Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session BK: Multiphase Flows II |
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Chair: Marcus Herrmann, Arizona State University Room: 101J |
Sunday, November 22, 2009 10:30AM - 10:43AM |
BK.00001: The Impact of Density Ratio on the Primary Atomization of a Turbulent Liquid Jet in Crossflow Marcus Herrmann Atomizing liquids by injecting them into crossflows is a common approach to generate fuel sprays in gas turbines and augmentors. Although correlations derived from experimental data exist for the jet penetration, predicting the drop size distribution resulting from the primary breakup of the liquid jet is a more challenging task. Furthermore, most correlations are derived from experimental data performed at ambient conditions, thereby not matching the density ratio found in most gas turbine applications. In this paper, we will study the impact of density ratio on the primary atomization of a turbulent liquid jet injected into a subsonic crossflow using detailed numerical simulations, leaving constant all other relevant characteristic numbers, i.e. jet and crossflow Weber numbers, Reynolds numbers, and momentum flux ratio. The influence of density ratio on the physical mechanisms causing the initial breakup of the jet, the resulting grid dependent/independent drop size distributions, and the jet penetration will be discussed. [Preview Abstract] |
Sunday, November 22, 2009 10:43AM - 10:56AM |
BK.00002: Modeling Electrohydrodynamic Atomization Bret Van Poppel, Olivier Desjardins, John Daily Over the past decade, there has been considerable interest in controlling the emissions from small engines in the size range of 200 cm$^3$ or smaller. Fuel injection schemes may reduce the incidence of pollutant emissions within this class of engines. However, the cost of implementation is a barrier to large scale adoption. One approach to small-scale fuel injection is to capitalize upon the benefits of electrohydrodynamics (EHD) and enhance fuel atomization. There are many possible benefits to EHD aided atomization for combustion, such as smaller droplets, wider spray cone, and the ability to control or ``tune" the spray for improved performance. In this work, we perform detailed numerical simulations of EHD-aided liquid breakup in the context of Diesel injection using the new adaptive spectrally refined interface (ASRI) tracking method coupled to a robust and accurate Navier-Stokes/Ghost fluid solver. This novel interface tracking methodology provides several features that improve the accuracy and resolution of the liquid structures. Relevant parameters, such as Weber number, electric Reynolds number, electric Bond number, and charge ratio, are varied to assess the effect of EHD on primary atomization. [Preview Abstract] |
Sunday, November 22, 2009 10:56AM - 11:09AM |
BK.00003: Detailed numerical simulation of primary atomization processes of liquid fuel jet Junji Shinjo, Akira Umemura In order to elucidate the physical mechanisms of primary atomization of liquid fuel jet, very detailed numerical simulations have been conducted that resolve all the relevant scales in the primary atomization regime. Three cases of Diesel- like fuel injection into quiescent air with different injection velocities are compared to see the breakup mechanism and the effect of Weber and Reynolds numbers. Surface instability development, ligament creation and droplet formation are observed in the results and characterization of each process has been done. As the injection velocity is increased, the length scale of liquid structure becomes smaller. Ligament formation is observed in the regime of O(1) local Weber number. Droplet formation is governed by the dynamic effect of surface tension waves as expected by our previous study using slow laminar liquid jets. Extension to modeling using these findings will be also discussed. [Preview Abstract] |
Sunday, November 22, 2009 11:09AM - 11:22AM |
BK.00004: Windswept droplets Kevin Njifenju, Jose Bico, Emmanuelle Andres, Marc Fermigier A droplet deposited on a flat surface (e.g. a car windshield) tends to remain pinned due to contact angle hysteresis. However the droplet may be displaced when sheared by airflow or under the action of gravity. We investigate the conditions that enable the motion of a windswept droplet and describe the liquid dynamics as a function of the combined action of wind shear, gravity and capillary forces. In particular we show that these dynamics can be rationalized in terms of non-dimensional Weber, Bond and Capillary numbers. We finally describe the interaction between multiple moving droplets. [Preview Abstract] |
Sunday, November 22, 2009 11:22AM - 11:35AM |
BK.00005: Evolution of a polydispersed spray in heated and in highly turbulent flow Florian Moreau, Rudy Bazile This work aims to study experimentally the dispersion and the evaporation of a polydispersed and bi-component spray in highly turbulent and heated flow. A chamber is designed to generate a heated turbulent flow in which two-component droplets are injected. The two components are octane ($85\%$) and 3-pentanone ($15\%$) and are chosen such that the 3-pentanone vapour concentration can be characterized by laser techniques. The experimental setup consists of a vertical channel with optical access. Before the heated air is injected in the channel, it passes through a turbulence generator. The carrier flow is characterized using Laser Doppler Anemometry. The turbulence is shown to have isotropic properties after a distance equal to four times the width of the channel and to have high levels up to $30\%$. The liquid phase is characterized with Phase Doppler Anemometry which allows to measure the diameter, the longitudinal and the radial velocity of the droplets. The spatial evolution of the diameter probability density function (PDF) and of the rms and mean velocities are obtained. Droplets mass fluxes are also calculated. In the mixture, 3-pentanone is the only component that fluoresces. So the vapour concentration of 3-pentanone in the carrier flow is determined using Laser Induced Fluorescence. [Preview Abstract] |
Sunday, November 22, 2009 11:35AM - 11:48AM |
BK.00006: Lattice Boltzmann Simulations of a Falling Droplet on a Rest Fluid Film YueHong Qian, Ke Zhang, Xuesheng Chu, Kai Yan A single-phase model based on lattice Boltzmann [1,2] method is used to investigate the motion of the free surface. To describe the topological deformation of the fluid interface, the cell in the single-phase free surface model is divided into three types: fluid cells, interface cells and the empty cells. The distinctive feature of the model is that the propagation and interaction processes are carried out only in the interface cell and the fluid cell. Numerical simulations of a droplet falling onto a resting fluid film [3] is presented. The Crown formation shown in figure 1 as well as the splashing droplets have been found at different dimensionless Reynolds and Weber numbers, Some comparison with experiment will be also made. REFERENCES [1] Y.H. Qian, D. D'Humi\`eres, P. Lallemand. Lattice BGK models for Navier-Stokes equation. Europhys. Lett 1992(17): 479-484. [2] N. Thurey, U. Rude. Interactive free surface fluids with the lattice Boltzmann method. Technical report 2005. University of Erlangen-Nuremberg, Germany. [3] Z.Y. Shi, Y.H. Yan, F. Yang, Y.H. Qian and G.H. Hu. A lattice Boltzmann method for simulation of a three dimensional drop impact on a liquid film. Journal of Hydrodynamics 2008,20 (3):267-272. [Preview Abstract] |
Sunday, November 22, 2009 11:48AM - 12:01PM |
BK.00007: Modeling Interaction between Impinging Droplet and Wall with Lattice Boltzmann Method Yong Li, Tian Tian The fluid mechanics of droplet wall interaction is of great importance in many applications. In different parameter range, the results could be totally different depends on the different magnitude of influence among surface tension, inertial force and viscous force. Experiment observation shows many kinds of interactions such as splashing, sticking, rebounding. The Lattice Boltzmann Method has shown promising progress in simulation multiphase flow. But the small density variation requirement limits the parameter range it can model. An enhanced Lattice Boltzmann Method is introduced to extend the applications to large droplet air density ratio ($\sim $1000) and high velocity ($\sim $30m/s) range. The parameter zones associated different phenomenon zones are explored. Modeling results explain the forming mechanisms of phenomena. Using droplet interaction with small feature on solid surface, the model capability is demonstrated. [Preview Abstract] |
Sunday, November 22, 2009 12:01PM - 12:14PM |
BK.00008: Collision between immiscible drops with large surface tension difference Marco Arienti, Xiaoyi Li, Marios Soteriou, Mark Sussman Immiscible drop collision, as occurring in fuel-oxidizer sprays or in the release of certain fire-extinguishing agents, tends to exhibit a much richer behavior with respect to miscible drops collision thanks to the formation of a liquid-liquid interface during impact. For instance, in near-head-on diesel-water drop collisions, ``overlaying'' may occur in which the diesel oil flows from the collision point around the water drop to gather at the opposite location of the drop. To simulate this class of multi-material flows, the combined volume-of-fluid / level set methodology that sharply captures a single liquid-gas interface (\textit{Sussman et al, J. of Comp. Phys., 2007}) needs to be duplicated for a second, independent interface. In this presentation, we will show that simulation results are not affected by the reconstruction order of the interfaces, as in other surface capturing methods. We will also propose different numerical solutions to treat surface tension in the triple point computational cells, and examine the characteristics of the flow developing at the contact line between the two liquids and air in overlaying head-on collisions. [Preview Abstract] |
Sunday, November 22, 2009 12:14PM - 12:27PM |
BK.00009: Study of Mass Distribution from Two Phase Unlike Impinging Injectors Rakesh Prabhakaran, B.N. Raghunandan, Sowmya Bolakonda Two phase impinging injectors as an alternative to conventional coaxial injectors in propulsive devices offer many advantages. In addition to simplicity of design and fabrication, spray shaping according to the need is possible with gas-liquid impingement. The fact that mass distribution can be varied as desired is the main theme of this study with air and water as working fluids. In the doublet configuration, the condition of the gas jet is varied and its effect on the mass distribution is studied. As can be visualized, the circularly symmetric spray mass distribution gets distorted in the presence of the gas jet. Even at low pressure ratios, near elliptical mass distribution results. As gas pressure increases, there is a tendency for the mass distribution to be shifted in the direction of gas jet. The effect of some of the geometric parameters on the mass distribution as well as drop-size distribution are studied. Mechanistic details of jet penetration and the inherent instability in the impinging system are discussed. The data base generated is expected to help designers in spray shaping applications. [Preview Abstract] |
Sunday, November 22, 2009 12:27PM - 12:40PM |
BK.00010: Injection and Disruption of Supersonic Droplets Y.J. Kim, R.G. Cerff, J.C. Hermanson The disruption of simulated fuel droplets in supersonic flow is examined experimentally in a draw-down supersonic wind tunnel. Mono-disperse 100 $\mu $m diameter neat fluid droplets are generated using a droplet-on-demand generator upstream of the tunnel entrance. The droplets are accelerated in the supersonic flow, achieving supersonic velocities relative to the surrounding air. The droplets are imaged by direct close-up single- and multiple-exposure imaging. The latter technique allows measurement of the droplet velocity, from which the Mach number relative to the droplet, as well as the Weber number, are determined. The droplets reach a relative Mach number of as high as 1.7 and Weber numbers as high as 260. Droplet deformation and breakup patterns for these conditions can be classified into four different flow regimes by considering the changes in the Weber with downstream distance as the droplet accelerates. The drag coefficients associated with the droplet disruption under locally supersonic conditions are generally higher than those expected for solid spheres. [Preview Abstract] |
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