Bulletin of the American Physical Society
2005 58th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 20–22, 2005; Chicago, IL
Session FH: Reacting Flows III |
Hide Abstracts |
Chair: Mark Short, University of Illinois, Urbana-Champaign Room: Hilton Chicago Williford B |
Monday, November 21, 2005 8:00AM - 8:13AM |
FH.00001: Premixed flame propagation and quenching in thin nonadiabatic channels David Kessler, Mark Short We investigate the effect of thermal expansion on the burning rate and quenching limits of premixed flames propagating in thin two-dimensional nonadiabatic channels, via the variable density, reacting Navier-Stokes equations. These solutions are compared with numerical and asymptotic results obtained by Daou and Matalon (2002) with a constant density model for a quiescent mixture as well as imposed Poiseuille inflow. The critical heat transfer coefficient necessary to completely quench the flame is determined as a function of channel width and inlet velocity intensity. We also present preliminary examples of flame structures obtained for small Lewis number mixtures. [Preview Abstract] |
Monday, November 21, 2005 8:13AM - 8:26AM |
FH.00002: Premixed flames with complex chemistry as gasdynamic discontinuities Yvan Bronner, Andreas G. Class, Karin Koenig, Ulrich Maas Recently, Class, Matkowsky \& Klimenko (JFM 491, 2002) proposed a model where a premixed flame is described as a gasdynamic discontinuity separating the burned and unburned gases. In the model a flame speed relation (pde) replaces the energy and mass conservation equations. The parameters in the flame speed relation account for the reaction mechanism and fluid properties. Explicit expressions have been derived for one-step high activation energy reaction kinetics. We now obtain quantitative parameters from 1D detailed flame structure simulations. We present both the modelling approach and numerical simulations of an unsteady premixed flame with inhomogeneous mixture composition. [Preview Abstract] |
Monday, November 21, 2005 8:26AM - 8:39AM |
FH.00003: Effects of Hydrogen Enrichment on Methane and Natural Gas Premixed Laminar Flames under SI-Engine Conditions Saket Priyadarshi, Daniel Haworth Hydrogen and hydrogen/hydrocarbon blends are being explored as alternatives to hydrocarbon fuels in reciprocating-piston IC engines. Here CHEMKIN, PREMIX, and XSENKPLOT have been employed to explore global properties and local structure of steady one- dimensional laminar premixed flames of methane and natural gas with varying levels of hydrogen enrichment under typical spark- ignition engine conditions. The ratio of hydrogen to methane or natural gas has been varied while holding the total energy of the reactants fixed. Simulations have been performed for equivalence ratios from the lean flammability limit to stoichiometric, and results from four chemical mechanisms have been compared. Effects of hydrogen enrichment on laminar flame speed, internal flame structure, reaction pathways, and NOx levels have been studied. It has been found that OH appears earlier in the flame and at higher concentrations with hydrogen in the reactants, confirming a flame-speed enhancement mechanism that had been proposed in the literature. The relative importance of molecular transport compared to chemical kinetics has been examined by varying the molecular transport model; for these steady one-dimensional laminar flames, the role of differential diffusion is minor. [Preview Abstract] |
Monday, November 21, 2005 8:39AM - 8:52AM |
FH.00004: Effects of flow shear on chemical reactions in non-premixed combustion Yoshito Kaga, Naoto Yokoyama, Jiro Mizushima Interactions between chemical reactions and flows are numerically investigated by use of a methane-air six-species and four-step reduced kinetic mechanism in axisymmetric jet diffusion flame. It is known that major heat release takes place owing to the water producing reaction and is present slightly outside of the classical flame surface defined by the stoichiometric mixture fraction. In the diffusion flame, the shape of the flame surface is maintained by merging of reactants into the flame surface. In this study, it is confirmed that the amount of heat release depends on the way how the reactants are supplied to the flame surface. Therefore, effects of the inflows of chemical reactants induced by the flow shear on the chemical reactions is investigated in detail. [Preview Abstract] |
Monday, November 21, 2005 8:52AM - 9:05AM |
FH.00005: Direct numerical simulations of the double scalar mixing layer Chong M. Cha, Stephen M. deBruynKops The use of complex, multi-stream mixing scenarios abound in practical combustion devices. The double scalar mixing layer (DSML) is a canonical problem for studying the turbulent mixing of multiple streams and, with reaction, combustion of the partially-premixed type. In a DSML, a third stream consisting of a premixture of the reactants is introduced in between the pure fuel and air streams of the classic twin-feed or binary mixing problem. Direct numerical simulations (DNS) are performed to test micro-scale mixing models which are required to practically compute turbulent combustion problems of engineering interest. Here, the mixing statistics of the passive scalar is considered. It is shown that modeling based on statistical inference alone, e.g., the popular beta-pdf and Pope's statistically most-likely distribution are inadequate or require too many statistical moments to construct a good representation of the fine-scale mixing. A mapping closure model which describes the mixing of multiple streams by Navier-Stokes turbulence is shown to yield excellent agreement with the DNS with only two moments of the mixture fraction. [Preview Abstract] |
Monday, November 21, 2005 9:05AM - 9:18AM |
FH.00006: Direct Numerical Simulation of Turbulence/Radiation Interactions in Nonpremixed Systems Kshitij Deshmukh, Daniel Haworth, Michael Modest An important issue in chemically reacting turbulent flows is turbulence/radiation interaction (TRI), which arises from highly nonlinear coupling between fluctuations in temperature and species composition of the flow field. Here direct numerical simulation has been employed to investigate TRI in canonical nonpremixed systems with multi-species finite-rate chemistry. Two methods have been used to solve the radiative transfer equation: a spherical harmonics (P-1) approximation and a photon Monte Carlo method. Radiation properties correspond to a nonscattering fictitious gray gas with a temperature-dependent Planck-mean absorption coefficient that mimics that of typical hydrocarbon-air combustion products. Individual contributions of emission and absorption TRI have been isolated and quantified. The temperature self-correlation, the absorption coefficient-Planck function correlation, and the absorption coefficient-intensity correlation have been examined for intermediate-to-large values of the optical thickness, and contributions from all three correlations have been found to be significant. [Preview Abstract] |
Monday, November 21, 2005 9:18AM - 9:31AM |
FH.00007: Unstable turbulence diffusion of reacting jet Satoshi Someya, Takahide Tabata, Masahiro Nakashima, Koji Okamoto A basic characteristics of a chemically reactive jet flow, an influence of chemical reaction on a development of turbulence, is rudimentarily investigated. The chemical reaction may affect the interfacial stability of turbulent jet while the turbulence enhances the chemical reaction. The development of turbulence was experimentally investigated using LIF-PIV technique in this study. In this paper, we selected a simple irreversible chemical reaction, i.e., the reaction between ammonia solution and acetic acid solution, which generates ammonia acetic acid solution. It is an exoergic reaction with negligible small reacting heat. NaCl solution was also used in order to investigate the effect of difference of densities. At first, a behavior of the jet diffusion, i.e., the interface stability, was investigated using images of the mixing dye. The transition point, which relates to the interface stability, was clearly visualized. With the chemical reaction, the transition point moved more downstream than that without the chemical reaction. The interface in the reacting condition was more stable than that in the non-reacting condition. [Preview Abstract] |
Monday, November 21, 2005 9:31AM - 9:44AM |
FH.00008: Extinction of Lifted Flames Under Normal and Micro-Gravity Conditions Andrew Lock, Ishwar Puri, Suresh Aggarwal, Uday Hegde Inert diluents are commonly used to suppress fires in both normal- and microgravity conditions. While previous work has elucidated the effects of introducing an inert diluent into a flow in which nonpremixed flames are established, little work has been done on the effect these diluents have on partially premixed flames (PPFs). PPFs are hybrid flames that have characteristics of both premixed and nonpremixed flames. Herein, experimental measurements and numerical simulations of PPF and nonpremixed flames diluted by CO$_2$ are conducted. Visual images are experimentally obtained in microgravity, while visual images, chemiluminescence, and radiation measurements are obtained in normal gravity . The resulting fluid dynamics and chemistry interactions are elucidated. PPFs and nonpremixed flames lift off as CO$_2$ is added to the flame prior to blowout. The quantity of CO$_2$ necessary for flame blowout decreases with increased partial premixing of the initial flow. The rich premixed reaction zone of a PPF is found to weaken as CO$_2$ is added to the flow. [Preview Abstract] |
Monday, November 21, 2005 9:44AM - 9:57AM |
FH.00009: A Numerical Study of Flame Liftoff and Blowout Using Fuel and Air Stream Dilution Alejandro Briones, Suresh Aggarwal, Viswanath Katta The effects of fuel and air stream dilution on the liftoff, stabilization, and blowout characteristics of nonpremixed (NPF) and partially premixed flames (PPF) in axisymmetric coflowing jets are investigated. While the undiluted PPF is in a burner-attached mode, the undiluted NPF is lifted. Both flames exhibit a double flame structure in the near-field region, where the flame stabilization depends on a balance between flame reactivity and scalar dissipation rate ($\chi )$. As diluent mole fraction (X$_{dil})$ is increased, the flames become weaker, moving downstream along the stoichiometric mixture fraction line, and stabilizing at a location of lower $\chi $. Further increase in X$_{dil}$ moves the flames further downstream into the far-field region, where both the NPF and PPF exhibit a triple flame structure, and the flame stabilization also depends on a balance between the triple flame speed and the local flow velocity at the flame base. With fuel stream dilution, PPFs are stabilized at a higher liftoff height (L$_{f})$ and blow out at a lower X$_{dil}$ compared to NPFs. In contrast, with air stream dilution, NPFs move to a higher L$_{f}$ and blow out at a lower X$_{dil}$ compared to PPFs. Simulations are used to examine the various mechanisms for the stabilization of lifted flames. [Preview Abstract] |
Monday, November 21, 2005 9:57AM - 10:10AM |
FH.00010: Head-on Quenching of a Non-premixed Flame by an Inert Wall Nidheesh Bharadwaj, Cyrus Madnia The quenching characteristics of a nonpremixed flame interacting with a wall have been studied via DNS. The vortex ring is generated by a brief discharge of cold methane fuel into hot air. The ignition of the vortex ring is controlled by adjusting the air temperature. The methane combustion has been modeled using detailed kinetic model GRI$3.0$. The flame is propelled in the axial direction by the ring induced velocity, and interacts head on with a chemically inert isothermal wall. Two wall conditions are examined, one with and one without a thermal boundary layer. The strength of the flame prior to its interaction with the wall is controlled by varying the distance of the wall from the inlet boundary. The effect of the wall on the heat release rate and the structure of the flame is studied. As the flame approaches the wall the magnitudes of vortex ring induced strain rates acting on the flame increase and the maximum wall heat flux occurs on the centerline. It is found that the increase in the strain rates affects the flame power significantly if there is no thermal boundary layer at the wall. Nondimensional wall heat flux, Peclet number, flame structure and near wall reaction mechanisms have been investigated for front flame quenching. For runs with thermal boundary layer, heat released from HO$_{2}$ reactions is found to be the major contributor to heat flux at the wall. [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