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 H27: Non-Newtonian Flows: Experimental Measurements and Numerical Studies |
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Chair: Juan Carlos del Alamo, University of California, San Diego Room: E147-148 |
Monday, November 21, 2016 10:40AM - 10:53AM |
H27.00001: Two-Point Particle Tracking Microrheology of Nematic Lyotropic Liquid Crystals Manuel Gomez-Gonzalez, Juan Carlos del Alamo Biological and technological complex fluids that are usually available in microscopic amounts (e.g. liquid crystals and biopolymer networks) can exhibit microstructural order leading to nematic rheological behavior. However, current microrheological methods cannot measure their directional viscoelastic coefficients. We recently introduced a directional two-point particle-tracking microrheology (D2PTM) technique to determine these coefficients (1). Here, we experimentally validate D2PTM by applying this method to disodium cromoglycate (DSCG), a lyotropic chromonic nematic liquid crystal that has recently sparked attention due to its biocompatibility and other interesting properties. We chose DSCG because its directional viscosity coefficients have been previously characterized by dynamic light scattering and are available in the literature. Our results suggest that D2PTM measurements agree well with measurements from previous methods. Furthermore, this new technique provides additional information about the microrheological response of nematic fluids that was not accessible via previous methods. (1) Gomez-Gonzalez, M and del Alamo, J C, ``Two-point particle tracking microrheology of nematic complex fluids'' Soft Matter 2016 12, 5758. [Preview Abstract] |
Monday, November 21, 2016 10:53AM - 11:06AM |
H27.00002: Rate of chaotic mixing in localized flows pierre jop, Jalila Boujlel, Emmanuelle Gouillart, Franck Pigeonneau Most of the pastes in building materials are yield-stress fluids. Mixing them efficiently is required for industrial processes but linking the rate of the mixing to the fluid properties is a challenge. We study experimentally the rate of chaotic mixing in viscoplastic fluids by using a rod-stirring protocol with a rotating vessel. Only a limited zone localized around the stirring rods is highly sheared at a given time. Using a dyed spot as the initial condition, we measure the decay of concentration fluctuations of dye as mixing proceeds. Due to numerical simulations and experimental measurements, we relate the volume of highly sheared fluid to the parameters of the flow. We propose a quantitative two-zone model for the mixing rate, taking into account the geometry of the highly sheared zone as well as the rate at which fluid is renewed inside this zone. The model predicts correctly the scaling of the exponential mixing rates during a first rapid stage and a second slower one. Moreover we show that an optimal mixing exists when varying the ratio of the rotation rate of the vessel and the velocity of the rods. [Preview Abstract] |
Monday, November 21, 2016 11:06AM - 11:19AM |
H27.00003: Spatial-temporal dynamics of Newtonian and viscoelastic turbulence in channel flow Sung-Ning Wang, Ashwin Shekar, Michael Graham Introducing a trace amount of polymer into liquid turbulent flows can result in substantial reduction of friction drag. This phenomenon has been widely used in fluid transport; however, the mechanism is not well understood. Past studies have found that in minimal domain turbulent simulations, there areoccasional time periods when flow exhibits features such as weaker vortices, lower friction drag and larger log-law slope; these have been denoted as ``hibernatingturbulence''. Here we address the question of whether similar behavior arises spatio-temporally in extended domains, focusing on turbulence at friction Reynolds numbers near transition and Weissenberg numbers resulting in low-medium drag reduction. By using image analysis and conditional sampling tools, we identify the hibernating states in extended domains and show that they display striking similarity as those in minimal domains. The hibernating states among different Weissenberg numbers exhibit similar flow statistics, suggesting they are unaltered by low to medium viscoelasticity. In addition, the polymer is much less stretched during hibernation. Finally, these hibernating states vanish as Reynolds number increases. However, they reoccur and gradually become dominant with increasing viscoelasticity. [Preview Abstract] |
(Author Not Attending)
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H27.00004: Extensional properties of mobile polymer solutions. Christophe Tirel, Marie-Charlotte Renoult, Christophe Dumouchel, Olivier Crumeyrolle, Denis Lisiecki, Innocent Mutabazi A deep understanding of the influence of viscoelasticity on the dynamics of liquid flows remains a challenge in the non-Newtonian fluid mechanics field. Previous work has revealed that the addition of minute amount (2.5 part per million) of high molecular weight polymer to water, forming a viscoelastic solution with strong extensional properties, modifies the fission process during droplet snap off with spectacular effects: inhibition of the singularity observed in the reference Newtonian case and formation of a long-lived (milli-second) filament. The measurement of the extensional properties for such mobile polymer solutions is one of the most pressing problem. Here, a global measurement technique, based on the multi-scale analysis of the capillary instability of a free falling jet of a mobile polymer solution, is introduced. The method of analysis allows the characterisation of the jet breakup mechanism from which the relaxation time of the polymer solution can be extracted. One of the advantages of the technique is the simple experiment it requires. [Preview Abstract] |
Monday, November 21, 2016 11:32AM - 11:45AM |
H27.00005: Yielding transition of Carbopol gel in a vertical pipe Yang Liu, John R.de Bruyn We have investigated the yielding transition of a simple yield-stress fluid (Carbopol 940) in a vertical pipe. The Carbopol gel was displaced by a Newtonian liquid injected at a constant, controlled rate at the bottom of the pipe. Rough- and smooth-walled pipes were used to study the effects of wall boundary conditions. The pressure in the Carbopol was measured by a pressure gauge fixed on the pipe wall, and the velocity profile in the Carbopol was measured by particle-image velocimetry (PIV). When the Newtonian liquid was injected, the rate of pressure increase was initially high, then decreased to a constant slow rate at later times. A time tc was defined by the intersection of straight lines fit to the pressure-time data at early and late times. In the rough pipe, the wall shear stress at tc is equal to the yield stress, suggesting that this time corresponds to yielding of the fluid. The velocity profiles were parabolic before yielding, and nearly a plug-like afterwards. In the smooth pipe, the pressure and velocity profiles appeared to show similar behavior to that in the rough pipe, but the wall shear stress at tc is substantially smaller than the yield stress and fluid motion was due to wall slip. [Preview Abstract] |
Monday, November 21, 2016 11:45AM - 11:58AM |
H27.00006: Time-Resolved imaging Studies of Laser-Induced Jet Formation in Non-Newtonian Liquid Films Emre Turkoz, Craig Arnold Blister-actuated laser-induced forward transfer (BA-LIFT) is a nozzle-less printing technique that offers an alternative to inkjet printing. The lack of a nozzle allows for a wider range of inks since clogging is not a concern. In this work, a focused laser pulse is absorbed within a polymer layer coated with a thin liquid film. The pulse causes a rapidly expanding blister to be formed that induces a liquid jet. Various well-studied non-Newtonian solutions are tested to examine how the shear-thinning and shear-thickening characteristics affect jet formation. The time delay between pulses is varied along with the energy, and different regimes of transfer are identified. We explore how Ohnesorge number, Weber number and spot size affect the jet formation and evaluate parameters that lead to breakup of jets into droplets. [Preview Abstract] |
Monday, November 21, 2016 11:58AM - 12:11PM |
H27.00007: Influence of temperature on the drainage of thermoresponsive polymer thin film Adrien Bussonniere, Matthew Jackman, Hin Long Leung, Bo Liu, Qingxia Liu, Peichun Amy Tsai Due to their switchable stability under external excitation, responsive aqueous foams have recently raised interests in various applications, such as washing, cleaning and mineral recovery, where stable foam and controlled destabilization are required. In this work, we investigate the influence of the temperature and polymer concentration on gravitational thin film drainage using a thermoresponsive polymer. The dynamics of film thinning was recorded on the thin film using a thickness measurement method. We successively illuminate the film with three LEDs of different wavelengths. The absolute thickness was accurately deduced using the three interference patterns. The results show an increase of drainage rates with increasing temperature but insignificant influence of polymer concentration (in the range between 50 and 300 mg/L). The thinning process was twice faster above the LCST (lower critical solution temperature) than that at room temperature. Our results of the temperate-dependent drainage show that the thermoresponsive solubility of polymer plays a key role in thin film stability. [Preview Abstract] |
Monday, November 21, 2016 12:11PM - 12:24PM |
H27.00008: Dynamics of complex fluids in rotary atomization Bavand Keshavarz, Gareth McKinley We study the dynamics of fragmentation for different Newtonian and viscoelastic liquids in rotary atomization. In this process, at the rim of a spinning cup, the centripetal acceleration destabilizes the formed liquid torus due to the Rayleigh-Taylor instability. The resulting ligaments leave the liquid torus with a remarkably repeatable spacing that scales linearly with the inverse of the rotation rate. Filaments then follow a well-defined geometrical path-line that is described by the involute of the circle. Knowing the geometry of this phenomenon we derive the detailed kinematics of this process and compare it with the experimental observations. We show that the ligaments elongate tangentially to the involute of the circle and thin radially as they separate from the cup. A theoretical form is derived for the spatial variation of the filament deformation rate. Once the ligaments are far from the cup they breakup into droplets since they are not stretched fast enough (compared to the critical rate of capillary thinning). We couple these derivations with the known properties of Newtonian and viscoelastic liquids to provide a physical analysis for this fragmentation process that is compared in detail with our experiments. [Preview Abstract] |
Monday, November 21, 2016 12:24PM - 12:37PM |
H27.00009: Nonlinear equilibrium states in viscoelastic Taylor-Couette flow Laura Nicolaou, Jacob Page, Tamer Zaki Viscoelastic Taylor-Couette flow exhibits a variety of instabilities, some of which can arise in the absence of inertia altogether. Nonlinear solutions of the equilibrium states are sought, where the distorted mean flow is unchanged and the finite-amplitude instability waves are saturated. A key assumption in the theory is that nonlinearity is restricted to the action of the perturbations on the mean flow. Therefore, the perturbation shape is preserved throughout its growth and saturation, and is specified as a weighted sum of the unstable, linear eigenmodes. At low elasticity, a single unstable mode exists in the form of a stationary Taylor vortex, and the predicted saturated state compares favourably with direct numerical simulation (DNS). DNS reveals that the higher harmonics are an order of magnitude weaker than the fundamental frequency, which substantiates the assumption adopted in the theory. At moderate elasticity, multiple modes become unstable, including axially-travelling elastic rolls and stationary vortices. Equilibrium solutions built from superpositions of these modes explain observations from experiments in the literature over a range of shear rates. [Preview Abstract] |
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