Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session M26: Reactive Flows VII |
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Chair: Antonio L. Sánchez, University Carlos III de Madrid Room: 31B |
Tuesday, November 20, 2012 8:00AM - 8:13AM |
M26.00001: Rate Ratio Asymptotic Analysis of the Influence of Hydrogen on the Structure and Mechanisms of Extinction of Methane Flames in Laminar Nonpremixed Flows Kalyanasundaram Seshadri, Xue-Song Bai, Forman Williams Rate-ratio asymptotic analysis is carried out to elucidate the influence of hydrogen on the structure and mechanisms of extinction of methane flames in laminar nonpremixed flows. Steady, axisymmetric, laminar flow of two counter-flowing streams toward a stagnation plane is considered. One stream is made up of a mixture of methane, hydrogen, and nitrogen. The other stream is made up of a mixture of oxygen, and nitrogen. A reduced four-step chemical kinetic mechanism is employed. Chemical reactions are presumed to take place in a thin reaction zone that is established in the vicinity of the stagnation plane. On either side of this thin reaction zone, the flow field is inert. These inert regions are called the outer structure. The outer structure is analyzed first. It gives the matching conditions that is required in the analysis of the reaction zone. In the thin reaction zone chemical reactions are presumed to take place in two layers--an inner layer and an oxidation layer. In the inner layer methane is consumed and hydrogen and carbon monoxide are formed. In the oxidation layer oxygen, carbon monoxide and hydrogen are consumed. Critical conditions of extinction are predicted and are compared with experimental data and with results of numerical computation. [Preview Abstract] |
Tuesday, November 20, 2012 8:13AM - 8:26AM |
M26.00002: Explosions in uncertain hydrogen-oxygen mixtures Javier Urzay, Nicolas Kseib, David F. Davidson, Gianluca Iaccarino, Ron K. Hanson Uncontrolled residuals abound in combustors as a result of complex chemistry. The question to answer here is: How can we give a measure of the explosive tendency of a gaseous mixture when the initial composition is not known with absolute certainty? This study addresses the influences of uncertain amounts of residual radical impurities, namely H, O, OH and HO2 radicals, on the calculation and experimental determination of autoignition times in H2-O2 mixtures. To illustrate this point, shock-tube data is obtained in which the presence of residual radicals is evidenced by i) the detection of trace amounts of OH radicals in initial oxygen-argon mixtures and ii) the need of shortening the autoignition times calculated after integrations of the conservation equations when matching with experimental kinetics data. Regime diagrams of autoignition catalyzed by impurities above and below crossover are proposed, thereby summarizing the potential effects of residual dirt in shock-tube experiments and calculations. An experimentally-inspired model based on Bayesian inference is proposed for the uncertainty in the H-atom impurities in shock tubes. Monte-Carlo calculations of the conservation equations are performed using this model to assess the induced variabilities in the autoignition time. [Preview Abstract] |
Tuesday, November 20, 2012 8:26AM - 8:39AM |
M26.00003: The simulation of a hydrogen-bubble reaction due to shock ignition Temistocle Grenga, Samuel Paolucci We simulate the combustion of a hydrogen bubble in air ignited by a shock wave. The three dimensional compressible model includes detailed chemical kinetics, multi-component diffusion, Soret and Dufour effects, and state dependent transport properties. The reaction mechanism involves 9 species and 19 reversible reactions. The possibility of using a reduced chemical kinetics mechanism obtained through the G-Scheme is also explored. Results are compared with other numerical and experimental studies. The simulation is challenging since the physical and chemical phenomena lead to a large multiscale problem, which we solve using the parallel Wavelet Adaptive Multiresolution Representation (pWAMR) method. The method exhibits an impressive compression of the solution when compared to other methods. The algorithm is parallelized using a domain decomposition approach based on a Hilbert space-filling curve. pWAMR is able to capture all structures of O($\mu$m) required for an accurate solution. The method is able to capture all scales using a relatively small number of degrees of freedom by adapting refinements to local demands of the solution. In addition, since the amplitudes of the wavelet transform provide a direct measure of the local error, we are able to produce a verified solution. [Preview Abstract] |
Tuesday, November 20, 2012 8:39AM - 8:52AM |
M26.00004: Numerical study of a jet-in-hot-coflow burner with hydrogen-addition using the Flamelet Generated Manifolds technique Seyed Ebrahim Abtahizadeh, Jeroen van Oijen, Philip de Goey Recently Mild combustion is subjected to intensive research because of its unique ability to provide high efficiency and low pollutant combustion simultaneously in industrial heating processes. In most practical Mild combustion applications, a fuel jet is ignited due to recirculation of hot burned gases. The impact of burned gases on autoignition and flame stabilization has been studied in a laboratory jet-in-hot-coflow (JHC) burner. Results of this study help us to understand recent experimental observations of the Delft group (DJHC burner) in which Dutch Natural Gas (DNG) is mixed with various amounts of H$_2$. The main focus is on the modeling of autoignition in the DJHC burner by using the Flamelet Generated Manifolds (FGM) technique. In this technique, kinetic information is tabulated with a few controlling variables which results in a significant decrease in simulation time. The FGM tabulation has been performed using igniting laminar counterflow diffusion flames. Since H$_2$ is present in the fuel composition, it is essential to include preferential diffusion effects in the table due to the high diffusivity of H$_2$. Based on results, the FGM table is capable to reproduce the autoignition of hydrogen containing fuel predicted by detailed chemistry in 1D counterflow flames. [Preview Abstract] |
Tuesday, November 20, 2012 8:52AM - 9:05AM |
M26.00005: Numerical analysis and simulation of diffusion-free ignition delay times of unreacted pockets Jonathan Regele Volumes of unreacted fluid surrounded by combustion products are observed in Deflagration-to-Detonation Transition (DDT) and unstable cellular detonations. The presence of this unburned reactant is typical of mixtures with large activation energies. Several different scales are involved in the consumption of unreacted pockets including the autoignition, diffusion, and acoustic times. Transport effects can influence the consumption rate of reactant within these pockets. In particular diffusion plays a major role when activations energies are large. In contrast, it has been shown that diffusion can play a minor role when reactive mixtures have small to moderately large activation energies. The current work focuses on the limit when diffusion effects are negligible and examines the dependence of delay time on initial temperatures and sizes. It is demonstrated that the ignition delay time is a function of both the initial temperature and the volumetric dimension of the fluid. Furthermore, the ignition delay time lies on a continuum scale with the constant pressure and constant volume ignition delay times demarcating the limiting extremes. [Preview Abstract] |
Tuesday, November 20, 2012 9:05AM - 9:18AM |
M26.00006: Numerical simulation of autoigniting flames Rajapandiyan Asaithambi, Krishnan Mahesh Autoignition is highly sensitive to temperature and mixing. A density based method for DNS/LES of compressible chemically reacting flows is proposed with an explicit predictor step for advection and diffusion terms, and a semi-implicit corrector step for stiff chemical source terms. This segregated approach permits independent modification of the Navier-Stokes solver and the time integration algorithm for the chemical source term. The algorithm solves the total chemical and sensible energy equation and heat capacities of species are obtained from thermodynamic tables. Chemical mechanisms in the Chemkin format is parsed and source terms are automatically linearized allowing the ability to simulate multiple fuels with minimal effort. Validation of the algorithm is presented and results from autoigniting non-premixed flames in vitiated coflow with different fuels are discussed. [Preview Abstract] |
Tuesday, November 20, 2012 9:18AM - 9:31AM |
M26.00007: Investigation of ignition dynamics in a mixing layer with a vortex Shyam Menon, Guillaume Blanquart Numerical simulations are developed to study ignition dynamics in a non-premixed H2/air layer where mixing is aided by an embedded vortex. A similar reacting flow situation is encountered in many practical devices including internal combustion engines and supersonic combustion. The current work improves upon previous work by using tabulated chemistry to predict ignition dynamics, greatly reducing the computational requirements. The key results include the prediction of ignition delay time as a function of hot air temperature and vortex characteristics such as vortex strength, characteristic size and center location. The simulations will be used to explore different regimes of ignition previously observed by varying vortex Reynolds numbers and oxidizer temperatures. [Preview Abstract] |
Tuesday, November 20, 2012 9:31AM - 9:44AM |
M26.00008: A Priori Analysis of an Unsteady Flamelet Formulation for Reacting Jet in Cross Flows Wai Lee Chan, Matthias Ihme, Hemanth Kolla, Jacqueline Chen The jet in cross flow (JICF) configuration is a common fuel-injection strategy in practical combustion systems. Characterized by anisotropic and three-dimensional turbulent structures, enhanced mixing, and flame-dynamical processes, the modeling of reacting JICF-configurations imposes several challenges for large-eddy simulations. The objective of this study is to assess the feasibility of using an unsteady flamelet model (USFM) for the simulation of reacting JICFs. To this end, an a priori analysis of the USFM is conducted using a direct numerical simulation database, and higher-order terms in the flamelet equations, representing cross-dissipation and secondary heat-transfer processes, are quantified. It is shown that these higher-order expansion terms that are commonly neglected in one-dimensional flamelet models become of importance at the flame-base and lee-side of the JICF. Possible model-extensions are discussed to account for these secondary processes. [Preview Abstract] |
Tuesday, November 20, 2012 9:44AM - 9:57AM |
M26.00009: Collisional-Radiative Kinetics in Monatomic Gases Hai Le, Ann Karagozian A detailed model of electronic excited states is essential in capturing all the nonequilibrium processes of a partially ionized plasma by means of collisional and radiative interactions. This collisional-radiative (CR) model allows us to consider deviations from equilibrium distribution of the internal states, and is now more commonly used in the study of plasma discharges. Prior studies by Kapper and Cambier\footnote{Kapper \& Cambier \textit{J. Appl. Phys.} 109, 113308, 2011} and Panesi et al.\footnote{Panesi, et al., \textit{J. Thermo. Heat Trans.}, 25, 3, 2011} suggest that this level of detail is needed for an accurate prediction of the flow field, and it is particularly relevant to plasma-combustion interactions. The required number of excited states needed to be included in the CR model is often prohibitively large due to the nonequilibrium condition of the plasma. The consequence is a large system of ODE's which needs to be solved at each time step. A reduced mechanism for the CR model can be attained by grouping the upper states of the atomic state distribution (ASDF) into a pseudo-level in which the population is characterized either by a uniform distribution or a Boltzmann distribution. This talk presents both detailed and reduced models for an ionizing shock in Argon. [Preview Abstract] |
Tuesday, November 20, 2012 9:57AM - 10:10AM |
M26.00010: A Multiphase, Multicomponent Model for Combustion in the Titanium-Boron System Sushil Kumar, John B. Bdzil, Moshe Matalon, D. Scott Stewart Modeling combustion by reaction diffusion processes in initially, separated pure compounds in the condensed phase of metals, their oxides and intermetallics, is an important area of research in material science. We present a one-dimensional combustion model of the Titanium-Boron system, which is thermodynamically consistent. A simplified stoichiometric reaction mechanism is used in which liquid Titanium and liquid Boron reacts to form Titanium diBoride. An analytical form, suggested by Fried and Howard [1], is used to represent the equilibrium equation of state (EOS) for the solid and liquid phases of all three substances. This EOS produces results that gives and excellent fit to the known experimental data for the pure chemical phases. A multicomponent mixture EOS is created to account for the phase transitions and reaction between the individual species. We use numerical simulations to examine the results from conservation equations at constant pressure and compare them to experiments.\\[4pt] [1] Fried, Laurence E., and W. Michael Howard. ``Explicit Gibbs Free Energy Equation of State Applied to the Carbon Phase Diagram.'' Physical Review B 61.13 (2000): 8734-743. [Preview Abstract] |
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