+publisher:"Georgia Tech" +contributor:("Yang, Vigor")

Georgia Tech

1. Muraleedharan, Murali Gopal gopal. Nanoscale heat transfer effects in the combustion of nanoenergetic materials.

Degree: PhD, Aerospace Engineering, 2018, Georgia Tech

► Metal-based composite energetic materials have substantially higher volumetric energy density when compared with monomolecular compounds such as trinitrotoluene (TNT). Micron-sized metal particles have been routinely… (more)

Subjects/Keywords: Nanoenergetic materials; Nanoscale heat transfer; Atomistic simulations; Molecular dynamics; Density functional theory

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APA (6^th Edition):

Muraleedharan, M. G. g. (2018). Nanoscale heat transfer effects in the combustion of nanoenergetic materials. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/62223

Chicago Manual of Style (16^th Edition):

Muraleedharan, Murali Gopal gopal. “Nanoscale heat transfer effects in the combustion of nanoenergetic materials.” 2018. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/62223.

MLA Handbook (7^th Edition):

Muraleedharan, Murali Gopal gopal. “Nanoscale heat transfer effects in the combustion of nanoenergetic materials.” 2018. Web. 22 Jan 2021.

Vancouver:

Muraleedharan MGg. Nanoscale heat transfer effects in the combustion of nanoenergetic materials. [Internet] [Doctoral dissertation]. Georgia Tech; 2018. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/62223.

Council of Science Editors:

Muraleedharan MGg. Nanoscale heat transfer effects in the combustion of nanoenergetic materials. [Doctoral Dissertation]. Georgia Tech; 2018. Available from: http://hdl.handle.net/1853/62223

Georgia Tech

2. Lioi, Christopher. Linear combustion stabiliy analysis of oxidizer-rich staged combustion engines.

Degree: PhD, Aerospace Engineering, 2019, Georgia Tech

URL: http://hdl.handle.net/1853/62579

► This thesis concerns the consistent linear acoustic stability analysis of an engine modeled on the RD-170, a prototypical example of an Oxidizer Rich Staged Combustion… (more)

▼ This thesis concerns the consistent linear acoustic stability analysis of an engine modeled on the RD-170, a prototypical example of an Oxidizer Rich Staged Combustion (ORSC) engine. Both the preburner-turbine assembly as well as the main combustion chamber are studied. The theoretical basis for the stability analysis is an inhomogeneous acoustic wave equation in the pressure. Boundary effects are accounted for by means of impedance boundary conditions. Theoretical impedance models are employed to describe the physics of various components: the turbine inlet blade row in the preburner assembly, and the flow distributor in the main chamber. In the main chamber, mean flow and combustion response effects are accounted for by means of right hand side source terms in the wave equation. Two cases are considered for mean flow: piecewise uniform and swirl flow. The swirl flow is generated by time averaging the results from LES of the main chamber injectors. It is found that the mean flow contributes significant damping to the system by means of convecting acoustic energy out of the domain. The swirl flow additionally provides acoustic refraction which further increases the damping. Overall the mean flow is found to far eclipse the other sources of damping. The response of the combustion to acoustic perturbations is quantified by means of a Flame Transfer Function (FTF). Spatially distributed fields for both the FTF gain and phase are computed from LES data using POD reduction for three different injector recess lengths. A chamber-level response field is constructed as a superposition of fields for individual injectors. It is found that as the recess length decreases, the system becomes more unstable, due to the fact that the base of the injector nonpremixed flame becomes more exposed to the transverse oscillations in the main chamber. A sensitivity analysis is conducted on a reduced set of scalar quantities which characterize the distributed combustion response fields. The eigenvalue results are found to be most sensitive to the maximum of the gain field, the axial spread of the gain about this maximum value, and the maximum axial slope of the phase field. The radial location of the maximum gain also affects the stability to a lesser extent. The results suggest that to maximize the stability margin of the engine the recess length of the injector should be maximized and the fluid conditions should be such that the flame is wide and combustion is distributed over as large an axial extent as possible. Advisors/Committee Members: Yang, Vigor (advisor), Ahuja, Krish (committee member), Sankar, Lakshmi (committee member), Lieuwen, Timothy (committee member), Funk, Robert (committee member).

Subjects/Keywords: Combustion instabilities; Acoustics; Liquid rocket engines; ORSC engines; Finite element analysis; LES; Flame transfer function

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APA (6^th Edition):

Lioi, C. (2019). Linear combustion stabiliy analysis of oxidizer-rich staged combustion engines. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/62579

Chicago Manual of Style (16^th Edition):

Lioi, Christopher. “Linear combustion stabiliy analysis of oxidizer-rich staged combustion engines.” 2019. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/62579.

MLA Handbook (7^th Edition):

Lioi, Christopher. “Linear combustion stabiliy analysis of oxidizer-rich staged combustion engines.” 2019. Web. 22 Jan 2021.

Vancouver:

Lioi C. Linear combustion stabiliy analysis of oxidizer-rich staged combustion engines. [Internet] [Doctoral dissertation]. Georgia Tech; 2019. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/62579.

Council of Science Editors:

Lioi C. Linear combustion stabiliy analysis of oxidizer-rich staged combustion engines. [Doctoral Dissertation]. Georgia Tech; 2019. Available from: http://hdl.handle.net/1853/62579

Georgia Tech

3. Khare, Prashant. Breakup of liquid droplets.

Degree: PhD, Aerospace Engineering, 2013, Georgia Tech

URL: http://hdl.handle.net/1853/53395

► Liquid droplet breakup and dynamics is a phenomena of immense practical importance in a wide variety of applications in science and engineering. Albeit, researchers have… (more)

▼ Liquid droplet breakup and dynamics is a phenomena of immense practical importance in a wide variety of applications in science and engineering. Albeit, researchers have been studying this problem for over six decades, the fundamental physics governing droplet deformation and fragmentation is still unknown, not to mention the formulation and development of generalized correlations to predict droplet dynamics. The presence of disparate length and time scales, along with the complex unsteady physics, makes this a formidable problem, theoretically, experimentally and computationally. One of the important applications of interest and the motivation for the current research is a liquid fueled propulsion device, such as diesel, gas turbine or rocket engine. Droplet vaporization and ensuing combustion is accelerated if the droplet size is smaller, which makes any process leading to a reduction in drop size of prime importance in the combustion system design. This thesis is an attempt to address several unanswered questions currently confronting the spray community. Unanswered questions include identification and prediction of breakup modes at varying operating conditions, quantitative description of fundamental processes underlying droplet breakup and generalized correlations for child droplet size distributions and drag coefficient associated with the deformation and fragmentation of Newtonian and non-Newtonian fluids. The present work is aimed at answering the above questions by investigating the detailed flowfield and structure dynamics of liquid droplet breakup process and extracting essential physics governing this complex multiphase phenomena. High-fidelity direct numerical simulations are conducted using a volume-of-fluid (VOF) interface capturing methodology. To isolate the hydrodynamic mechanisms dictating droplet breakup phenomena, evaporation and compressibility are neglected, and numerical studies are performed for incompressible fluids at isothermal conditions. For Newtonian fluids, four different mechanisms are identified- oscillatory, bag, multimode and shear breakup modes. Various events during the deformation and fragmentation process are quantitatively identified and correlations are developed to predict the breakup mechanisms and droplet size distributions for a broad range of operating conditions. It was found that for We > 300 and Oh < 0.1 for rho_l/rho_g = 8.29, the child droplet size distributions can be modeled by a log-normal distribution. A correlation to predict the sauter mean diameter, d32, is also developed, given by d32 / D = 8We^-0.72 / Cd. Temporal evolution of momentum balance and droplet structure are also used to calculate the drag coefficient at each time step from first principles. Results show that the drag coefficient first increases to a maximum as the droplet frontal area increases and then decreases at the initiation of breakup. The drag coefficient reaches a steady value at the end of droplet lifetime, corresponding to the momentum retained by the droplet. A… Advisors/Committee Members: Yang, Vigor (advisor), Menon, Suresh (committee member), Zinn, Ben T. (committee member), Lieuwen, Timothy C. (committee member), Genzale, Caroline L. (committee member).

Subjects/Keywords: Liquid droplets; VOF; Bag breakup; Multimode breakup; Oscillatory breakup; Shear breakup

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APA (6^th Edition):

Khare, P. (2013). Breakup of liquid droplets. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/53395

Chicago Manual of Style (16^th Edition):

Khare, Prashant. “Breakup of liquid droplets.” 2013. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/53395.

MLA Handbook (7^th Edition):

Khare, Prashant. “Breakup of liquid droplets.” 2013. Web. 22 Jan 2021.

Vancouver:

Khare P. Breakup of liquid droplets. [Internet] [Doctoral dissertation]. Georgia Tech; 2013. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/53395.

Council of Science Editors:

Khare P. Breakup of liquid droplets. [Doctoral Dissertation]. Georgia Tech; 2013. Available from: http://hdl.handle.net/1853/53395

Georgia Tech

4. Wang, Xingjian. Swirling fluid mixing and combustion dynamics at supercritical conditions.

Degree: PhD, Mechanical Engineering, 2016, Georgia Tech

URL: http://hdl.handle.net/1853/58565

► A unified theoretical and numerical framework is established to study supercritical mixing and combustion over the entire range of fluid thermodynamic states of concern. Turbulence… (more)

▼ A unified theoretical and numerical framework is established to study supercritical mixing and combustion over the entire range of fluid thermodynamic states of concern. Turbulence closure is achieved using a large-eddy-simulation (LES) technique. A steady laminar flamelet approach is implemented to model turbulence/chemistry interactions. Three-dimensional flow dynamics of a liquid oxygen (LOX) swirl injector at supercritical pressure is studied for the first time. Various mechanisms governing the flow evolution, including hydrodynamic instabilities, acoustic waves, and their interactions are explored using spectral analysis and proper orthogonal decomposition. Then, the mixing and combustion characteristics of LOX/kerosene bi-swirl injectors are investigated under conventional rocket engine operating conditions. Emphasis is placed on the near-field flow and flame development downstream of the inner swirler. The flame is stabilized by two counter-rotating vortices in the wake region of the LOX post which is covered by the kerosene-rich mixture. The influence of important injector design attributes, including the recess length, LOX post thickness, and kerosene annulus width, upon mixing and combustion characteristics is examined. The results provide critical information for future injector designs. In addition, counterflow diffusion flames of general fluids are investigated in a wide range of pressures and flow strain rates. An improved two-point flame-controlling continuation method is employed to solve the singularity problem at the turning points of the flame-response curve (the S-curve). General similarities are developed in terms of flame temperature, species concentrations, flame thickness, and heat-release rate for all pressures of concern. This can be utilized to improve computational efficiency for turbulent combustion models using tabulated chemistry. Advisors/Committee Members: Lieuwen, Timothy C. (advisor), Yang, Vigor (advisor), Menon, Suresh (committee member), Sun, Wenting (committee member), Ranjan, Devesh (committee member).

Subjects/Keywords: Supercritical fluid; Swirl Injector; Large eddy simulation; Combustion dynamics; Flame stabilization; Liquid oxygen; Kerosene; Flamelet; Counterflow diffusion flame; S-curve

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Wang, X. (2016). Swirling fluid mixing and combustion dynamics at supercritical conditions. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/58565

Chicago Manual of Style (16^th Edition):

Wang, Xingjian. “Swirling fluid mixing and combustion dynamics at supercritical conditions.” 2016. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/58565.

MLA Handbook (7^th Edition):

Wang, Xingjian. “Swirling fluid mixing and combustion dynamics at supercritical conditions.” 2016. Web. 22 Jan 2021.

Vancouver:

Wang X. Swirling fluid mixing and combustion dynamics at supercritical conditions. [Internet] [Doctoral dissertation]. Georgia Tech; 2016. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/58565.

Council of Science Editors:

Wang X. Swirling fluid mixing and combustion dynamics at supercritical conditions. [Doctoral Dissertation]. Georgia Tech; 2016. Available from: http://hdl.handle.net/1853/58565

Georgia Tech

5. Nagaraja, Sharath. Multi-scale modeling of nanosecond plasma assisted combustion.

Degree: PhD, Aerospace Engineering, 2014, Georgia Tech

URL: http://hdl.handle.net/1853/52228

► The effect of temperature on fuel-air ignition and combustion (thermal effects) have been widely studied and well understood. However, a comprehensive understanding of nonequilibrium plasma… (more)

▼ The effect of temperature on fuel-air ignition and combustion (thermal effects) have been widely studied and well understood. However, a comprehensive understanding of nonequilibrium plasma effects (in situ generation of reactive species and radicals combined with gas heating) on the combustion process is still lacking. Over the past decade, research efforts have advanced our knowledge of electron impact kinetics and low temperature chain branching in fuel-air mixtures considerably. In contrast to numerous experimental investigations, research on modeling and simulation of plasma assisted combustion has received less attention. There is a dire need for development of self-consistent numerical models for construction and validation of plasma chemistry mechanisms. High-fidelity numerical models can be invaluable in exploring the plasma effects on ignition and combustion in turbulent and high-speed flow environments, owing to the difficulty in performing spatially resolved quantitative measurements. In this work, we establish a multi-scale modeling framework to simulate the physical and chemical effects of nonequilibrium, nanosecond plasma discharges on reacting flows. The model is capable of resolving electric field transients and electron impact dynamics in sub-ns timescales, as well as calculating the cumulative effects of multiple discharge pulses over ms timescales. Detailed chemistry mechanisms are incorporated to provide deep insight into the plasma kinetic pathways. The modeling framework is utilized to study ignition of H₂-air mixtures subjected to pulsed, nanosecond dielectric barrier discharges in a plane-to-plane geometry. The key kinetic pathways responsible for radicals such as O, H and OH generation from nanosecond discharges over multiple voltage pulses (ns-ms timescales) are quantified. The relative contributions of plasma thermal and kinetic effects in the ignition process are presented. The plasma generated radicals trigger partial fuel oxidation and heat release when the temperature rises above 700 K, after which the process becomes self-sustaining leading to igntion. The ignition kernel growth is primarily due to local plasma chemistry effects rather than flame propagation, and heat transport does not play a significant role. The nanosecond pulse discharge plasma excitation resulted in nearly simultaneous ignition over a large volume, in sharp contrast to hot-spot igniters. Next, the effect of nanosecond pulsed plasma discharges on the ignition characteristics of nC₇H₁₆ and air in a plane-to-plane geometry is studied at a reduced pressure of 20.3 kPa. The plasma generated radicals initiate and significantly accelerate the H abstraction reaction from fuel molecules and trigger a “self-accelerating” feedback loop via low-temperature kinetic pathways. Application of only a few discharge pulses at the beginning reduces the initiation time of the first-stage temperature rise by a factor of 10. The plasma effect after the first stage is shown to be predominantly thermal. A novel plasma-flame modeling… Advisors/Committee Members: Yang, Vigor (advisor), Jagoda, Jeff (committee member), Menon, Suresh (committee member), Adamovich, Igor (committee member), Sun, Wenting (committee member).

Subjects/Keywords: Plasma assisted combustion; Computational fluid dynamics; Nanosecond plasma discharges; Plasma modeling

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APA (6^th Edition):

Nagaraja, S. (2014). Multi-scale modeling of nanosecond plasma assisted combustion. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/52228

Chicago Manual of Style (16^th Edition):

Nagaraja, Sharath. “Multi-scale modeling of nanosecond plasma assisted combustion.” 2014. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/52228.

MLA Handbook (7^th Edition):

Nagaraja, Sharath. “Multi-scale modeling of nanosecond plasma assisted combustion.” 2014. Web. 22 Jan 2021.

Vancouver:

Nagaraja S. Multi-scale modeling of nanosecond plasma assisted combustion. [Internet] [Doctoral dissertation]. Georgia Tech; 2014. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/52228.

Council of Science Editors:

Nagaraja S. Multi-scale modeling of nanosecond plasma assisted combustion. [Doctoral Dissertation]. Georgia Tech; 2014. Available from: http://hdl.handle.net/1853/52228

Georgia Tech

6. Lympany, Shane V. Acoustic damping mechanisms of half-wave resonators in a rocket engine environment.

Degree: PhD, Aerospace Engineering, 2018, Georgia Tech

URL: http://hdl.handle.net/1853/60266

► Combustion instabilities in rocket engines are caused by coupling between the combustion processes and pressure oscillations in a combustor, and they are characterized by the… (more)

▼ Combustion instabilities in rocket engines are caused by coupling between the combustion processes and pressure oscillations in a combustor, and they are characterized by the frequencies and shapes of the acoustic modes of the combustion chamber. Acoustic resonators are commonly installed in combustors to provide passive acoustic damping and prevent combustion instabilities. Previously, it has been proposed that the propellant injectors in a combustor can be tuned to act as half-wave resonators and provide acoustic damping. This requires a thorough understanding of the acoustic damping mechanisms of injectors, and producing this understanding forms the basis of the work described in this dissertation. In this work, the acoustic damping of propellant injectors is measured experimentally. A new experimental facility is developed and employed to measure the sound power reflection, transmission, and dissipation under the conditions of mean flow, high temperature, high acoustic amplitude, and higher-order modes. The effects of common design parameters—namely, the typical features of an injector, the ratio between the cross-sectional area of the injectors and the combustion chamber, the number of injectors, and the relative position of the injectors within the cross-section of the combustion chamber—on the acoustic absorption coefficient are investigated experimentally using the new facility. Measurements of the fraction of sound power dissipated by the injectors and the velocity flow fields at the ends of the injectors are used to elucidate the physical mechanisms responsible for the acoustic damping. Attempts are made to quantify the separate contributions of viscothermal dissipation and the conversion of acoustic energy into vorticity. Analytical and numerical models incorporating some of these dissipation mechanisms are developed to predict the absorption coefficient of the injectors. Advisors/Committee Members: Yang, Vigor (committee member), Ruzzene, Massimo (committee member), Cunefare, Kenneth A. (committee member), Gavin, Joseph R. (committee member), Jones, Michael G. (committee member).

Subjects/Keywords: Acoustics; Acoustic damping; Acoustic resonators; Half-wave resonators; Acoustic impedance; Absorption coefficient; Scattering; Impedance tube; Nonlinear acoustics; Higher-order modes; Combustion instability; Propellant injectors

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Lympany, S. V. (2018). Acoustic damping mechanisms of half-wave resonators in a rocket engine environment. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/60266

Chicago Manual of Style (16^th Edition):

Lympany, Shane V. “Acoustic damping mechanisms of half-wave resonators in a rocket engine environment.” 2018. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/60266.

MLA Handbook (7^th Edition):

Lympany, Shane V. “Acoustic damping mechanisms of half-wave resonators in a rocket engine environment.” 2018. Web. 22 Jan 2021.

Vancouver:

Lympany SV. Acoustic damping mechanisms of half-wave resonators in a rocket engine environment. [Internet] [Doctoral dissertation]. Georgia Tech; 2018. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/60266.

Council of Science Editors:

Lympany SV. Acoustic damping mechanisms of half-wave resonators in a rocket engine environment. [Doctoral Dissertation]. Georgia Tech; 2018. Available from: http://hdl.handle.net/1853/60266

Georgia Tech

7. Chang, Yu-Hung. High-fidelity emulation of spatiotemporally evolving flow dynamics.

Degree: PhD, Aerospace Engineering, 2018, Georgia Tech

URL: http://hdl.handle.net/1853/60842

► This dissertation utilizes a comprehensive interdisciplinary approach to demonstrate a paradigm for a novel design strategy for new generation engineering. Computational fluid dynamics (CFD), reduced-basis… (more)

▼ This dissertation utilizes a comprehensive interdisciplinary approach to demonstrate a paradigm for a novel design strategy for new generation engineering. Computational fluid dynamics (CFD), reduced-basis modeling, statistics, uncertainty quantification, and machine learning are employed to develop this strategy. In the real world, designing a new product or device may require months or years. It is therefore crucial to develop more time-efficient strategies for reducing investigation and development costs. Using a rocket engine injector as an example, this dissertation addresses fundamental issues critical to the development of an efficient and robust capability for understanding, analyzing, and predicting fluid dynamics and enhancing the interpretation of physical characteristics for future propulsion systems. The presented work demonstrates recent breakthroughs in modeling and data analytics techniques to substantially improve modeling capabilities at many levels. Due to the high-pressure requirements of cryogenic propellants, such as those of liquid rocket engines, physical experiments are expensive. Furthermore, it is difficult to observe the physical mechanisms of the combustion process via optical diagnostics. High-fidelity CFD, such as large eddy simulations (LES), has been employed for decades to better capture the flowfield and combustion characteristics that occur in rocket engines, but these computationally expensive calculations are impractical for design purposes. A 2D axisymmetric LES case, for instance, can take 6-14 days with 200-350 CPU cores in parallelization, which is extremely costly and time-inefficient. Further, a full-size 3D LES case with the same grid resolution and CPU cores as a 2D case may take over a month to complete. To develop an efficient design strategy for new generation engines, therefore, an interdisciplinary revolution, spanning fields from statistics to engineering, is needed. Taking a swirl injector as a demonstration example, Design of Experiment (DoE) is formulated based on few pivotal geometric design parameters and the corresponding ranges for each of these parameters. Drawing upon prior knowledge of the major contributing geometric parameters, the sample size is determined based on semi-empirical approaches, with a recommended six to ten simulations per design variable. This approach facilitates the design process and reduces the number of total sample points required to efficiently scrutinize the design space. To effectively and efficiently examine the physical mechanisms and dynamic details of instantaneous flow features for a new swirl injector design, serial novel data reduction methods are developed and employed to reduce the data size while keeping dominating physics information. These methods include low-fidelity models such as common proper orthogonal decomposition (CPOD), kernel-smoothed proper orthogonal decomposition (KSPOD), and common kernel-smoothed proper orthogonal decomposition (CKSPOD). The reduced data are used to train the high-fidelity simulation… Advisors/Committee Members: Yang, Vigor (advisor), Sankar, Lakshmi (committee member), Oefelein, Joseph (committee member), Wu, C. F. Jeff (committee member), Vengazhiyil, Roshan (committee member).

Subjects/Keywords: Design study; High-fidelity simulation; Kriging; Data reduction; Surrogate model; Swirl injector

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APA (6^th Edition):

Chang, Y. (2018). High-fidelity emulation of spatiotemporally evolving flow dynamics. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/60842

Chicago Manual of Style (16^th Edition):

Chang, Yu-Hung. “High-fidelity emulation of spatiotemporally evolving flow dynamics.” 2018. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/60842.

MLA Handbook (7^th Edition):

Chang, Yu-Hung. “High-fidelity emulation of spatiotemporally evolving flow dynamics.” 2018. Web. 22 Jan 2021.

Vancouver:

Chang Y. High-fidelity emulation of spatiotemporally evolving flow dynamics. [Internet] [Doctoral dissertation]. Georgia Tech; 2018. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/60842.

Council of Science Editors:

Chang Y. High-fidelity emulation of spatiotemporally evolving flow dynamics. [Doctoral Dissertation]. Georgia Tech; 2018. Available from: http://hdl.handle.net/1853/60842

Georgia Tech

8. Li, Yixing. High-fidelity numerical simulation and emulation of bi-fluid swirl injector flow and combustion dynamics.

Degree: PhD, Aerospace Engineering, 2019, Georgia Tech

URL: http://hdl.handle.net/1853/61698

► Injectors are critical components of combustion devices in liquid-fueled propulsion systems. By controlling the atomization and mixing of propellants, injectors can affect combustion efficiency, dynamic… (more)

▼ Injectors are critical components of combustion devices in liquid-fueled propulsion systems. By controlling the atomization and mixing of propellants, injectors can affect combustion efficiency, dynamic characteristics, and engine life cycle. This work conducts a comprehensive study of the gas-centered liquid-swirl coaxial (GCLSC) injectors, operating at supercritical conditions. The study is composed of two parts. The first part investigates flow and combustion dynamics of GCLSC injectors based on high-fidelity large eddy simulations (LES), and the second part presents a high-fidelity emulation framework for the prediction of spatiotemporally evovling flow and combustion in a significantly shorter turnaround time. For the first part of the study, LES simulations are conducted to study supercritical fluid flow dynamics and combustion characteristics of GCLSC injectors. Gaseous oxygen is axially injected into the center post at a temperature of 687.7K, while kerosene is tangentially introduced into the coaxial annulus at a temperature of 492.2K. The operating pressure is 25.3 MPa, well above the thermodynamic critical points of the propellants involved. Based on LES results, For non-reacting flows, detailed flow physics and structures are identified, followed by comprehensive analyses of mechanisms controlling key dynamic characteristics. These mechanisms include vortex shedding near the fuel injection slit, the shear layer instability in the recess region, and vortical expansion and merging in the taper region. For reacting flows, the flow field is categorized into four regions: propellant injection, flame initialization, flame development, and intensive combustion. Detailed flow structures and the flame evolution in each region are elaborated in detail. Moreover, the effects of the recess length on mixing, flow dynamics and combustion dynamics are investigated. The second part presents a high-fidelity data-driven emulation framework, which utilizes training data from LES and enables flow field emulation in reasonable turnaround time. The framework employs common kernel-smoothed proper orthogonal decomposition (CKSPOD) as the surrogate model, which is able to extract dominant coherent flow structures through hadamard-based POD and kriging, and reconstruct them to predict the flow field of a new case. Significant improvements, including common grid interpolation and physics-based conditions, are incorporated to this framework to accommodate the prediction of complicated mixing and combustion dynamics. In the current study, CKSPOD utilizes LES results of GCLSC injectors as training data, and recess length is chosen as the varying design parameter. Detailed evaluations of the predicted flow fields are carried out, and the current framework is able to capture both instantaneous and time-averaged flow fields with high accuracy. Moreover, the improved CKSPOD presents uncertainty quantification (UQ) of the predicted flow field, providing a metric for model fit. The proposed framework is further extended to injector design… Advisors/Committee Members: Yang, Vigor (advisor), Lieuwen, Timothy (committee member), Sankar, Lakshmi (committee member), Oefelein, Joseph (committee member), Wu, Jeff (committee member), Wang, Xingjian (committee member).

Subjects/Keywords: Large Eddy simulation; Emulation

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APA (6^th Edition):

Li, Y. (2019). High-fidelity numerical simulation and emulation of bi-fluid swirl injector flow and combustion dynamics. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/61698

Chicago Manual of Style (16^th Edition):

Li, Yixing. “High-fidelity numerical simulation and emulation of bi-fluid swirl injector flow and combustion dynamics.” 2019. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/61698.

MLA Handbook (7^th Edition):

Li, Yixing. “High-fidelity numerical simulation and emulation of bi-fluid swirl injector flow and combustion dynamics.” 2019. Web. 22 Jan 2021.

Vancouver:

Li Y. High-fidelity numerical simulation and emulation of bi-fluid swirl injector flow and combustion dynamics. [Internet] [Doctoral dissertation]. Georgia Tech; 2019. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/61698.

Council of Science Editors:

Li Y. High-fidelity numerical simulation and emulation of bi-fluid swirl injector flow and combustion dynamics. [Doctoral Dissertation]. Georgia Tech; 2019. Available from: http://hdl.handle.net/1853/61698

9. Shin, Dong-hyuk. Premixed flame kinematics in a harmonically oscillating velocity field.

Degree: PhD, Aerospace Engineering, 2012, Georgia Tech

URL: http://hdl.handle.net/1853/45950

► Air pollution regulations have driven modern power generation systems to move from diffusion to premixed combustion. However, these premixed combustion systems are prone to combustion… (more)

▼ Air pollution regulations have driven modern power generation systems to move from diffusion to premixed combustion. However, these premixed combustion systems are prone to combustion instability, causing high fluctuations in pressure and temperature. This results in shortening of component life, system failure, or even catastrophic disasters. A large number of studies have been performed to understand and quantify the onset of combustion instability and the limit cycle amplitude. However, much work remains due to the complexity of the process associated with flow dynamics and chemistry. This thesis focuses on identifying, quantifying and predicting mechanisms of flame response subject to disturbances. A promising tool for predicting combustion instability is a flame transfer function. The flame transfer function is obtained by integrating unsteady heat release over the combustor domain. Thus, the better understanding of spatio-temporal characteristics of flame is required to better predict the flame transfer function. The spatio-temporal flame response is analyzed by the flame kinematic equation, so called G-equation. The flame is assumed to be a thin interface separating products and reactant, and the interface is governed by the local flow and the flame propagation. Much of the efforts were done to the flame response subject to the harmonic velocity disturbance. A key assumption allowing for analytic solutions is that the velocity is prescribed. For the mathematical tools, small perturbation theory, Hopf-Lax formula and numerical simulation were used. Solutions indicated that the flame response can be divided into three regions, referred to here as the near-field, mid-field, and farfield. In each regime, analytical expressions were derived, and those results were compared with numerical and experimental data. In the near field, it was shown that the flame response grows linearly with the normal component of the velocity disturbance. In the mid field, the flame response shows peaks in gain, and the axial location of these peaks can be predicted by the interference pattern by two characteristic waves. Lastly, in the far field where the flame response decreases, three mechanisms are studied; they are kinematic restoration, flame stretch, and turbulent flow effects. For each mechanism, key parameters are identified and their relative significances are compared. Advisors/Committee Members: Lieuwen, Tim (Committee Chair), Liu, Yingjie (Committee Member), Menon, Suresh (Committee Member), Yang, Vigor (Committee Member), Zinn, Ben (Committee Member).

Subjects/Keywords: Combustion instability; Combustion dynamics; Flame stability; Combustion; Combustion engineering; Combustion Research

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APA (6^th Edition):

Shin, D. (2012). Premixed flame kinematics in a harmonically oscillating velocity field. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/45950

Chicago Manual of Style (16^th Edition):

Shin, Dong-hyuk. “Premixed flame kinematics in a harmonically oscillating velocity field.” 2012. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/45950.

MLA Handbook (7^th Edition):

Shin, Dong-hyuk. “Premixed flame kinematics in a harmonically oscillating velocity field.” 2012. Web. 22 Jan 2021.

Vancouver:

Shin D. Premixed flame kinematics in a harmonically oscillating velocity field. [Internet] [Doctoral dissertation]. Georgia Tech; 2012. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/45950.

Council of Science Editors:

Shin D. Premixed flame kinematics in a harmonically oscillating velocity field. [Doctoral Dissertation]. Georgia Tech; 2012. Available from: http://hdl.handle.net/1853/45950

10. Acharya, Vishal Srinivas. Dynamics of premixed flames in non-axisymmetric disturbance fields.

Degree: PhD, Aerospace Engineering, 2013, Georgia Tech

URL: http://hdl.handle.net/1853/50213

► With strict environmental regulations, gas turbine emissions have been heavily constrained. This requires operating conditions wherein thermo-acoustic flame instabilities are prevalent. During this process the… (more)

▼ With strict environmental regulations, gas turbine emissions have been heavily constrained. This requires operating conditions wherein thermo-acoustic flame instabilities are prevalent. During this process the combustor acoustics and combustion heat release fluctuations are coupled and can cause severe structural damage to engine components, reduced operability, and inefficiency that eventually increase emissions. In order to develop an engine without these problems, there needs to be a better understanding of the physics behind the coupling mechanisms of this instability. Among the several coupling mechanisms, the “velocity coupling” process is the main focus of this thesis. The majority of literature has treated axisymmetric disturbance fields which are typical of longitudinal acoustic forcing and axisymmetric excitation of ring vortices. Two important non-axisymmetric disturbances are: (1) transverse acoustics, in the case of circumferential modes of a multi-nozzle annular combustor and (2) helical flow disturbances, seen in the case of swirling flow hydrodynamic instabilities. With significantly less analytical treatment of this non-axisymmetric problem, a general framework is developed for three-dimensional swirl-stabilized flame response to non-axisymmetric disturbances. The dynamics are tracked using a level-set based G-equation applicable to infinitely thin flame sheets. For specific assumptions in a linear framework, general solution characteristics are obtained. The results are presented separately for axisymmetric and non-axisymmetric mean flames. The unsteady heat release process leads to an unsteady volume generation at the flame front due to the expansion of gases. This unsteady volume generation leads to sound generation by the flame as a distributed monopole source. A sound generation model is developed where ambient pressure fluctuations are generated by this distributed fluctuating heat release source on the flame surface. The flame response framework is used to provide this local heat release source input. This study has been specifically performed for the helical flow disturbance cases to illustrate the effects different modes have on the generated sound. Results show that the effects on global heat release and sound generation are significantly different. Finally, the prediction from the analytical models is compared with experimental data. First, a two-dimensional bluff-body stabilized flame experiment is used to obtain measurements of both the flow and flame position in time. This enables a local flame response comparison since the data are spatially resolved along the flame. Next, a three-dimensional swirl-stabilized lifted flame experiment is considered. The measured flow data is used as input to the G-equation model and the global flame response is predicted. This is then compared with the corresponding value obtained using global CH* chemilumenescence measurements. Advisors/Committee Members: Lieuwen, Timothy C. (advisor), Yang, Vigor (committee member), Menon, Suresh (committee member), Jagoda, Jeff (committee member), Han, Fei (committee member).

Subjects/Keywords: Level-set; Trasverse acoustics; Helical modes; Swirling flow; Modeling; Combustion Research; Aircraft gas-turbines; Gas-turbines; Aircraft gas-turbines Combustion; Aircraft gas-turbines Combustion chambers; Flames; Combustion

…had over my time here at Georgia Tech. In no particular order, I would like to thank Manisha…

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APA (6^th Edition):

Acharya, V. S. (2013). Dynamics of premixed flames in non-axisymmetric disturbance fields. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/50213

Chicago Manual of Style (16^th Edition):

Acharya, Vishal Srinivas. “Dynamics of premixed flames in non-axisymmetric disturbance fields.” 2013. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/50213.

MLA Handbook (7^th Edition):

Acharya, Vishal Srinivas. “Dynamics of premixed flames in non-axisymmetric disturbance fields.” 2013. Web. 22 Jan 2021.

Vancouver:

Acharya VS. Dynamics of premixed flames in non-axisymmetric disturbance fields. [Internet] [Doctoral dissertation]. Georgia Tech; 2013. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/50213.

Council of Science Editors:

Acharya VS. Dynamics of premixed flames in non-axisymmetric disturbance fields. [Doctoral Dissertation]. Georgia Tech; 2013. Available from: http://hdl.handle.net/1853/50213

11. Sundaram, Dilip Srinivas. Multi-scale modeling of thermochemical behavior of nano-energetic materials.

Degree: PhD, Aerospace Engineering, 2013, Georgia Tech

URL: http://hdl.handle.net/1853/50225

► Conventional energetic materials which are based on monomolecular compounds such as trinitrotoluene (TNT) have relatively low volumetric energy density. The energy density can be significantly… (more)

▼ Conventional energetic materials which are based on monomolecular compounds such as trinitrotoluene (TNT) have relatively low volumetric energy density. The energy density can be significantly enhanced by the addition of metal particulates. Among all metals, aluminum is popular because of its high oxidation enthalpy, low cost, and relative safety. Micron-sized aluminum particles, which have relatively high ignition temperatures and burning times, have been most commonly employed. Ignition of micron-sized aluminum particles is typically achieved only upon melting of the oxide shell at 2350 K, thereby resulting in fairly high ignition delay. Novel approaches to reduce the ignition temperatures and burning times and enhance the energy content of the particle are necessary. Recently, there has been an enormous interest in nano-materials due to their unique physicochemical properties such as lower melting and ignition temperatures and shorter burning times. Favorably, tremendous developments in the synthesis technology of nano-materials have also been made in the recent past. Several metal-based energetic materials with nano-sized particles such as nano-thermites, nano-fluids, and metalized solid propellants are being actively studied. The “green” reactive mixture of nano-aluminum particles and water/ice mixture (ALICE) is being explored for various applications such as space and underwater propulsion, hydrogen generation, and fuel-cell technology. Strand burning experiments indicate that the burning rates of nano-aluminum and water mixtures surpass those of common energetic materials such as ammonium dinitramide (ADN), hydrazinium nitroformate (HNF), and cyclotetramethylene tetranitramine (HMX). Sufficient understanding of key physicochemical phenomena is, however, not present. Furthermore, the most critical parameters that dictate the burning rate have not been identified. A multi-zone theoretical framework is established to predict the burning properties and flame structure by solving conservation equations in each zone and enforcing the mass and energy continuities at the interfacial boundaries. An analytical expression for the burning rate is derived and physicochemical parameters that dictate the flame behavior are identified. An attempt is made to elucidate the rate-controlling combustion mechanism. The effect of bi-modal particle size distribution on the burning rate and flame structure are investigated. The results are compared with the experimental data and favorable agreement is achieved. The ignition and combustion characteristics of micron-sized aluminum particles can also be enhanced by replacing the inert alumina layer with favorable metallic coatings such as nickel. Experiments indicate that nickel-coated aluminum particles ignite at temperatures significantly lower than the melting point of the oxide film, 2350 K due to the presence of inter-metallic reactions. Nickel coating is also attractive for nano-sized aluminum particles due to its ability to maximize the active aluminum content. Understanding… Advisors/Committee Members: Yang, Vigor (advisor), Seitzman, Jerry (committee member), Lieuwen, Timothy (committee member), Jagoda, Jechiel (committee member), Yetter, Richard (committee member).

Subjects/Keywords: Aluminum; Nano-particle; Molecular dynamics; Energetic materials; Nanostructured materials; Nanocomposites (Materials); Thermodynamics; Propellants; Combustion

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APA (6^th Edition):

Sundaram, D. S. (2013). Multi-scale modeling of thermochemical behavior of nano-energetic materials. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/50225

Chicago Manual of Style (16^th Edition):

Sundaram, Dilip Srinivas. “Multi-scale modeling of thermochemical behavior of nano-energetic materials.” 2013. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/50225.

MLA Handbook (7^th Edition):

Sundaram, Dilip Srinivas. “Multi-scale modeling of thermochemical behavior of nano-energetic materials.” 2013. Web. 22 Jan 2021.

Vancouver:

Sundaram DS. Multi-scale modeling of thermochemical behavior of nano-energetic materials. [Internet] [Doctoral dissertation]. Georgia Tech; 2013. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/50225.

Council of Science Editors:

Sundaram DS. Multi-scale modeling of thermochemical behavior of nano-energetic materials. [Doctoral Dissertation]. Georgia Tech; 2013. Available from: http://hdl.handle.net/1853/50225

12. Masquelet, Matthieu Marc. Large-eddy simulations of high-pressure shear coaxial flows relevant for H2/O2 rocket engines.

Degree: PhD, Aerospace Engineering, 2013, Georgia Tech

URL: http://hdl.handle.net/1853/47522

► The understanding and prediction of transient phenomena inside Liquid Rocket Engines (LREs) have been very difficult because of the many challenges posed by the conditions… (more)

▼ The understanding and prediction of transient phenomena inside Liquid Rocket Engines (LREs) have been very difficult because of the many challenges posed by the conditions inside the combustion chamber. This is especially true for injectors involving liquid oxygen LOX and gaseous hydrogen GH₂. A wide range of length scales needs to be captured from high-pressure flame thicknesses of a few microns to the length of the chamber of the order of a meter. A wide range of time scales needs to be captured, again from the very small timescales involved in hydrogen chemistry to low-frequency longitudinal acoustics in the chamber. A wide range of densities needs to be captured, from the cryogenic liquid oxygen to the very hot and light combustion products. A wide range of flow speeds needs to be captured, from the incompressible liquid oxygen jet to the supersonic nozzle. Whether one desires to study these issues numerically or experimentally, they combine to make simulations and measurements very difficult whereas reliable and accurate data are required to understand the complex physics at stake. This thesis focuses on the numerical simulations of flows relevant to LRE applications using Large Eddy Simulations (LES). It identifies the required features to tackle such complex flows, implements and develops state-of-the-art solutions and apply them to a variety of increasingly difficult problems. More precisely, a multi-species real gas framework is developed inside a conservative, compressible solver that uses a state-of-the-art hybrid scheme to capture at the same time the large density gradients and the turbulent structures that can be found in a high-pressure liquid rocket engine. Particular care is applied to the implementation of the real gas framework with detailed derivations of thermodynamic properties, a modular implementation of select equations of state in the solver. and a new efficient iterative method. Several verification cases are performed to evaluate this implementation and the conservative properties of the solver. It is then validated against laboratory-scaled flows relevant to rocket engines, from a gas-gas reacting injector to a liquid-gas injector under non-reacting and reacting conditions. All the injectors considered contain a single shear coaxial element and the reacting cases only deal with H₂-O₂ systems. A gaseous oyxgen-gaseous hydrogen (GOX-GH₂) shear coaxial injector, typical of a staged combustion engine, is first investigated. Available experimental data is limited to the wall heat flux but extensive comparisons are conducted between three-dimensional and axisymmetric solutions generated by this solver as well as by other state-of-the-art solvers through a NASA validation campaign. It is found that the unsteady and three-dimensional character of LES is critical in capturing physical flow features, even on a relatively coarse grid and using a 7-step mechanism instead of a 21-step mechanism. The predictions of the wall heat flux, the only available data,… Advisors/Committee Members: Menon, Suresh (Committee Chair), Oefelein, Joseph (Committee Member), Ruffin, Stephen (Committee Member), Seitzman, Jerry (Committee Member), Yang, Vigor (Committee Member).

Subjects/Keywords: Combustion; Supercritical; Scaling; LES; LRE; CFD; Computational fluid dynamics; Propulsion systems; Rocket engines; Rocket engines Combustion; Liquid propellant rocket engines

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APA (6^th Edition):

Masquelet, M. M. (2013). Large-eddy simulations of high-pressure shear coaxial flows relevant for H2/O2 rocket engines. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/47522

Chicago Manual of Style (16^th Edition):

Masquelet, Matthieu Marc. “Large-eddy simulations of high-pressure shear coaxial flows relevant for H2/O2 rocket engines.” 2013. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/47522.

MLA Handbook (7^th Edition):

Masquelet, Matthieu Marc. “Large-eddy simulations of high-pressure shear coaxial flows relevant for H2/O2 rocket engines.” 2013. Web. 22 Jan 2021.

Vancouver:

Masquelet MM. Large-eddy simulations of high-pressure shear coaxial flows relevant for H2/O2 rocket engines. [Internet] [Doctoral dissertation]. Georgia Tech; 2013. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/47522.

Council of Science Editors:

Masquelet MM. Large-eddy simulations of high-pressure shear coaxial flows relevant for H2/O2 rocket engines. [Doctoral Dissertation]. Georgia Tech; 2013. Available from: http://hdl.handle.net/1853/47522

13. Yang, Suo. Effects of detailed finite rate chemistry in turbulent combustion.

Degree: PhD, Aerospace Engineering, 2017, Georgia Tech

URL: http://hdl.handle.net/1853/58672

► The development of advanced combustion energy-conversion systems requires accurate simulation tools, such as Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES), for capturing and… (more)

▼ The development of advanced combustion energy-conversion systems requires accurate simulation tools, such as Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES), for capturing and understanding ignition, combustion instability, lean blowout, and emissions. However, the characteristic timescales in combustion systems can range from milliseconds to picoseconds or even lower. This renders the use of detailed finite rate chemistry prohibitive in DNS/LES of turbulent combustion, which requires the calculation of a large number of species and reactions on a large number of grid cells. Due to these high computational costs, DNS and LES typically employ either a flamelet model with detailed chemistry or a simplified/reduced finite rate chemistry with non-stiff reactions. Both approaches, however, are of limited accuracy and may reduce the overall prediction quality. To address this, a framework with high fidelity by incorporating finite rate chemistry, while mitigating additional computational cost, is necessary for the development of advanced combustion systems. In this dissertation, a new numerical framework for DNS and LES of turbulent combustion is established employing correlated dynamic adaptive chemistry (CoDAC), correlated evaluation of transport properties (CoTran), and a point-implicit stiff ODE solver (ODEPIM). CoDAC utilizes a path flux analysis (PFA) method to reduce the large chemical kinetics mechanism to a smaller size for each location and time step. Thermo-chemical correlation zones are introduced and only one PFA calculation is required for each zone, which diminishes the CPU overhead of CoDAC to negligible computation costs. CoTran uses a similar correlation method to accelerate the evaluation of mixture-averaged diffusion (MAD) coefficients. This framework is firstly applied to investigate the non-equilibrium plasma discharge of C2H4/O2/Ar mixtures in a low-temperature flow reactor. The accelerated case has been verified against the benchmark case by both temporal evolution and spatial distribution of several key species and gas temperature. Simulation results show that it accelerates the total computation time by a factor of 3.16, the calculation of chemical kinetics by a factor of 80, and the evaluation of MAD coefficients by a factor of 836. The high accuracy and efficiency of this proposed framework illustrate its promise in the simulation of diverse combustion problems. Secondly, this framework is evaluated for a canonical turbulent premixed flame employing a conventional jet fuel kinetics model. Again, the results show that the new framework provides a significant speed-up of chemical kinetics and transport computation, enabling DNS with large kinetics mechanisms while maintaining high accuracy and good parallel scalability. Detailed diagnostics show that, for this test case, calculation of the chemical source term with ODEPIM is 17 times faster than that of a pure implicit solver. CoDAC further speeds up the calculation of chemical source terms by 2.7 times. CoTran makes the… Advisors/Committee Members: Sun, Wenting (advisor), Yang, Vigor (advisor), Menon, Suresh (committee member), Ju, Yiguang (committee member), Liu, Yingjie (committee member).

Subjects/Keywords: Turbulent combustion; Chemical kinetics; Modeling and simulation; Finite-rate effects; Extinction and ignition

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APA (6^th Edition):

Yang, S. (2017). Effects of detailed finite rate chemistry in turbulent combustion. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/58672

Chicago Manual of Style (16^th Edition):

Yang, Suo. “Effects of detailed finite rate chemistry in turbulent combustion.” 2017. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/58672.

MLA Handbook (7^th Edition):

Yang, Suo. “Effects of detailed finite rate chemistry in turbulent combustion.” 2017. Web. 22 Jan 2021.

Vancouver:

Yang S. Effects of detailed finite rate chemistry in turbulent combustion. [Internet] [Doctoral dissertation]. Georgia Tech; 2017. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/58672.

Council of Science Editors:

Yang S. Effects of detailed finite rate chemistry in turbulent combustion. [Doctoral Dissertation]. Georgia Tech; 2017. Available from: http://hdl.handle.net/1853/58672

14. Yeh, Shiang-Ting. Common proper orthogonal decomposition-based emulation and system identification for model-based analysis of combustion dynamics.

Degree: PhD, Aerospace Engineering, 2018, Georgia Tech

URL: http://hdl.handle.net/1853/59965

► For high-performance power generation and propulsion systems, such as those of airbreathing and rocket engines, physical experiments are expensive due to the harsh requirements of… (more)

▼ For high-performance power generation and propulsion systems, such as those of airbreathing and rocket engines, physical experiments are expensive due to the harsh requirements of operating conditions. In addition, it is difficult to gain insight into the underlying mechanisms of the physiochemical processes involved because of the typical reliance upon optical diagnostics for experimental measurements. High-fidelity simulations can be employed to capture more salient features of the flow and combustion dynamics in engines, but these computations are often too expensive and time-consuming for design and development purposes. To enable usage of modeling/simulation in the design workflow, the present study proposes a data-driven framework for modeling and analysis to facilitate decision making for combustor designs. Its core is a surrogate model employing a machine-learning technique called kriging, which is combined with data-driven basis functions to extract and model the underlying coherent structures from high-fidelity simulation results. This emulation framework encompasses key design parameter sensitivity analysis, physics-guided classification of design parameter sets, and flow evolution modeling for efficient design survey. A sensitivity analysis using Sobol’ indices and a decision tree are incorporated into the framework to better inform the model. This information improves the surrogate model training process, which employs basis functions as regression functions over the design space for the kriging model. The novelty of the proposed approach is the construction of the surrogate model through Common Proper Orthogonal Decomposition, allowing for data-reduction and extraction of common coherent structures. The accuracy of prediction of mean flow features for new swirl injector designs is assessed and the dynamic flowfield is captured in the form of power spectrum densities. This data-driven framework also demonstrates the uncertainty quantification of predictions, providing a metric for model fit. The significantly reduced computation time required for evaluating new design points enables efficient survey of the design space. To further utilize model results, a data analytic methodology to quantify the combustion dynamics is used to link the component-level simulations to the system-level stability performance. Comprehensive combustion stability analysis and a good understanding of the coupling process would reduce the amount of testing and level of capital required for engine development. The proposed methodology leverages high-fidelity large eddy simulation (LES) in combination with machine-learning techniques to quantify the spatial combustion response, which is intended to serve as an acoustic source term in the generalized wave equation. The acoustic eigenmode analysis can be used to assess the stability of propulsion systems. Treating the extracted coherent structures as time series signals, the combustion response can be deduced through autoregressive model selection, accounting for data sparsity,… Advisors/Committee Members: Yang, Vigor (advisor), Wu, C.F. Jeff (committee member), Lieuwen, Tim (committee member), Sankar, Lakshmi (committee member), Oefelein, Joseph (committee member).

Subjects/Keywords: Emulation; Combustion response

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APA (6^th Edition):

Yeh, S. (2018). Common proper orthogonal decomposition-based emulation and system identification for model-based analysis of combustion dynamics. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/59965

Chicago Manual of Style (16^th Edition):

Yeh, Shiang-Ting. “Common proper orthogonal decomposition-based emulation and system identification for model-based analysis of combustion dynamics.” 2018. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/59965.

MLA Handbook (7^th Edition):

Yeh, Shiang-Ting. “Common proper orthogonal decomposition-based emulation and system identification for model-based analysis of combustion dynamics.” 2018. Web. 22 Jan 2021.

Vancouver:

Yeh S. Common proper orthogonal decomposition-based emulation and system identification for model-based analysis of combustion dynamics. [Internet] [Doctoral dissertation]. Georgia Tech; 2018. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/59965.

Council of Science Editors:

Yeh S. Common proper orthogonal decomposition-based emulation and system identification for model-based analysis of combustion dynamics. [Doctoral Dissertation]. Georgia Tech; 2018. Available from: http://hdl.handle.net/1853/59965

15. Shreekrishna. Response mechanisms of attached premixed flames to harmonic forcing.

Degree: PhD, Aerospace Engineering, 2011, Georgia Tech

URL: http://hdl.handle.net/1853/42759

► The persistent thrust for a cleaner, greener environment has prompted air pollution regulations to be enforced with increased stringency by environmental protection bodies all over… (more)

▼ The persistent thrust for a cleaner, greener environment has prompted air pollution regulations to be enforced with increased stringency by environmental protection bodies all over the world. This has prompted gas turbine manufacturers to move from non-premixed combustion to lean, premixed combustion. These lean premixed combustors operate quite fuel-lean compared to the stochiometric, in order to minimize CO and NOx productions, and are very susceptible to oscillations in any of the upstream flow variables. These oscillations cause the heat release rate of the flame to oscillate, which can engage one or more acoustic modes of the combustor or gas turbine components, and under certain conditions, lead to limit cycle oscillations. This phenomenon, called thermoacoustic instabilities, is characterized by very high pressure oscillations and increased heat fluxes at system walls, and can cause significant problems in the routine operability of these combustors, not to mention the occasional hardware damages that could occur, all of which cumulatively cost several millions of dollars. In a bid towards understanding this flow-flame interaction, this research works studies the heat release response of premixed flames to oscillations in reactant equivalence ratio, reactant velocity and pressure, under conditions where the flame preheat zone is convectively compact to these disturbances, using the G-equation. The heat release response is quantified by means of the flame transfer function and together with combustor acoustics, forms a critical component of the analytical models that can predict combustor dynamics. To this end, low excitation amplitude (linear) and high excitation amplitude (nonlinear) responses of the flame are studied in this work. The linear heat release response of lean, premixed flames are seen to be dominated by responses to velocity and equivalence ratio fluctuations at low frequencies, and to pressure fluctuations at high frequencies which are in the vicinity of typical screech frequencies in gas turbine combustors. The nonlinear response problem is exclusively studied in the case of equivalence ratio coupling. Various nonlinearity mechanisms are identified, amongst which the crossover mechanisms, viz., stoichiometric and flammability crossovers, are seen to be responsible in causing saturation in the overall heat release magnitude of the flame. The response physics remain the same across various preheat temperatures and reactant pressures. Finally, comparisons between the chemiluminescence transfer function obtained experimentally and the heat release transfer functions obtained from the reduced order model (ROM) are performed for lean, CH4/Air swirl-stabilized, axisymmetric V-flames. While the comparison between the phases of the experimental and theoretical transfer functions are encouraging, their magnitudes show disagreement at lower Strouhal number gains show disagreement. Advisors/Committee Members: Lieuwen, Timothy Charles (Committee Chair), Han, Fei (Committee Member), Menon, Suresh (Committee Member), Seitzman, Jerry (Committee Member), Yang, Vigor (Committee Member).

Subjects/Keywords: Reduced order modeling; Flame transfer function; G-equation; Flame response; Combustion dynamics; Gas turbines; Thermoacoustic instabilities; Combustion instabilities; Gas-turbines; Aircraft gas-turbines; Combustion engineering

…all the great times that we have spent together. My last year at Georgia Tech was absolutely… …providing me with the culture of my country and hometown very close to Georgia Tech, that I would…

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APA (6^th Edition):

Shreekrishna. (2011). Response mechanisms of attached premixed flames to harmonic forcing. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/42759

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Chicago Manual of Style (16^th Edition):

Shreekrishna. “Response mechanisms of attached premixed flames to harmonic forcing.” 2011. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/42759.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

MLA Handbook (7^th Edition):

Shreekrishna. “Response mechanisms of attached premixed flames to harmonic forcing.” 2011. Web. 22 Jan 2021.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Vancouver:

Shreekrishna. Response mechanisms of attached premixed flames to harmonic forcing. [Internet] [Doctoral dissertation]. Georgia Tech; 2011. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/42759.

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

Council of Science Editors:

Shreekrishna. Response mechanisms of attached premixed flames to harmonic forcing. [Doctoral Dissertation]. Georgia Tech; 2011. Available from: http://hdl.handle.net/1853/42759

Note: this citation may be lacking information needed for this citation format:
Author name may be incomplete

16. Pakmehr, Mehrdad. Towards verifiable adaptive control of gas turbine engines.

Degree: PhD, Aerospace Engineering, 2013, Georgia Tech

URL: http://hdl.handle.net/1853/49025

► This dissertation investigates the problem of developing verifiable stable control architectures for gas turbine engines. First, a nonlinear physics-based dynamic model of a twin spool… (more)

▼ This dissertation investigates the problem of developing verifiable stable control architectures for gas turbine engines. First, a nonlinear physics-based dynamic model of a twin spool turboshaft engine which drives a variable pitch propeller is developed. In this model, the dynamics of the engine are defined to be the two spool speeds, and the two control inputs to the system are fuel flow rate and prop pitch angle. Experimental results are used to verify the dynamic model of JetCat SPT5 turboshaft engine. Based on the experimental data, performance maps of the engine components including propeller, high pressure compressor, high pressure, and low pressure turbines are constructed. The engine numerical model is implemented using Matlab. Second, a stable gain scheduled controller is described and developed for a gas turbine engine that drives a variable pitch propeller. A stability proof is developed for a gain scheduled closed-loop system using global linearization and linear matrix inequality (LMI) techniques. Using convex optimization tools, a single quadratic Lyapunov function is computed for multiple linearizations near equilibrium and non-equilibrium points of the nonlinear closed-loop system. This approach guarantees stability of the closed-loop gas turbine engine system. To verify the stability of the closed-loop system on-line, an optimization problem is proposed which is solvable using convex optimization tools. Through simulations, we show the developed gain scheduled controller is capable to regulate a turboshaft engine for large thrust commands in a stable fashion with proper tracking performance. Third, a gain scheduled model reference adaptive control (GS-MRAC) concept for multi-input multi-output (MIMO) nonlinear plants with constraints on the control inputs is developed and described. Specifically, adaptive state feedback for the output tracking control problem of MIMO nonlinear systems is studied. Gain scheduled reference model system is used for generating desired state trajectories, and the stability of this reference model is also analyzed using convex optimization tools. This approach guarantees stability of the closed-loop gain scheduled gas turbine engine system, which is used as a gain scheduled reference model. An adaptive state feedback control scheme is developed and its stability is proven, in addition to transient and steady-state performance guarantees. The resulting closed-loop system is shown to have ultimately bounded solutions with a priori adjustable bounded tracking error. The results are then extended to GS-MRAC with constraints on the magnitudes of multiple control inputs. Sufficient conditions for uniform boundedness of the closed-loop system is derived. A semi-global stability result is proven with respect to the level of saturation for open-loop unstable plants, while the stability result is shown to be global for open-loop stable plants. Simulations are performed for three different models of the turboshaft engine, including the nominal engine model and two models… Advisors/Committee Members: Feron, Eric (advisor), Johnson, Eric (committee member), Yang, Vigor (committee member), Shamma, Jeff (committee member), Wolf, Marilyn (committee member), Paduano, James (committee member).

Subjects/Keywords: Adaptive control; Gain scheduled control; Gas turbine engines; Aerospace software verification; Gas-turbines; Jet engines; Adaptive control systems

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APA (6^th Edition):

Pakmehr, M. (2013). Towards verifiable adaptive control of gas turbine engines. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/49025

Chicago Manual of Style (16^th Edition):

Pakmehr, Mehrdad. “Towards verifiable adaptive control of gas turbine engines.” 2013. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/49025.

MLA Handbook (7^th Edition):

Pakmehr, Mehrdad. “Towards verifiable adaptive control of gas turbine engines.” 2013. Web. 22 Jan 2021.

Vancouver:

Pakmehr M. Towards verifiable adaptive control of gas turbine engines. [Internet] [Doctoral dissertation]. Georgia Tech; 2013. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/49025.

Council of Science Editors:

Pakmehr M. Towards verifiable adaptive control of gas turbine engines. [Doctoral Dissertation]. Georgia Tech; 2013. Available from: http://hdl.handle.net/1853/49025

Georgia Tech

17. Ukai, Satoshi. Richtmyer-Meshkov instability with reshock and particle interactions.

Degree: MS, Aerospace Engineering, 2010, Georgia Tech

URL: http://hdl.handle.net/1853/34724

► Richtmyer-Meshkov instability (RMI) occurs when an interface of two fluids with different densities is impulsively accelerated. The main interest in RMI is to understand the… (more)

▼ Richtmyer-Meshkov instability (RMI) occurs when an interface of two fluids with different densities is impulsively accelerated. The main interest in RMI is to understand the growth of perturbations, and numerous theoretical models have been developed and validated against experimental/numerical studies. However, most of the studies assume very simple initial conditions. Recently, more complex RMI has been studied, and this study focuses on two cases: reshocked RMI and multiphase RMI. It is well known that reshock to the species interface causes rapid growth of interface perturbation amplitude. However, the growth rates after reshock are not well understood, and there are no practical theoretical models yet due to its complex interface conditions at reshock. A couple of empirical expressions have been derived from experimental and numerical studies, but these models are limited to certain interface conditions. This study performs parametric numerical studies on various interface conditions, and the empirical models on the reshocked RMI are derived for each case. It is shown that the empirical models can be applied to a wide range of initial conditions by choosing appropriate values of the coefficient. The second part of the study analyzes the flow physics of multiphase RMI. The linear growth model for multiphase RMI is derived, and it is shown that the growth rates depend on two nondimensional parameters: the mass loading of the particles and the Stokes number. The model is compared to the numerical predictions under two types of conditions: a shock wave hitting (1) a perturbed species interface surrounded by particles, and (2) a perturbed particle cloud. In the first type of the problem, the growth rates obtained by the numerical simulations are in agreement with the multiphase RMI growth model when Stokes number is small. However, when the Stokes number is very large, the RMI motion follows the single-phase RMI growth model since the particle do not rapidly respond while the RMI instability grows. The second type of study also shows that the multiphase RMI model is applicable if Stokes number is small. Since the particles themselves characterize the interface, the range of applicable Stokes number is smaller than the first study. If the Stokes number is in the order of one or larger, the interface experiences continuous acceleration and shows the growth profile similar to a Rayleigh-Taylor instability. Advisors/Committee Members: Menon, Suresh (Committee Chair), Sankar, Lakshmi (Committee Member), Yang, Vigor (Committee Member).

Subjects/Keywords: Multiphase flow; Shock; Instability; Richtmyer-Meshkov instability; Navier-Stokes equations; Fluid dynamics

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APA (6^th Edition):

Ukai, S. (2010). Richtmyer-Meshkov instability with reshock and particle interactions. (Masters Thesis). Georgia Tech. Retrieved from http://hdl.handle.net/1853/34724

Chicago Manual of Style (16^th Edition):

Ukai, Satoshi. “Richtmyer-Meshkov instability with reshock and particle interactions.” 2010. Masters Thesis, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/34724.

MLA Handbook (7^th Edition):

Ukai, Satoshi. “Richtmyer-Meshkov instability with reshock and particle interactions.” 2010. Web. 22 Jan 2021.

Vancouver:

Ukai S. Richtmyer-Meshkov instability with reshock and particle interactions. [Internet] [Masters thesis]. Georgia Tech; 2010. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/34724.

Council of Science Editors:

Ukai S. Richtmyer-Meshkov instability with reshock and particle interactions. [Masters Thesis]. Georgia Tech; 2010. Available from: http://hdl.handle.net/1853/34724

Georgia Tech

18. Hemchandra, Santosh. Dynamics of turbulent premixed flames in acoustic fields.

Degree: PhD, Aerospace Engineering, 2009, Georgia Tech

URL: http://hdl.handle.net/1853/29615

► This thesis describes computational and theoretical studies of fundamental physical processes that influence the heat-release response of turbulent premixed flames to acoustic forcing. Attached turbulent… (more)

▼ This thesis describes computational and theoretical studies of fundamental physical processes that influence the heat-release response of turbulent premixed flames to acoustic forcing. Attached turbulent flames, as found in many practical devices, have a non-zero mean velocity component tangential to the turbulent flame brush. Hence, flame surface wrinkles generated at a given location travel along the flame sheet while being continuously modified by local flow velocity disturbances, thereby, causing the flame sheet to respond in a non-local manner to upstream turbulence fluctuations. The correlation length and time scales of these flame sheet motions are significantly different from those of the upstream turbulence fluctuations. These correlation lengths and times increase with turbulence intensity, due to the influence of kinematic restoration. This non-local nature of flame sheet wrinkling (called 'non-locality') results in a spatially varying distribution of local consumption speed (i.e. local mass burning rate) even when the upstream flow statistics are isotropic and stationary. Non-locality and kinematic restoration result in coupling between the responses of the flame surface to coherent acoustic forcing and random turbulent fluctuations respectively, thereby, causing the coherent ensemble averaged component of the global heat-release fluctuation to be different in magnitude and phase from its nominal (laminar) value even in the limit of small coherent forcing amplitudes (i.e. linear forcing limit). An expression for this correction, derived from an asymptotic analysis to leading order in turbulence intensity, shows that its magnitude decreases with increasing forcing frequency because kinematic restoration limits flame surface wrinkling amplitudes. Predictions of ensemble averaged heat release response from a different, generalized modeling approach using local consumption and displacement speed distributions from unforced analysis shows good agreement with the exact asymptotic result at low frequencies. Advisors/Committee Members: Lieuwen, Tim (Committee Chair), Menon, Suresh (Committee Member), Peters, Norbert (Committee Member), Yang, Vigor (Committee Member), Zinn, Benjamin (Committee Member).

Subjects/Keywords: Heat release response; Turbulent flames; Level-set; Non-locality; Turbulent flame speed; Transfer function; Consumption speed; Turbulence; Combustion; Kinematics

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Hemchandra, S. (2009). Dynamics of turbulent premixed flames in acoustic fields. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/29615

Chicago Manual of Style (16^th Edition):

Hemchandra, Santosh. “Dynamics of turbulent premixed flames in acoustic fields.” 2009. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/29615.

MLA Handbook (7^th Edition):

Hemchandra, Santosh. “Dynamics of turbulent premixed flames in acoustic fields.” 2009. Web. 22 Jan 2021.

Vancouver:

Hemchandra S. Dynamics of turbulent premixed flames in acoustic fields. [Internet] [Doctoral dissertation]. Georgia Tech; 2009. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/29615.

Council of Science Editors:

Hemchandra S. Dynamics of turbulent premixed flames in acoustic fields. [Doctoral Dissertation]. Georgia Tech; 2009. Available from: http://hdl.handle.net/1853/29615

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Open Access Theses and Dissertations