Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session M25: Microscale Flows: Particle Inertia |
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Chair: Mattia Gazzola, University of Illinois Urbana-Champaign Room: Georgia World Congress Center B313 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M25.00001: Chaotic tumbling and steady drifting of bananas in shear flow Ian R. Thorp, John R. Lister The motion of an axisymmetric ellipsoid immersed in a shear flow at zero Reynolds number is simple: the ellipsoid rotates periodically and is advected downstream by the fluid. However, bending the ellipsoid into a banana shape radically changes both its rotational and translational dynamics. The rotation becomes quasiperiodic or chaotic and particles can drift steadily across the streamlines in the gradient and/or the vorticity directions of the shear flow. We explain the origins of drift and the changes in rotational dynamics in terms of the symmetry group of the particle (shared by T-shapes and square pyramids) and the reversibility of Stokes flow, which establish a connection to KAM theory. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M25.00002: Flow-induced rotation and inertial focusing of complex shaped particles in channel flow Rajat Mittal, Jung-Hee Seo, Soojung Claire Hur Inertial focusing of particles in a spatially varying shear flow is potentially an effective technique for the manipulation and segregation of microparticles. While the inertial migration of spherical/circular particles has been studied theoretically, experimentally, and numerically in many previous studies, little attention has been paid to the behavior of particles with complex, asymmetric shapes. Given that most real particles have non-simple shapes, the effect of particle shape on their inertial movement in flow is particularly important to investigate. In the present study, the inertial focusing and rotation characteristics of a class of complex-shaped particles in channel flow are investigated by using a sharp-interface immersed boundary method. The effects of particle shape, size, and flow Reynolds number on particle focusing and rotation are examined. Based on the simulations, we present physical insights and scaling laws for this phenomenon. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M25.00003: Controlling trajectories via particle shape in confined flows Jean Cappello, Marine Daieff, Mathias Bechert, François Gallaire, Camille Duprat, Anke Lindner Transport properties of particles in confining geometries show very specific characteristics, as for example lateral drift for fibers inclined with respect to the flow direction. Due to viscous friction with top and bottom walls particles act like moving obstacles and induce strong flow perturbations. These perturbations are at the origin of the observed lateral drift, oscillatory movement between lateral walls or the deformation of flexible fibers. Modifying the fiber shape by adding for example an additional arm leads to an L shaped fiber and thus breaks the previous fiber symmetry. This induces fiber rotation until a stable equilibrium orientation is reached. Lateral drift is then observed until interaction with side walls becomes important. Tuning the fiber asymmetry and confinement allows for a precise control of particle trajectories, including the approach of side walls, even robust against small perturbations. Our investigation combines precise microfluidic experiments as well as numerical simulations based on modified Brinkman equations. The knowledge gained here can be used for targeted delivery or particle capture inside microchannels. |
Tuesday, November 20, 2018 8:39AM - 8:52AM |
M25.00004: Dynamics of particles in liquid-liquid stratified flow in a microchannel T Krishnaveni, T Renganathan, S Pushpavanam Inertial focusing is a separation technique where particles migrate laterally to equilibrium positions in the presence of finite inertia. These equilibrium positions are predominantly governed by two counteracting forces namely the wall lift force and the shear gradient force. The equilibrium positions can be altered by changing the velocity profile of the fluid. This is done for the separation and recovery of cells from one fluid to the other. In this work, we model the inertial focusing of particles in the laminar, liquid-liquid stratified flow in a microchannel. The particles are sent through one fluid and due to variation in shear gradient (curvature in velocity profile), the particles migrate towards the other fluid. Towards this, we develop a 2D model (pressure driven flow between infinite parallel plates) based on the immersed boundary method to study the hydrodynamics and particle migration. The effect of fluid and particle properties and the operating conditions such as phase holdup and Reynolds number is analyzed on the particle migration. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M25.00005: Flow Characteristics and Deposit Structure for Particle-laden Rivulets Aref Ghafouri, Timothy Singler, Xin Yong, Paul Chiarot The structure of the deposit left behind by a nanoparticle-laden rivulet is governed by fluid transport during its evaporation. In this work, we used fluorescent tracers and optical microscopy to measure this evolving flow inside aqueous rivulets printed using inkjet. The use of a chemically treated substrate prevented the breakup of the rivulet by decreasing the receding contact angle close to zero. We investigated the effects of (i) adding small surfactants (sodium dodecyl sulfate) and (ii) using binary (water-alcohol) solvent on the flow characteristics and final deposit structure. The binary mixture created a strong solutal Marangoni flow (i.e. eddies) during evaporation and resulted in a “twin line” deposit. In contrast, the presence of surfactant at high concentrations induced rapid dewetting of the rivulet at the final stages of evaporation to create a “single line” deposit. For mixed binary-surfactant solutions, the particle transport was highly dependent on the presence of alcohol rather than surfactants at the early stages of evaporation. However, during the later stages, surfactant plays a more important role in governing the transport dynamics. |
Tuesday, November 20, 2018 9:05AM - 9:18AM |
M25.00006: Modeling Inertial Particle Focusing in Curvilinear Microchannels Mike Garcia, Sumita Pennathur The focusing of particles in curvilinear microchannels at high Reynolds number has received great attention in recent years as a tool to separate bioparticles. However, in order to design a curvilinear channel for a specific separation process one must rely on empirical results, as no complete theoretical model currently exists. This is because the existing models that predict the total forces on a particle in a curvilinear geometry do so by superposing inertial forces with a Dean force calculated using a point particle assumption. The ability to add these two forces may hold under certain regimes, but as the inertia associated with the Dean flow increases, it is crucial to take into account the finite size of the particle. In our work we model the full flow physics of a particle migrating in a curvilinear channel in a reference frame that is rotating with the particle by including both Coriolis and Centripetal forces. Here we investigate the three dimensional focusing behavior of inertial particles and the applicability of the point particle assumption previous models have proposed. Finally, we propose a new linear model that takes into account the full physics, but relies on a perturbation expansion where the perturbation parameter is the curvature ratio of the channel. |
Tuesday, November 20, 2018 9:18AM - 9:31AM |
M25.00007: Flow focusing of nanofibrils is controlled by effective interfacial tension Fredrik Lundell, KrishneGowda Vijayakumar, Christophe Brouzet, Thibault Lefranc, Daniel Söderberg Flow focusing of a cellulose nanofibrils (CNF) suspension is studied numerically and experimentally. The geometry is flat and consists of 1x1 mm2 channels that meet in the form of a plus (+). Three of the four branches are inlets and one is the outlet. A central flow consisting of a suspension of CNF in water is focused by pure water flowing from two channels that are orthogonal to the central flow, whereafter all fluid is ejected through the outlet. The flow case has been chosen since it has been demonstrated that it can be used to assemble very strong cellulose filaments (ACS Nano 12, 7, 6378-6388). Optical Coherence Tomography (OCT) is used to determine the shape and velocity of the central flow, and the experimental data are matched to multiphase computational fluid dynamics simulations. The behaviour of the colloidal suspension in the central flow is seen to be controlled by the effective interfacial tension between the pure water and the water with CNF. It turns out that a weak surface tension must be applied in the simulations in order to get a good agreement with the experimental data. When properly tuned, the agreement between simulations and experiments is excellent. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M25.00008: Particle/droplet manipulation-on-chip Ankur Kislaya, Daniel Seewai Tam, Peter Veenstra, Jerry Westerweel The interest in manipulating particles & droplets have found its applications in diverse fields of engineering. Generally, manipulation activities carried out in micro-devices have a fixed design for a specific task, which makes different analyses unfeasible on a single device. To address this issue, we designed a Hele-Shaw flow cell with "virtual" channels generated by sources & sinks. This device provides us the opportunity to integrate multiple functionalities onto a single-chip. This work focuses on manipulating individual or several particles/droplets in the flow cell by using multiple sources & sinks to deviate streamlines. Since the depth-averaged velocity over the channel in a Hele-Shaw cell is irrotational, we use potential flow theory to predict source/sink strength for manipulating particles/droplets. This includes tasks such as deflecting particles/droplets to a different position and trapping & releasing. Hence, this single device can be used for multiple purposes such as sorting, droplet coalescence, etc., which are of interest to the oil, food and medical industries. |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M25.00009: Hydrodynamic Self-assembly in Suspensions of Microrollers: a Dynamical System Insight Blaise Delmotte
Hydrodynamic self-assembly has been observed in suspensions of colloidal microrollers [Driscoll, M., Delmotte, B., Youssef, M., Sacanna, S., Donev, A. and Chaikin, P. (2017). Nature Physics, 13(4), 375]. Microrollers rotate about an axis parallel to the floor and generate strong, slowly decaying, advective flows. Here we show that pairs of microrollers can exhibit various hydrodynamic bound states whose nature depends on a dimensionless number, denoted $B$, that compares the relative strength of gravitational forces and external torques. Using a dynamical system framework we characterize these various states in phase space. We analyze the various bifurcations of the system as $B$ varies. In particular, we show that there is a critical value of $B$ for the existence of stable motile orbiting trajectories, reminiscent of the ``colloidal creatures" observed by Driscoll \textit{et al}. These results help us understand the hydrodynamic mechanisms that lead to spontaneous self-assembly and to envision particle transport using microroller suspensions. |
Tuesday, November 20, 2018 9:57AM - 10:10AM |
M25.00010: Microparticle migration in Transport Flows: Oscillation-induced Rectification Forces Siddhansh Agarwal, David Vijay Raju, Sascha Hilgenfeldt The oscillation of interfaces in a fluid leads to rectified dynamics on time scales much longer than that of the oscillation, affecting the motion of both fluid elements (streaming) and particles in the medium (inertial migration). We have recently developed a scale separation |
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