Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session L27: Non-Newtonian Flows: Applications |
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Chair: Federico Toschi, Technische Universiteit Eindhoven Room: E147-148 |
Monday, November 21, 2016 4:30PM - 4:43PM |
L27.00001: Dynamics and morphology of flexible membranes in a nematic liquid crystal Arthur Evans, Michael Graham, Saverio Spagnolie Cellular membranes and nanoscale capsules inhabit highly viscous environments, and their overall dynamics and morphology depend on the fluid in which they are immersed. While some fluids of interest are purely Newtonian, biologically and industrially relevant materials often involve complex molecular constituents that imbue the surroundings with anisotropy or viscoelasticity. Moreover, fluid stresses are often comparable to the elastic resistance of immersed membranes or capsules, so that these structures deform in response to flow and order in the fluid. In this talk I will present a numerical implementation for examining immersed elastic bodies in a flowing liquid crystal, and discuss the implications for biological materials and self-assembly of soft structures. Even in the case of zero flow for rigid particles, the presence of topological defects in nematics leads to intriguing inter-particle interactions. For flexible membranes, the liquid crystal defect structure not only affects long-range interactions, but ultimately the morphology of the membranes themselves. [Preview Abstract] |
Monday, November 21, 2016 4:43PM - 4:56PM |
L27.00002: Inferring earthquake statistics from soft-glass dynamics below yield stress Pinaki Kumar, Federico Toschi, Roberto Benzi, Jeannot Trampert The current practice to generate synthetic earthquake catalogs employs purely statistical models, mechanical methods based on ad-hoc constitutive friction laws or a combination of the above. We adopt a new numerical approach based on the multi-component Lattice Boltzmann method to simulate yield stress materials. Below yield stress, under shear forcing, we find that the highly intermittent in time, irreversible T1 topological changes in the soft-glass (termed plastic events) bear a statistical resemblance to seismic events, radiating elastic perturbations through the system. Statistical analysis reveals scaling laws for magnitude similar to the Gutenberg-Richter law for quakes, a recurrence time scale with similar slope, a well-defined clustering of events into causal-aftershock sequences and Poisson events leading to the Omori law. Additionally space intermittency reveals a complex multi-fractal structure, like real quakes, and a characterization of the stick-slip behavior in terms of avalanche size and time distribution agrees with the de-pinning transition. The model system once properly tuned using real earthquake data, may help highlighting the origin of scaling in phenomenological seismic power laws. [Preview Abstract] |
Monday, November 21, 2016 4:56PM - 5:09PM |
L27.00003: The Sedimentation of Particles under Orthogonal Shear in Viscoelastic Fluids William L. Murch, Sreenath Krishnan, Eric S. G. Shaqfeh Many engineering applications, including oil and gas recovery, require the suspension of particles in viscoelastic fluids during fluid transport and processing. A topic of specific importance involves such particle suspensions experiencing an applied shear flow in a direction perpendicular to gravity (referred to as orthogonal shear). Previously, it has been shown that particle sedimentation coupled with an orthogonal shear flow can reduce the particle settling rate in elastic fluids. The underlying mechanism of this enhanced coupling drag is not fully understood, particularly at finite Weissenberg numbers. This talk examines the role of fluid elasticity on a single, non-Brownian, rigid sphere settling in orthogonal shear using experiments and numerical simulations. New experiments were performed in a Taylor-Couette flow cell using Boger fluids to study the coupling drag as a function of the shear and sedimentation Weissenberg numbers as well as particle confinement. The elastic effect was also studied with fully 3D simulations of flow past a rigid sphere, using the FENE-P constitutive model to describe the polymeric fluid rheology. These simulations show good agreement with the experiments and allow for further insight into the mechanism of elasticity-enhanced drag. [Preview Abstract] |
Monday, November 21, 2016 5:09PM - 5:22PM |
L27.00004: Modelling Polymer Deformation and Welding Behaviour during 3D Printing Claire McIlroy, Peter Olmsted 3D printing has the potential to transform manufacturing processes, yet improving the strength of printed parts, to equal that of traditionally-manufactured parts, remains an underlying issue. The most common method, fused deposition modelling, involves melting a thermoplastic, followed by layer-by-layer extrusion of the material to fabricate a three-dimensional object. The key to the ensuring strength at the weld between these layers is successful inter-diffusion. However, as the printed layer cools towards the glass transition temperature, the time available for diffusion is limited. In addition, the extrusion process significantly deforms the polymer micro-structure prior to welding and consequently affects how the polymers ``re-entangle'' across the weld. We have developed a simple model of the non-isothermal printing process to explore the effects that typical printing conditions and amorphous polymer rheology have on the ultimate weld structure. In particular, we incorporate both the stretch and orientation of the polymer using the Rolie-Poly constitutive equation to examine how the melt flows through the nozzle and is deposited onto the build plate. We then address how this deformation relaxes and contributes to the thickness and structure of the weld. [Preview Abstract] |
Monday, November 21, 2016 5:22PM - 5:35PM |
L27.00005: Straining soft colloids in aqueous nematic liquid crystals Saverio Spagnolie, Peter Mushenheim, Joel Pendery, Douglas Weibel, Nicholas Abbott Liquid crystals (LCs) are anisotropic, viscoelastic fluids that can be used to direct colloids into organized assemblies with unusual optical, mechanical, and electrical properties. In past studies, the colloids have been sufficiently rigid that their individual shapes and properties have not been strongly coupled to elastic stresses imposed by the LCs. We will discuss how soft colloids (micrometer-sized shells) behave in LCs. We reveal a sharing of strain between the LC and shells, resulting in formation of spindle-like shells and other complex shapes. These results hint at previously unidentified designs of reconfigurable soft materials with applications in sensing and biology. Related effects relevant to biolocomotion will also be touched upon. [Preview Abstract] |
Monday, November 21, 2016 5:35PM - 5:48PM |
L27.00006: Viscoelastic fluid-structure interaction between a non-Newtonian fluid flow and flexible cylinder Anita Dey, Yahya Modarres-Sadeghi, Jonathan Rothstein It is well known that when a flexible or flexibly-mounted structure is placed perpendicular to the flow of a Newtonian fluid, it can oscillate due to the shedding of separated vortices at high Reynolds numbers. If the same flexible object is placed in non-Newtonian flows, however, the structure's response is still unknown. Unlike Newtonian fluids, the flow of viscoelastic fluids can become unstable at infinitesimal Reynolds numbers due to a purely elastic flow instability. In this talk, we will present a series of experiments investigating the response of a flexible cylinder placed in the cross flow of a viscoelastic fluid. The elastic flow instabilities occurring at high Weissenberg numbers can exert fluctuating forces on the flexible cylinder thus leading to nonlinear periodic oscillations of the flexible structure. These oscillations are found to be coupled to the time-dependent state of viscoelastic stresses in the wake of the flexible cylinder. The static and dynamic responses of the flexible cylinder will be presented over a range of flow velocities, along with measurements of velocity profiles and flow-induced birefringence, in order to quantify the time variation of the flow field and the state of stress in the fluid. [Preview Abstract] |
Monday, November 21, 2016 5:48PM - 6:01PM |
L27.00007: Orientation of contravariant and covariant polymers and associated energy transfer in elasto-inertial turbulence Kiyosi Horiuti, Aoi Suzuki It is generally assumed that the polymers in viscoelastic turbulence are advected affinely with the macroscopically-imposed deformation, while de Gennes (1986) hypothesized that stretched polymers may exhibit rigidity. We conduct assessment on this hypothesis in homogeneous isotropic turbulence by connecting mesoscopic Brownian description of elastic dumbbells to macroscopic DNS. The dumbbells are advected either affinely (contravariant) or non-affinely (covariant). We consider the elasto-inertial regime (Valente et al. 2014). Using the approximate solution of the constitutive equation for the polymer stress, we show that when the dumbbells are highly stretched, $-S_{ik}S_{kl}S_{li}$ term ($S_{ij}$ is strain-rate tensor) governs the transfer of solvent energy either to dissipation or to the elastic energy stored in the polymers. In the contravariant polymer, the elastic energy production term $P_e<0$ and the dissipation production term $P_\varepsilon>0$. The elastic energy is transferred backwardly into the solvent and dissipation is enhanced. In the covariant polymer, $P_e>0$ and $P_\varepsilon>0$. When the dumbbells are aligned with one of eigenvectors of $S_{ij}$, $P_e $ predominates $P_\varepsilon$, and marked reduction of drag is achieved. [Preview Abstract] |
Monday, November 21, 2016 6:01PM - 6:14PM |
L27.00008: In a sea of sticky molasses: The physics of the Boston Molasses Flood Nicole Sharp, Jordan Kennedy, Shmuel Rubinstein On January 15$^{\mathrm{th}}$, 1919, shortly after 12:40 pm local time, a giant storage tank collapsed in Boston's crowded North End, releasing more than 8.7 million liters of molasses. Contemporary accounts estimated the initial wave was 7.6 meters tall and moved at more than 15 m/s. In moments, molasses engulfed the Commercial Street area, flattening buildings, damaging the elevated train, killing 21 people, and injuring 150 more. Molasses is a viscoelastic fluid 1.5 times as dense as water with a viscosity roughly 4000 times greater. This talk will explore the physics of the Boston Molasses Flood, including the effects of temperature fluctuations and molasses rheology on events leading up to the tank's collapse and their impact on subsequent rescue efforts. [Preview Abstract] |
Monday, November 21, 2016 6:14PM - 6:27PM |
L27.00009: Nonlinear viscoelasticity and generalized failure criterion for biopolymer gels Thibaut Divoux, Bavand Keshavarz, Sébastien Manneville, Gareth McKinley Biopolymer gels display a multiscale microstructure that is responsible for their solid-like properties. Upon external deformation, these soft viscoelastic solids exhibit a generic nonlinear mechanical response characterized by pronounced stress- or strain-stiffening prior to irreversible damage and failure, most often through macroscopic fractures. Here we show on a model acid-induced protein gel that the nonlinear viscoelastic properties of the gel can be described in terms of a 'damping function' which predicts the gel mechanical response quantitatively up to the onset of macroscopic failure. Using a nonlinear integral constitutive equation built upon the experimentally-measured damping function in conjunction with power-law linear viscoelastic response, we derive the form of the stress growth in the gel following the start up of steady shear. We also couple the shear stress response with Bailey's durability criteria for brittle solids in order to predict the critical values of the stress $\sigma_c$ and strain $\gamma_c$ for failure of the gel, and how they scale with the applied shear rate. This provides a generalized failure criterion for biopolymer gels in a range of different deformation histories. [Preview Abstract] |
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