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Daniel Guggenheim School of Aerospace Engineering
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ItemEffect of flame temperature ratio on bluff body wakes(Georgia Institute of Technology, 2012-05-07) Lundrigan, JuliaSafe operation of aircraft and aeroderivative industrial gas turbine engines relies heavily on the stability of the combustion process. Combustion instabilities are of interest because they may lead to harmful pressure oscillations and increases in temperatures within the engine that could be destructive to engine components. Fluid dynamics in the combustor directly affects combustion instabilities and is the subject of this research. The two types of hydrodynamic instabilities linked with combustion instabilities explored in this research are the Kelvin-Helmholtz and the Benard/von Karman instabilities. Previous research has shown that a high flame temperature ratio (the ratio between the temperature of the products and the temperature of the unburned reactants) suppresses the Von Karman street, allowing for the wake to be characterized by the higher frequency Kelvin-Helmholtz instability from which vortices are shed by the shear layers. However, at a low temperature ratio, the flame loses its ability to suppress the Von Karman instability. The result of the changing of wake structures is fluctuations in heat release and pressure, which can result in damaged hardware and loud audible tones. Research previously conducted in Georgia Tech's Ben T. Zinn Combustion Laboratory using chemiluminescence has given an approximation of the flow field disturbances caused by the Von Karman response by measuring flame response. The proposed research will utilize knowledge gained from previous flow field disturbance approximations and improve the approximations by using data acquisition hardware that will allow for the exact flow field to be measured. The purpose of this research is to demonstrate that hydrodynamic stability calculations can be used to predict the onset of the Benard/von Karman instability in bluff body flames.
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ItemMulti-point Optimization of Airfoils(Georgia Institute of Technology, 2011-05-09) Chiguluri, Bhanu S.Many previous studies focused on developing optimum airfoils for steady flight conditions. However, with minimal extensions airfoils could be designed to perform better at the take-off conditions which would result in the efficient take-offs at shorter runways. An inverse design technique called the Modified Garabedian McFadden (MGM) technique was applied to NACA 0012 airfoil which resulted in an airfoil with drag bucket at the normal flight operation conditions. A newly developed optimization technique was applied to the three-element take-off configuration and a configuration that produced higher lift was obtained. Future work could be conducted on extending these design techniques for various airfoil configurations.
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ItemDevelopment and application of a rapid military model development framework(Georgia Institute of Technology, 2010-12-20) Andriano, Nelson GregoryMilitary operations are complex systems composed of the interactions of many smaller discrete systems, or assets: aircraft, watercraft, troops, etc. Historically, the requirements for new assets have been created based on standalone optimization. It is not just necessary to optimize requirements for a single scenario, such as a wartime operation, but instead to optimize the requirements that will benefit the entire military operation as a whole in a number of different scenarios, such as wartime and peace time. To better define future military assets it is necessary sample a large number of scenarios. To capture all of the interactions and develop a complete understanding of the overall system, it is necessary to model both combat and logistics, which have traditionally been modeled and analyzed separately. To characterize military operations and the assets that contribute to them, it is necessary to move beyond the traditional models that use aggregated approximations for combat and stand alone nodal analysis for logistics. A unique need for a framework which captures the complex interaction between combat and logistics while allowing a large number of automated cases and scenarios to run with no human in the loop. The framework this paper discusses was created to facilitate the making of models to analyze and characterize military operations and the effects that future assets will have on entire operations. The framework is agent-based, allowing bottom up definition and the gathering of emergent behavior, and uses a modified Hughes salvo method for combat, the Foundation for Intelligent Physical Agents messaging structure, and the beliefs, desires, and intentions (BDI) agent model. The modeling of communication and BDI creates myopic agents that are constrained by the information they can obtain, process, and react to. In this paper, the framework is first depicted and then validated by the creation of a model with the purposes of defining the requirements for a future asset, the Transformable Craft. The creation and testing of the model prove that the requirements for the framework have been met with success. The potential applications of the framework ranges from data-farming military operations models for future asset requirement, characterizing military operations systems, and providing a stepping stone for future agent-based military operations modeling and simulation work.
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ItemDynamics of non-premixed v-gutter stabilized flames in high temperature flow(Georgia Institute of Technology, 2010-05-12) Fricker, Aimee NicoleThis study investigated the dynamics of bluff body stabilized combustion of liquid fuel jets injected into the cross flow of preheated air just upstream of V-guttered bluff body s wake. The dynamics of investigated combustion process were determined by using advanced analytical methods to analyze high speed movies of the combustion process and measured acoustic pressure oscillations. The objective of the analysis was to determine the dependence of the flame and flow characteristics upon the flow Mach number, temperature, oxygen content and fuel to air momentum ratio. The investigated flame and flow characteristics included distribution of heat release within the combustion region and the frequencies and amplitudes of excited asymmetrically shed vortices, first explained by Bérnard/von-Kármán. Tests were performed over a wide range of incoming Mach numbers, fuel-air ratios and V-gutter flame holder widths. It is shown that the intensity of von-Kármán oscillations increases as both equivalence ratio and the momentum ratio increase.
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ItemDynamics of Acoustic Forcing on Turbulent Flames(Georgia Institute of Technology, 2010-05-11) Ma, Hsin-Hsiao (Jim)This research is motivated by instabilities in lean, premixed, swirl combustors. Two experimental setups including a Bunsen burner and a swirl combustor were used along with visualization methods such as Planar Laser Induced Fluorescence (PLIF) and Particle Image Velocimetry (PIV) to capture data. Error analysis of the two microphone technique was investigated to accurately record acoustic velocity. The flame transfer function was found and reveals that increasing forcing amplitude does not always yield increasing flame response. Several physical mechanisms that influences flame response were also found at a wide range of experimental conditions and forcing frequencies including: (1) the oscillating velocity of the annular jet, oscillations in (2) position and (3) strength of the vortex breakdown bubble and separation bubble, (4) unsteady liftoff of the flame, and (5) an oscillating turbulent flame speed. These processes generally occur simultaneously, with non-monotonic dependencies upon forcing amplitudes.