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 A33: Drops I: Pinch-off and Coalescence |
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Chair: Jose Gordill, Universidad de Sevilla Room: 404 |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A33.00001: Scaling transitions during the thinning of viscous dripping droplets Alfonso A. Castrejon-Pita, J. Rafael Castrejon-Pita, Sumeet S. Thete, Krishnaraj Sambath, E. John Hinch, Ian M. Hutchings, John R. Lister, Osman A. Basaran The dynamics of filament thinning during the formation of viscous Newtonian drops is studied experimentally and numerically. High speed shadowgraph imaging and sub-pixelar image analysis are used to extract the minimum neck diameter in terms of the time $\tau$ to breakup. Aqueous solutions of glycerol with viscosities ranging from 20 to 360 mPa s are used as the working fluids. In addition, nozzles of different diameters were used to vary the initial dynamic conditions. High resolution numerical simulations were performed to extract the instantaneous Reynolds number to understand the transition between different scaling regimes (presented in detail in a complementary presentation). Our results seem to suggest that, under some conditions, the transition from Potential Flow (PF) to an inertial-viscous (IV) regime is intertwined by a viscous regime (V). [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A33.00002: Analysis of scaling during pinch-off of Newtonian filaments by numerical simulation Sumeet Thete, Krishnaraj Sambath, Osman Basaran, Rafael Castrej{\'o}n-Pita, Alfonso Castrej{\'o}n-Pita, Ian Hutchings, John Hinch, John Lister Drop formation is ubiquitous in diverse applications, e.g. ink-jet printing and atomization. As a drop is about to form, it is connected by a thinning filament to the rest of the liquid attached to a nozzle. Hence, the physics of filament thinning is key to understanding drop formation. For Newtonian liquids, it is known that the dynamics of filament thinning initially falls in one of two scaling regimes, a potential flow regime if liquid viscosity $\mu$ is small or a viscous regime if $\mu$ is large. Regardless of $\mu$, the dynamics ultimately transitions to a final asymptotic regime, the inertial$-$viscous regime, where all forces$-$viscous, inertial, and surface tension$-$compete as the filament nears pinch$-$off. While the global dynamics of drop formation and these scaling regimes are well understood, less well appreciated is what happens during transitions between the initial and final regimes. Here, we investigate the dynamics during these transitions by computation. We also show that computed predictions accord well with experiments detailed in a complementary presentation. [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A33.00003: Dynamics of Contracting Asymmetric Viscoelastic Filaments Christopher Anthony, Sumeet Thete, Santosh Appathurai, Pradeep Bhat, Osman Basaran, Michael Harris In ink-jet printing and atomization, slender filaments are routinely formed.~~Such filaments either contract to form a single drop or breakup into multiple drops, e.g. by end pinching. Beginning with papers by Schulkes (1996) and Notz {\&} Basaran (2004), past studies have focused exclusively on the contraction dynamics of Newtonian filaments.~~Also in these studies, initial filament shapes are taken to be long cylinders terminated by two identical spherical caps (symmetric filaments).~~In emerging applications, e.g. ink-jet printing of complex fluids, the filaments are viscoelastic (VE) fluids.~~Moreover, older experiments by Notz et al. (2001) and more recent ones by Castrej\'{o}n-Pita et al. (2012) show that initial filament shapes resemble long, tapered cylinders terminated by hemispherical caps of unequal radii (asymmetric filaments).~~Therefore, we analyze the contraction dynamics of both asymmetric and symmetric filaments of VE fluids using the Giesekus model.~~Rather than solving the full set of equations governing the problem, we take advantage of filament slenderness and solve a much simpler set of 1D equations (Eggers, 1997).~~We then use a finite element method with Streamline Upwind/Petrov Galerkin (SUPG) formulation (Brooks {\&} Hughes, 1982) to solve the reduced equations. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A33.00004: Dynamics of contracting surfactant-covered filaments Pritish Kamat, Sumeet Thete, Qi Xu, Osman Basaran When drops are produced from a nozzle, a thin liquid thread connects the primary drop that is about to form to the rest of the liquid in the nozzle. Often, the thread becomes disconnected from both the primary drop and the remnant liquid mass hanging from the nozzle and thereby gives rise to a free filament. Due to surface tension, the free filament then contracts or recoils. During recoil, the filament can either contract into a single satellite droplet or break up into several small satellites. Such satellite droplets are undesirable in applications where they can, for example, cause misting in a manufacturing environment and mar product quality in ink-jet printing. In many applications, the filaments are coated with a monolayer of surfactant. In this work, we study the dynamics of contraction of slender filaments of a Newtonian fluid that are covered with a monolayer of surfactant when the surrounding fluid is a passive gas. Taking advantage of the fact that the filaments are long and slender, we use a 1D-slender-jet approximation of the governing system of equations consisting of the Navier-Stokes system and the convection-diffusion equation for surfactant transport. We solve the 1D system of equations by a finite element based numerical method. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A33.00005: Stretching and Rupture of Suspension Bridges, of the Fluid Variety Kevin Connington, Mark Miskin, Taehun Lee, Mark Shattuck, Jeffrey Morris, Heinrich Jaeger A ``suspension bridge'' is similar to a liquid bridge but contains solid particles suspended in the liquid. In this work, experiments and numerical simulations are performed to examine the dynamics of the stretching of a suspension bridge, and the eventual rupture. The experiments are performed using a suspension density matched with the surrounding immiscible liquid to minimize gravitational effects; the simulations are performed using a multi-component lattice-Boltzmann(LB) method coupled with an established method for LB simulation of suspended solids. The focus is on particle rearrangements and rupture dynamics, as well as the force required to stretch the bridge, with comparisons made between the case of a suspension bridge and simple liquid bridge. It is found that even under dilute particle loading, the rupture dynamics are significantly altered by the influence of particles. Under concentrated conditions, the rearrangements of the particles are associated with significant distortion of the interface, and a simpler simulation tool which balances particle interactions with the capillary forces from the boundary appears to capture salient features of the dynamics. The ultimate rupture dynamics are compared to the pinch-off behavior in drop formation from suspensions. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A33.00006: Inducing coalescence by a superposition of two Rayleigh-Plateau instabilities: Theoretical analysis Theo Driessen, Pascal Sleutel, Frits Dijksman, Roger Jeurissen, Detlef Lohse We demonstrate a novel method of producing a stream of widely spaced high-velocity droplets by imposing a combination of two unstable modes on a liquid jet. The wavelengths of the two modes are chosen close to the wavelength of the most unstable mode. After the initial breakup of the jet into small droplets, these droplets coalesce to produce a stream of larger droplets spaced at a much larger distance than the wavelength of the most unstable mode of the jet. We analytically derive sets of perturbations that robustly induce this process, and we investigate the influence of the nonlinear interactions in the Rayleigh-Plateau instabilities on the coalescence process. Experiments and numerical simulations demonstrate that the jet breakup and the subsequent droplet merging are governed completely by the selected modes. [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A33.00007: Inducing coalescence by a superposition of two Rayleigh-Plateau instabilities: Experimental implementation Pascal Sleutel, Theo Driessen, Roger Jeurissen, Frits Dijksman, Detlef Lohse In this work we present an experimental method to efficiently breakup and coalesce multiple droplets from a jet by a superposition of two Rayleigh-Plateau perturbations. A continuous liquid jet is ejected from a glass capillary which has a piezo electric actuator attached to it. The periodical pressure perturbations applied by the piezo induce two growing modes on the jet. By choosing the perturbation wavenumbers close to wavelength of the most unstable mode, fast coalescence and a stable stream of droplets are obtained. By tuning the phase between the two perturbations we control the coalescence time and the satellite droplet formation. When the coalescence process is finished, the final droplet size is set by the low frequency beating wavelength. This means that stable streams of mono-disperse droplets can be generated at inter-droplet distances and droplet velocities very different from a single Rayleigh-Plateau instability. Our experimental results are compared with numerical results and there is agreement in great detail. [Preview Abstract] |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A33.00008: Multiscale computations of thin films between colliding drops Bahman Aboulhasanzadeh, Sadegh Dabiri, Gretar Tryggvason In multiphase flows thin films frequently appear between fluid blobs colliding with each other. These films can become very thin and be difficult to resolve accurately in numerical simulations, particularly in DNS of many co-flowing drops, requiring very fine resolution and resulting in excessive computational cost due to very fine uniform grids or time consuming adaptive mesh refinement. Here, we describe an algorithm for detecting thin films using a front tracking method. We also propose a subscale model to describe the physics and the evolution of a thin film between two drops. Comparison between results for a fully resolved film on a fine grid and simulations using a much coarser grid plus the model for the description of the film, shows good agreement. [Preview Abstract] |
Sunday, November 24, 2013 9:44AM - 9:57AM |
A33.00009: Transition from partial to complete coalescence Bahni Ray, Taehun Lee The lattice Boltzmann equation (LBE) method is used to simulate satellite drop formed during coalescence of unequal size drops first shown experimentally by Zhang, Li and Thoroddsen [Phys. Rev. Lett. \textbf{102}, 104502 (2009)]. Partial coalescence is commonly observed for drop impact on flat surface for a particular range of initial drop diameter. Important criterion for partial coalescence is the increasing horizontal momentum of the drop relative to the vertical momentum. The experimental observation of similar phenomena with two unequal size drops emphasize on the fact that the curvature of the surface has an important contribution as well. Simulations are performed to show that the drop curvature and drop liquid drainage time effects the satellite drop formation. Furthermore the study is extended to drops with surrounding liquid medium and compared to drop coalescence on flat surface. [Preview Abstract] |
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