (LAOS) has attracted interest given the rich rheological response that is obtained. However, the interpretation at the microstructural level of the LAOS response is still limited to specific systems. Here we perform numerical simulations of the DoiHess equation in oscillatory shear for the molecular orientational distribution function using Brownian dynamics and an expansion in spherical harmonics. A new methodology to switch between the nematic and isotropic orientation state thanks to the transient nature of the flow is proposed. Moreover, oscillatory shear flow is found to be more efficient than the simple shear flow to capture the full microstructural dynamics. Hence this methodology can provide a new strategy for experimental characterization of nematic colloidal suspensions. [Preview Abstract] 
Tuesday, November 26, 2019 9:29AM  9:42AM 
Q04.00009: Extensional rheology of a dilute suspension of spheres in a dilute polymer solution Arjun Sharma, Donald Koch We investigate the steadystate rheology of a dilute suspension of spherical particles in a dilute polymer solution modeled by the FENEP constitutive relation. This work uses a semianalytical method based on ensemble averaged equations, a perturbation for small polymer concentration and the generalized reciprocal to determine the polymers' influence on the particle stresslet and the particles' influence on the polymer stress. In the undisturbed flow, polymers undergo a rapid transition from a coiled to almost fully stretched state at a critical Deborah number (ratio of polymer relaxation to flow time scale) of $De_{c}$=0.5. The particlepolymer contribution enhances the averaged stress below $De_{c}$ due to a strong local stretch enhancement in specific regions of the flow. Above $De_{c}$, polymers passing around the particle tend to collapse in response to a time history of strain rates which on average are smaller near the particle. These insights are elucidated through a variant of the Finitetime Lyapunov exponent for the Stokes velocity around the sphere. Similar to the undisturbed stress, below $De_{c}$ we find the particle polymer contribution to the average stress to be independent of the maximum stretching length (L) and for higher De to scale as $L^2$ for $L\gg1$. [Preview Abstract] 
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