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 G3: Multiphase Flows IV |
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Chair: Sean Garrick, University of Minnesota Room: 325 |
Monday, November 25, 2013 8:00AM - 8:13AM |
G3.00001: Simulation of sprays using a Lagrangian filtered density function approach WanJiao Liu, Sean Garrick Sprays and atomization have wide applications in industry, including combustion/engines, pharmaceutics and agricultural spraying. Due to the complexity of the underlying processes, much of the underlying phenomena are not fully understood. Numerical simulation may provide ways to investigate atomization and spray dynamics. Large eddy simulation (LES) is a practical approach to flow simulation as it resolves only the large-scale structures while modeling the sub-grid scale (SGS) effects. We combine a filtered density function (FDF) based approach with a Lagrangian volume-of-fluid method to perform LES. This resulting methodology is advantageous in that it has no diffusive or dissipative numerical errors, and the highly non-linear~surface tension force appears in closed form thus the modeling of the SGS surface tension is not needed when simulating turbulent, multiphase flows. We present the methodology and some results for the simulation of multiphase jets. [Preview Abstract] |
Monday, November 25, 2013 8:13AM - 8:26AM |
G3.00002: Eulerian CFD modeling and X-ray validation of non-evaporating diesel spray Qingluan Xue, Sibendu Som, Shaoping Quan, Eric Pomraning, P.K. Senecal This work implemented an Eulerian single-phase approach by Vallet et al. [1] into CFD software (Convergent) for diesel spray simulations. This Eulerian approach considers liquid and gas phase as a complex mixture of a single flow with a highly variable density to describe the near nozzle dense sprays. The mean density is obtained form the Favre-averaged liquid mass fraction. Liquid mass fraction is transported with a model for the turbulent liquid diffusion flux into the gas. A mean gradient-based model is employed for the diffusion flux in this study. A non-evaporating diesel spray was measured using x-ray radiography at Argonne National Laboratory. The quantitative and time-resolved data of liquid penetration and mass distribution in the dense spray region are used to validate this approach. The different turbulence models are also used for the simulations. The comparison between the simulated results and experimental data and the turbulence model effect are discussed. \\[4pt] [1] Vallet et al., Atomization and Sprays, vol. 11, pp. 619-642, 2001. [Preview Abstract] |
Monday, November 25, 2013 8:26AM - 8:39AM |
G3.00003: LES/FMDF of High Speed Spray Combustion Abolfazl Irannejad, Farhad Jaberi High speed evaporating and combusting sprays are computed with the hybrid two-phase large eddy simulation (LES)/filtered mass density function (FMDF) methodology. In this methodology, the resolved fluid velocity is obtained by solving the filtered form of the compressible Navier-Stokes equations with high-order finite difference schemes. The scalar (temperature and species mass fractions) field is obtained by solving the FMDF transport equation with a Lagrangian stochastic method. The spray is simulated with the Lagrangian droplets together with stochastic breakup and finite rate heat and mass transfer models. The liquid volume fraction is included in the LES/FMDF for denser spray regions. Simulations of high speed evaporating sprays with and without combustion for a range of gas and spray conditions indicate that the two-phase LES/FMDF results are consistent and compare well with the experimental results for global spray variables such as the spray penetration and flame lift-off lengths. The gas velocity and turbulence generated by the spray are found to be very significant in all simulated cases. A broad spectrum of droplet sizes is also found to be generated by the complex and coupled effects of the gas flow turbulence, droplet breakup, evaporation and combustion. [Preview Abstract] |
Monday, November 25, 2013 8:39AM - 8:52AM |
G3.00004: Analysis of an Electrostatic Spray Injector Matthew Ryan, Jonathan Tennis, Chol-Bum Kweon, Michael Benson, Bret Van Poppel The objective of the current research is to assess the effects of electrostatic injector designs and charge energy on the spray break-up process. Electrostatic injectors have a potential to improve the liquid fuel spray atomization at low fuel pressures. The application areas include carbureted and port fuel injections in small engines to improve fuel-air mixing. In this study, two different electrostatic injector designs are tested in an ambient chamber with four optical windows. Shadowgraphy and Mie scattering techniques are used to measure the major spray parameters such as spray patterns, spray angles, and liquid fuel penetration length. Shadowgraphy with a micro zoom lens is used to measure droplet distributions and droplet pressures. An analysis of the results is presented to inform electrostatic injector design. [Preview Abstract] |
Monday, November 25, 2013 8:52AM - 9:05AM |
G3.00005: ABSTRACT WITHDRAWN |
Monday, November 25, 2013 9:05AM - 9:18AM |
G3.00006: Direct numerical simulation of leaky dielectrics with application to electrohydrodynamic atomization Mark Owkes, Olivier Desjardins Electrohydrodynamics (EHD) have the potential to greatly enhance liquid break-up, as demonstrated in numerical simulations by Van Poppel et al. (JCP (229) 2010). In liquid-gas EHD flows, the ratio of charge mobility to charge convection timescales can be used to determine whether the charge can be assumed to exist in the bulk of the liquid or at the surface only. However, for EHD-aided fuel injection applications, these timescales are of similar magnitude and charge mobility within the fluid might need to be accounted for explicitly. In this work, a computational approach for simulating two-phase EHD flows including the charge transport equation is presented. Under certain assumptions compatible with a leaky dielectric model, charge transport simplifies to a scalar transport equation that is only defined in the liquid phase, where electric charges are present. To ensure consistency with interfacial transport, the charge equation is solved using a semi-Lagrangian geometric transport approach, similar to the method proposed by Le Chenadec and Pitsch (JCP (233) 2013). This methodology is then applied to EHD atomization of a liquid kerosene jet, and compared to results produced under the assumption of a bulk volumetric charge. [Preview Abstract] |
Monday, November 25, 2013 9:18AM - 9:31AM |
G3.00007: ABSTRACT WITHDRAWN |
Monday, November 25, 2013 9:31AM - 9:44AM |
G3.00008: Large Scale Behavior and Droplet Size Distributions in Crude Oil Jets and Plumes Joseph Katz, David Murphy, David Morra The 2010 \textit{Deepwater Horizon} blowout introduced several million barrels of crude oil into the Gulf of Mexico. Injected initially as a turbulent jet containing crude oil and gas, the spill caused formation of a subsurface plume stretching for tens of miles. The behavior of such buoyant multiphase plumes depends on several factors, such as the oil droplet and bubble size distributions, current speed, and ambient stratification. While large droplets quickly rise to the surface, fine ones together with entrained seawater form intrusion layers. Many elements of the physics of droplet formation by an immiscible turbulent jet and their resulting size distribution have not been elucidated, but are known to be significantly influenced by the addition of dispersants, which vary the Weber Number by orders of magnitude. We present experimental high speed visualizations of turbulent jets of sweet petroleum crude oil (MC 252) premixed with Corexit 9500A dispersant at various dispersant to oil ratios. Observations were conducted in a 0.9 m x 0.9 m x 2.5 m towing tank, where large-scale behavior of the jet, both stationary and towed at various speeds to simulate cross-flow, have been recorded at high speed. Preliminary data on oil droplet size and spatial distributions were also measured using a videoscope and pulsed light sheet. [Preview Abstract] |
Monday, November 25, 2013 9:44AM - 9:57AM |
G3.00009: Experimental and computational investigation of underwater buoyant oil jets Leandre Berard, Mehdi Raessi, Michael Bauer, Peter Friedman, Stephen Codyer We present experimental and numerical results on the breakup of underwater positively buoyant oil jets at a wide range of Reynolds, Weber and Richardson numbers and several viscosity ratios. Three main jet breakup regimes are observed: atomization, skirt-type and pinch-off. A threshold Weber number for the atomization regime is found to be around 100, varying slightly with the jet E\"otv\"os number. The Ohnesorge-Reynolds correlation proposed by Masutani and Adams as the boundary for the atomization regime is shown to be applicable to our broader data set as well. Results suggest that the breakup of a positive buoyancy-driven jet occurs only when the jet is accelerated to a point where the local Richardson number becomes less than 0.4, in which case the local Weber number is above 10. The numerical results reveal the mechanisms leading to formation of small droplets around the perimeter of energetic jets and umbrella-shaped jet separations at less energetic cases. The time-averaged lateral expansion of the simulated jets, representing four different conditions, are presented as a function of the height along the jet. [Preview Abstract] |
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