Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session L38: Flow Instability: Jets, Drops, and Bubbles |
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Chair: Mickael Bourgoin, LEGI/CNRS Room: Portland Ballroom 255 |
Monday, November 21, 2016 4:30PM - 4:43PM |
L38.00001: Numerical study of three-dimensional liquid jet breakup with adaptive unstructured meshes Zhihua Xie, Dimitrios Pavlidis, Pablo Salinas, Christopher Pain, Omar Matar Liquid jet breakup is an important fundamental multiphase flow, often found in many industrial engineering applications. The breakup process is very complex, involving jets, liquid films, ligaments, and small droplets, featuring tremendous complexity in interfacial topology and a large range of spatial scales. The objective of this study is to investigate the fluid dynamics of three-dimensional liquid jet breakup problems, such as liquid jet primary breakup and gas-sheared liquid jet breakup. An adaptive unstructured mesh modelling framework is employed here, which can modify and adapt unstructured meshes to optimally represent the underlying physics of multiphase problems and reduce computational effort without sacrificing accuracy. The numerical framework consists of a mixed control volume and finite element formulation, a ‘volume of fluid’ type method for the interface capturing based on a compressive control volume advection method and second-order finite element methods, and a force-balanced algorithm for the surface tension implementation. Numerical examples of some benchmark tests and the dynamics of liquid jet breakup with and without ambient gas are presented to demonstrate the capability of this method. [Preview Abstract] |
Monday, November 21, 2016 4:43PM - 4:56PM |
L38.00002: Bubble Impact with a Solid Wall Vishrut Garg, Sumeet Thete, Osman Basaran In diverse natural and industrial processes, and in particular in process equipment widely used in oil and gas production, bubbles and drops that are immersed in a continuous liquid phase frequently collide with solid walls. In this talk, the impact with a solid wall of a gas bubble that is surrounded by a liquid that is either a Newtonian or a non-Newtonian fluid is analyzed by numerical simulation. Special attention is paid to the thin film that forms between the approaching bubble and the solid wall. Flow regimes that arise as the film thickness decreases are scrutinized and rationalized by comparison of the computational predictions to well-known and new analytical results from lubrication theory based thin film literature. Finally, flow transitions that occur as the lubrication theory breaks down and inertia becomes significant are investigated. [Preview Abstract] |
Monday, November 21, 2016 4:56PM - 5:09PM |
L38.00003: Explicit demonstration of the role of Marangoni effect in the breakup of nanoscale liquid filaments Ivana Seric, Kyle Mahady, Shahriar Afkhami, Chris Hartnett, Jason Fowlkes, Philip Rack, Lou Kondic We consider a breakup of bi-metal filaments deposited on a solid substrate. These filaments are exposed to laser irradiation and, while in the liquid phase, evolve by a process resembling breakup of a liquid jet governed by the Rayleigh-Plateau instability. The novel element is that the Marangoni effect, resulting from a different surface tension of the two metals from which the filament is built, is crucial in understanding the instability development. In particular, Marangoni effect may lead to the inversion of the breakup process, producing droplets at the locations where according to the Rayleigh-Plateau theory dry spots would be expected. We present experimental results carried out with Cu-Ni filaments, as well as direct numerical simulations based on a novel algorithm that includes variable surface tension in a Volume-of-Fluid based Navier-Stokes solver. These results suggest the possibility of using Marangoni effect for the purpose of self- and directed-assembly on the nanoscale. [Preview Abstract] |
Monday, November 21, 2016 5:09PM - 5:22PM |
L38.00004: Three dimensional direct numerical simulation of complex jet flows Seungwon Shin, Lyes Kahouadji, Damir Juric, Jalel Chergui, Richard Craster, Omar Matar We present three-dimensional simulations of two types of very challenging jet flow configurations. The first consists of a liquid jet surrounded by a faster coaxial air flow and the second consists of a global rotational motion. These computations require a high spatial resolution and are performed with a newly developed high performance parallel code, called BLUE, for the simulation of two-phase, multi-physics and multi-scale incompressible flows, tested on up to 131072 threads with excellent scalability performance. The method for the treatment of the fluid interfaces uses a hybrid Front Tracking/Level Set technique that defines the interface both by a discontinuous density field as well as by a local triangular Lagrangian mesh. Coriolis forces are taken into account and solved via an exact time-integration method that ensures numerical accuracy and stability. [Preview Abstract] |
Monday, November 21, 2016 5:22PM - 5:35PM |
L38.00005: Numerical simulations of vibrating sessile drop Lyes Kahouadji, Jalel Chergui, Damir Juric, Seungwon Shin, Richard Craster, Omar Matar A vibrated drop constitutes a very rich physical system, blending both interfacial and volume phenomena. A remarkable experimental study was performed by M. Costalonga (PhD. Université Paris Diderot, 2015) highlighting sessile drop motion subject to horizontal, vertical and oblique vibration. Several intriguing phenomena are observed such as drop walking and rapid droplet ejection. We perform three-dimensional direct numerical simulations of vibrating sessile drops where the phenomena described above are computed using the massively parallel multiphase code BLUE. [Preview Abstract] |
Monday, November 21, 2016 5:35PM - 5:48PM |
L38.00006: Structure build-up and evolution in the drying of sessile blood droplets Richard Craster, Aran Uppal, Omar Matar Experimental observations have recorded blood undergoing a sol-gel transition during the evaporation process. Consequently, the rheology becomes non-uniform throughout the droplet and exhibits transitional complex phenomena that we must capture if we wish to accurately model the evaporative/cracking process. We propose a model where thixotropy is introduced to capture the evolving rheology as evaporation occurs. Thixotropy is often used to describe fluids which exhibit a decrease in viscosity due to flow and subsequent slow recovery of viscosity after the cessation of the flow. We introduce an additional parameter to describe the internal structure of the fluid at each point and consider a droplet in the limit of the lubrication approximation. We present a discussion of our results that demonstrates the dependence of structure build-up, which accompanies the spatio-temporal evolution of the drop, on system parameters. [Preview Abstract] |
Monday, November 21, 2016 5:48PM - 6:01PM |
L38.00007: Formation of surfactant-laden drops: comparison of experimental and numerical results Nina Kovalchuk, Lyes Kahouadji, Mark Simmons, Richard Craster, Omar Matar, Damir Juric, Jalel Chergui, Seungwon Shin Drop formation is ubiquitous in many industrial processes, with surfactants being commonly used to stabilise drops. Thus, understanding the regularities of drop formation and accompanying processes, such as formation of satellite droplets in the presence of surfactant is of high importance. Here we present the results of a comparative experimental and numerical study on formation of surfactant-laden drops over a range of flow rates and surfactant concentrations. The precise parameters of the surface tension isotherm for surfactants used in the experimental study are implemented in the numerical code enabling quantitative comparison between the two approaches. It is shown that the effect of surfactant depends not only on concentration, but also on the value of critical micellar concentration (cmc). The transition to the regime where satellite droplets are no longer released was observed when the flow rate exceeded a threshold value depending on surfactant concentration and cmc value. [Preview Abstract] |
Monday, November 21, 2016 6:01PM - 6:14PM |
L38.00008: Three-dimensional simulations of thin ferro-fluid films and drops in magnetic fields Devin Conroy, Alex Wray, Omar Matar We consider the interfacial dynamics of a thin, ferrofluidic film flowing down an inclined substrate, under the action of a magnetic field, bounded above by an inviscid gas. The fluid is assumed to be weakly-conducting. Its dynamics are governed by a coupled system of the steady Maxwell’s, the Navier-Stokes, and continuity equations. The magnetisation of the film is a function of the magnetic field, and is prescribed by a Langevin function. We make use of a long-wave reduction in order to solve for the dynamics of the pressure, velocity, and magnetic fields inside the film. The potential in the gas phase is solved with the use of Fourier Transforms. Imposition of appropriate interfacial conditions allows for the construction of an evolution equation for the interfacial shape, via use of the kinematic condition, and the magnetic field. We consider the three-dimensional evolution of the film to spawise perturbations by solving the non-linear equations numerically. The constant flux configuration is considered, which corresponds to a thin film and drop flowing down an incline, and a parametric study is performed to understand the effect of a magnetic field on the stability and structure of the formed drops. [Preview Abstract] |
Monday, November 21, 2016 6:14PM - 6:27PM |
L38.00009: Evolution of the dynamic Rayleigh-Plateau instability on liquid jets Fabian Denner, Fabien Evrard, Berend van Wachem, Alfonso Arturo Castrejon-Pita, Jose Rafael Castrejon-Pita The Rayleigh-Plateau instability (RPI) is the dominating mechanism leading to the breakup of surface-tension-dominated liquid jets. Although linear stability analysis has proven to be a powerful tool to study the evolution of the RPI for (quasi-)static liquid jets and filaments, in typical practical applications (e.g. inkjet printing) the inertia of liquid jets is significant, giving rise to nonlinear effects that influence the spatiotemporal evolution of the RPI and which are not captured by linear stability analysis. Using direct numerical simulation and laboratory experiments, we study the evolution of the dynamic RPI on liquid jets with different Weber and Ohnesorge numbers as well as different velocity profiles, perturbation amplitudes and wavenumbers. Our results show how inertia as well as the amplitude/wavenumber of the perturbation change the velocity and pressure fields of the liquid jet, which changes the spatiotemporal growth of the dynamic RPI and, consequently, the breakup length of the jet, with a local reversal of the RPI under certain conditions. We identify the key mechanisms that govern the complex evolution of the dynamic RPI and highlight the main differences between static and dynamic RPI. [Preview Abstract] |
Monday, November 21, 2016 6:27PM - 6:40PM |
L38.00010: Experimental study of splashing mechanisms by an immersed rotating body Mickael Bourgoin, Diego Rodriguez, Saksham Gakhar, Jean-Philippe Matas, Remi Berger We study the entrainment of water by a rotating wheel, as a function of the rotation frequency, wheel radius and depth of immersion. The entrainment leads to the formation of a liquid sheet on the ascending side, and of ligaments on the descending side. These structures are captured via simple models. We measure via image processing the liquid flux ejected by the wheel. [Preview Abstract] |
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