Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 54, Number 19
Sunday–Tuesday, November 22–24, 2009; Minneapolis, Minnesota
Session MM: Reacting Flows III |
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Chair: Moshe Matalon, University of Illinois at Urbana-Champaign Room: 200B |
Tuesday, November 24, 2009 8:00AM - 8:13AM |
MM.00001: Effects of backround turbulence on a wrinkled flame Francesco Creta, Moshe Matalon We study the propagation of a premixed flame in the wrinkled laminar flamelet regime within the context of a hydrodynamic theory, i.e., where flame thickness is considered small compared to fluid flow characteristic length scales. The flame sheet separates burnt and unburnt zones each at a given constant density. We solve a level set equation for the flame interface propagating at a flame speed modeled by flame stretch and modulated by a Markstein length and advected by the local fluid flow. The ensuing dual density pattern is fed to the Navier-Stokes equations, which provide the updated advecting velocity field. To investigate the influence of background turbulence on flame propagation, the flame is subjected to a turbulent field parameterized by its intensity and integral scale at the flame interface. To hold these parameters constant a feedback control system is implemented acting on the inflow characteristics. The local flow field affects the wrinkling of the flame and its overall propagation speed through a purely kinematic process. The influence of the chemical and diffusive processes is studied by varying functional parameters, such as Markstein length and expansion ratio. Thus, the influence of turbulence intensity and scale on the overall flame propagation is statistically determined with the additional parametric effect of each of the functional parameters and of flame curvature and strain rate. [Preview Abstract] |
Tuesday, November 24, 2009 8:13AM - 8:26AM |
MM.00002: Experimental Study of Reaction and Vortex Breakdown in a Swirl-Stabilized Combustor Chukwueloka O.U. Umeh, Zvi Rusak, Ephraim J. Gutmark Non-reacting and lean reacting flow experiments are conducted in a swirl-stabilized combustor with several configurations of a TARS fuel injector. The test chamber is composed of the TARS swirler at the inlet of a straight cylindrical fuel pre-mixing section, followed by a sudden expansion and a finite-length concentric chamber, open to the atmosphere and with optical access. Non-reacting flow tests are conducted with air at 300K and 600K, while reacting flow tests use premixed air (at 600K) and gaseous propane fuel. Simultaneous PIV measurements and OH chemiluminescence is taken and used to describe the velocity field and location of vortex breakdown and reaction zones. Results show the complex dynamical interaction between the flame and breakdown zone, and the oscillations in the position of both. In the non-reacting cold flows, the breakdown zone appears near the expansion plane. In the non-reacting pre-heated flows it is pushed downstream of the expansion plane. For reacting flows with equivalence ratios near the lean blow out point, the breakdown zone is anchored near the expansion plane, while the flame oscillates inside it. At higher equivalence ratios, the flame is anchored near the expansion plane while the breakdown zone oscillates behind it. Measured swirl numbers show nice correlation with breakdown position and satisfy necessary theoretical conditions. [Preview Abstract] |
Tuesday, November 24, 2009 8:26AM - 8:39AM |
MM.00003: Heat release in freely-propagating lean premixed hydrogen-methane mixtures Xinfeng Gao, Marcus Day, John Bell Freely-propagating lean premixed hydrogen-air flames are thermo-diffusively unstable and burn in localized regions of intensified reaction. The flames propagate by the ``active species-diffusion'' mechanism, rather than the ``thermal propagation mode'' adopted by lean methane mixtures. We are interested in understanding mechanisms potentially explaining the influence of hydrogen on the flame structure of hydrogen-methane-air flames. The combustion behavior of hydrogen-methane fuel mixtures is then described with a set of relations derived from the heat release structures. The heat release characteristics of freely propagating flames resemble those of flat steady flames across a broad range of inlet fuel mixtures. [Preview Abstract] |
Tuesday, November 24, 2009 8:39AM - 8:52AM |
MM.00004: Distributed flames and Damk\"ohler ``small-scale turbulence'' in type Ia supernovae Andrew Aspden, John Bell, Stan Woosley High-resolution three-dimensional simulations of carbon-burning flames in type Ia supernovae are used to examine the distributed burning regime (high Karlovitz numbers), or the ``small-scale turbulence'' regime as it was referred to by Damk\"ohler (1940). He predicted that the turbulent flame speed and width are determined by the nuclear burning time scale and a diffusion coefficient prescribed by the turbulence. The scaling predicts its own breakdown when the turbulent Damk\"ohler number reaches unity. We demonstrate that the simulations are in agreement with the scaling predictions, and propose a method for predicting the limiting flame speed and width based on small-scale simulations. This flame speed can then be used to construct a turbulent flame model to study very large scale distributed supernova flames. [Preview Abstract] |
Tuesday, November 24, 2009 8:52AM - 9:05AM |
MM.00005: Linear stability and long-time evolution of planar lean premixed H2/air flames C. Altantzis, C.E. Frouzakis, S. Kerkemeier, A.G. Tomboulides, K. Boulouchos In the absence of buoyancy and acoustic interactions, two mechanisms can render premixed propagating flames unstable: hydrodynamic instabilities, stemming from the density jump across the flame, and thermal-diffusive instabilities in subunity Lewis number mixtures. In the present study, the linear stability of lean H$_2$/air flames as well as their long-term evolution is studied using both single-step and detailed chemistry in 2D rectangular domains of height h=3 to 80 laminar flame thicknesses with periodic boundary conditions imposed along the horizontal boundaries. At the inflow boundary, the lean (equivalence ratio $\phi=0.6$) mixture enters with a velocity equal to the laminar flame speed, temperature T=298 K and pressure p=5 atm. At these conditions, the Lewis number of the fresh mixture is sufficiently lower than unity (Le=0.4) and the expansion ratio ($\sigma=6.2$) is large enough so that both mechanisms play a destabilizing role. [Preview Abstract] |
Tuesday, November 24, 2009 9:05AM - 9:18AM |
MM.00006: Surface Tension of Premixed Flames as Gasdynamic Discontinuities: Principle and Quantitative Evaluation Hannes Dirks, Andreas G. Class, Christian Bruzzese Viewed on hydrodynamic length scales, a typical premixed laminar flame is thin and can be described as a gasdynamic discontinuity separating the fresh mixture from the burned products. We perform an integral momentum analysis of cylindrical premixed flames viewed as gasdynamic discontinuities and quantitatively investigate the jump of momentum at the surface of discontinuity. We interpret the jump of momentum as the result of a localised force and compute the surface tension of the surface of discontinuity, exploiting numerical data and detailed chemical kinetics. Surface tension of premixed flames is shown to be negative. Therefore, in order to establish a stable flame more stringent conditions must be satisfied than one would expect from a pure consideration of the flame speed relation. For numerical simulations, we suggest an implementation based on distributions that implicitly satisfies the momentum balance. [Preview Abstract] |
Tuesday, November 24, 2009 9:18AM - 9:31AM |
MM.00007: Dissolution of a solid particle in a linear velocity field in the presence of chemical reactions Donna Blackmond, Devin Conroy, Omar Matar The growth or dissolution rate of a particle in a steady linear velocity field is investigated. The particle contains a pure composition of species $D$ and the outer liquid contains species $D$ and $L$ which undergo a reversible reaction. The governing equations are solved asymptotically in the limit of a small Reynolds number based on a particle length scale, with the Prandtle number of order one and a large Schmidt number. We explore the rate of growth or dissolution as a function of the particle curvature, Stefan number, Reynolds number and a scale for the concentration difference. [Preview Abstract] |
Tuesday, November 24, 2009 9:31AM - 9:44AM |
MM.00008: Visualization of transverse annular jets Philipp Boettcher, Ioannis G. Mikellides, David A. Vaughan, Joseph E. Shephard, Jason Damazo Transverse injection of fluid into an annular jet is a mechanism resulting in good mixing and is therefore utilized in engineering applications such as pintle rocket engines. Vigorous mixing occurs between the two jets. However, much of what we know about the flow behavior of such devices has been learned empirically with very limited studies exploring the fluid dynamics. The geometry under investigation is an axisymmetric radial jet of variable width impinging a fixed annular jet. The main capability of the current facility is to reproduce start-up and quasi-steady flow conditions through the use of a fast acting valve which opens a pressurized reservoir. The flow is then observed using a schlieren system which shows the shock wave from the start-up and the subsequent mixing between the jets. The main parameters under investigation were the reservoir pressure and the area ratio between the axial and radial jet. The effect of these parameters on the qualitative flow behavior is discussed. This effort was carried out in conjunction with modeling efforts at JPL. [Preview Abstract] |
Tuesday, November 24, 2009 9:44AM - 9:57AM |
MM.00009: Estimating soot emissions from an elevated flare Victor Almanza, Gustavo Sosa Combustion aerosols are one of the major concerns in flaring operations, due to both health and environmental hazards. Preliminary results are presented for a 2D transient simulation of soot formation in a reacting jet with exit velocity of 130 m/s under a 5 m/s crossflow released from a 50 m high elevated flare and a 50 cm nozzle. Combustion dynamics was simulated with OpenFOAM. Gas-phase non-premixed combustion was modeled with the Chalmers PaSR approach and a $\kappa -\varepsilon $ turbulence model. For soot formation, Moss model was used and the ISAT algorithm for solving the chemistry. Sulfur chemistry was considered to account for the sourness of the fuel. Gas composition is 10 {\%} H2S and 90 {\%} C2H4. A simplified Glassman reaction mechanism was used for this purpose. Results show that soot levels are sensitive to the sulfur present in the fuel, since it was observed a slight decrease in the soot volume fraction. NSC is the current oxidation model for soot formation. Predicted temperature is high (about 2390 K), perhaps due to soot-radiation interaction is not considered yet, but a radiation model implementation is on progress, as well as an oxidation mechanism that accounts for OH radical. Flame length is about 50 m. [Preview Abstract] |
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