Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session LE: Multiphase Flows: General III |
Hide Abstracts |
Chair: Kenneth Kiger, University of Maryland Room: Hilton Chicago Continental B |
Tuesday, November 22, 2005 8:00AM - 8:13AM |
LE.00001: Two-Phase Filtered Density Function Approach for Large Eddy Simulation of a Water Droplet Laden 2D Mixing Layer Mark Carrara, Paul DesJardin In this study, the two-phase velocity-scalar filtered density function (TVSFDF) transport equation for large eddy simulation (LES) is considered in the limit of a continuum-dispersed phase two-phase flow. All quantities conditionally filtered in the dispersed phase marginal filtered density function transport equation are disregarded leaving only terms conditionally filtered on the phase interface. These conditionally surface-filtered terms account for phase-coupling between the dispersed and continuum phases of the flow. Closure models are presented and implemented for both the gas phase and for phase coupling terms for a 2D water droplet laden temporally developing turbulent mixing layer. Modeled marginal FDF transport equations are presented and a statistically equivalent set of Ito stochastic differential equations (SDE) are derived from each marginal FDF equation. Simulations are conducted via a full stand-alone Lagrangian particle Monte-Carlo method and the effect of variable Stokes number on turbulent dispersion characteristics of evaporating and non-evaporating two-way coupled droplets is discussed. [Preview Abstract] |
Tuesday, November 22, 2005 8:13AM - 8:26AM |
LE.00002: Direct Numerical Simulations of Low Mach Number Turbulence and Sprays Wei Liu, Yunliang Wang, Christopher Rutland Direct numerical simulations are being performed to investigate spray-turbulence interactions. Spray models, such as the injection, drag force, and evaporation models, are implemented into a three-dimensional direct numerical simulation (DNS) code with low Mach number approximations. Complete two-way couplings of mass, momentum, and energy between the spray and the gas phase flow are included in the formulations. The gas phase flow is discretized in a Eulerian frame, and the droplets are tracked in a Lagrangian frame. Results for the cases of the single droplet evaporation and the cases for the penetration length of the injected sprays have been compared to experimental measurements, and reasonable matches have been achieved. An analysis of the effects of the droplet evaporation on the gas phase turbulence has been conducted for both single droplet and spray simulations. It is found that the evaporation of droplets has a great impact on the generation of turbulence. Current work for this research includes three-dimensional simulations of sprays interacting with different initial gas field. A-priori studies for large eddy simulation (LES) models are also conducted using spray-turbulence DNS results. [Preview Abstract] |
Tuesday, November 22, 2005 8:26AM - 8:39AM |
LE.00003: Holographic Measurements of Fuel Droplet Diffusion in Isotropic Turbulence Balaji Gopalan, Edwin Malkiel, Joseph Katz High-speed digital holographic cinematography was used to investigate the diffusion of slightly buoyant fuel droplets in locally isotropic turbulence. High turbulence levels with a weak mean velocity was generated at the center of a tank by four rotating grids. 0.3-1.5mm droplets were injected here and tracked using in-line holography. To obtain all three components of velocity, we simultaneously recorded holograms of the central 37x37x37 mm$^{3}$ volume from two perpendicular directions. These were numerically reconstructed to provide focused images of the droplets. An automated code was developed to identify the 3-D droplet trajectories from the two views, and then calculate time series of their velocity. After subtracting the local mean fluid velocity, the time series were used to obtain the 3-D Lagrangian autocorrelation function of droplet velocity. Averaging over many trajectories provided the autocorrelation functions as a function of direction and droplet sizes. As expected, the correlation was higher in the vertical direction due to the effect of gravity. Data analysis is still in progress. [Preview Abstract] |
Tuesday, November 22, 2005 8:39AM - 8:52AM |
LE.00004: Numerical simulation of a liquid jet in a cross-flow using Refined Level Set Grid method Dokyun Kim, Marcus Herrmann, Sourabh Apte, Jorg Schluter, Parviz Moin Numerical simulations are conducted to investigate the breakup mechanism of a liquid jet injected into a turbulent cross-flow using an unstructured grid LES solver. A Refined Level Set Grid (RLSG) method coupled to a Lagrangian spray model is used to capture the whole breakup process of the liquid jet. In the near field of liquid injection where the primary breakup occurs, the liquid jet penetrates into a cross-flow, bends in the cross-flow direction, and breaks into large drops. The position, motion and topological changes of this liquid column are described by the RLSG method. In the far field spray region, on the other hand, the Lagrangian stochastic spray model is used for the secondary breakup. The characteristics of the breakup process and the liquid jet, such as jet trajectories, jet cross-sections, and flattening, are examined in detail using this method. Our numerical result is compared with the experimental data, showing the applicability and feasibility of our method for simulation of the atomization process of liquid jets and sheets in turbulent flows. [Preview Abstract] |
Tuesday, November 22, 2005 8:52AM - 9:05AM |
LE.00005: Control of atomizer turbulence characteristics with indeterminate origin nozzles Fangjun Shu, Mirai Ito, Michael Plesniak, Paul Sojka Minimizing overspray is a key concern in spray painting, not only to reduce the raw material costs but also to minimize pollution. Sprays emanating from indeterminate origin (IO) nozzles were evaluated to determine to what extent modification of the turbulence at the spray exit will affect the transfer efficiency (TE) of small droplets near the target region (TE is the fraction of the total mass of liquid sprayed that deposits on the target). Two-peak and four-peak crown nozzles were investigated and compared with a baseline round nozzle spray. Spray results are compared to previous results obtained in a precursor study of the near-field of a large scale water jet with IO nozzle. In these companion studies flow visualization images were taken, as well as PIV and LDV data to examine the influence of IO nozzles on the turbulence characteristics. In the spray, transfer efficiency was measured directly to compare the efficiency of each nozzle [Preview Abstract] |
Tuesday, November 22, 2005 9:05AM - 9:18AM |
LE.00006: Stable Jets of Viscoelastic Fluids and Self-assembled Cylindrical Capsules by Hydrodynamic Flow Focusing Kazem Edmond, Manuel Marquez, Anthony Dinsmore, Jonathan Rothstein In recent years, a number of studies have investigated the use of flows developed within microfluidic devices to generate emulsions with precisely controlled drop sizes and polydispersity. In this talk, we will present a series of hydrodynamic flow focusing experiments designed to produce long-lived cylindrical jets of viscoelastic polymer solutions. These stable cylinders are then subsequently used as templates for the assembly of nanoparticles at the oil-water interface in order to form rigid, semi-permeable cylinders with potential applications in encapsulation and in novel structural materials. In the flow-focusing device, an aqueous solution of polyacrylamide flows coaxially with an immiscible oil, experiences a strong extensional flow over a short distance, and then flows into a uniform cylindrical tube. At sufficiently high flow rates, the aqueous phase forms a cylindrical jet with a diameter of 10-90 microns which can remain stable for several centimeters downstream. A simple analysis is presented to account for the role of extensional rheology and first normal stress difference on the stability of the viscoelastic jets. The model is found to agree well with the data. [Preview Abstract] |
Tuesday, November 22, 2005 9:18AM - 9:31AM |
LE.00007: Particle Sorting by Aerodynamic Vectoring Zachary Humes, Barton Smith, Angela Minichiello An experimental and numerical demonstration of a new, non-contact particle sorting technique called Aerodynamic Vectoring Particle Sorting (AVPS) is presented. AVPS uses secondary blowing and suction control flows to sharply turn a 2D, particle-laden jet. As the jet is turned, particles present in the flow experience a resultant force, dependent upon their size and due to the combined effects of pressure, inertia, and drag. Since the balance of these forces determines the particle's trajectory, turning the flow leads to a separation of particles downstream. This simple, low-pressure-drop sorting technique classifies particles with less risk of damage or contamination than currently available sorting devices.~ AVPS is experimentally demonstrated using a rectangular air jet. Particle size and trajectory are measured using the Shadowgraphy method.~ Numerical simulations are performed using the commercial CFD solver FLUENT to calculate the 2D turbulent vectored jet flow field using a RANS approach. FLUENT's discrete phase model is used to simulate the trajectory of particles present in the flow field. Examination of the mean and the standard deviation of measured and computed particle trajectories is used to determine the range of particle sizes that can be effectively sorted using AVPS. [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