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 A8: Particle-Laden Flows I: Liquid-Solid Flows |
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Chair: Andrea Prosperetti, Johns Hopkins University Room: 330 |
Sunday, November 24, 2013 8:00AM - 8:13AM |
A8.00001: Natural particles in turbulent aquatic environments: when do they differ from fluid parcels? Evan Variano, Laura Mazzaro, Margaret Byron, Rachel Allen, Ian Tse We explore if, and when, natural particles act differently than fluid parcels. We focusing on the case of aquatic environments with high-Reynolds number turbulence. The particles of interest in such environments are suspended sediment (often in the form of porous aggregates), plankton, and droplets (such as oil droplets). We use laboratory experiments (described below) and literature review to build a description of the cases in which these particles display kinematics different than that of fluid parcels which passively follow the flow. Specifically, we explore the effect of size, shape, and density on settling, diffusion, and clustering. The goal for each case is specify critical values at which behavior departs from that of fluid parcels. The laboratory experiments we use employ a simple 3D particle-tracking camera (based on the defocusing principle by Willert and Gharib [1992] and currently used in ``V3V'' velocimetry). With this, we study a variety of particles in laboratory flow. These data, and the analysis presented herein, is a precursor to studies conducted directly in estuarine environments. Willert, C. E. and Gharib, M. 1992 Three-dimensional particle imaging with a single camera. Experiments in Fluids, 12(6), 353-358. [Preview Abstract] |
Sunday, November 24, 2013 8:13AM - 8:26AM |
A8.00002: The motion of spherical particles falling in a cellular flow field Elisabeth Guazzelli, Gilles Bouchet, Laurence Bergougnoux The objective of the present study is to understand the influence of turbulence on the settling of particles under the action of gravity. This effect is intimately related to the interactions of particles with local spatial structures of the flow, e.g. large vortices. These vortical structures have a significant effect on the local particle transport and concentration. We present a jointed experimental and numerical study to examine these issues. The two-dimensional model experiment uses electroconvection to generate a two-dimensional arrays of controlled vortices which mimic a simplified turbulent flow. Particle image-velocimetry or tracking are used to examine the motion of the particles within this vortical flow. The numerical simulation is inspired by the model developed by Maxey (Phys. Fluids 30, 1915, 1987). [Preview Abstract] |
Sunday, November 24, 2013 8:26AM - 8:39AM |
A8.00003: Modeling the rheology of concentrated fluid-sediment mixtures Allison Penko, Julian Simeonov, Joseph Calantoni Common formulations to model the rheology in highly concentrated fluid-sediment mixtures include using a velocity damping function or an enhanced effective viscosity dependent on the local sediment concentration. Here, we implemented a three-dimensional mixture theory model (SedMix3D) to compare the results from the two different rheological formulations. The former assumes the mixture behaves as a Newtonian fluid and exponentially damps the mixture velocity dependent on the magnitude of the local sediment concentration. The latter formulation treats the mixture as a visco-plastic in which an enhanced effective viscosity depends on the Reynolds stresses and the critical stress of the sediment. SedMix3D treats a fluid-sediment mixture as a continuum by employing closures for the bulk parameters of the mixture (diffusion, hindered settling velocity, and effective viscosity) to simulate three-dimensional, bottom boundary layer flow over dynamic sediment beds. The two different rheologies were tested with simulations of an avalanching sediment pile forced with gravity only and simulations of oscillatory flow over rippled sand beds. Comparisons of the simulated hydrodynamics and sediment dynamics resulting from the two rheologies will be presented. [Preview Abstract] |
Sunday, November 24, 2013 8:39AM - 8:52AM |
A8.00004: Numerical modeling of bidensity suspensions in gravity-driven, thin-film flows Jeffrey Wong, Sungyon Lee, Aliki Mavromoustaki, Andrea Bertozzi We present an equilibrium model for bidisperse suspensions consisting of negatively buoyant particles with two different densities that flow down an incline. In the case of monodisperse suspensions, it has been shown experimentally and theoretically that particles either settle to the substrate or accumulate at the fluid surface (these are referred to as the ``settled'' and ``ridged'' regimes, respectively), depending on the inclination angle and total particle volume fraction. When there are two species, the heavier particles settle to the substrate while the lighter particles exhibit a similar transition between settled and ridged regimes, which now also depends on the relative concentration. We investigate the model numerically and compare the predicted transition between settled and ridged regimes with experimental results. In addition, we discuss the effect of shear-induced self-diffusion in the model, which leads to some mixing of the particle layers. [Preview Abstract] |
Sunday, November 24, 2013 8:52AM - 9:05AM |
A8.00005: Erosion and transport of particulates by forced jet impinging jet on a mobile sediment bed Kyle Corfman, Rahul Mulinti, Kenneth Kiger The work reports on the erosion and suspended flux characteristics of a forced impinging jet, as a prototypical surrogate to better understand the problem of rotorcraft brownout. Coherent vortex rings are generated through oscillatory forcing of a vertical impinging jet onto a sediment bed. Early in the flow development, annular ripple dunes are formed and steadily grow, the wavelength and growth rate depending largely on the particle size and flow conditions. In order to provide a reliable prediction of erosion for more realistic flows, such as those found in rotorcrafts, a parametric study was performed for several particle sizes and mixtures. PTV is used to correlate vertical and horizontal fluxes with resulting changes in the ground profiles. A single-phase PIV study detailing the changes in the vortex ring characteristics after the bed has reached a stable erosion pattern is also reported. [Preview Abstract] |
Sunday, November 24, 2013 9:05AM - 9:18AM |
A8.00006: Collision Driven Particle Dynamics Simulations for Analyzing Flows of Particulate Sprays and Jets Debanjan Mukherjee, Tarek Zohdi This work presents a detailed overview of the development of a computer simulation tool based on neighbor-list collision driven particle dynamics to investigate the flow of particulate sprays and jets. A detailed discussion of a hierarchical modeling approach to represent coupled, multi-physical phenomena through simple models for underlying physical interactions is presented. The models are based on the concept of individual ``particles'' or ``discrete elements'' - which could be actual particles in some applications, and a meso-scale idealized computational unit in others. Particularly, the work focuses on the overall flow behavior in the presence of collisions and interactions with surrounding fluid, and representative simulation examples are presented to illustrate the dispersed particle ensemble dynamics. The simulations were found to be reasonable in performance time using readily available computational resources. From the perspective of engineering software development, the work also briefly addresses the issue of simulation architecture and user front-end. Since this is part of an ongoing research, the status of current development, future research directions, and possibilities of open collaborations both in terms of simulation development and applications will be addressed [Preview Abstract] |
Sunday, November 24, 2013 9:18AM - 9:31AM |
A8.00007: Pop up height of buoyant spheres Tadd Truscott, Randy Munns We examine the rising and surface breaching dynamics of buoyant spheres released at varying depths beneath the free surface in water over a range of Reynolds numbers (Re = $3\times 10^4$ to $5\times 10^5$ using high-speed imaging and particle image velocimetry. Buoyant spheres of sufficient speed pop up out of the free surface in varying ways depending on the conditions under the surface. Altering the release depth reveals varying exit angles, velocities, accelerations, and pop up heights at surface exit. Vortex shedding prior to free surface exit causes decelerations contributing to the variation in exit velocities and resulting pop up heights. Through a comprehensive study the phenomenon is extremely predictable. At lower Re, spheres released from shallow depths result in greater accelerations, velocities and pop up heights at the free surface compared to lower pop up heights when released from deeper depths (contrary to intuition). As the depth of release is increased the pop up height oscillates between a maximum and minimum. This is directly related to the proximity of the shed vortex to the free surface. For spheres of greater Re, pop up height increases linearly with release depth, demonstrating continued accelerations at free surface exit. [Preview Abstract] |
Sunday, November 24, 2013 9:31AM - 9:44AM |
A8.00008: Shock Dynamics for particle-laden thin film Li Wang, Andrea Bertozzi We study the shock dynamics for a recently proposed system of conservation laws (Murisic et. al [J. Fluid Mech. 2013]) describing gravity-driven thin film flow of a suspension of particles down an incline. When the particle concentration is above a critical value, singular shock solutions can occur. We analyze the Hugoniot topology associated with the Riemann problem for this system, describing in detail how the transition from a double shock to a singular shock happen. We also derive the singular shock speed based on a key observation that the particles pilling up at the maximum packing fraction near the contact line. These results are further applied to constant volume case to generate a rarefaction-singular shock solution. The particle/fluid front are shown to move linearly to \emph{the leading order} with time to the one-third power as predicted by the Huppert solution for clear fluid. [Preview Abstract] |
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