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 H25: Minisymposium: Bubbles, Drops and Particles in Non-Newtonian Fluids |
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Chair: Andrea Prosperetti, University of Houston Room: 607 |
Monday, November 25, 2019 8:00AM - 8:26AM |
H25.00001: Hydrodynamic interaction of a bubble pair ascending in-line in a viscoelastic liquid Invited Speaker: Roberto Zenit When the liquid in a bubbly flow is non Newtonian, a strong tendency to form large clusters and aggregates has been observed. In order to understand the mechanisms that lead to clustering in these liquids, we conduct experiments to determine the hydrodynamic interactions for a pair of bubbles rising in-line in a quiescent liquid. We fabricate viscoelastic fluids with shear-dependent viscosity with water-glycerin mixtures and polyacrylamide. Bubble pairs of different sizes are produced with capillaries of different inner diameters; the control of the bubble formation is achieved using a pulsatile syringe pump and a set of rapid-closing valves. The motion of bubbles is visualized with a high-speed camera. The results are contrasted with those from a Newtonian reference fluid. We observe that the interaction is significantly different from the so-called drafting-kissing-tumbling process that occurs for bubble pairs Newtonian liquids. In general, for viscoelastic fluids we observe no-kissing (how sad). Also, the bubbles do not drift apart indefinitely after interacting; instead, the bubble-pair continues to rise at a constant separation distance and angle. Furthermore, the interaction process appears to me mediated by the appearance, or not, of the negative wake behind the bubbles. Preliminary results will be shown and discussed. [Preview Abstract] |
Monday, November 25, 2019 8:26AM - 8:52AM |
H25.00002: Particle-laden viscoelastic turbulence in channel flow Invited Speaker: Tamer Zaki Individually, viscoelasticity and particles can appreciably modify channel-flow turbulence: The addition of polymers can quench the turbulent shear stress and enlarge the coherent streamwise velocity-perturbation structures; it can also cause the turbulence to cycle between an active and a hibernating state. In contrast, dilute particle concentrations can enhance the turbulent shear stress and weaken the streamwise velocity disturbances. When both viscoelasticity and the particle phase are present, the dynamics become much more intriguing as we demonstrate using direct numerical simulations of particle-laden viscoelastic turbulence in a channel. A dilute concentration (5\%) of neutrally buoyant particles can aggressively amplify the cycles of hibernating and active viscoelastic turbulence. These cycles, in turn, modulate the particle migration between the channel centre and the near-wall region. Within the global dynamics is interesting micro-scale phenomenology: The particle-pair distribution function indicates that viscoelasticity leads to an exclusion corridor upstream and downstream of the particle, in the streamwise direction. An explanation is provided by contrasting the conditionally averaged fields around the particles in the Newtonian and viscoelastic conditions. [Preview Abstract] |
Monday, November 25, 2019 8:52AM - 9:18AM |
H25.00003: Exotic shapes and microscale structure of a bubble rising in hydrophobically modified alkali-soluble emulsion polymer solutions Invited Speaker: Mitsuhiro Ohta The motion of single air bubbles rising through 1.3 and 2.1 wt{\%} hydrophobically modified alkali-soluble emulsion polymer (HASE) solutions are experimentally examined. As reported in past research (Ohta et. al, 2015), a bubble rising in a HASE solution will have a shape that is distinct from a bubble rising in a typical non-Newtonian fluid. A bubble rising in a HASE solution can attain a shape with a very long thin trailing edge, long branched trailing edges, blade-shaped (two-dimensional thin plate shape) trailing edges, and more. By intuition, it is predicted that these distinct bubble shapes are formed due to the contribution of the elastic effect of HASE solutions. It has been discovered experimentally that the microstructure at the trailing edge of a rising bubble is intimately related to the concentration of HASE material in the liquid surrounding a bubble and the bubble size. The various HASE induced microstructures observed are categorized: (1) herring bone, (2) fish backbone, and (3) dendritically-expanded. It is hypothesized that the determination of one of these 3 shapes cannot be explained by straightforward surface tension considerations, and instead one must investigate localized interactions between the individual polymers in a HASE solution and the gas phase in the bubble. [Preview Abstract] |
Monday, November 25, 2019 9:18AM - 9:44AM |
H25.00004: Nonlinear physics in bubble `buku-buku' process with application to quasi-periodic volcanic eruptions Invited Speaker: Mie Ichihara To mimic in the laboratory the acoustic phenomena due to bubbles rising in magma, we have investigated sounds produced by successive bubbles rising through fluid in a container. In a viscous Newtonian fluid, most of the bubbles were ”silent,” while in the non-newtonian fluid all bubbles except the first one generated sound wave at their bursting on the fluid surface. We observed a modulation pattern of the acoustic waveform through time. Moreover, we found the existence of a precursor acoustic signal previous to each bursting. The time delay between this precursor and the bursting signal is well correlated with the bursting signal frequency content. Their joint modulation through time is driven by the memory of previous bubbles, especially the presence of small satellite bubbles trapped in the fluid due to the yield stress. At volcanoes, repetitive acoustic signals with modulation are often observed as seismic or atmospheric waves, which have been interpreted as a result of changes of the system parameters. Our experimental results have pointed out a new possibility that the non-Newtonian nature of magma with its memory effect spontaneously generates such modulations. [Preview Abstract] |
Monday, November 25, 2019 9:44AM - 10:10AM |
H25.00005: Suspensions of non-Brownian particles in non-Newtonian fluids Invited Speaker: Sarah Hormozi This talk aims at introducing our current understanding of the rheology of suspensions of non-Brownian particles in non-Newtonian fluids. These complex suspensions can be found in natural settings such as landslides, mudslides, and submarine avalanches as well as industrial applications such as in mining operations, chemical mechanical, conversion of biomass into fuel, the petroleum industry, etc. Biological and smart materials can be complex suspensions, making relevant problems in physiology, biolocomotion, shock absorbers, and beyond. Therefore, there is a compelling need to study the rheological behaviors of these complex suspensions in order to be able to predict their flow dynamics in various situations. The main scientific challenge is to establish a continuum framework and refine it through microstructure investigations. Suspensions may vary on the particle scale from Stokesian behavior to inertial behavior depending on the flow configuration, the type of suspending fluids, etc. We present a tensorial continuum framework based on our recent computational, experimental and theoretical works and discuss how this framework can be used to study the dispersion of solids in industrial processes and geophysical flows. [Preview Abstract] |
Monday, November 25, 2019 10:10AM - 10:36AM |
H25.00006: Self-similar breakup of polymeric threads as described by the Oldroyd-B model Invited Speaker: Jens Eggers When a drop of fluid containing long, flexible polymers breaks up, it forms threads of almost constant thickness, whose size decreases exponentially in time. Using an Oldroyd-B fluid as a model, we show that the thread profile, rescaled by the thread thickness, converges to a similarity solution. Using the correspondence between viscoelastic fluids and non-linear elasticity, we derive similarity equations for the full three-dimensional axisymmetric flow field in the limit that the viscosity of the solvent fluid can be neglected. A conservation law balancing pressure and elastic energy permits to calculate the thread thickness exactly. The explicit form of the velocity and stress fields can be deduced from a solution of the similarity equations. Results are validated by detailed comparison with numerical simulations. [Preview Abstract] |
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