Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session A33: Atomization, Breakup and Interfacial Flows |
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Chair: Luis Bravo, United States Army Research Laboratory Room: 2022 |
Sunday, November 23, 2014 8:00AM - 8:13AM |
A33.00001: ABSTRACT WITHDRAWN |
Sunday, November 23, 2014 8:13AM - 8:26AM |
A33.00002: High Fidelity Simulation of Primary Atomization in Diesel Engine Sprays Christopher Ivey, Luis Bravo, Dokyun Kim A high-fidelity numerical simulation of jet breakup and spray formation from a complex diesel fuel injector at ambient conditions has been performed. A full understanding of the primary atomization process in fuel injection of diesel has not been achieved for several reasons including the difficulties accessing the optically dense region. Due to the recent advances in numerical methods and computing resources, high fidelity simulations of atomizing flows are becoming available to provide new insights of the process. In the present study, an unstructured un-split Volume-of-Fluid (VoF) method coupled to a stochastic Lagrangian spray model is employed to simulate the atomization process. A common rail fuel injector is simulated by using a nozzle geometry available through the Engine Combustion Network. The working conditions correspond to a single orifice (90 $\mu$m) JP-8 fueled injector operating at an injection pressure of 90 bar, ambient condition at 29 bar, 300K filled with 100\% nitrogen with $Re_l$ = 16,071, $We_l$ = 75,334 setting the spray in the full atomization mode. The experimental dataset from Army Research Lab is used for validation in terms of spray global parameters and local droplet distributions. The quantitative comparison will be presented and discussed. [Preview Abstract] |
Sunday, November 23, 2014 8:26AM - 8:39AM |
A33.00003: Numerical simulation of evaporating liquid jet in crossflow Marios Soteriou, Xiaoyi Li Atomization of liquid fuel jets by cross-flowing air is critical to combustor performance. Ability to experimentally probe the fundamentals of this multiscale two phase flows has been hampered by limitations in experimental techniques and the challenges posed by operating conditions. Direct numerical simulation has recently emerged as a promising alternative due to advances in computer hardware and numerical methods. Using this approach, we recently demonstrated the ability to reproduce the physics of atomization of a liquid jet in cross-flow (LJIC) under ambient conditions. In this work we consider this flow in a high temperature environment. The inclusion of evaporation is the major new element. The numerical approach employs the CLSVOF method to capture the liquid-gas interface. Interface evaporation is solved directly with proper treatment of interface conditions and reproduces the relevant species/temperature fields there. A Lagrangian droplet tracking approach is used for the small droplets which are transferred from the Eulerian phase and evaporate using a traditional d$^{\mathrm{2}}$ law model. Other key algorithms of the massively parallelized solver include a ghost fluid method, a multi-grid preconditioned conjugate gradient approach and an adaptive mesh refinement technique. The overall method is verified using canonical problems. Simulations of evaporating LJIC point to the significant effect that evaporation has on the evolution of this flow and elucidate the downstream fuel species patterns. [Preview Abstract] |
Sunday, November 23, 2014 8:39AM - 8:52AM |
A33.00004: A Computational Study of an Atomizing Liquid Sheet Suraj Deshpande, Mario Trujillo Atomization of a liquid sheet is studied using simulations based on a volume of fluid (VoF) method. Our aim is to evaluate the primary atomization models which are often used in Lagrangian-Eulerian simulations, a prominent spray simulation method. The models assume that growth of sinuous unstable waves on the sheet causes its breakup and use linear theory to predict the wavelength [Dombrowski {\&} Johns 1963; Senecal et al. 1999]. With respect to this, we address two points: (1) applicability of linear theory to instability prediction, and (2) relevance of this prediction to sheet breakup. To this end, a more general linear analysis considering capillary, viscous and boundary layer is performed using Orr-Sommerfeld (OS) theory. Our VoF simulations show that instability mechanism does selectively amplify indistinct noise into discernible interfacial waves, which are very well predicted by OS analysis. These waves, however, do not cause sheet breakup, and this contrasts prior linear theories. The structures which eventually do lead to breakup are shown to be practically independent of viscous and surface tension effects (unlike the linear waves). They scale with sheet thickness, and are $\sim$ $O$(100) times larger than predicted by linear theories. [Preview Abstract] |
Sunday, November 23, 2014 8:52AM - 9:05AM |
A33.00005: Numerical simulation of liquid-layer breakup on a moving wall due to an impinging jet Taejong Yu, Hojoon Moon, Donghyun You, Dokyun Kim, Andrey Ovsyannikov Jet wiping, which is a hydrodynamic method for controlling the liquid film thickness in coating processes, is constrained by a rather violent film instability called splashing. The instability is characterized by the ejection of droplets from the runback flow and results in an explosion of the film. The splashing phenomenon degrades the final coating quality. In the present research, a volume-of-fluid (VOF)-based method, which is developed at Cascade Technologies, is employed to simulate the air-liquid multiphase flow dynamics. The present numerical method is based on an unstructured-grid unsplit geometric VOF scheme and guarantees strict conservation of mass of two-phase flow, The simulation results are compared with experimental measurements such as the liquid-film thickness before and after the jet wiping, wall pressure and shear stress distributions. The trajectories of liquid droplets due to the fluid motion entrained by the gas-jet operation, are also qualitatively compared with experimental visualization. Physical phenomena observed during the liquid-layer breakup due to an impinging jet is characterized in order to develop ideas for controlling the liquid-layer instability and resulting splash generation and propagation. [Preview Abstract] |
Sunday, November 23, 2014 9:05AM - 9:18AM |
A33.00006: Experimental investigation of two oil dispersion pathways by breaking waves Cheng Li, Joseph Katz This experimental study focuses on generation and size distribution of airborne and subsurface oil droplets as breaking surface waves interact with a crude oil slick (MC252 surrogate). Experiments in a specialized wave tank investigate the effects of wave height and wave properties (e.g. spilling vs. plunging), as well as drastically reducing the oil-water interfacial tension by orders of magnitude by introducing dispersant (Coexist 9500-A). This dispersant is applied at varying dispersant-to-oil ratios either by premixing or surface spraying, the latter consistent with typical application. The data include high-speed visualizations of processes affecting the entrainment of subsurface oil and bubbles as well as airborne aerosols. High-speed digital holographic cinematography is employed to track the droplet trajectories, and quantify the droplet size distributions above and below the surface. Introduction of dispersants drastically reduces the size of subsurface droplets to micron and even submicron levels. Ahead of the wave, the 25 $\mu $m (our present resolution limit) to 2 mm airborne droplet trajectories are aligned with the wave direction. Behind the wave, these droplets reverse their direction, presumably due to the airflow above the wave. [Preview Abstract] |
Sunday, November 23, 2014 9:18AM - 9:31AM |
A33.00007: Heat transfer and convective structure of evaporating films under pressure-modulated conditions Juan Carlos Gonzalez-Pons, James Hermanson, Jeffrey Allen The interfacial stability, convective structure, and evaporation rate of upward-facing, thin liquid films were studied experimentally. Dichloromethane films approximately 2 mm thick were subjected to impulsive, time-varying superheating. The films resided on a temperature controlled, copper surface in a closed, initially degassed test chamber. Superheating was achieved by modulating the pressure of the saturated pure vapor in the test chamber. The dynamic film thickness was measured at multiple points using ultrasound, and the convective structure information was visualized by schlieren imaging. Two distinct raises in heat transfer rate under unsteady conditions were observed. The first transition appears to be associated with conduction within the film only; the second, to a change in the pattern of convection within the film. Different pressure-modulation cycles were studied to capture one or both of the observed rises in heat transfer. The total film thickness change over multiple cycles, as indicated by ultrasound, allowed determination of the total heat rejected into the evaporating films. Results suggest that there are cycle combinations that lead to an elevation in the average rate of heat transfer compared to films undergoing quasi-steady evaporation. [Preview Abstract] |
Sunday, November 23, 2014 9:31AM - 9:44AM |
A33.00008: Effects of Soluble Surfactant on Lateral Migration of a Bubble in a Shear Flow Metin Muradoglu, Gretar Tryggvason Motivated by the recent experimental study of Takagi et al. (2008), direct numerical simulations are performed to examine effects of soluble surfactant on the lateral migration of a deformable bubble in a pressure-driven channel flow. The interfacial and bulk surfactant concentration evolution equations are solved fully coupled with the incompressible Navier-Stokes equations. A non-linear equation of state is used to relate interfacial surface tension to surfactant concentration at the interface. A multiscale method is developed to handle the mass exchange between the interface and bulk fluid at high Peclet numbers, using a boundary-layer approximation next to the bubble and a relatively coarse grid for the rest of the flow. It is found that the surfactant induced Marangoni stresses can dominate over the shear-induced lift force and thus alter the behavior of the bubble completely, i.e., the contaminated bubble drifts away from the channel wall and stabilizes at the center of the channel in contrast with the corresponding clean bubble that drifts toward the wall and stabilizes near the wall. [Preview Abstract] |
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