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 E38: Non-Newtonian Flows: Polymer SolutionsNon-Newtonian
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Chair: Gabriel Juarez, University of Illinois Room: 304 |
Sunday, November 19, 2017 4:55PM - 5:08PM |
E38.00001: Buckling and migration of semi-flexible filaments Brato Chakrabarti, Yanan Liu, Olivia Du Roure, Anke Lindner, David Saintillan The dynamics of polymeric fluids exhibit rich and sometimes counter-intuitive behaviors, which can be traced back to the complex conformations of polymer molecules in shear flow. The tumbling of rigid bodies in shear flow at low Reynolds number has been understood since the pioneering work of Jeffery. The effect of polymer chain flexibility, however, has non-trivial consequences in this classical problem. Here we study the dynamics of actin filaments, which are semi-flexible filaments usually found in the cell cytoplasm, in an externally applied simple shear flow. We model these inextensible filaments using Euler-Bernoulli beam and use nonlocal slender body theory (SBT) in the presence of Brownian fluctuations to probe their dynamics, and compare our numerical simulations to microfluidic experiments. We systematically explore the parameter space by varying the length of the polymer and changing the shear rate. A series of conformational transitions is observed with increasing shear rate, from quasi-periodic tumbling to nontrivial buckling regimes due to the destabilizing effect of compressive viscous forces, and physical mechanisms are proposed for these transitions. [Preview Abstract] |
Sunday, November 19, 2017 5:08PM - 5:21PM |
E38.00002: Viscoplastic sculpting in stable triple layer heavy oil transport flow Parisa Sarmadi, Sarah Hormozi, Ian A. Frigaard In [1] we introduced a novel methodology for efficient transport of heavy oil via a triple layer core-annular flow. Pumping pressures are significantly reduced by concentrating high shear rates to a lubricating layer, while ideas from Visco-Plastic Lubrication [2] are used to eliminate interfacial instabilities. We purposefully position a shaped unyielded skin of a viscoplastic fluid between the transported oil and the lubricating fluid layer to balance the density difference between the fluids. Here we address the sculpting of the shaped skin within a concentric inflow manifold. We use the quasi-steady model to provide inputs to an axisymmetric triple layer computation, showing the development of the streamwise skin profile and establishment of the flow. For this, we use a finite element discretization with the augmented-Lagrangian method to represent the yield surface behaviour accurately and a PLIC method to track the interface motion. [1] P. Sarmadi, S. Hormozi and I.A. Frigaard,'' Triple-layer configuration for stable high-speed lubricated pipeline transport'', Phys. Rev. Fluids, 2(4) pp 044302, (2017). [2] S. Hormozi, G. Dunbrack, I. Frigaard, ``Visco-plastic sculpting'', Phys. Fluids, 26 pp. 093101 (2014). [Preview Abstract] |
Sunday, November 19, 2017 5:21PM - 5:34PM |
E38.00003: Viscoelastic levitation Roberto Zenit, Alfonso Castillo, Lailai Zhu, On Shun Pak The effects of viscoelasticity in a flow have been shown to manifest themselves via symmetry breaking (Pak et al. 2012). In this presentation, we show a novel phenomenon that arises from this idea. We observe that when a dense sphere is rotated near a wall (the rotation being aligned with the wall-normal direction and gravity), it levitates at a fixed distance. Since the shear is larger in the gap (between the sphere and the wall) than that on the open side of the sphere, the elastic stresses are asymmetric leading to a net elastic force. The elastic force is balanced by the sphere’s net weight, which leads to the levitation of the rotating sphere at a stationary position from the wall. We report experiments for magnetically rotated spheres of various sizes and weights, in a Boger-type fluid. A scaling for the problem is proposed, along with supplementary numerical results. [Preview Abstract] |
Sunday, November 19, 2017 5:34PM - 5:47PM |
E38.00004: Probing the molecular microstructure of polymeric fluids with semi-dilute DNA solutions Gabriel Juarez, Paulo E. Arratia We present experimental results on semi-dilute viscous DNA solutions undergoing planar extensional flow in microfluidic cross-slot devices. Bulk flow characterization shows that low molecular weight (MW) DNA solutions behave similar to a Newtonian fluid while high MW DNA solutions behave similar to a viscoelastic fluid and exhibit a symmetry-breaking flow instability. High-speed epifluorescent microscopy shows that DNA molecules approach the central stagnation point pre-stretched and aligned with the flow direction. At large strain rates compared to the polymer relaxation time, elongated molecules are rapidly compressed, leading to folded and kinked molecular states. This alternating stretch-coil to coil-stretch transition of buckled molecules yields scission of partially extended molecules. Semi-dilute DNA solutions provide a useful model system for further investigation of the molecular origin of viscoelastic instabilities. [Preview Abstract] |
Sunday, November 19, 2017 5:47PM - 6:00PM |
E38.00005: Brownian dynamics of wall tethered polymers in shear flow Tiras Y. Lin, Amir Saadat, Amit Kushwaha, Eric S.G. Shaqfeh The dynamics of a wall tethered polymer in shear flow is studied using Brownian dynamics. Simulations are performed with bead-spring chains, and the effect of hydrodynamic interactions (HI) is incorporated through Blake's tensor with a finite size bead correction. We characterize the configuration of the polymer as a function of the Weissenberg number by investigating the regions the polymer explores in both the flow-gradient and flow-vorticity planes. The fractional extension in the flow direction, the width in the vorticity direction, and the thickness in the gradient direction are reported as well, and these quantities are found to compare favorably with the experimental data of the literature. The cyclic motion of the polymer is demonstrated through analysis of the mean velocity field of the end bead. We characterize the collision process of each bead with the wall as a Poisson process and extract an average wall collision rate, which in general varies along the backbone of the chain. The inclusion of HI with the wall for a tethered polymer is found to reduce the average wall collision rate. We anticipate that results from this work will be directly applicable to, e.g., the design of polymer brushes or the use of DNA for making nanowires in molecular electronics. [Preview Abstract] |
Sunday, November 19, 2017 6:00PM - 6:13PM |
E38.00006: Modeling and measuring non-Newtonian shear flows of soft interfaces. Juan Lopez, Aditya Raghunandan, Patrick Underhill, Amir Hirsa Soft interfaces of polymers, particles, and proteins between fluid phases are ubiquitous in industrial and natural processes. The flow response of such systems to deformation is often not linear, as one would expect for Newtonian interfaces. The resistance to (pure shear) flow of interfaces is generally characterized by a single intrinsic material property, the surface shear viscosity. Predicted shear responses of Newtonian interfaces have achieved consensus across a wide range of flow conditions and measurement devices, when the nonlinear hydrodynamic coupling to the bulk phase is correctly accounted for. However, predicting the flows of sheared non-Newtonian interfaces remains a challenge.\\ \\Here, we introduce a computational model that incorporates a non-Newtonian constitutive equation for the sheared interface and properly accounts for the coupled interfacial and bulk phase flows. We compare predictions to experiments performed with a model phospholipid system, DPPC - the main constituent of mammalian lung surfactant. Densely packed films of DPPC are directly sheared in a knife-edge surface viscometer. Yield-stress and shear thinning behaviors are shown to be accurately captured across hydrodynamic regimes straddling the Stokes flow limit to inertia dominated flows. [Preview Abstract] |
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