Bulletin of the American Physical Society
68th Annual Meeting of the APS Division of Fluid Dynamics
Volume 60, Number 21
Sunday–Tuesday, November 22–24, 2015; Boston, Massachusetts
Session E5: Combustion II |
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Chair: Amy Lang, University of Alabama Room: 104 |
Sunday, November 22, 2015 4:50PM - 5:03PM |
E5.00001: Localized structures in gaseous combustion Edgar Knobloch, David Lo Jacono, Alain Bergeon We consider a flame between a pair of porous walls at $x=\pm1$ that allow fuel and oxidizer to diffuse into the burn region from opposite sides. The burn process is described by a binary one-step process of Arrhenius type. The heat released is redistributed via radiation. Convection is ignored. In 1D the low and high temperature states are connected by an S-shaped branch with a fold at low Damk\"ohler number below which extinction takes place. Various instabilities occur on the upper (flame) branch leading to different time-dependent but 1D flames. In 2D the situation is dramatically modified: near the extinction region the burn front breaks up into structures that are localized in the direction along the front, with multiple branches of such states bifurcating from the fold. These correspond to states with $n=1,2,\dots$ identical and equispaced hotspots. Further bifurcations generate states in which the hotspots are nonidentical and separated by unequal distances. All these states are present in the same parameter interval, implying great sensitivity of the system to initial conditions. [Preview Abstract] |
Sunday, November 22, 2015 5:03PM - 5:16PM |
E5.00002: ABSTRACT WITHDRAWN |
Sunday, November 22, 2015 5:16PM - 5:29PM |
E5.00003: Experimental and Numerical Investigation of Vortical Structures in Lean Premixed Swirl-Stabilized Combustion Soufien Taamallah, Nadim Chakroun, Santosh Shanbhogue, Gaurav Kewlani, Ahmed Ghoniem A combined experimental and LES investigation is performed to identify the origin of major flow dynamics and vortical structures in a model gas turbine's swirl-stabilized turbulent combustor. Swirling flows in combustion lead to the formation of complex flow dynamics and vortical structures that can interact with flames and influence its stabilization. Our experimental results for non-reacting flow show the existence of large scale precession motion. The precessing vortex core (PVC) dynamics disappears with combustion but only above a threshold of equivalence ratio. In addition, large scale vortices along the inner shear layer (ISL) are observed. These structures interact with the ISL stabilized flame and contribute to its wrinkling. Next, the LES setup is validated against the flow field's low-order statistics and point temperature measurement in relevant areas of the chamber. Finally, we show that LES is capable of predicting the precession motion as well as the ISL vortices in the reacting case: we find that ISL vortices originate from a vortex core that is formed right downstream of the swirler's centerbody. The vortex core has a conical spiral shape resembling a corkscrew that interacts - as it winds out - with the flame when it reaches the ISL. [Preview Abstract] |
Sunday, November 22, 2015 5:29PM - 5:42PM |
E5.00004: 3-Dimensional Aerospike Nozzle Design Benjamin Stevens, Richard Branam Our research has developed a computational tool that can characterize the performance of an aerospike nozzle. Performance characteristics that must be analyzed include thrust, nozzle weight, and specific impulse. The program employs an iterative method of characteristics algorithm to solve for the 3-dimensional flow field around a specified aerospike nozzle geometry, and uses the results to compute a better geometry. Compared to a conical aerospike nozzle, where the radius decreases linearly along the nozzle, the aerospike optimal design offers extremely high performance. The optimal design features a radius that decreases very quickly initially, but becomes more gradual along the axial direction. This design increases specific impulse, increases thrust, and decreases weight, giving the aerospike the potential to lower launch costs significantly. [Preview Abstract] |
Sunday, November 22, 2015 5:42PM - 5:55PM |
E5.00005: High-Energy X-ray Absorption Diagnostics as an Experimental Combustion Technique Jared Dunnmon, Sadaf Sobhani, Waldo Hinshaw, Rebecca Fahrig, Matthias Ihme X-ray diagnostics such as X-ray Computed Tomography (XCT) have recently been utilized for measurement of scalar concentration fields in gas-phase flow phenomena. In this study, we apply high-energy X-ray absorption techniques to visualize a laboratory-scale flame via fluoroscopic measurements by using krypton as a radiodense tracer media. Advantages of X-ray absorption diagnostics in a combustion context, including application to optically inaccessible environments and lack of ambient photon interference, are demonstrated. Analysis methods and metrics for extracting physical insights from these data are presented. The accuracy of the diagnostic is assessed via comparison to known results from canonical flame configurations, and the potential for further applications is discussed. [Preview Abstract] |
Sunday, November 22, 2015 5:55PM - 6:08PM |
E5.00006: Electric field effects on droplet burning Advitya Patyal, Dimitrios Kyritsis, Moshe Matalon The effects of an externally applied electric field are studied on the burning characteristics of a spherically symmetric fuel drop including the structure, mass burning rate and extinction characteristics of the diffusion flame. A reduced three-step chemical kinetic mechanism that reflects the chemi-ionization process for general hydrocarbon fuels has been proposed to capture the production and destruction of ions inside the flame zone. Due to the imposed symmetry, the effect of the ionic wind is simply to modify the pressure field. Our study thus focuses exclusively on the effects of Ohmic heating and kinetic effects on the burning process. Two distinguished limits of weak and strong field are identified, highlighting the relative strength of the internal charge barrier compared to the externally applied field, and numerically simulated. For both limits, significantly different charged species distributions are observed. An increase in the mass burning rate is noticed with increasing field in either limit with negligible change in the flame temperature. Increasing external voltages pushes the flame away from the droplet and causes a strengthening of the flame with a reduction in the extinction Damkh\"{o}ler number. [Preview Abstract] |
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