Bulletin of the American Physical Society
66th Annual Meeting of the APS Division of Fluid Dynamics
Volume 58, Number 18
Sunday–Tuesday, November 24–26, 2013; Pittsburgh, Pennsylvania
Session L26: Reacting Flows VII: Experiments |
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Chair: Bruce Chehroudi, Advanced Technology Consultants Room: 321 |
Monday, November 25, 2013 3:35PM - 3:48PM |
L26.00001: Experimental investigation of laboratory fire whirls Katherine Hartl, Alexander Smits A fire whirl is a swirling diffusion flame that may occur to great destructive effect in urban fires or wildfires. To study fire whirls in the laboratory, we use a burner flame, using DME as fuel, and induce the swirl by entraining air through a split cylinder surrounding the central flame. Stereo Particle Image Velocimetry (PIV) is used to obtain distributions of the three components of velocity outside the fire whirl core. The effects of fuel flow rate, gap width, and height along the flame are examined, and the scaling behavior is investigated. [Preview Abstract] |
Monday, November 25, 2013 3:48PM - 4:01PM |
L26.00002: Laser-Diagnostic Mapping of Temperature and Soot Statistics in a 2-m Diameter Turbulent Pool Fire Sean Kearney We present spatial profiles of temperature and soot-volume-fraction statistics from a sooting 2-m base diameter turbulent pool fire. Dual-pump coherent anti-Stokes Raman scattering (CARS) and laser-induced incandescence (LII) are utilized to obtain profiles of temperature and soot probability density functions (pdf) at three vertical heights above the surface of the methanol/toluene fuel pool. The experiments are conducted in the unique Sandia FLAME facility, which has recently been modified to allow for vertical translation of the optical systems and horizontal translation of the liquid fuel burner. Results are presented both in the fuel vapor-dome region at 0.25 base diameter and in the actively burning region at 0.5 and 0.75 diameters above the fuel surface. The evolution of the soot and temperature pdfs is discussed, profiles of the temperature and soot mean and rms statistics are provided, and initial estimates of the joint temperature/soot statistics, which describe soot radiative emission, are presented. [Preview Abstract] |
Monday, November 25, 2013 4:01PM - 4:14PM |
L26.00003: Experimental investigation of boundary-layer flashback in swirl flames Dominik Ebi, Noel Clemens Swirling flows are widely employed for flame stabilization purposes in gas turbine combustors. However, flames in swirling flows are more prone to flashback, a potentially catastrophic phenomenon leading to thermal damage of the burner. The physical mechanism driving flashback in a swirling flow is not yet fully understood. The mechanism is particularly complex if the upstream flame propagation interacts with a boundary layer. In a previous study we showed that the flame/boundary-layer interaction is important for burners, which include an axial swirler and a central body attached to the swirler hub. We are investigating the mechanism of flashback in atmospheric pressure lean-premixed methane/hydrogen-air flames inside the mixing tube of our confined model swirl combustor. Flashback occurs at an equivalence ratio of approximately 0.7. The effect of hydrogen is investigated by testing different methane-to-hydrogen ratios. The duration of a single flashback event is on the order of 100 ms, requiring high-speed diagnostic techniques. We are applying simultaneous stereoscopic PIV, flame front detection based on Mie scattering, and chemiluminescence imaging to investigate the flame/flow interaction during flashback events. [Preview Abstract] |
Monday, November 25, 2013 4:14PM - 4:27PM |
L26.00004: Oscillatory Flame Response in Acoustically Driven Fuel Droplet Combustion Brett Lopez, Cristhian Sevilla, Takeshi Shoji, Ari Ekmekji, Owen Smith, Ann Karagozian This experimental study focuses on droplet combustion characteristics for various liquid fuels during exposure to external acoustical perturbations generated within an acoustic waveguide. The study examines combustion during excitation conditions in which the droplet is situated in the vicinity of a pressure node (PN). In response to such acoustic excitation, the flame surrounding the droplet is deflected, on average, with an orientation depending on the droplet's relative position with respect to the PN. Flame orientation is always found to be consistent with the sign of a theoretical bulk acoustic acceleration, analogous to a gravitational acceleration.\footnote{Tanabe, et al., PCI, 2000} Yet experimentally measured acoustic accelerations based on mean flame deflection differ quantitatively from that predicted by the theory. Phase-locked OH* chemiluminescence imaging reveals temporal oscillations in flame standoff distance from the droplet as well as chemiluminescent intensity which are especially pronounced when the droplet is situated close to the PN. Quantification of combustion-acoustic coupling via the Rayleigh index reveals a more detailed understanding of dynamical phenomena. [Preview Abstract] |
Monday, November 25, 2013 4:27PM - 4:40PM |
L26.00005: Similarity and Scaling of Turbulent Flame Speeds for Expanding Premixed Flames of C$_{4}$-C$_{8} n$-alkanes Fujia Wu, Abhishek Saha, Swetaprovo Chaudhuri, Sheng Yang, Chung K. Law We experimentally investigated the propagation speed of constant-pressure expanding flames in near isotropic turbulence using a dual-chamber, fan-stirred vessel. The motivation is to test whether the fuel similarity concept among C$_{4}$-C$_{8}$ $n$-alkanes on laminar flames also holds for turbulent flames. Previously it was found that the laminar flame speed and Markstein length are almost identical for C$_{4}$-C$_{8}$ $n$-alkanes. If this fuel similarity concept can also be shown for turbulent flames, it will suggest a canonical flame structure for large hydrocarbon fuels, $i.e.$, large fuels always decompose to small C$_{0}$-C$_{4}$ fuel fragments before being oxidized, and would significantly simplify the description of the flames. Preliminary results show that in the flamelet and thin-reaction zone, turbulent flame speeds of C$_{4}$-C$_{8}$ $n$-alkanes are indeed largely similar at various conditions, thereby suggesting the fuel similarity for turbulent flames. In addition, it is found that the normalized turbulent flame speed also approximately scales with the square root of an appropriately-defined Reynolds number recently found for C$_{0}$-C$_{4}$ fuels. [Preview Abstract] |
Monday, November 25, 2013 4:40PM - 4:53PM |
L26.00006: Structure and Dynamics of a Reacting Jet in a Swirling Vitiated Crossflow Pratikash Panda, Mario Roa, Robert Lucht A reacting jet issuing into a vitiated, swirled cross flow operating at a pressure of 5.5 bars is investigated using high repetition rate (5 kHz) Particle Image Velocimetry (PIV). A premixed jet composed of natural gas and air is injected into the vitiated stream through an extended nozzle downstream of a low swirl burner (LSB) that produces the vitiated, swirled flow. The jet-to-crossflow momentum flux ratio is varied to study the corresponding impact on the flow structures. The raw PIV images indicate a strong influence of the swirling crossflow on the jet at planes closest and farthest away from the nozzle exit. The mean flow field is found to preserve the counter-rotating vortex pair (CRVP) which is the most dominant flow structure in a jet in crossflow flow-field. The instantaneous vector field indicates presence of a very interesting oscillatory motion of the CRVP indicating a in plane jet flapping behavior. This oscillatory motion is affected by the accelerating flow above and below the CRVP which could be correlated to the instantaneous heat release at that location. Proper Orthogonal Decomposition (POD) is used to extract the frequency characteristics and dynamics of this flapping jet. [Preview Abstract] |
Monday, November 25, 2013 4:53PM - 5:06PM |
L26.00007: Construction and Characterization of a Shock Tube for Ignition and Pollutant Formation Studies Cory Prykull, Robert Dreiker, Marcos Fernandes, Mazen Eldeeb, Ben Akih-Kumgeh Shock tubes are versatile research facilities with wide applications in aerodynamics, high-temperature chemical kinetics and medical research. We discuss the construction and the gas dynamics characterization of such a facility for combustion studies with a focus on ignition and pollutant formation. Measures to achieve high quality post-reflected shock conditions with minimal shock-boundary layer interactions are discussed. Characterization of the facility is first carried out using non-reactive gases in order to assess the quality of the post-reflected shock conditions and the available test times. The incident velocity is determined using fast response pressure transducers. Experimentally observed post-reflected shock pressure profiles are compared with predictions of one dimensional shock equations, which also allow for the calculation of temperature. Subsequent shock tube ignition experiments are carried out for selected fuel and oxidizer systems from the literature in order to validate and thereby, demonstrate the suitability of the facility for combustion studies. Further measurements of soot volume fractions under fuel rich conditions are realized by means of laser extinction. [Preview Abstract] |
Monday, November 25, 2013 5:06PM - 5:19PM |
L26.00008: ABSTRACT WITHDRAWN |
Monday, November 25, 2013 5:19PM - 5:32PM |
L26.00009: Schlieren Imaging of Chemically-Induced Flow Instabilities During Step-Growth Polymerization Patrick Bunton, Michael Rawat, Simone Stewart, Anne De Wit, John Pojman Schlieren imaging was used to observe the dependence on degree of reactivity on flow instabilities during step-growth polymerization. For example a solution of a 2,2'-(ethylenedioxy)- diethanethiol containing varying concentrations of Octylamine as initiator was used to displace a trimethylolpropane triacrylate monomer. The concentration of initiator was used to control the degree of reactivity of the solutions and therefore the Damkohler Number which is the ratio of the chemical to the hydrodynamic timescale. By varying the concentration of initiator and/or the functionality of the monomers, one can tune the reaction product from a viscous liquid, to gel, or even a solid. Resulting flow patterns were found to depend on degree of reactivity and effects were observed regardless of the direction of flow. Also observed was evidence of three-dimensional effects on the resultant flow patterns. [Preview Abstract] |
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