Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session M02: Reacting Flows: Experiments |
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Chair: Subith Vasu, University of Central Florida Room: Georgia World Congress Center B203 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M02.00001: Conditions for Formation of the Blue Whirl Sriram Bharath Hariharan, Yu Hu, Michael J Gollner, Elaine S Oran The blue whirl is a regime of the fire whirl with peak temperatures around 2000 K, and burns a variety of liquid hydrocarbons directly with little visible soot. Here, the conditions required for blue whirl formation are investigated in a fixed-frame self-entraining fire whirl setup. The parameters governing the fire whirl regime are buoyancy (determined by Q ̇, heat release rate from combustion) and level of swirl (determined by Γ, circulation due to entrainment). The two parameters are coupled in a self-entraining configuration, causing only certain regimes of the fire whirl to stably form. Q ̇ is controlled over a wide range of values by adjusting the fuel supply rate, and the resulting inlet velocities into the fire whirl enclosure are measured using a hot-wire anemometer. A graph of Q ̇ vs. Γ for the different regimes shows that stable blue whirl formation occurs in a narrow region close to the extinction limit found in literature. Two scaling approaches are outlined to predict the formation conditions for different enclosure sizes, and further understand the physical processes controlling blue whirl formation. The scaling approach shows that the blue whirl occurs in a circulation-dominated flow field. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M02.00002: Abstract Withdrawn
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Tuesday, November 20, 2018 8:26AM - 8:39AM |
M02.00003: ABSTRACT WITHDRAWN
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Tuesday, November 20, 2018 8:39AM - 8:52AM |
M02.00004: High Pressure Methane Ignition Delay Measurements under Supercritical Carbon Dioxide Conditions Miad Karimi, Bradley Ochs, Wenting Sun, Devesh Ranjan An inquiry to be investigated for supercritical carbon dioxide (sCO2) oxy-combustion is how well existing chemical kinetic models perform as no experimental data exists at relevant conditions. Autoignition delays are reported for CH4/O2/CO2 mixtures above the CO2 critical pressure (up to 200 bar) and for a temperature range of 1139 to 1433 K. Experiments reveal that a widely used kinetic model, GRI 3.0, underpredicts the ignition delay by a factor of 3 at 100 bar. However, kinetic models Aramco 2.0, USC Mech II, HP-Mech, and FFCM1 are capable of predicting autoignition delays though previously not validated at this pressure. At 100 bar, CH3 recombination to form C2H6 through CH3+CH3+M=C2H6+M becomes dominant compared to direct oxidation to form CH3O. The branching ratio of these two reaction pathways dictates the autoignition delay. The experimental results at 200 bar however, shows that only one chemical kinetics mechanism could capture the ignition behavior. Simulation results using Aramco 2.0 kinetics mechanism is determined to have a reasonable agreements to predict ignition delay times at 200 bar and a temperature range of 1139 K to 1250 K. No chemical effect from CO2 on autoignition was observed at supercritical conditions. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M02.00005: High-Speed 3-D Imaging of Ignition in a Circular Shock Tube Erik Ninnemann, Owen Pryor, Sneha Neupane, Subith Vasu The primary reference fuels isooctane and n-heptane have been studied extensively in laboratory settings including rapid compression machines, shock tubes, jet-stirred reactors, and flames. These experimental investigations have been imperative to determining reaction rates and pathways to build comprehensive chemical kinetic mechanisms, but they do not provide information about the dynamics of ignition structure or behavior. In this work, high-speed three-dimensional images were taken at moderate temperatures and low pressures in a circular shock tube for the first time. This new imaging technique combines the end wall facing camera with a second high-speed camera that is placed perpendicular to the first, providing information on the ignition down the depth of the tube. With this novel technique, a better understanding of the three-dimensional exothermicity is achieved. Preliminary results show that the ignition for isooctane begins in the lower portion of the tube though ignition never completely consumes the entire test section. This work provides the next step in high-speed shock tube diagnostics and provides valuable insight into the ignition structure of the primary reference fuels. |
Tuesday, November 20, 2018 9:05AM - 9:18AM |
M02.00006: Diffusion and finite kinetics Reaction in a Hele-Shaw cell Emilie Guilbert, Christophe Almarcha, Emmanuel Villermaux Making use of an original chemical reaction between two transparent reactants (fluorescin and potassium ferricyanide) producing a fluorescent product in water (fluorescein) which allows for the quantitative measurement of the product formation, we investigate the interplay between molecular diffusion and reaction kinetics in a variety of situations. When a drop of fluorescin is injected in a Hele-Shaw cell filled with potassium ferricyanide, we distinguish two limits depending on the value of the Damkhöler number Da = τDiff/τReac, with τDiff and τReac the characteristic times of diffusion, and reaction. In the diffusion limited regime(Da > 1), the total quantity of product increases as √t with a maximum concentration CF constant in time t. In the chemical limited regime (Da < 1), CF relaxes exponentially toward a final concentration which depends on the radial position r in the cell within a characteristic time also a function of r. We will underline the potential interest of this method to fundamental concerns in mixing, and other fields of application. |
Tuesday, November 20, 2018 9:18AM - 9:31AM |
M02.00007: Vessel confinement contributions to thermo-acoustic instabilities of premixed flames Daniel Martinez-Ruiz, Fernando Veiga-Lopez, Mario Sanchez-Sanz An experimental study of the behavior of hydrocarbon premixed flames propagating in quasi-2D configurations is presented here. The experiments were performed using a Hele-Shaw cell of dimensions (1~10 mm)x(500 mm)x(1000 mm) as a combustion chamber with the ignition located at the open end and the flame propagating towards the closed end of the cell. The development of instabilities, such as Darrieus- Landau (DL), Saffman-Taylor (ST), diffusive-thermal (DT), etc., as well as the propagation rate and the presence or absence of quenching or partial burning have been previously studied. In the present work, the experimental setup is used to characterize the dependence of the channel thickness (ranging from 1 to 10 mm) and the material properties of the plates enclosing the Hele-Shaw cell in the arising of thermo-acoustic instabilities of propane, methane and dimethyl ether premixed flames. Preliminary results are shown here and discussed. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M02.00008: Vertical shear affects chemical front speed in thin-layer flows Thomas Nevins, Douglas H Kelley The dynamics of a chemical reaction in a flow can be described through the motion of a front which divides reacted from unreacted regions. These fronts advance because of the production of new reaction product and are advected by flow, so we expect the front velocity to be the vector sum of a constant chemical velocity and the flow velocity, consistent with the Eikonal equation. However, in previous quasi-two-dimensional experiments we measured chemical velocities many times larger than expected, and they seemed to increase with flow velocity. Vertical shear explains the discrepancy, even in the absence of out of plan flow such as from Ekman pumping. We present simulations using the Eikonal equation and accounting for shear, resulting in a close match to chemical velocities measured in our experiments. We also show that adding a lubrication layer reduces shear and makes experimental measurements of chemical velocity match two-dimensional theory more closely. Compensating for vertical shear may allow more accurate identification of the flow structures which cause other advection-reaction-diffusion phenomena like extinction. |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M02.00009: Investigation on Hydrodynamic Effect on Eutectic Melting Shota Ueda, Kenta Inagaki, Masahiro Kondo, Koji Okamoto Eutectic melting (EM) is melting of the crystal due to the exposure to the surface of another adjacent phase. EM is common for multi-component systems. Empirical equations have been developed for the prediction of EM progress; however, EM speed significantly varies depending on the experimental conditions such as a specimen geometry. It may be considered that the difference of specimen geometry causes the different flow conditions in liquid phases and thus EM speed changes. However, there was no investigation on how the flow condition in the liquid phase affects the EM progress. In this study, the hydrodynamic effect on EM of Sn-Bi binary system has been experimentally investigated. The solid specimen made of tin was soaked in the Sn-Bi eutectic melt while controlling the flow around the specimen. Tuning-fork sensors measured the apparent weight of the submerged specimen in a time-resolved manner as a degree of the EM. Consequently, the EM was significantly enhanced by the flow on turbulent conditions. The influence of the flow condition on EM was also observed as the wavy-shaped interface. |
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