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 L28: General Fluid Dynamics |
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Chair: Richard McLaughlin, University of North Carolina at Chapel Hill Room: Georgia World Congress Center B316 |
Monday, November 19, 2018 4:05PM - 4:18PM |
L28.00001: The Hydrodynamics of High Diving Caroline Cohen, Thibault Guillet, Mélanie Mouchet, Sarah Fay, David Quéré, Per Lundstam, Anette E. Hosoi, Christophe Clanet Diving is the sport of jumping or falling into water from a platform, usually while performing acrobatics. For high diving competitions the initial height is 27 meters. From this height, the entry in water occurs at 85 km/h and is very technical to avoid injuries. The first major risk comes out of the violent impact at the air/water interface and the formation and collapse of the air cavity around the diver, if its body is not perfectly vertical and stiffened. The other issue among diver, underlined by David Colturi, a top level RedBull Cliff Diver, is the injury of adductor muscles due to the spreading of legs underwater, and which limits the number of dives a jumper is able to perform per competition day. In this study, we investigate experimentally the dynamics of the jumper underwater and the hydrodynamics causes of injuries in high diving, both in the field by monitoring several dives of David Colturi during his training and in simplified laboratory experiments in order to understand the underlying physics. |
Monday, November 19, 2018 4:18PM - 4:31PM |
L28.00002: Investigation of Drug Mixing Profile in the Eye Jinglin Huang, Morteza Gharib Age-related macular degeneration (AMD) is the leading cause of central vision loss in the developed world. In the case of wet AMD, it can be managed through serial intravitreal injections of anti-vascular endothelial growth factor (anti-VEGF) agents. However, sometimes the treatment is ineffective. Given that half-life time of the drug is limited, one possible cause of the ineffective treatment is inefficient drug mixing in the eye. Here, we focus on the understanding of drug mixing in vitreous chamber and parameters that could potentially influence mixing profiles. The study outcomes will not only be useful for achieving fundamental understandings of fluid dynamics in the eye, but also helpful in developing better strategy for intravitreal injection and improving the quality of care for patients. |
Monday, November 19, 2018 4:31PM - 4:44PM |
L28.00003: Towards control of liquid-layer deposition over topography in additive manufacturing Andrei Kozhevnikov, Rudie Kunnen, Gregor van Baars, Herman Clercx A well known additive manufacturing technique, stereolithography, uses a liquid photopolymer selectively solidified by a UV laser. Mechanical properties of the final product as well as dimensional accuracy depend significantly on the quality of the liquid-layer deposition leading up to the irradiation step. Since the building geometry can vary in the direction of recoater movement, the deposition of liquid resin onto the surface of a previously cured layer is not a trivial issue. This study focuses on the understanding how the underlying geometry influences free-surface deformation during the liquid layer application. For this purpose, CFD simulations are used which allow to account for surface tension together with moving objects over varying topography. The problem is modeled assuming a 2D configuration, and the used range of parameters (such as recoater speed and spatial dimensions of topography and recoating system) cover most of the typical values used in modern apparatuses. The results are compared with experiments. We want to use our understanding of the liquid-layer deformation as a function of topography to develop a control system for uniform layer deposition. |
Monday, November 19, 2018 4:44PM - 4:57PM |
L28.00004: Compressible Lubrication Flows in Non-Concentric Cylinders at Supercritical Pressures Ssu-Ying Chien, M.S. Cramer We employ an analytical approach to approximate the load and loss generated by high speed lubrication flows of pressurized gases between non-concentric cylinders. The flows are taken to be two-dimensional, steady, laminar, compressible and single-phase. While the load and loss for ideal gases are functions of eccentricity only, these global parameters are found to also depend on the density dependence of the bulk modulus and shear viscosity when the pressures and temperatures are on the order of those at the thermodynamic critical point. When the speed number is large, we find that the load will increase and the loss will decrease with pressurization. |
Monday, November 19, 2018 4:57PM - 5:10PM |
L28.00005: Analysis of micro-fluidic tweezers in the Stokes regime Longhua Zhao, Li Zhang, Yang Ding Nanowire fluidic tweezers have been developed to gently and accurately capture, manipulate, and deliver micro objects. The mechanism behind the capture and release process has not yet been well explained. Utilizing the method of regularized Stokeslet, we study a cylindrical nanowire tumbling and interacting with spherical particles in the Stokes regime. The capture phenomenon observed in experiments is reproduced and illustrated with the trajectories of micro-spheres and fluid tracers. The flow structure and the region of capture are quantitatively examined and compared for different sizes of particles, various tumbling rates, and dimensions of the tweezers. We find that pure kinematic effects can explain the mechanism of capture and transport of particles. We further reveal the relation between the capture region and stagnation points in the displacement field, i.e., the displacement for tracer particles in the moving frame within one rotation of the wire. |
Monday, November 19, 2018 5:10PM - 5:23PM |
L28.00006: Viscous flow and lubrication theory in slowly-varying channels Elena Luca, Stefan Llewellyn Smith Understanding the flow through non-uniform channels remains a major technological goal. Lubrication theory is a well-known approach to analyzing such flows. In a recent study, Tavakol, Froehlicher, Holmes & Stone (2018) considered pressure-driven viscous flows in channels with both smooth and sharp changes using extended lubrication theory to analyze the problems. They proposed an approximation up to O(δ4), with δ being the height-to-length ratio, to surpass the limitations of standard lubrication theory. The aim of our study is to extend the lubrication theory model by generating terms of much higher orders and to understand the behavior of the flow in this limit. We examine a Domb-Sykes plot for piecewise affine channels. Discontinuities in channel slope lead to matching regions that transition between lubrication theory away from the locations of discontinuity. |
Monday, November 19, 2018 5:23PM - 5:36PM |
L28.00007: Diffusion of Passive Tracers Advected by Laminar Shear Flow in Triangular Capillary Pipes Francesca Bernardi, Roberto Camassa, Gabrielle M Hobson, Richard M McLaughlin We investigate the dispersion of a passive tracer in laminar shear flow through triangular capillary pipes. We show through simulation and experiments how the longitudinal asymmetry of the tracer distribution changes in time. We observe a change in the longitudinal concentration profile from back-loaded to front-loaded, corresponding to a sign-change in the (cross-sectionally averaged) skewness. Future directions will be discussed. |
Monday, November 19, 2018 5:36PM - 5:49PM |
L28.00008: Watercolor painting: Pigment pattern formation in drying aqueous droplets Jorge Gonzalez-Gutierrez, Evanimar Martinez, Octavio Moctezuma, Roberto Zenit Watercolor paintings have been used by humans throughout history to capture our perception of the natural world. From early men to modern artists, this painting technique has not changed significantly. It uses pigments, initially suspended in an aqueous solution, which is placed on a wet or dry surface, commonly paper. After the evaporation of the solvent, fascinating textures, which form part of the artwork, emerge. In this investigation, we used fluid mechanics to understand the complex mechanisms behind the watercolor paintings materialization. By conducting experiments, we scrutinize the effect of the pigment concentration, paper humidity, and ethanol content on the formation of the patterns derived from evaporation of droplets. We observe that the patterns evolve as pigment concentration increases, changing from coffee-ring-type to quasi-uniform stains. However, when the paper humidity and ethanol concentrations are also changed, the deposition process of pigments is altered, leading to a wide variety of patterns in the deposit. We discuss the complex flow mechanisms within the drying drop, such as percolation, aggregation and Marangoni processes, that are behind the pattern formation. |
Monday, November 19, 2018 5:49PM - 6:02PM |
L28.00009: Surface-Tension- and Injection-Driven Thin-Film Flow Kristian Kiradjiev, Chris Breward, Ian Griffiths Gore’s GMCS filter removes sulphur dioxide from flue gases by passing the gas through a |
Monday, November 19, 2018 6:02PM - 6:15PM |
L28.00010: The role of surface morphology in aerodynamics of biomimetic fog harvesting Aida Shahrokhian, Jiansheng Feng, Hunter King Harvesting water by intercepting atmospheric fog is a proven solution in certain regions where surface water is scarce. The strategy of fog harvesting in Stenocara, the Namib desert beetle with bumpy elytra, is repeatedly explained in a narrative involving hydrophilic bumps and hydrophobic valleys that modify the transport of the accumulated water. While transport can be crucial in some cases, the potentially dominant role of the bumps as aerodynamic features that change the boundary layer and subsequent impaction rate of droplets has not yet been studied. In this study, we investigate the influence of surface morphology on the dynamics of droplet impaction and explore non-trivial geometries for potential enhanced performance. For this purpose, a custom, low speed table-top wind tunnel with fog inlet was implemented to measure the initial accumulation rate on targets with various surface morphologies, before coalescence and surface transport. Results show an approximately threefold increase in impaction rate of microdroplets with the addition of bumps in a beetle-like geometry. We hypothesize that the bumpy adaptation, where present in fog basking beetles, was driven by their aerodynamic role in accumulation, rather than their role in wetting properties and surface transport. |
Monday, November 19, 2018 6:15PM - 6:28PM |
L28.00011: Dynamics of thin liquid films on vertical cylindrical fibers Claudia Falcon, Hangjie Ji, Abolfazl Sadeghpour, Zezhi Zeng, Y.Sungtaek Ju, Andrea L Bertozzi Recent experiments of thin films flowing down a vertical fiber with varying nozzle diameters present a wealth of new dynamics that illustrate the need for more advanced theory. We present a detailed analysis for a full lubrication model that includes slip boundary conditions, nonlinear curvature terms, and generalized van der Waals physics. This study brings to focus the presence of a stable liquid substrate playing an important role in the full dynamics. We propose a combination of these physical effects to explain the observed velocity and stability of traveling droplets in the experiments and their transition to isolated droplet. This is also supported by stability analysis of the traveling wave solution of the model. |
Monday, November 19, 2018 6:28PM - 6:41PM |
L28.00012: The physics of tossing fried rice Hungtang Ko, David L Hu Fried rice is a 1500-year-old dish that is savored in both fine restaurants and as a street food. One of the secrets to cooking fried rice is the wok-tossing, the rapid motion of the wok to allow the food to be cooked at temperatures of up to 1200 degrees Celsius. In this experimental study, we report the wok-tossing kinematics of two Taiwanese restaurant chefs. The high-speed tossing motion occurs in 0.3 seconds and involves four independent stages, whose translation and rotation allows the wok's rounded sides to act like a ski-jump for the fried rice. We discuss how the wok motion mixes and cools the rice to facilitate even cooking. |
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