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Title: High fidelity simulation and analysis of liquid jet atomization in a gaseous crossflow at intermediate Weber numbers

Abstract

Recent advances in numerical methods coupled with the substantial enhancements in computing power and the advent of high performance computing have presented first principle, high fidelity simulation as a viable tool in the prediction and analysis of spray atomization processes. The credibility and potential impact of such simulations, however, has been hampered by the relative absence of detailed validation against experimental evidence. The numerical stability and accuracy challenges arising from the need to simulate the high liquid-gas density ratio across the sharp interfaces encountered in these flows are key reasons for this. In this work we challenge this status quo by presenting a numerical model able to deal with these challenges, employing it in simulations of liquid jet in crossflow atomization and performing extensive validation of its results against a carefully executed experiment with detailed measurements in the atomization region. We then proceed to the detailed analysis of the flow physics. The computational model employs the coupled level set and volume of fluid approach to directly capture the spatiotemporal evolution of the liquid-gas interface and the sharp-interface ghost fluid method to stably handle high liquid-air density ratio. Adaptive mesh refinement and Lagrangian droplet models are shown to be viable optionsmore » for computational cost reduction. Moreover, high performance computing is leveraged to manage the computational cost. The experiment selected for validation eliminates the impact of inlet liquid and gas turbulence and focuses on the impact of the crossflow aerodynamic forces on the atomization physics. Validation is demonstrated by comparing column surface wavelengths, deformation, breakup locations, column trajectories and droplet sizes, velocities, and mass rates for a range of intermediate Weber numbers. Analysis of the physics is performed in terms of the instability and breakup characteristics and the features of downstream flow recirculation, and vortex shedding. Formation of “Λ” shape windward column waves is observed and explained by the combined upward and lateral surface motion. The existence of Rayleigh-Taylor instability as the primary mechanism for the windward column waves is verified for this case by comparing wavelengths from the simulations to those predicted by linear stability analyses. Physical arguments are employed to postulate that the type of instability manifested may be related to conditions such as the gas Weber number and the inlet turbulence level. The decreased column wavelength with increasing Weber number is found to cause enhanced surface stripping and early depletion of liquid core at higher Weber number. A peculiar “three-streak-two-membrane” liquid structure is identified at the lowest Weber number and explained as the consequence of the symmetric recirculation zones behind the jet column. It is found that the vortical flow downstream of the liquid column resembles a von Karman vortex street and that the coupling between the gas flow and droplet transport is weak for the conditions explored.« less

Authors:
;  [1]
  1. United Technologies Research Center, East Hartford, Connecticut 06108 (United States)
Publication Date:
OSTI Identifier:
22598913
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Fluids; Journal Volume: 28; Journal Issue: 8; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 42 ENGINEERING; AERODYNAMICS; AIR; ATOMIZATION; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; DENSITY; DROPLET MODEL; DROPLETS; GAS FLOW; INTERFACES; JETS; LAGRANGIAN FUNCTION; LIQUIDS; MEMBRANES; RAYLEIGH-TAYLOR INSTABILITY; STRIPPING; SURFACES; TURBULENCE; VALIDATION; WAVELENGTHS

Citation Formats

Li, Xiaoyi, E-mail: lixy2@utrc.utc.com, and Soteriou, Marios C.. High fidelity simulation and analysis of liquid jet atomization in a gaseous crossflow at intermediate Weber numbers. United States: N. p., 2016. Web. doi:10.1063/1.4959290.
Li, Xiaoyi, E-mail: lixy2@utrc.utc.com, & Soteriou, Marios C.. High fidelity simulation and analysis of liquid jet atomization in a gaseous crossflow at intermediate Weber numbers. United States. doi:10.1063/1.4959290.
Li, Xiaoyi, E-mail: lixy2@utrc.utc.com, and Soteriou, Marios C.. 2016. "High fidelity simulation and analysis of liquid jet atomization in a gaseous crossflow at intermediate Weber numbers". United States. doi:10.1063/1.4959290.
@article{osti_22598913,
title = {High fidelity simulation and analysis of liquid jet atomization in a gaseous crossflow at intermediate Weber numbers},
author = {Li, Xiaoyi, E-mail: lixy2@utrc.utc.com and Soteriou, Marios C.},
abstractNote = {Recent advances in numerical methods coupled with the substantial enhancements in computing power and the advent of high performance computing have presented first principle, high fidelity simulation as a viable tool in the prediction and analysis of spray atomization processes. The credibility and potential impact of such simulations, however, has been hampered by the relative absence of detailed validation against experimental evidence. The numerical stability and accuracy challenges arising from the need to simulate the high liquid-gas density ratio across the sharp interfaces encountered in these flows are key reasons for this. In this work we challenge this status quo by presenting a numerical model able to deal with these challenges, employing it in simulations of liquid jet in crossflow atomization and performing extensive validation of its results against a carefully executed experiment with detailed measurements in the atomization region. We then proceed to the detailed analysis of the flow physics. The computational model employs the coupled level set and volume of fluid approach to directly capture the spatiotemporal evolution of the liquid-gas interface and the sharp-interface ghost fluid method to stably handle high liquid-air density ratio. Adaptive mesh refinement and Lagrangian droplet models are shown to be viable options for computational cost reduction. Moreover, high performance computing is leveraged to manage the computational cost. The experiment selected for validation eliminates the impact of inlet liquid and gas turbulence and focuses on the impact of the crossflow aerodynamic forces on the atomization physics. Validation is demonstrated by comparing column surface wavelengths, deformation, breakup locations, column trajectories and droplet sizes, velocities, and mass rates for a range of intermediate Weber numbers. Analysis of the physics is performed in terms of the instability and breakup characteristics and the features of downstream flow recirculation, and vortex shedding. Formation of “Λ” shape windward column waves is observed and explained by the combined upward and lateral surface motion. The existence of Rayleigh-Taylor instability as the primary mechanism for the windward column waves is verified for this case by comparing wavelengths from the simulations to those predicted by linear stability analyses. Physical arguments are employed to postulate that the type of instability manifested may be related to conditions such as the gas Weber number and the inlet turbulence level. The decreased column wavelength with increasing Weber number is found to cause enhanced surface stripping and early depletion of liquid core at higher Weber number. A peculiar “three-streak-two-membrane” liquid structure is identified at the lowest Weber number and explained as the consequence of the symmetric recirculation zones behind the jet column. It is found that the vortical flow downstream of the liquid column resembles a von Karman vortex street and that the coupling between the gas flow and droplet transport is weak for the conditions explored.},
doi = {10.1063/1.4959290},
journal = {Physics of Fluids},
number = 8,
volume = 28,
place = {United States},
year = 2016,
month = 8
}
  • X-ray in-line phase-contrast imaging along with a single-image phase retrieval reconstruction was used to visualize the near-nozzle breakup of optically dense water jets atomized by a high-speed, annular air flow. The influence of the atomizing air on water mass distribution was investigated to reveal the complex air/liquid interactions at various breakup stages. Unlike low-Weber-number jets, the breakup of high-Weber-number jets can occur in the liquid core, which causes sudden decreases in liquid volume fraction.
  • The Knudsen effusion mass spectrometric technique has been used to determine the thermodynamic properties of the molecules LaC and La{sub 2}C. The enthalpies of the reactions La(g) + C(graphite) = LaC(g) and 2La(g) + C(graphite) + La{sub 2}C(g) were measured in two runs in the temperature ranges 2286-2609 and 2767-2835 K, respectively, resulting in {Delta}H{sub 0}{degree} (reaction 1) = 253 {plus minus} 18 kJ mol{sup {minus}1} and {Delta}H{sub 0}{degree} (reaction 2) = -234 {plus minus} 25 kJ mol{sup {minus}1}. From these values the atomization energies, {Delta}H{sub a}{degree}{sub 0}, and standard heats of formation, {Delta}H{sub f}{degree}{sub 298.15}, were obtained as 458more » {plus minus} 20 and 685 {plus minus} 20 and 685 {plus minus} 20 kJ mol{sup {minus}1} for LaC and 945 {plus minus} 28 and 625 {plus minus} 28 kJ mol{sup {minus}1} for La{sub 2}C.« less
  • Gaseous carbides of uranium, UC, UC/sub 2/, UC/sub 3/, UC/sub 4/, UC/sub 5/, and UC/sub 6/ have been observed in a mass spectrometric investigation of the Knudsen cell effusate from a thorium--uranium--rhodium--graphite system at high temperatures. Partial pressures of the carbide molecules were measured as a function of temperature in the 2300--2700/sup 0/ K range. Second and third law methods were employed to determine enthalpy changes for the reactions of the type U(g)+nC(graphite) =UC/sub n/(g), n=1 to 6, and for additional reactions with graphite involving two gaseous carbide species and various homogeneous gas phase reactions. The experimental enthalpies when combinedmore » with thermodynamic data taken from literature yielded the following atomization energies, ..delta..H/sup 0//sub at,298/, and standard heats of formation, ..delta..H/sup 0//sub f,298/:« less
  • Abstract not provided.
  • An improved mass conserving level set method for detailed numerical simulations of liquid atomization is developed to address the issue of mass loss in the existing level set method. This method introduces a mass remedy procedure based on the local curvature at the interface, and in principle, can ensure the absolute mass conservation of the liquid phase in the computational domain. Three benchmark cases, including Zalesak's disk, a drop deforming in a vortex field, and the binary drop head-on collision, are simulated to validate the present method, and the excellent agreement with exact solutions or experimental results is achieved. Itmore » is shown that the present method is able to capture the complex interface with second-order accuracy and negligible additional computational cost. The present method is then applied to study more complex flows, such as a drop impacting on a liquid film and the swirling liquid sheet atomization, which again, demonstrates the advantages of mass conservation and the capability to represent the interface accurately.« less