Browsing by Author "Kevin Lyons, Committee Chair"

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Combined Effects of Dilution and Co-flow on the Stability of Lifted Non-premixed Gaseous Flames
(2005-04-27) Wilson, David Andrew; Kevin Lyons, Committee Chair; Richard Johnson, Committee Member; Taofang Zeng, Committee Member
This research documents experiments and analysis of turbulent, lifted, non-premixed diffusion flames in co-flow and with dilution with implications for the development and operation of biogas-fueled combustors. Fuels used in this study were methane and ethylene. The diluent used was nitrogen. General trends were observed in the liftoff and reattachment behavior as affected by dilution of the fuel stream. Initial liftoff velocity was observed to decrease linearly with dilution, while initial lift height behavior was bimodal. Reattachment conditions were similar in overall behavior to liftoff conditions. Co-flow effects were not included in liftoff and reattachment studies. Combined effects of dilution and co-flow were also studied. Stabilization height compared to radial stabilization was found to be bimodal, with behavior differing in the potential core region compared with the far-field region. Dilution was found to decrease the radial stabilization distance, and co-flow tended to increase the radial stabilization distance. However, both effects were minor. The major results involve heat release effects. For given stabilization heights, stabilization velocity was found to decrease with dilution faster than laminar burning velocity with dilution. Stabilization height was also found to increase rapidly with dilution beyond a certain diluent concentration. Flames were also found to taper inward and become more cylindrical in shape as dilution increases. Implications for several flame stabilization theories are discussed. Future work for confirming the results of this research are also discussed.
Investigation of Turbulent Lifted Jet Flame Stabilization using Experimental Methods and Simulations.
(2010-07-07) Wang, Wei; Kevin Lyons, Committee Chair; Tarek Echekki, Committee Chair; William Roberts, Committee Member; Daniel Gruehn, Committee Member; Tiegang Fang, Committee Member
Investigations in Gas-Solid Multiphase Flows
(2003-08-20) Desai, Nehal; Kevin Lyons, Committee Chair
Gas-solid multiphase flows are used extensively in both science and industry. Understanding these flows is great commercial and academic interest. One tool use to further our understanding of solid-gas flows is theoretical and computer modeling. One of the least understood areas of multiphase flows is the momentum transfer or coupling of the phases. Depending on the nature of the flow, such momentum transfer can have substantial effect on the flow. In this thesis, we investigate two novel and interesting aspects of momentum exchange in gas-solid multiphase flows. Until recently, Euler-Lagrangian techniques were only applied to dilute solid-gas flows, because of the computational expense required to calculate the particle-particle interactions. The first investigation in this thesis deals with extending the Euler-Lagrangian to dense solid-gas flows and the modifications required to make this technique a viable alternative to continuum techniques. The results of the various simulation and comparisons are presented and in general are in very good agreement with experimental data; capturing unique and previous unreported experimental features. In the second investigation, we apply inverse parameter estimation to the problem of determining the coefficients of an generalized Ergun type momentum exchange. The results of the investigation indicate that for flows under consideration, the momentum exchange term has small influence on the flow. This would also explain many of the results reported in the literature which use simplistic or physically unrealistic momentum exchange.
A Methodology for Translating Detonation Wave Effects between One and Two Dimensions
(2008-05-12) Susi, Bryan; Kevin Lyons, Committee Chair; Tarek Echekki, Committee Member; Tiegang Fang, Committee Member
This research focuses on evaluating empirical methods and implementing a prototype Transitional Airblast Model (TRAM) for facilitating communication between one-dimensional and two-dimensional airblast models. An overview of detonation phenomena is presented, especially concerning detonation waves and accompanying airblast effects. Two existing airblast models are discussed that were designed to predict the effects of a detonation in two separate types of geometries, one-dimensional and two-dimensional. The functionality and behavior of each airblast model will be scrutinized giving particular insight into their performance in applications with both one-dimensional and two-dimensional components. The strengths and deficiencies of the different airblast models will offer motivation for the development of the TRAM prototype. The TRAM prototype consists of two separate methodologies, one for translating one-dimensional airblast propagation to two dimensions, and another for translating two-dimensional airblast propagation to one dimension. The selection of those two methodologies will be presented, along with results of detonation scenarios using both existing airblast models as well as the TRAM prototype. The TRAM prototype performed well for both types of detonation scenarios and is recommended for further development.
On Flame Stability In The Hysteresis Regime In Co-Flow
(2005-04-19) Terry, Stephen D; Richard Johnson, Committee Member; Joel DuCoste, Committee Member; William Roberts, Committee Member; Herbert Eckerlin, Committee Member; Kevin Lyons, Committee Chair
This study documents experiments performed on lifted turbulent diffusion flames in the hysteresis regime with air co-flow. Undiluted methane, ethylene, and propane were used as fuels and two nozzle sizes were used. The results confirm the non-linearity of the lift-off height with nozzle velocity, showing a previously undocumented region where lifted flame height increases as fuel velocity is decreased and that reattachment nozzle velocity varies linearly with co-flow. Using jet relations from Tieszen, the local excess jet velocity was computed and found to vary linearly for flames lifted well above the nozzle. The effect of co-flow was captured using an effective local excess jet velocity, similar to the effective nozzle jet velocity proposed by Montgomery used in conjunction with the results of Khalghatgi. Local excess jet velocities at the reattachment point were also compared for varying co-flow and found to be consistent between co-flow cases. This threshold velocity was found to vary with the inverse of the laminar burning velocity of the fuel squared. Relations for reattachment nozzle velocity and flame lift-off height at reattachment were also determined. The results extend the work of Khalghatgi into the hysteresis regime and complement the work of Gollahalli in determining the mechanisms that support flame stability in the hysteresis regime. Any comprehensive theory for flame stability will have to explain some of the unexpected results seen in the hysteresis regime and incorporate the findings of this study.
Static Efficiency of Positive and Negative Pin-Ring Type Electrohydrodynamic Air Moving Devices.
(2010-09-29) June, Michael; Kevin Lyons, Committee Chair; Thomas Ward, Committee Member; Alexei Saveliev, Committee Member; Tiegang Fang, Committee Member; Akhtarhusein Tayebali, Committee Member