Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session D3: Multiphase Flows II |
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Chair: John R. Saylor, Clemson University Room: 325 |
Sunday, November 24, 2013 2:15PM - 2:28PM |
D3.00001: Surface wetting effects on drop passage through a confining orifice Ankur Bordoloi, Ellen Longmire The motion of gravity-driven drops (Bo $\sim$ 2-10) through a sharp-edged confining orifice is studied in a liquid/liquid system for both hydrophobic (HPB) and hydrophilic (HPL) orifice surfaces. The drop interface is tracked by high-speed imaging, and fluid velocity fields are obtained by PIV. When a drop impacts the leading edge of the orifice, the drop fluid contacts the solid surface immediately, and the resulting interfacial contact lines begin propagating away from the edge. The final drop outcome (capture, release or break-up) is influenced by the motion of the contact lines as well as the contact force between the drop fluid and the orifice surface. In the HPB case, the contact line motion is limited, and the contact force acting against drop passage is weak. In the HPL case, the contact line motion strongly inhibits drop passage by spreading fluid across the upper surface of the orifice plate. For drops that break into multiple volumes, the wettability influences both the break-up location and fractional volume of the resulting satellite drop. [Preview Abstract] |
Sunday, November 24, 2013 2:28PM - 2:41PM |
D3.00002: Simulations of Three-dimensional Droplet Deformation in a Square-Duct at Moderate Reynolds numbers Jeremy Horwitz, Purushotam Kumar, Pratap Vanka We present results of numerical simulations of deformation of a confined droplet in a three-dimensional square-duct flow using a multiphase Lattice Boltzmann Method. We have studied the effects of capillary number, Reynolds number, and viscosity ratio on the droplet deformation characteristics. Unlike in the Stokes' limit where deformation is governed by a competition between viscous shear and interfacial tension, at higher Reynolds numbers, inertial effects play an increasingly important role. We observe that the deformation history is non-monotonic and contains an overshoot before relaxing to a steady deformed state. In contrast, the capillary number is seen to affect the magnitude of the deformation history and the time at which the peak deformation occurs. The viscosity ratio has a relatively modest effect on the magnitude of the deformation compared with the effects of Reynolds and capillary numbers. However, compared with the Reynolds number, the viscosity ratio and capillary number have a significant effect on the time to reach a steady state. [Preview Abstract] |
Sunday, November 24, 2013 2:41PM - 2:54PM |
D3.00003: A Three-dimensional Numerical Study of Immiscible Droplet Deformation in a right angle bend Purushotam Kumar, Jeremy Horwitz, Surya Vanka We present a numerical study of deformation of an immiscible droplet in a right angle bend. We have used volume-of-fluid method to track the interface and variable density Navier-Stokes equations to solve for the flow field. A second-order accurate fractional step algorithm is used to integrate the equations. The VOF is also coupled to a level-set method to get a smoothed interface shape for surface tension calculations. We study the effects of density and viscosity ratios (between droplet and carrier fluids), Reynolds number, Capillary number and aspect ratio between droplet and duct size on the deformation characteristics. We investigate the elongation of the droplet in axial direction and the stretching or contraction of the droplet in the lateral direction. Depending on the value of above mentioned parameters droplet can take different shapes, namely, spherical, bullet and parachute. At moderately higher Reynolds numbers we also observe satellite droplet breaking from the original droplet. [Preview Abstract] |
Sunday, November 24, 2013 2:54PM - 3:07PM |
D3.00004: Breakup of an oil slick mixed with dispersants by breaking wave Cheng Li, Anne Holser, Joseph Katz After oil spill, coherent oil slick are entrained by breaking ocean waves together with air, which produces a complicated three-phase flow, involving a wide range of length and time scales. The oil droplet size distribution is a crucial factor affecting the physical and chemical dispersion of oil spills, but little is known about oil droplet formation mechanism and droplet size distributions during and immediately after the impact of breaking waves. In our experimental study, we investigate the breakup of an oil slick in a specialized wave tank. The widely used dispersant Coexist 9500-A at different dispersant to oil ratio is used for varying the surface tension of crude oil (MC252 surrogate) in the 10$^{\mathrm{-1\thinspace }}$to$^{\mathrm{\thinspace }}$10 mN/m range. The dispersant is applied either by premixing or surface spraying, the latter consistent with typical application. The results include high-speed images of the oil and bubbles' entrainment, showing the resulting formation of a series of droplet clouds during multiple ``plunges'' associated with a single propagating breaking wave. High-speed inline digital holographic cinematography is employed to quantify the oil droplet size distribution, and the impact of droplet-bubble interactions on the entrainment process for varying Weber numbers, and wave properties, from spilling to plunging breakers. [Preview Abstract] |
Sunday, November 24, 2013 3:07PM - 3:20PM |
D3.00005: Inkjet Printer Drop Impact on Coated and Uncoated Papers Saman Hosseini, Rafael Orsi Koga, Nasser Ashgriz, Sanjeev Chandra The impact of ink drops generated by a solid ink inkjet printer on coated and uncoated papers were investigated. Ink drops are different impact velocities and different initial temperatures were tested. A Xerox solid ink inkjet is used in this study. In this printer, the solid ink is heated to temperatures of about 90C and then ejected out of the printed. The ink drop solidifies as soon as it impact on the paper. Small, about 39 micron droplets were impacted on a paper positioned 0.5 mm from the print head. SEM images of individual drops were obtained and analyzes to determine the droplet spread diameter, droplet height, and droplet contact angles. In addition, the texture and shape of the drops were categorized according to the impact parameters. There is a substantial difference between the droplet impact results for coated versus uncoated papers. In addition, the temperature of the substrate at the time of impact made a significant difference, since small drops cool very fast and they do not attach properly to the paper at room temperatures. [Preview Abstract] |
Sunday, November 24, 2013 3:20PM - 3:33PM |
D3.00006: Tribonucleation of bubbles Sander Wildeman, Henri Lhuissier, Chao Sun, Andrea Prosperetti, Detlef Lohse We report on the nucleation of bubbles on solids that are gently rubbed against each other while immersed in a gas-supersaturated liquid. For given supersaturation and surface material, bubble nucleation is only observed beyond a certain threshold for the rubbing force and velocity. Above this threshold, a regularly spaced row of growing bubbles is left behind on the surface. Direct observation through the bottom of a transparent solid shows that each bubble in the row results from the early coalescence of several microscopic bubbles. From a detailed study of the wear tracks it seems that these gas nuclei originate from a local fracturing of the surface asperities in the contact area. [Preview Abstract] |
Sunday, November 24, 2013 3:33PM - 3:46PM |
D3.00007: Stability analysis applied to the early stages of viscous drop breakup by a high-speed gas stream Juan C. Padrino, Ellen K. Longmire The instability of a liquid drop suddenly exposed to a high-speed gas stream behind a shock wave is studied by considering the gas-liquid motion at the drop interface. The discontinuous velocity profile given by the uniform, parallel flow of an inviscid, compressible gas over a viscous liquid is considered, and drop acceleration is included. Our analysis considers compressibility effects not only in the base flow, but also in the equations of motion for the perturbations. Recently published high-resolution images of the process of drop breakup by a passing shock have provided experimental evidence supporting the idea that a critical gas dynamic pressure can be found above which drop piercing by the growth of acceleration-driven instabilities gives way to drop breakup by liquid entrainment resulting from the gas shearing action. For a set of experimental runs from the literature, results show that, for shock Mach numbers $\geq$ 2, a band of rapidly growing waves forms in the region well upstream of the drop's equator at the location where the base flow passes from subsonic to supersonic, in agreement with experimental images. Also, the maximum growth rate can be used to predict the transition of the breakup mode from Rayleigh-Taylor piercing to shear-induced entrainment. [Preview Abstract] |
Sunday, November 24, 2013 3:46PM - 3:59PM |
D3.00008: Break-up of droplets in a concentrated emulsion flowing through a narrow constriction Sindy Tang, Lin Fan, Yunhan Chen, Liat Rosenfeld We describe the break-up of droplets in a concentrated emulsion during its flow as a 2D monolayer in a microchannel consisting of a narrow constriction. Analysis of the behavior of over 4000 drops shows that the number of break-ups increases with increasing flow rate, entrance angle to the constriction, and size of the drops. As single drops do not break at the highest flow used, break-ups arise primarily from droplet-droplet interactions. Droplet-droplet interactions are stochastic; they cause fluctuations in the local strain rate and deformation each drop experiences. Analysis of droplet properties at a temporal resolution of 10 microseconds makes it possible to relate drop deformation with break-up probability. Similar to previous studies on single drops, no break-up is observed below certain critical flow rates and droplet deformations. Unlike previous studies, however, not all drops break above the critical values. Instead, the probability of break-up increases with flow rate and the local deformation of the drops. [Preview Abstract] |
Sunday, November 24, 2013 3:59PM - 4:12PM |
D3.00009: Droplet impact on falling liquid films Omar Matar, Zhizhao Che, Ivan Zadrazil, Geoffrey Hewitt, Christos Markides Droplet impact is a ubiquitous phenomenon in nature, and has a wide range of applications; these include inkjet printing, spray painting, and surface cleaning. In this study, we examine the impact of droplets on falling liquid films, which is an event that occurs in various two-phase flows, such as annular flows and spray cooling. High-speed photography is used to visualise droplet impact, and associated phenomena, on a uniform falling liquid film, which is created on a flat substrate with controllable thickness and flow speed. Different phenomena are observed and analysed for droplet impact at different impact speeds, angles, and film thicknesses and flow speeds. The results of the present work are part of a programme to elucidate the complex dynamics of multiphase flows and to develop validated numerical tools for accurate predictions. [Preview Abstract] |
Sunday, November 24, 2013 4:12PM - 4:25PM |
D3.00010: Theoretical and numerical investigation of turbulence/interface interactions due to surface tension effects Jeremy McCaslin, Chian Yeh Goh, Olivier Desjardins The interaction between turbulence and an interface subjected to surface tension is studied by inserting an interface into a triply periodic box of decaying homogeneous isotropic turbulence, simulated with a volume-of-fluid scheme on a mesh of size $512^3$. Unity density and viscosity ratios are used in order to isolate the interaction between turbulent eddies and the surface tension force. Interfacial height correlations are used to study the spatial scales of corrugations on the interface. At a Taylor-microscale Reynolds number of ${\rm Re}_\lambda=146$, a case with zero surface tension is first considered, yielding a passive interface that moves materially with the fluid. Simulation results confirm a theoretically predicted universal $\kappa^{-2}$ scaling of the corrugation power spectral density, where $\kappa$ is the wavenumber. In the presence of surface tension, the corrugation spectrum follows the $\kappa^{-2}$ law for large scales, but then deviates towards a $\kappa^{-11/3}$ scaling once inertia becomes balanced by surface tension. Coupling between the interface and surrounding fluid modulates the turbulent flow, and a transfer of turbulent kinetic energy from low to high wavenumbers is observed in the energy spectrum. [Preview Abstract] |
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