Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session G34: Flow Instability: Kelvin-Helmholtz |
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Chair: Jacob A. McFarland, University of Missouri Room: 616 |
Sunday, November 24, 2019 3:48PM - 4:01PM |
G34.00001: Velocity Measurements and Phase Tracking in a Shock-Driven Multiphase Instability Vasco O. Duke Walker, John Middlebrooks, Roy Allen, William Maxon, Almuhna Sahir, Samra Karabegovic, Jacob A. McFarland An experimental investigation has been performed to study physical phenomena induced by the impulsive acceleration of a heterogeneously seeded multiphase flow-field within a shock tube system. In order to achieve this, a cylindrical interface comprising of nitrogen, seeded with micron-sized acetone droplets, was generated within the shock tube's test section and accelerated by a planar shock wave. The nitrogen gas itself was saturated with acetone vapor tracer and mixed into the interface to prevent premature droplet evaporation. The development of both the dispersed and carrier phases was captured through a series of Planar Laser Mie Scattering (PLMS) and Planar Laser Induced Fluorescence (PLIF) images, respectively. In addition, lag effects between the phases were visualized and quantified. The results were compared to simulations for validation. This experimental investigation has a multitude of applications in a variety of scientific and engineering systems; with a particular relevance to systems that involve high-speed or shock-induced multiphase combustion. [Preview Abstract] |
Sunday, November 24, 2019 4:01PM - 4:14PM |
G34.00002: Liquid film dryout in vertical two-phase annular flow in a rectangular channel Roman Morse, Tiago Moreira, Kristofer Dressler, Gherhardt Ribatski, Louise Mccarrol, Evan Hurlburt, Gregory Nellis, Arganthaël Berson The entire liquid-film dryout~process~in~a~vertical two-phase annular flow~is~characterized experimentally, from inception to completion.~This study presents experiments conducted using saturated R245fa at high vapor qualities (0.84 to 0.99) in a rectangular channel with a hydraulic diameter of 18 mm with aspect ratio of 1/3. The walls of the test section are~made of~glass coated with Fluorine-doped Tin Oxide (FTO). Heat fluxes up to 30 kW/m$^{\mathrm{2}}$~are generated at the inner surface of the window by passing an electrical current through the FTO coating. Instantaneous pressure and temperature in the test section, temperature on the outer wall of the test section, and high-speed videos were recorded simultaneously during the dryout~event. In addition, the state (wet or dry) of the heated surface was measured using thermoreflectance~as a function of time. During the inception of dryout, dry patches on the heated surface may rewet intermittently. The ability of the surface to rewet near dryout is studied under steady state and pulsatile conditions. [Preview Abstract] |
Sunday, November 24, 2019 4:14PM - 4:27PM |
G34.00003: Backflow at liquid-gas interface driven by Marangoni effects Hongyuan Li, Pengyu Lv, Huiling Duan Liquid-gas interface on submerged structured surfaces is ubiquitous in nature and has various practical applications. These interfaces, however, are subject to non-uniform surface tension induced by surfactant concentration gradient. Careful PIV experiments with surfactant-laden fluorescent particle solutions show that even trace of surfactants have significantly decrease on slip velocity than numerical predictions for surfactant-free flow, and even can produce negative slip velocity (i.e., backflow). We present the mechanism of backflow, which is induced by surfactant concentration gradient. Meanwhile, we investigate the characteristics of backflow. This work is expected to be essential for the design of slippery surfaces and microfluidic devices that are unaffected by Marangoni stress, and it can provide guidance for correcting PIV measurements, especially for the case of liquid-gas interface. [Preview Abstract] |
Sunday, November 24, 2019 4:27PM - 4:40PM |
G34.00004: Interfacial structure of upward gas-liquid annular flow in an inclined pipe Adam Fershtman, Lulkas Robers, Horst-Michael Prasser, Dvora Barnea, Lev Shemer In this study, the instantaneous circumferential distribution of the liquid film thickness is examined in upward annular flow of various pipe inclinations. The temporal variation of the film thickness was measured simultaneously across the entire pipe circumference using a multi-range conductance sensor covering about 7 cm in the axial direction. The recording of the temporal and spatial distribution of the film thickness allows investigation of characteristic interfacial wave parameters such as mean film thickness, frequency, wave height distribution, wave propagation velocities, wave length, and more. The interfacial waves observed across the pipe periphery vary with pipe inclination angle, liquid flow rate and circumference position. These waves were categorized as ripples, disturbance waves or rogue waves, based on parameters as frequency, wave height and exceedance. The distribution and the total mass transported by the shear driven waves is also examined. For a low liquid flow rate, a transition from stratified wavy to annular flow was documented with increase in pipe inclination. This data is crucial for better understanding and modeling of evolution of annular and stratified flow regimes as a function of gas and liquid flow rates and pipe inclination. [Preview Abstract] |
(Author Not Attending)
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G34.00005: Liquid-liquid phase separation in sessile drops induced by evaporation. Hosein Sadafi, Ramin Rabbani, Sam Dehaeck, Hatim Machrafi, Benoit Haut, Pierre Dauby, Pierre Colinet The interplay between two phase change mechanisms of evaporation and liquid-liquid phase separation (demixing) in binary sessile drops of partially miscible liquids is investigated. To determine the onset of the demixing phenomenon, a simple model is developed, which predicts a considerable temperature reduction in the mixture due to evaporative cooling. Temperature reduction alongside with the change of composition lead to demixing in the mixtures. Five stages of the process are identified and explained. For the cases studied here, once the demixing begins through nucleation, a growing fingering pattern is formed at the contact line. The length of the fingers is a function of the initial concentration of the low volatile component. Moreover, the final area of deposition increases with the initial concentration. Experimental tests were performed using a double telecentric setup. [Preview Abstract] |
Sunday, November 24, 2019 4:53PM - 5:06PM |
G34.00006: Turbulent Faraday instabilities at the interface between miscible fluids Louis Gostiaux, Antoine Briard, Benoît-Joseph Gréa We studied turbulent mixing between two miscible fluids of different densities occuring when the stable interface between the denser and lighter fluids is periodically accelerated. Vertical oscillations trigger the well known Faraday instability, that degenerates into turbulence in the case of a miscible interface. Very few studies have been dedicated to the thickening and saturation of this turbulent mixing zone, and to the associated mass transfers. We realized a large set of idealized experiments in a large container (72x12x90cm), where a two layer system of fresh and salty water was subject to sinusoidal vertical oscillations. Motion was controlled by an hexapod providing vertical accelerations up to 0.7g. We could predict, for a given Atwood number and forcing parameters, the saturated asymptotic state of the turbulent mixed layer between the two fluids. This process can be used to obtain a well-controlled turbulent interface, which constitutes an interesting initial condition for potential industrial applications. Direct numerical simulations and theoretical developments complete this study. [Preview Abstract] |
Sunday, November 24, 2019 5:06PM - 5:19PM |
G34.00007: Two-phase flow instability at a~channel outlet Paul R. Kaneelil, Amir A. Pahlavan, Kenalpha Kipyegon, Kristen LeRoy, Kylie Stengel, Samuel Warner, Anna M. Galea, Howard A. Stone Parallel flow of two immiscible liquids in a microfluidic channel has~a variety of applications including solvent extraction, membrane fabrication, chemical processing, and biomedical design.~Here, we investigate a system where two immiscible liquids~with the same viscosity~enter a channel via two inlets, come into contact and form an interface as they flow side-by-side, and~subsequently~exit the channel via two outlets.~We observe an instability at the~exit junction,~where the interface periodically oscillates and leads to droplet shedding. By systematically exploring the influence of geometric features and fluid flow on the instability, we characterize the underlying mechanism of the instability and offer pathways to control and suppress it. [Preview Abstract] |
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