Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session HQ: Particle Laden Flows III |
Hide Abstracts |
Chair: Lance R. Collins, Cornell University Room: 202B |
Monday, November 24, 2008 10:30AM - 10:43AM |
HQ.00001: Particle Transport and Deposition in Wavy Channels Mark Goodwin, Pratap Vanka Wavy channels have rich flow physics, consisting of trapped vortices in the troughs and instabilities induced by the shear layers and curved boundaries. At modest Reynolds numbers, the flow becomes unsteady by Kelvin-Helmholtz (bellowed channels) or Tollmien-Schlichting instabilities (serpentine channels). The fluid dynamic and heat /mass transfer characteristics of wavy channels have been studied previously. Such flow phenomena can also have significant effect on particle transport. In this paper we have studied particle transport and deposition in bellowed and serpentine channels for different Reynolds numbers and particle Stokes numbers. A computational technique that solves the governing equations using a fractional step procedure on a Cartesian grid has been used. The complex boundary has been simulated by the Immersed Boundary Method (IBM). Particle concentration patterns as well as deposition rates are presented under varied conditions. [Preview Abstract] |
Monday, November 24, 2008 10:43AM - 10:56AM |
HQ.00002: Comparing particle-resolved simulation methods for moving particles in a viscous fluid Lian-Ping Wang, Hui Gao, Li-Shi Luo, Yan Peng, Kyong Min Yeo, Martin R. Maxey In recent years, quite a few particle-resolved simulation methods have emerged for treating moving solid particles in a viscous fluid. A common advantageous feature shared by these methods is the use of a simple fixed mesh. The no-slip boundary condition on the surface of a particle is handled locally by a consistent coupling or interaction scheme. Here we examine four such methods: lattice Boltzmann equation (LBE) with interpolated bounce back scheme, LBE with immersed boundary method, a hybrid method (Physalis) developed by Prosperetti and co-workers, and a force-coupling method. Our main objective is to inter-compare these methods in terms of accuracy of the simulated flow field, force / torque, and computational efficiency. Two benchmark cases are used: a particle moving in a 3D Couette flow and a 3D flow induced by a spinning sphere at finite Reynolds number. The results are discussed in terms of flow Reynolds number and geometric parameters. We will also comment on the range of relevant physical parameters accessible in these methods. [Preview Abstract] |
Monday, November 24, 2008 10:56AM - 11:09AM |
HQ.00003: Fully-resolved DNS of finite-size particles exposed to a turbulent stream Lorenzo Botto, Andrea Prosperetti A field of homogeneous isotropic turbulence is convected with a mean velocity past a group of fixed, finite-size particles and the structure and intensity of the resulting downstream turbulence are compared to the particle-free case. The diameter of the particles is larger than the Kolmogorov scale and is of the order of the Taylor micro-scale. The results illustrate the central role played by the particle wakes in destroying the isotropy and homogeneity of the incident turbulence. Furthermore, as a result of wake interactions, the time-dependent hydrodynamic forces on the downstream and upstream spheres are correlated. The numerical simulations are carried out on a uniform grid by employing the ``Physalis'' method which can be regarded as a combination of an immersed boundary and spectral method. Among other advantages, it does not require interpolation and its spectral convergence permits computations with relatively few grid nodes per particle. [Preview Abstract] |
Monday, November 24, 2008 11:09AM - 11:22AM |
HQ.00004: Flow structure spontaneously formed in 3-D bubbling gas-fluidized bed Takuya Tsuji, Keizo Yabumoto, Toshihiro Kawaguchi, Toshitsugu Tanaka Bubbling gas-fluidized beds are widely used in vast engineering applications. Bubbles spontaneously formed in the bed enhance the dispersion and mixing of the particles and it greatly contributes to the improvement of equipment performance. Hence, it is important to know about the bubbles' behavior and the flow structures induced by bubbles. However, much is not known yet because the flow inside of the bed is unsteady and quite complex. In addition, it is difficult to observe the internal flow structure due to the existence of regions of high particle concentration. In the present study, the flows occur in a large-scale 3-D bubbling gas-fluidized bed are numerically investigated by a Eulerian-Lagrangian coupling scheme between discrete element method and computational fluid dynamics (DEM-CFD). The code was parallelized and nine million particles are tracked in the maximum case. Three-dimensional bubble's shape and its behaviors are directly observed. Circulation structures of the flow induced by bubbles are also verified in detail. Bubbles are preferentially generated under the uniform inflow condition and induce upward flows in the bed. [Preview Abstract] |
Monday, November 24, 2008 11:22AM - 11:35AM |
HQ.00005: Large-eddy simulation of particle-laden atmospheric boundary layer Marcel Ilie, Stefan Llewellyn Smith Pollen dispersion in the atmospheric boundary layer (ABL) is numerically investigated using a hybrid large-eddy simulation (LES) Lagrangian approach. Interest in prediction of pollen dispersion stems from two reasons, the allergens in the pollen grains and increasing genetic manipulation of plants leading to the problem of cross pollination. An efficient Eulerian-Lagrangian particle dispersion algorithm for the prediction of pollen dispersion in the atmospheric boundary layer is outlined. The volume fraction of the dispersed phase is assumed to be small enough such that particle-particle collisions are negligible and properties of the carrier flow are not modified. Only the effect of turbulence on particle motion has to be taken into account (one-way coupling). Hence the continuous phase can be treated separate from the particulate phase. The continuous phase is determined by LES in the Eulerian frame of reference whereas the dispersed phase is simulated in a Lagrangian frame of reference. Numerical investigations are conducted for the convective, neutral and stable boundary layer as well different topographies. The results of the present study indicate that particles with small diameter size follow the flow streamlines, behaving as tracers, while particles with large diameter size tend to follow trajectories which are independent of the flow streamlines. Particles of ellipsoidal shape travel faster than the ones of spherical shape. [Preview Abstract] |
Monday, November 24, 2008 11:35AM - 11:48AM |
HQ.00006: Inverse modeling: reconstructing the initial conditions of a turbidity current Lutz Lesshafft, Brendon Hall, Eckart Meiburg, Ben Kneller, Alison Marsden A new approach is introduced for generating models of submarine sediment deposits laid down by turbidity currents (turbidites). Initial conditions of the original turbidity current are reconstructed via a derivative-free optimization algorithm based on information of the deposit properties at isolated control points; where the problem is in the subsurface (e.g. in an oil or gas field), this information is typically obtained from well data. Towards this end, results from successive numerical flow simulations are matched against the available partial well data. Upon convergence, these simulations provide a process-based estimation of the properties of the entire deposit. The validity of the approach is demonstrated in the context of particle-driven lock-exchange flows, simulated via DNS. [Preview Abstract] |
Monday, November 24, 2008 11:48AM - 12:01PM |
HQ.00007: Multiphase multi-velocity discrete population balance model of fragmenting particulate flows Mahesh Panchagnula, Prasad Rayapati, John Peddieson Fragmenting particulate flows are studied using discrete population balance modeling. The range of particle sizes is divided into N classes with each size class being allowed to behave as an individual fluid-like phase. The particulate phases are embedded in a continuous phase with which they share a pressure field and are coupled through drag forces. The particulate material is therefore modeled as a mixture of N+1 inter-penetrating continua. The fragmentation process is modeled using the population balance approach which allows for parent size-class particles to break up into any of the smaller daughter size-classes following a pre-defined breakage phenomenology. The accompanying mass and momentum exchange between the size-classes is modeled as source terms in the conservation equations. The model is applied to a micro-centrifuge flow field. We show here that the larger particles, while being encouraged to break up are also preferentially transported towards the walls of the centrifuge, owing to the swirl induced radial pressure gradient. By experimenting with various breakage phenomenologies, we show that the classical log-normal particle size distribution can be recovered in the long time limit for all breakage phenomenologies but the short time evolution of the particle size distribution is sensitive to that choice. [Preview Abstract] |
Monday, November 24, 2008 12:01PM - 12:14PM |
HQ.00008: Examining the Equilibrium State in Lagrangian Particle Dynamics Mario F. Trujillo, Alex Parkhill In a number of applications the particle size and flow conditions are such that to a great extent the motion of particles occurs under an equilibrium state, in which case the particle forces are practically in perfect balance. The exact conditions that lead particles into and out of this state are studied within the framework of Stokes drag and one-way momentum couple flows. It is shown that the primary parameter that governs deviation from equilibrium is the product of the particle time constant and the maximum eigenvalue of the velocity gradient tensor. This parameter is proposed as a redefinition of the Stokes number for particulate flow. The implications clearly indicate that traditional definitions of the particle Stokes number, which are generally represented by ratios of particle time constant and flow characteristic times are insufficient in providing a rigorous criterion for equilibrium. The new Stokes number's effectiveness in predicting departures from equilibrium is demonstrated mathematically and numerically. The conclusions derived are supported by simulations of particle transport in 2-D and 3-D analytical flow fields. The Lagrangian analysis presented here stands in contrast to earlier Eulerian formulations presented in the literature. [Preview Abstract] |
Monday, November 24, 2008 12:14PM - 12:27PM |
HQ.00009: Analysis of preferential particle concentration Karim Shariff It is known from simulations of particle laden turbulent flows (Squires and Eaton 1991; Wang and Maxey 1993) that particles having a relaxation time nearly equal to the Kolmogorov time preferentially concentrate in regions of weak vorticity. Here we consider the set of equations for \textit{particle dilatation}, strain, and rotation which provides an understanding of this behavior. This set is derived from the two-fluid equations for the coupled fluid and particle phases. Fluid strain induces particle strain, which causes particle dilatation to always decrease. Fluid rotation, on the other hand, induces particle rotation, which causes particle dilatation to always increase. Illustrative solutions are provided for spatially linear flows and the case of pure strain nicely illustrates how particles concentrate. The analysis also suggests devices and flows that would be particularly good at concentrating particles. [Preview Abstract] |
Monday, November 24, 2008 12:27PM - 12:40PM |
HQ.00010: Transport of a solid sphere in liquid foam Nicolas Louvet, Olivier Pitois, Florence Rouyer, Elise Lorenceau In many foam applications, particles flow through the liquid network of aqueous foam made of channels and nodes. These channels named Plateau border are the junctions between three soap films and have fluid interfaces (non zero velocity). To understand the complex behaviour of this transport, we focus our experiments on a single particle flowing with the liquid through i) a single fluid channel and ii) aqueous foam. In each experiment we control the following parameters: - mobility of the fluid interfaces -- average liquid velocity - aspect ratio d/d$_{lim}$, where d is the particle diameter and d$_{lim}$ the maximum diameter of the sphere that can pass through the channel. We measure the velocity of individual particles. Unexpectedly, for small d/d$_{lim}$ and mobile interfaces, the particle velocity is smaller than the average liquid velocity. To explain this result, we assume that counter flows take place in the soap films due to Marangoni flows and thus modify the boundary conditions of the liquid flow by having an upward velocity instead of a zero velocity in the corner. We are working on a model that reproduce experimental data assuming counter flow and real network geometry. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700