Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V35: General Fluid Mechanics |
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Sponsoring Units: DFD DCMP Chair: Saad Bhamla, Stanford University Room: 298 |
Thursday, March 16, 2017 2:30PM - 2:42PM |
V35.00001: A GPU Accelerated DG-FDF Simulator for Large Eddy Simulation of Reacting Turbulent Flows Medet Inkarbekov, Aidyn Aitzhan, Aset Koldas, Aidarkhan Kaltayev, Peyman Givi A GPU accelerated simulator is developed and implemented for large eddy simulation (LES) of reacting turbulent flows. In this simulator, the problem of the unresolved scalar fluctuations is solved by applying the filtered density function (FDF) methodology. The advantage of the methodology is that the effect of chemical reactions appears in a closed form. The base filtered transport equations are solved numerically by a Discontinuous Galerkin (DG) method, while the FDF transport equation is solved by a particle based Lagrangian Monte-Carlo (MC) method. A very important advantage of DG method is that it can provide high order accuracy with fewer degrees of freedom. Because of the compact formulations of the hybrid DG-MC scheme, it is very well suited for parallelization on general purpose GPUs. The performance of the code is compared against a standard serial code and it is shown to give as much as \textasciitilde 20 times acceleration on GeForce GTX Titan Black. [Preview Abstract] |
Thursday, March 16, 2017 2:42PM - 2:54PM |
V35.00002: DSMC Simulation of High Mach Number Taylor-Couette Flow Dr. Sahadev Pradhan The main focus of this work is to characterise the Taylor-Couette flow of an ideal gas between two coaxial cylinders at Mach number \textit{Ma }$=$\textit{ (U\textunderscore w / }$\backslash $\textit{sqrt\textbraceleft kb T\textunderscore w / m\textbraceright )}in the range 0.01 \textless Ma \textless 10, and Knudsen number \textit{Kn }$=$\textit{ (1 / (}$\backslash $\textit{sqrt\textbraceleft 2\textbraceright }$\backslash $\textit{pi d\textasciicircum 2 n\textunderscore d (r\textunderscore 2 - r\textunderscore 1))) }in the range 0.001 \textless Kn \textless 5, using two-dimensional (2D) direct simulation Monte Carlo (DSMC) simulations. Here, \textit{r\textunderscore 1}and \textit{r\textunderscore 2}are the radius of inner and outer cylinder respectively, \textit{U\textunderscore w}is the circumferential wall velocity of the inner cylinder, \textit{T\textunderscore w}is the isothermal wall temperature, \textit{n\textunderscore d}is the number density of the gas molecules, $m$and $d$ are the molecular mass and diameter, and \textit{kb}is the Boltzmann constant. The cylindrical surfaces are specified as being diffusely reflecting with the thermal accommodation coefficient equal to one. In the present analysis of high Mach number compressible Taylor-Couette flow using DSMC method, wall slip in the temperature and the velocities are found to be significant. Slip occurs because the temperature/velocity of the molecules incident on the wall could be very different from that of the wall, even though the temperature/velocity of the reflected molecules is equal to that of the wall. Due to the high surface speed of the inner cylinder, significant heating of the gas is taking place. The gas temperature increases until the heat transfer to the surface equals the work done in moving the surface. The highest temperature is obtained near the moving surface of the inner cylinder at a radius of about (1.26 r\textunderscore 1). [Preview Abstract] |
Thursday, March 16, 2017 2:54PM - 3:06PM |
V35.00003: Adaptation of an immersed interface method for high-speed flows Vinicius Aurichio, Attilio Cucchieri, Maria Bambozzi We propose a new hybrid method for simulating high-speed flows past bluff bodies. An immersed interface method accounts for material discontinuities precisely located on the body surface. Shock waves may form in high-speed flows and their exact locations are unknown, since they are spread across a narrow region. A new high-order shock detector finds near discontinuities in the fluid and the Weighted Essentially Non-Oscillatory (WENO) method is applied on these regions. WENO's embedded shock detector can yield false positives due to its low order; the use of a high-order detector helps to partially solve this problem. [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V35.00004: Liquid-grain mixing suppresses droplet spreading and splashing during impact Devaraj van der Meer, SongChuan Zhao, Rianne de Jong Would a raindrop impacting on a coarse beach behave differently from that impacting on a desert of fine sand? We study this question by a series of model experiments, where the packing density of the granular target, the wettability of individual grains, the grain size, the impacting liquid, and the impact speed are varied. We find that by increasing the grain size and/or the wettability of individual grains the maximum droplet spreading undergoes a transition from a capillary regime towards a viscous regime, and splashing is suppressed. The liquid-grain mixing is discovered to be the underlying mechanism. An effective viscosity is defined accordingly to quantitatively explain the observations. [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V35.00005: The slow electric discharge of charged drops Martin Brandenbourger, Pierre-Brice Bintein, Stephane Dorbolo The presence of an excess electric charge in droplets is commonly used to justify unexpected behaviors. Although the charging mechanism of droplets is well understood, the charge loss of droplets is still debated. Previous research showed that drops only in contact with ambient air lose their charge by two different phenomena, the charge evaporation and the Coulomb explosion. These two processes are supposed to occur for highly charged droplets or very small (micrometric) droplets. In this context, we studied the charge over time for millimetric drops charged under the Coulomb explosion limit. These charged drops were stored on a vibrating bath, which allowed to keep them only in contact with ambient air. The charge of the droplets was measured by dropping them in a Faraday cup. Thanks to these measurements, we highlighted a new charge loss mechanism for charged droplets. This new mechanism occurs on a long time scale (several minutes) contrary to other charge loss mechanisms. The droplet charge loss is found to be dependent on the droplet initial charge, but independent on the liquid composition and the bouncing mode. A model corresponding to the charge loss of a capacitor correctly adjusts our observations. [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V35.00006: On-Chip generation of polymer microcapsules through droplet coalescence Md Danish Eqbal, Venkat Gundabala Alginate microbeads and microcapsules have numerous applications in drug delivery, tissue engineering and other biomedical areas due to their unique properties. Microcapsules with liquid core are of particular interest in the area of cell encapsulation. Various methods such as coacervation, emulsification, micro-nozzle, etc. exist for the generation of microbeads and microcapsules. However, these methods have several drawbacks like coagulation, non-uniformity, and polydispersity. In this work we present a method for complete on chip generation of alginate microcapsules (single core as well as double core) through the use of droplet merging technique. For this purpose, a combined Coflow and T-junction configuration is implemented in a hybrid glass-PDMS (Polydimethylsiloxane) microfluidic device. Efficient generation is achieved through precise matching of the generation rates of the coalescing drops. Through this approach, microcapsules with intact single and double (liquid) cores surrounded by alginate shell have been successfully generated and characterized. [Preview Abstract] |
Thursday, March 16, 2017 3:42PM - 3:54PM |
V35.00007: Pushing and Pulling: Understanding and Controlling Forces on Particles near Oscillating Interfaces Siddhansh Agarwal, Bhargav Rallabandi, David Raju, Sascha Hilgenfeldt Oscillations of an interface in a fluid give rise to periodic flows that rectify into steady streaming. Particles near such an interface experience additional displacements beyond that of the fluid elements, which can be exploited in a variety of microfluidic applications, such as sorting or trapping. We quantify, in experiment and theory, the forces acting on microparticles on both the oscillatory time scale and the slower time scale of steady streaming. Time scale separation results in modified Maxey-Riley equations exclusively on the slow time scale, allowing for efficient calculation and direct physical interpretation of the forces experienced by the particles. It is found that particles are attracted or repelled depending on their size and density, as well as other parameters under experimental control. These forces are inertial in nature, but act much faster than previously discussed inertial forces in microfluidics. Experiments demonstrating sorting and trapping of particles in agreement with the theory are presented. [Preview Abstract] |
Thursday, March 16, 2017 3:54PM - 4:06PM |
V35.00008: Abstract Withdrawn
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Thursday, March 16, 2017 4:06PM - 4:18PM |
V35.00009: Flow diversion and permeability modification due to polymer flow in porous media Shima Parsa, Ariel Amir, David A Weitz Polymer flow through porous media is of particular interest in applications such as enhanced oil recovery and ground water remediation. We use confocal microscopy and bulk permeability measurements to probe the effects of polymer flow on the permeability and local velocity distribution of a single phase flow in 3D micromodel of porous media. Our measurements show considerable reduction in permeability and increased velocity fluctuations with fluid velocities being diverted in some pores after polymer flow. We also find that the average velocity in the medium at constant imposed flow rate scales with the inverse square root of permeability. Using a simple model of porous medium we verify this scaling from physical length scales of the medium. [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V35.00010: The Catastrophic Failure of Plant Hydraulic Networks Examined in Leaves Philippe Marmottant, Diane Bienaimé, Timothy Brodribb Plants live a dangerous game: they have to facilitate water transport in their xylem conduits while minimizing the consequence of hydraulic failure. Indeed, as water flows under negative pressure inside these conduits, cavitation bubbles can spontaneously occur. By preventing the sap transport, they could lead to the plant death. This failure dynamics of this hydraulic network is poorly studied, while it has important ecological and bioengineering implications. Here, by using a simple optical method, we were able to directly visualize the spreading of cavitation bubbles within leaves. The air invasion also progresses by stop and go, from largest veins to smallest ones. In fact, in plants, conducts are linked by small valves called pits. By temporarily blocking bubbles they delay air invasion, until the pressure difference exceeds a threshold. To test the impact of these singular valves on the air invasion, we build a simulation based on the electrokinetic analogy. Taking in account the elasticity of the channel, each conduct becomes a hydraulic resistance coupled with a capacity. We show that we can reproduce the stop and go propagation in a variety of different network architectures. [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V35.00011: Space Weather Research in the Equatorial Region: A Philosophical Reinforcement Victor Chukwuma, Rasaki Odunaike, John Laoye Investigations using radio waves reflected from the ionosphere, at high-and mid-latitudes indicate that ionospheric absorption can strongly increase following geomagnetic storms; which appears to suggest some definite relationship between ionospheric radio wave absorption and geomagnetic storms at these latitudes. However, corresponding earlier studies in the equatorial region did not appear to show any explicit relationship between ionospheric radio wave absorption and geomagnetic storm activity. This position appeared acceptable to the existing scientific paradigm, until in an act of paradigm shift, by a change of storm selection criteria, some more recent space weather investigations in the low latitudes showed that ionospheric radio wave absorption in the equatorial region clearly increases after intense storms. Given that these results in the equatorial region stood against the earlier results, this paper presently attempts to highlight their philosophical underpinning and posit that they constitute a scientific statement. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V35.00012: Paperfuge: An ultralow-cost, hand-powered paper-centrifuge inspired by the mechanics of a whirligig toy M. Saad Bhamla, Brandon Benson, Chew Chai, Georgios Katsikis, Aanchal Johri, Manu Prakash From a global-health context, commercial centrifuges are expensive, bulky and electricity-powered, and thus constitute a critical bottleneck in the development of decentralized, battery-free-point-of-care (POC) diagnostic devices. Here, we report an ultralow-cost (20 cents), lightweight (2 g), human-powered paper centrifuge (which we name 'paperfuge') designed on the basis of a theoretical model inspired by the fundamental mechanics of an ancient whirligig (or buzzer toy; 3300 B.C.E). The paperfuge achieves speeds of 125,000 rpm (and equivalent centrifugal forces of 30,000 g), with theoretical limits predicting one million rpm. We demonstrate that the paperfuge can separate pure plasma from whole blood in less than 1.5 minutes, and isolate malaria parasites in 15 minutes. We also show that paperfuge-like centrifugal microfluidic devices can be made of polymethylsiloxane, plastic and 3D-printed polymeric materials. Ultracheap, power-free centrifuges should open up opportunities for POC diagnostics in resource-poor settings. [Preview Abstract] |
Thursday, March 16, 2017 4:54PM - 5:06PM |
V35.00013: Abstract Withdrawn |
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