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 M37: Drops: Complex Fluids |
Hide Abstracts |
Chair: Carl D. Meinhart, University of California Santa Barbara Room: Portland Ballroom 252 |
Tuesday, November 22, 2016 8:00AM - 8:13AM |
M37.00001: Dynamics and shapes of ferrofluid drops under spatially uniform magnetic fields Payam Rowghanian, Friedhelm Serwane, David Kealhofer, Carl D. Meinhart, Otger Campas We study the shape and dynamics of a Newtonian ferrofluid drop immersed in a Newtonian and non-magnetic viscous fluid under the action of a uniform external magnetic field. We obtain the exact equilibrium drop shapes for arbitrary ferrofluids which describe unexplained previous experiments, characterize the extent of deviations of the exact shape from the commonly assumed ellipsoidal shape, and analyze the smoothness of highly curved tips in elongated drops. We present a comprehensive study of drop deformation for a Langevin ferrofluid. Using a computational scheme that allows fast and accurate simulations of ferrofluid drop dynamics, we show that the dynamics of drop deformation by an applied magnetic field is described up to a numerical factor by the same time scale as drop relaxation in the absence of any magnetic field. The numerical factor depends on the ratio of viscosities and the ratio of magnetic to capillary stresses, but is independent of the nature of the ferrofluid in most practical cases. Finally, we use the shape and dynamics of the magnetic drops to measure the rheology of complex fluids. [Preview Abstract] |
Tuesday, November 22, 2016 8:13AM - 8:26AM |
M37.00002: Pattern formation and temporal undulations of plane magnetic droplet Chamkor Singh, Arup Kumar Das, Prasanta Kumar Das In this study, we numerically investigate the time-dependent response of a ferrofluid droplet under an impulsively applied uniform magnetic field in a zero gravity environment. It is identified that two characteristic non-dimensional groups, namely, the Laplace number $La$ and the magnetic Bond number $Bo_m$, primarily influence the response of the droplet. It is found that the nature of the time response can be either monotonic or undulating depending on the parameters. The transition between the two is smooth. In addition to the previously well-known regimes of elliptic and acicular ferrofluid droplet shapes, a new regime on the $La-Bo_m$ plane is found where we observe some unique bifurcating patterns at the poles of the droplet. The temporal aperiodic to periodic mode transition on the $La-Bo_m$ plane is found to be governed by $La$ and the spatial droplet deformation and its final equilibrium configuration is found to be governed by $Bo_m$. The mechanism behind the elliptic to non-elliptic or elliptic to bifurcated shape transitions is discussed. [Preview Abstract] |
Tuesday, November 22, 2016 8:26AM - 8:39AM |
M37.00003: Magnetophoretic interaction of ferrofluid droplets in a rotating magnetic field Mingfeng Qiu, Shahriar Afkhami, Ching-Yao Chen, James Feng Recent experiments have discovered a mode of planetary motion of a pair of ferrofluid droplets in a rotating magnetic field. It consists of the self-spin of individual droplets and the global revolution of the pair with a phase lag from the rotating field. This talk describes a volume-of-fluid simulation that explores this phenomenon. By studying the magnetic and hydrodynamic interactions between the droplets, we determine the time scale of the planetary motion under different operating conditions. The numerical results are compared to predictions using a simple dipole interaction model and the experiments. Finally we simulate the motion of a multiple-droplet chain in a rotating field, and compare the results to experimental observations that the drops assemble into a regular and compact array that rotates with the field with a phase lag. [Preview Abstract] |
Tuesday, November 22, 2016 8:39AM - 8:52AM |
M37.00004: A Theory of Shape-Shifting Droplets Pierre Haas, Raymond Goldstein, Stoyan Smoukov, Nikolai Denkov Recent observations of cooled oil emulsion droplets uncovered a remarkable array of shape transformations\footnote{N.~Denkov, S.~Tcholakova, I.~Lesov, D.~Cholakova, and S.~K.~Smoukov, Self-shaping of oil droplets via the formation of intermediate rotator phases upon cooling, Nature {\bf 528}, 392 (2015)}: the initially spherical droplets flatten into polygonal shapes, first hexagons, then triangles or quadrilaterals that ultimately grow thin protrusions from their corners. These transformations are driven by a partial phase transition of the bulk liquid phase. In this talk, we explore theoretically the simplest geometric competition between this phase transition and surface tension in planar polygons. We recover the experimental sequence of shapes and predict shape statistics in qualitative agreement with experiments. Extending the model to capture some of the three-dimensional structure of the droplets, we analyse the topological transition of droplet puncture observed in experiments. [Preview Abstract] |
Tuesday, November 22, 2016 8:52AM - 9:05AM |
M37.00005: Dynamics of spreading thixotropic droplets Aran Uppal, Richard Craster, Omar Matar Thixotropy has become of increasing interest for a variety of applications in recent years. The lubrication approximation has been often used in the study of such fluids, especially in the presence of a free surface. The lubrication approximation aims to remove the explicit depth dependence from the resulting evolution equations by utilising the naturally occurring small aspect ratio. However, this is not possible with the inclusion of a structure parameter to describe the thixotropic behaviour. Thus, we consider a range of closures to simplify the evolution equations and compare against the full simulation results. [Preview Abstract] |
Tuesday, November 22, 2016 9:05AM - 9:18AM |
M37.00006: Drop dynamics on a stretched viscoelastic filament: An experimental study Jorge Peixinho, Marie-Charlotte Renoult, Olivier Crumeyrolle, Innocent Mutabazi Capillary pressure can destabilize a thin liquid filament during breakup into a succession of drops. Besides, the addition of a linear, high molecular weight, flexible and soluble polymer is enough to modify the morphology of this instability. In the time period preceding the breakup, the development of beads-on-a-string structures where drops are connected by thin threads is monitored. The drops dynamics involve drop formation, drop migration and drop coalescence. Experiments using a high-speed camera on stretched bridges of viscoelastic polymeric solutions were conducted for a range of viscosities and polymer concentrations. The rheological properties of the solutions are also quantified through conventional shear rheology and normal stress difference. The overall goal of this experimental investigation is to gain more insight into the formation and time evolution of the drops. [Preview Abstract] |
Tuesday, November 22, 2016 9:18AM - 9:31AM |
M37.00007: Rolling, sliding, and sticking of viscoplastic xanthan gum solution drops on a superhydrophobic surface Minyoung Kim, Eungjun Lee, Do Hyun Kim, Rhokyun Kwak Dynamics of Newtonian fluid on a non-wettable substrate have been reported, but those of non-Newtonian fluid, especially of viscoplastic fluid showing a yield stress, are not fully characterized yet. Here, we investigate three distinct behaviors of a viscoplastic drop (xanthan gum solution) -rolling, sliding, and sticking- on an inclined superhydrophobic surface with various inclined angles (1-24 degree) and xanthan gum concentrations (0.25-1.5 {\%}). At a low concentration of xanthan gum (low yield stress) and/or a high inclined angle (high gravitational stress), the drop rolls down the surface as the gravitational stress exceeds the yield stress. As the concentration increases, and thus the yield stress exceeds the gravitational stress, the drop stays on the surface like a solid (sticking). However, if we adjust the gravitational stress to induce an adhesive failure between the xanthan gum drop and the surface (but still lower than the yield stress), the drop slides down the surface without rolling. To the best of our knowledge, this is the first direct characterization of the behavior of the viscoplastic drops on an inclined surface considering gravitational stress, yield stress, and adhesive failure. [Preview Abstract] |
Tuesday, November 22, 2016 9:31AM - 9:44AM |
M37.00008: Coalescence dynamics of a Non-Newtonian drop in a Hele-Shaw cell Panagiota Angeli, Victor Voulgaropoulos, Maxime Chinaud In this study, the quasi-2D coalescence of an aqueous droplet with a flat interface is studied. The two immiscible liquids used in the coalescence experiments are a water/glycerol mixture and low viscosity oil. Experiments are conducted in a Hele-Shaw cell with an aspect ratio of 14 by 8 by 0.125 cm while time resolved velocity fields are obtained by using high-speed bright field Particle Image Velocimetry measurements. The aim of the present study is to investigate the effect of a polymer (i.e. xanthan gum), which results in a shear-thinning behaviour of the aqueous phase. It was found that the time evolution of the neck at the initial stages of coalescence follows a linear trend, which suggests that the shear-thinning behaviour at the neck region at this stage of coalescence can be considered quasi-constant in time. In addition, velocity and vorticity fields are computed inside the coalescing droplet and the bulk homophase. It is found that two pair of counter rotating vortices are generated just after the rupture of the film which separates the drop from the homophase. Furthermore, the polymer addition reduced the magnitude of the corresponding vorticity peaks in the drop and slowed down the coalescence dynamics. [Preview Abstract] |
Tuesday, November 22, 2016 9:44AM - 9:57AM |
M37.00009: Regimes in secondary atomization of shear thinning inelastic drops Varun Kulkarni, Jonathan Rocha, Paul Sojka Secondary atomization plays a key role in the determining the eventual drop size distribution of a spray from an injector. Studies until recently have primarily focused on drops made of Newtonian or viscoelastic fluids. However, little is known about the breakup of single drop made of a shear thinning fluid subjected to cross flow of air. In this study we attempt to classify, experimentally, the regimes of breakup and morphology of an inelastic, shear thinning drop. Six different CMC water/glycerine based solutions are tested. The morphological patterns are classified on a \textit{We}/\textit{Oh}$^{\mathrm{2}}$ - 1/\textit{Oh}$^{\mathrm{2}}$ plot using the zero shear rate viscosity where \textit{We} denotes the Weber number and \textit{Oh} is the Ohnesorge number. The regime boundaries for the various breakup patterns are juxtaposed with their Newtonian counterparts to highlight the differences. We observe a dependence on the Carreau number, \textit{Cu} and power law index, $n$. The results converge to the Newtonian limit for particular cases of \textit{Cu} and $n$. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2025 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700