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 GP: Multiphase Flows III |
Hide Abstracts |
Chair: Pushpendra Singh, New Jersey Institute of Technology Room: 202A |
Monday, November 24, 2008 8:00AM - 8:13AM |
GP.00001: Detailed Numerical Simulations of 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. While 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. This is in part due to the fact that often, several different atomization mechanisms occur on the jet's surface at the same time. Detailed numerical simulations can help study the simultaneously occurring mechanisms, even in regions of the liquid jet, where traditional experimental methods cannot observe the phase interface dynamics. To handle the large range of time and length scales that occur during atomization, we employ the Refined Level Set Grid (RLSG) method, coupled to a finite volume, balanced force, incompressible LES flow solver. We will present results for a momentum flux ratio 6.6 turbulent liquid jet of Weber number 330 and Reynolds number 14,000 injected into a gaseous crossflow of Reynolds number 740,000, taking the detailed geometry of the injector into account. 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] |
Monday, November 24, 2008 8:13AM - 8:26AM |
GP.00002: Topological Transitions in Direct Numerical Simulations of Multiphase Flows Gretar Tryggvason, Jiacai Lu, Siju Thomas Topological transitions are ubiquitous in multiphase flows and can change the nature of such flows dramatically. Here we first briefly describe a new algorithm to accomplish topology changes in front tracking simulations of multiphase flows. The algorithm, allows detailed control of when topology changes take place. The method is then used to examine regime transitions in vertical gas-liquid channel flow, when bubbly flows transition to slug or annular flows. Nearly buoyant spherical bubbles, rising in an upflow in a vertical channel, will form a bubble rich layer near the walls. The high bubble concentration increases the probability of bubble coalescence. As bubbles coalesce, they deform and move away from the walls. For the relatively narrow channels studied here, the final flow configuration consists of either slugs in the middle of the channel or annular core, depending on the void fraction. The overall evolution for this particular problem is relatively insensitive to the exact film thickness used to initiate coalescence. The present algorithm is only concerned with achieving the topology change. Capturing exactly when a thin film ruptures requires the inclusion of models for the physical processes responsible for the rupture. We end by briefly discussing how to incorporate such models. [Preview Abstract] |
Monday, November 24, 2008 8:26AM - 8:39AM |
GP.00003: Modeling primary break-up of turbulent liquid jets in cross-flow using detailed numerical simulations Madhusudan Pai, Olivier Desjardins, Heinz Pitsch Combustion efficiency and pollutant emissions from internal combustion engines and gas turbines are determined by the atomization of the liquid fuel. When injected into a quiescent or moving ambient gas, the liquid jet develops instabilities due to various causes (such as aerodynamic effects, pressure fluctuations and cavitation) which in turn lead to the primary break-up of the liquid jet. The ability to understand and accurately quantify these instabilities can provide avenues to model liquid primary break-up. Such statistics are accessible only in accurate numerical simulations of liquid jet break-up. A spectrally-refined interface (SRI) tracking method for interface transport coupled to an accurate and robust Navier-Stokes/Ghost-fluid method solver is employed to perform detailed numerical simulations of liquid-jets in cross-flow. For validation purposes, predictions from the numerical simulations for the liquid-column trajectory and liquid-jet penetration are compared with experimental datasets. Statistics of energy fluctuations due to turbulence and aerodynamic instabilities in the liquid jet, and the impact of these fluctuations on the shedding of ligaments and droplets from the surface of the liquid jet are quantified. Based on the results from the numerical simulations, a framework for modeling primary break-up of liquid jets is proposed. [Preview Abstract] |
Monday, November 24, 2008 8:39AM - 8:52AM |
GP.00004: Partial Cavity Drag Reduction Simo Makiharju, Keary Lay, Ryo Yakushiji, Marc Perlin, Steven Ceccio The notion of using air to reduce a ship's frictional drag dates back to the 19$^{th}$ century. Bubbles, air layers and air filled cavities have been proposed, but there has been little systematic research published. To address this, partial cavity drag reduction experiments were carried out at the W. B. Morgan Large Cavitation Channel. The partial cavity was investigated at Reynolds numbers to 70 million and stable cavities with frictional drag reduction of more than 95{\%} were attained. The model used was a 3 m wide and 12 m long flat plate with a plenum on the bottom. The design of the cavity was based on both linear gravity wave theory and two-dimensional inviscid numerical calculations. To create the partial cavity, air was injected at the base of an 18 cm backwards facing step 1.5 m from the nose of the plate. Frictional loads, free stream speed, air flow and cavity pressures were measured over a range of flow speeds and air fluxes. High speed video was used to investigate the unsteady three dimensional cavity closure. Cloud shedding, similar to sheet-cloud cavitation shedding with natural cavitation on hydrofoils, was observed at the closure. [Preview Abstract] |
Monday, November 24, 2008 8:52AM - 9:05AM |
GP.00005: A comparison of lattice-Boltzmann and Brownian dynamics simulations of dilute polymer solutions Tony Ladd, Rahul Kekre, Jason Butler We have compared lattice-Boltzmann and Brownian dynamics simulations of a single flexible polymer, in isolation and in confined geometries. In the case of the isolated chain we find agreement to within 1\% in the diffusion coefficient and the Rouse mode relaxation times. We have obtained good agreement for the concentration profiles in a bounded shear flow, but the Brownian dynamics simulations currently use a superposition of the hydrodynamic fields generated by the walls. We expect to know the effects of the inter-wall correction by the time of the meeting. We have gone to some lengths to match the conditions of both simulations as closely as possible. We use identical potential parameters and correct for the differences between the periodic boundaries used in the LB simulations and the unbounded domains used in the BD simulations. We use very long runs, of the order of 10000 times the longest relaxation time, to reduce the statistical uncertainties to less than 0.1\%. We find excellent agreement in the relaxation times over a wide range of temperatures and fluid viscosity. The most quantitative agreement is achieved in the weak coupling limit, where the hydrodynamic radius of the monomers is less than one quarter of the lattice spacing. [Preview Abstract] |
Monday, November 24, 2008 9:05AM - 9:18AM |
GP.00006: Numerical simulations of turbulent buoyant mixing in tilted tubes Yannick Hallez, Jacques Magnaudet We study the concentration and velocity distributions in the mixing zone of interpenetrating light and heavy fluids placed in an inclined tube using direct numerical simulation. The results of our simulations agree with the joint experimental work of Znaien et al. showing that when the tilt angle $\theta$ increases and the Atwood number $At$ decreases, the flow regime in the mixing region evolves from a turbulent shear flow towards a laminar counterflow with three well-defined layers of different concentrations. The computational results are averaged in time as well as in the streamwise direction to study the variation of the various statistics accross the tube. The transverse distribution of second-order moments is found to differ significantly from that found in a classical pipe flow, with maxima of the second-order diagonal Reynolds stresses reached on the pipe axis. The analysis of the averaged momentum balance reveals that three-dimensional effects related to the presence of inclined streamwise vortices in the flow significantly contribute to the turbulent transfer. [Preview Abstract] |
Monday, November 24, 2008 9:18AM - 9:31AM |
GP.00007: Bubbly Turbulent Drag Reduction Is a Boundary Layer Effect Dennis P.M. van Gils, Thomas H. van den Berg, Daniel P. Lathrop, Detlef Lohse In turbulent Taylor-Couette flow, the injection of bubbles reduces the overall drag. On the other hand, rough walls enhance the overall drag. In this work, we inject bubbles into turbulent Taylor-Couette flow with rough walls (with a Reynolds number up to $4\cdot10^5$), finding an enhancement of the dimensionless drag as compared to the case without bubbles. The dimensional drag is unchanged. As in the rough-wall case no smooth boundary layers can develop, the results demonstrate that bubbly drag reduction is a pure boundary layer effect. [Preview Abstract] |
Monday, November 24, 2008 9:31AM - 9:44AM |
GP.00008: Velocity and concentration fields in turbulent buoyant mixing in tilted tubes J. Znaien, F. Moisy, J.P. Hulin, D. Salin, E.J. Hinch $2D$ PIV and $LIF$ measurements have been performed on buoyancy driven flows of two miscible fluids of the same viscosity in a tube tilted at different angles $\theta$ from vertical and at different density contrasts (characterized by the Atwood number $At$). As $\theta$ increases and $At$ decreases, the flow regime evolves, behind the front, from a turbulent shear flow towards a laminar counter flow with $3$ layers of different concentrations. Time variations of the structure function show that both intermittent and developed turbulence occur in intermediate conditions. In the turbulent regime ($Re_\lambda \sim 60$) the magnitudes of the longitudinal $\overline{u'^2}$ and transverse $\overline{v'^2}$ velocity fluctuations and of the component $\overline{u'v'}$ of the Reynolds stress tensor are shown to be largest on the tube axis while viscous stresses is only important close to the walls. The analyzis of the momentum transfer in the flow with buoyancy forces estimated from the concentration gradients demonstrates that $3D$ effects are required to achieve the momentum balance. These results are discussed in the framework of classical turbulence models. [Preview Abstract] |
Monday, November 24, 2008 9:44AM - 9:57AM |
GP.00009: Light particle dispersion in stably stratified turbulence H.J.H. Clercx, M. van Aartrijk The trajectories of small inertial particles with densities of $O(\rho_{f})$ in turbulent flows can be computed using the Maxey-Riley equation. By means of direct numerical simulations we study the dispersion behavior of these light particles in statistically stationary stably stratified turbulence. The importance of the different forces that are acting on the particles is examined. It strongly depends on the density ratio. For $\rho_{p}/\rho_{f}=O(1)$ most forces are of the same order of magnitude. With increasing density ratio the relative importance of the different forces with respect to the Stokes drag decreases. For $\rho_{p}/\rho_{f}=O(10)$ mainly the Stokes drag, gravity, the pressure gradient and the Basset force remain relevant. Furthermore, the effect of the different forces on the dispersion and preferential concentration behavior of light particles will be discussed. The results are compared with those obtained for heavy particles. The results for light and heavy particles show a strong resemblance when the Stokes number is used as the parameter to express the particle properties. Moreover, the similarities and the differences between the behavior of light particles in isotropic and in stratified turbulence will be considered. [Preview Abstract] |
Monday, November 24, 2008 9:57AM - 10:10AM |
GP.00010: Evaporating shear-driven liquid film Elizaveta Gatapova, Oleg Kabov The study of an evaporating shear-driven liquid film with a localized heating is motivated by potential application in cooling of microelectronics on earth and in space. The work is also a part of the preparation of the ESA SAFIR experiment onboard the ISS. The modeling of evaporating thin liquid film driven by body force or shear stress is important both from a practical point of view and as task in investigation of film local dry-out resulting in formation of apparent contact lines. Two types of models for shear-driven liquid film with phase transitions have been developed. One of them is a two-sided model that is capable to evaluate the evaporation effect on heat transfer enhancement. Some quantitative and qualitative comparisons with experimental results are presented. The one-sided mathematical model is developed in the framework of the lubrication approximation describing the behavior of contact line. Evaporation, slip, disjoining pressure, capillarity and shear stresses effects are included in the model. The effect of the slip condition at the solid-liquid surface has been examined. [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