+publisher:"Georgia Tech" +contributor:("Menon, Suresh")

Georgia Tech

1. Dzanic, Tarik. Investigation of ODE-based non-equilibrium wall shear stress models for large eddy simulation.

Degree: MS, Aerospace Engineering, 2019, Georgia Tech

► For high Reynolds number flows, wall modeling is essential for performing large eddy simulation at a reasonable computational cost. In this work, a novel low-cost… (more)

▼ For high Reynolds number flows, wall modeling is essential for performing large eddy simulation at a reasonable computational cost. In this work, a novel low-cost ODE-based non-equilibrium wall model is introduced for wall shear stress modeling in LES. Using polynomial approximations of the pressure gradient and convective terms obtained from interpolation of the LES solution, as opposed to direct evaluation of these gradients within the wall model, the governing wall model equations reduce from coupled PDEs to uncoupled ODEs that do not require an embedded wall model grid within the LES grid. Additionally, the steady form of the wall model equations was utilized, feasible due to the spatial decoupling of the wall model equations, and the effects of the temporal evolution on the wall shear stress were modeled. The effects of polynomial degree on the accuracy of the wall shear stress predictions were explored, and an empirical lag model was built to model the unsteady effects without requiring the solution of a time-stepping problem. Wall resolved large eddy simulations of separated flow around the NASA wall mounted hump and an iced NACA 63A213 airfoil were performed and used as a reference for the comparison of the non-equilibrium wall model to a commonly used equilibrium wall model. The proposed non-equilibrium wall model was able to predict separated flow and laminar flow regions in much better agreement with the wall resolved results than the equilibrium wall model. Underpredictions in the skin friction coefficient in non-equilibrium flow regimes were reduced from 20-50% to less than 10% between the equilibrium and the non-equilibrium wall modeled approaches. Minor improvements in the pressure coefficient predictions were observed with the non-equilibrium model in the separated flow region of the iced airfoil. The results suggest that the proposed wall model can offer better predictions of separated and/or laminar flows compared to equilibrium wall models with negligible computational cost increase. Advisors/Committee Members: Oefelein, Joseph (advisor), Menon, Suresh (advisor), Yeung, P. K. (advisor).

Subjects/Keywords: Large eddy simulation; Wall model; Non-equilibrium

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APA (6^th Edition):

Dzanic, T. (2019). Investigation of ODE-based non-equilibrium wall shear stress models for large eddy simulation. (Masters Thesis). Georgia Tech. Retrieved from http://hdl.handle.net/1853/62711

Chicago Manual of Style (16^th Edition):

Dzanic, Tarik. “Investigation of ODE-based non-equilibrium wall shear stress models for large eddy simulation.” 2019. Masters Thesis, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/62711.

MLA Handbook (7^th Edition):

Dzanic, Tarik. “Investigation of ODE-based non-equilibrium wall shear stress models for large eddy simulation.” 2019. Web. 22 Jan 2021.

Vancouver:

Dzanic T. Investigation of ODE-based non-equilibrium wall shear stress models for large eddy simulation. [Internet] [Masters thesis]. Georgia Tech; 2019. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/62711.

Council of Science Editors:

Dzanic T. Investigation of ODE-based non-equilibrium wall shear stress models for large eddy simulation. [Masters Thesis]. Georgia Tech; 2019. Available from: http://hdl.handle.net/1853/62711

Georgia Tech

2. Sanyal, Anuradha. Large eddy simulation of syngas-air diffusion flames with artificial neural networks based chemical kinetics.

Degree: MS, Aerospace Engineering, 2011, Georgia Tech

URL: http://hdl.handle.net/1853/42785

► In the present study syngas-air diffusion flames are simulated using LES with artificial neural network (ANN) based chemical kinetics modeling and the results are compared… (more)

▼ In the present study syngas-air diffusion flames are simulated using LES with artificial neural network (ANN) based chemical kinetics modeling and the results are compared with previous direct numerical simulation (DNS) study, which exhibits significant extinction-reignition and forms a challenging problem for ANN. The objective is to obtain speed-up in chemistry computation while still having the accuracy of stiff ODE solver. The ANN methodology is used in two ways: 1) to compute the instantaneous source term in the linear eddy mixing (LEM) subgrid combustion model used within LES framework, i.e., laminar-ANN used within LEMLES framework (LANN-LEMLES), and 2) to compute the filtered source terms directly within the LES framework, i.e., turbulent-ANN used within LES (TANN-LES), which further dicreases the computational speed. A thermo-chemical database is generated from a standalone one-dimensional LEM simulation and used to train the LANN for species source terms on grid-size of Kolmogorov scale. To train the TANN coefficients the thermo-chemical database from the standalone LEM simulation is filtered over the LES grid-size and then used for training. To evaluate the performance of the TANN methodology, the low Re test case is simulated with direct integration for chemical kinetics modeling in LEM subgrid combustion model within the LES framework (DI-LEMLES), LANN-LEMLES andTANN-LES. The TANN is generated for a low range of Ret in order to simulate the specific test case. The conditional statistics and pdfs of key scalars and the temporal evolution of the temperature and scalar dissipation rates are compared with the data extracted from DNS. Results show that the TANN-LES methodology can capture the extinction-reignition physics with reasonable accuracy compared to the DNS. Another TANN is generated for a high range of Ret expected to simulate test cases with different Re and a range of grid resolutions. The flame structure and the scalar dissipation rate statistics are analyzed to investigate success of the same TANN in simulating a range of test cases. Results show that the TANN-LES using TANN generated fora large range of Ret is capable of capturing the extinction-reignition physics with a very little loss of accuracy compared to the TANN-LES using TANN generated for the specific test case. The speed-up obtained by TANN-LES is significant compared to DI-LEMLES and LANN-LEMLES. Advisors/Committee Members: Menon, Suresh (Committee Chair), Jagoda, Jechiel (Committee Member), Ruffin, Stephen (Committee Member).

Subjects/Keywords: Artificial Neural Netwoks; LEM; LES; Extinction-reignition; Neural networks (Computer science); Eddies Mathematical models

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APA (6^th Edition):

Sanyal, A. (2011). Large eddy simulation of syngas-air diffusion flames with artificial neural networks based chemical kinetics. (Masters Thesis). Georgia Tech. Retrieved from http://hdl.handle.net/1853/42785

Chicago Manual of Style (16^th Edition):

Sanyal, Anuradha. “Large eddy simulation of syngas-air diffusion flames with artificial neural networks based chemical kinetics.” 2011. Masters Thesis, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/42785.

MLA Handbook (7^th Edition):

Sanyal, Anuradha. “Large eddy simulation of syngas-air diffusion flames with artificial neural networks based chemical kinetics.” 2011. Web. 22 Jan 2021.

Vancouver:

Sanyal A. Large eddy simulation of syngas-air diffusion flames with artificial neural networks based chemical kinetics. [Internet] [Masters thesis]. Georgia Tech; 2011. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/42785.

Council of Science Editors:

Sanyal A. Large eddy simulation of syngas-air diffusion flames with artificial neural networks based chemical kinetics. [Masters Thesis]. Georgia Tech; 2011. Available from: http://hdl.handle.net/1853/42785

Georgia Tech

3. Karimi, Miad. Investigation of high-pressure methane and syngas autoignition delay times.

Degree: PhD, Aerospace Engineering, 2019, Georgia Tech

URL: http://hdl.handle.net/1853/62295

► This thesis reports methane (CH4) and a syngas mixture (H2/CO=95:5) autoignition delay measurements relevant to operating conditions of supercritical carbon dioxide (sCO2) power cycle (100… (more)

▼ This thesis reports methane (CH4) and a syngas mixture (H2/CO=95:5) autoignition delay measurements relevant to operating conditions of supercritical carbon dioxide (sCO2) power cycle (100 to 300 bar) combustors. To acquire data at these conditions as part of this thesis, a new high-pressure shock tube is designed, fabricated and commissioned. The experiments are conducted for diluted carbon dioxide environments at 100 and 200 bar and at temperatures within the range of approximately 1100–1400 K. To investigate the chemical effect of CO2 at supercritical conditions, experiments are conducted at similar pressures and temperatures by substituting CO2 with an inert bath gas, Ar (argon). Obtaining ignition delay times in Ar bath gas allows to systematically study the chemical effect of CO2 on ignition chemistry. Methane ignition delay times are compared to several chemical kinetic models, such as Aramco 2.0, FFCM-1, HP-Mech, USC Mech II and GRI 3.0. For the conditions of this study, predictions of the Aramco 2.0 kinetic model show the overall best agreement with experimental measurements. Following the experimental data, brute-force sensitivity analyses and reaction pathway flux analyses are utilized to gain insight into details of the ignition chemistry of the fuels (CH4 and H2/CO=95:5). These analyses indicate that methyl (CH3) recombination to form ethane (C2H6) and oxidation of CH3 to form methoxide (CH3O) are the most important reactions controlling the ignition behavior of methane at temperatures greater than approximately 1250 K. However, at temperatures below approximately 1250 K, an additional reaction pathway for methyl radicals is found through CH3+O2+M=CH3O2+M, which leads to formation of methyldioxidanyl (CH3O2). This reaction pathway plays a distinct role in dictating the ignition trends at lower temperature conditions. Replacing CO2 with argon as the bath gas reveals that CO2 does not have major effects on ignition chemistry of CH4. A similar approach is taken to obtain experimental data at 100 bar and 200 bar for a syngas fuel mixture of 95% H2 (hydrogen) and 5% CO (carbon monoxide) in CO2 and Ar bath gasses. Aramco 2.0 kinetic model, FFCM-1 kinetic model, HP-Mech and USC Mech II show good agreement with the measured ignition delay times. Detailed sensitivity analyses of these kinetic models highlight the importance of the third-body reaction between hydrogen atoms (H) and oxygen molecules (O2) through H+O2+M=HO2+M to form hydroperoxyl (HO2). In both cases, irrespective of the diluents, this reaction is the most influential reaction to hinder ignition. Ignition delay times obtained from both mixtures not only show a similar trend, but also the same magnitude when compared to the CO2 mixture. While this observation may suggest that CO2 has no chemical effect on ignition chemistry, it is found to play a counterbalancing role on syngas ignition at the elevated pressures and temperatures of this study. CO2 increases the OH (hydroxyl) radical production by colliding with hydrogen peroxide (H2O2) through… Advisors/Committee Members: Ranjan, Devesh (advisor), Sun, Wenting (advisor), Menon, Suresh (committee member), Lieuwen, Timothy (committee member), Loutzenhiser, Peter (committee member).

Subjects/Keywords: High-pressure ignition delay times; Chemical kinetics; Supercritical CO2

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APA (6^th Edition):

Karimi, M. (2019). Investigation of high-pressure methane and syngas autoignition delay times. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/62295

Chicago Manual of Style (16^th Edition):

Karimi, Miad. “Investigation of high-pressure methane and syngas autoignition delay times.” 2019. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/62295.

MLA Handbook (7^th Edition):

Karimi, Miad. “Investigation of high-pressure methane and syngas autoignition delay times.” 2019. Web. 22 Jan 2021.

Vancouver:

Karimi M. Investigation of high-pressure methane and syngas autoignition delay times. [Internet] [Doctoral dissertation]. Georgia Tech; 2019. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/62295.

Council of Science Editors:

Karimi M. Investigation of high-pressure methane and syngas autoignition delay times. [Doctoral Dissertation]. Georgia Tech; 2019. Available from: http://hdl.handle.net/1853/62295

Georgia Tech

4. Ochs, Bradley Alan. Ignition, topology, and growth of turbulent premixed flames in supersonic flows.

Degree: PhD, Aerospace Engineering, 2019, Georgia Tech

URL: http://hdl.handle.net/1853/62313

► Supersonic combustion ramjets (scramjets) are currently the most efficient combustor technology for air breathing hypersonic flight, however, lack of fundamental understanding and numerous engineering challenges… (more)

▼ Supersonic combustion ramjets (scramjets) are currently the most efficient combustor technology for air breathing hypersonic flight, however, lack of fundamental understanding and numerous engineering challenges hinder regular deployment of these devices. This work addresses scramjet-relevant knowledge gaps in supersonic turbulent premixed combustion, including laser ignition, numerical modeling, and flame-compressibility interaction. One of the main contributions of this work is introduction of a new turbulent premixed flame arrangement where flame-compressibility interaction can be systematically explored: flame kernels in an expanding flow field. The scramjet flow path is replaced by a simplified channel geometry with a well characterized mean flow acceleration that mimics flow field expansion typically imposed on scramjet combustors to avoid thermal choking. Spherically expanding flames are created via laser ignition and subsequent flame growth and morphology are investigated using combined physical and numerical experiments. Pressure-density misalignment due to flame-compressibility interaction produces vorticity at the flame surface through baroclinic torque, i.e. flame-compressibility interaction acts like a turbulence source. The flame ultimately evolves into a reacting vortex ring that increases the flame speed and enhances reactant consumption. To explore the relative importance of turbulence and compressibility on flame dynamics, the Mach number (M=1.5,1.75,2), equivalence ratio (φ= 1.0,0.9,0.8,0.7), and root-mean-squared turbulent velocity (u'=3.98,4.14,4.45 m/s) are varied systematically. This work also introduces flame kernels in an expanding flow field as a canonical numerical validation test case for flame-compressibility interaction. Inaccuracies in simulation results are easily identified due to high flow velocity and simplicity of the problem. The numerical setup and models are scrutinized to minimize errors. Using the appropriately verified numerical models, simulation results show very reasonable agreement with experimental data. Validated simulations are instrumental in enhancing understanding of the underlying physics of supersonic flame kernels. Laser ignition studies in supersonic flows have historically focused on ignition of non-premixed fuels within cavity flame holders. This work introduces a far simpler and more tractable problem: laser ignition of a fully premixed supersonic gas. Ignition experiments with a range of laser settings are performed to determine supersonic breakdown and ignition probabilities, length of time the ignition event influences flame growth, and Mach number influence on the ignition process. The ignition event has a long-lasting effect on kernel growth, but the influence can be minimized by properly selecting the laser energy. Mach number has a minimal impact on the ignition process, but does affect the initial kernel shape due to flow field variations with Mach number. Kernel growth matches low speed studies closely at early times, but deviates at later times due… Advisors/Committee Members: Menon, Suresh (advisor), Ranjan, Devesh (committee member), Seitzman, Jerry (committee member), Sun, Wenting (committee member), Pitz, Robert (committee member), Carter, Campbell (committee member).

Subjects/Keywords: Hypersonics; Supersonic flows; Supersonic combustion; Laser ignition; Turbulent flames; Premixed flames

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

APA (6^th Edition):

Ochs, B. A. (2019). Ignition, topology, and growth of turbulent premixed flames in supersonic flows. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/62313

Chicago Manual of Style (16^th Edition):

Ochs, Bradley Alan. “Ignition, topology, and growth of turbulent premixed flames in supersonic flows.” 2019. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/62313.

MLA Handbook (7^th Edition):

Ochs, Bradley Alan. “Ignition, topology, and growth of turbulent premixed flames in supersonic flows.” 2019. Web. 22 Jan 2021.

Vancouver:

Ochs BA. Ignition, topology, and growth of turbulent premixed flames in supersonic flows. [Internet] [Doctoral dissertation]. Georgia Tech; 2019. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/62313.

Council of Science Editors:

Ochs BA. Ignition, topology, and growth of turbulent premixed flames in supersonic flows. [Doctoral Dissertation]. Georgia Tech; 2019. Available from: http://hdl.handle.net/1853/62313

Georgia Tech

5. Keshava Iyer, Kartik P. Studies of turbulence structure and turbulent mixing using petascale computing.

Degree: PhD, Aerospace Engineering, 2014, Georgia Tech

URL: http://hdl.handle.net/1853/52260

► A large direct numerical simulation database spanning a wide range of Reynolds and Schmidt number is used to examine fundamental laws governing passive scalar mixing… (more)

▼ A large direct numerical simulation database spanning a wide range of Reynolds and Schmidt number is used to examine fundamental laws governing passive scalar mixing and turbulence structure. Efficient parallel algorithms have been developed to calculate quantities useful in examining the Kolmogorov small-scale phenomenology. These new algorithms are used to analyze data sets with Taylor scale Reynolds numbers as high as 650 with grid-spacing as small as the Kolmogrov length scale. Direct numerical simulation codes using pseudo-spectral methods typically use transpose based three-dimensional (3D) Fast Fourier Transforms (FFT). The ALLTOALL type routines to perform global transposes have a quadratic dependence on message size and typically show limited scaling at very large problem sizes. A hybrid MPI/OpenMP 3D FFT kernel has been developed that divides the work among the threads and schedules them in a pipelined fashion. All threads perform the communication, although not concurrently, with the aim of minimizing thread-idling time and increasing the overlap between communication and computation. The new algorithm is seen to reduce the communication time by as much as 30% at large core-counts, as compared to pure-MPI communication. Turbulent mixing is important in a wide range of fields ranging from combustion to cosmology. Schmidt numbers range from O(1) to O(0.01) in these applications. The Schmidt number dependence of the second-order scalar structure function and the applicability of the so-called Yaglomﾒs relation is examined in isotropic turbulence with a uniform mean scalar gradient. At the moderate Reynolds numbers currently achievable, the dynamics of strongly diffusive scalars is inherently different from moderately diffusive Schmidt numbers. Results at Schmidt number as low as 1/2048 show that the range of scales in the scalar field become quite narrow with the distribution of the small-scales approaching a Gaussian shape. A much weaker alignment between velocity gradients and principal strain rates and a strong departure from Yaglomﾒs relation have also been observed. Evaluation of different terms in the scalar structure function budget equation assuming statistical stationarity in time shows that with decreasing Schmidt number, the production and diffusion terms dominate at the intermediate scales possibly leading to non-universal behavior for the low-to-moderate Peclet number regime considered in this study. One of the few exact, non-trivial results in hydrodynamic theory is the so-called Kolmogorov 4/5th law. Agreement for the third order longitudinal structure function with the 4/5 plateau is used to measure the extent of the inertial range, both in experiments and simulations. Direct numerical simulation techniques to obtain the third order structure structure functions typically use component averaging, combined with time averaging over multiple eddy-turnover times. However, anisotropic large scale effects tend to limit the inertial range with significant variance in the components of the structure… Advisors/Committee Members: Yeung, Pui-Kuen (advisor), Menon, Suresh (committee member), Vuduc, Richard (committee member), Walker, Mitchell (committee member), Sreenivasan, Katepalli (committee member).

Subjects/Keywords: Turbulence; Direct numerical simulations

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APA (6^th Edition):

Keshava Iyer, K. P. (2014). Studies of turbulence structure and turbulent mixing using petascale computing. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/52260

Chicago Manual of Style (16^th Edition):

Keshava Iyer, Kartik P. “Studies of turbulence structure and turbulent mixing using petascale computing.” 2014. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/52260.

MLA Handbook (7^th Edition):

Keshava Iyer, Kartik P. “Studies of turbulence structure and turbulent mixing using petascale computing.” 2014. Web. 22 Jan 2021.

Vancouver:

Keshava Iyer KP. Studies of turbulence structure and turbulent mixing using petascale computing. [Internet] [Doctoral dissertation]. Georgia Tech; 2014. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/52260.

Council of Science Editors:

Keshava Iyer KP. Studies of turbulence structure and turbulent mixing using petascale computing. [Doctoral Dissertation]. Georgia Tech; 2014. Available from: http://hdl.handle.net/1853/52260

Georgia Tech

6. 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

7. 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

8. Buaria, Dhawal. Lagrangian investigations of turbulent dispersion and mixing using petascale computing.

Degree: PhD, Aerospace Engineering, 2016, Georgia Tech

URL: http://hdl.handle.net/1853/58572

► In many fields of science and engineering important to society, such as study of air/water quality, pollutant dispersion, cloud physics, design of improved combustion devices,… (more)

▼ In many fields of science and engineering important to society, such as study of air/water quality, pollutant dispersion, cloud physics, design of improved combustion devices, etc., the ability of turbulent flow to provide efficient transport of entities such as pollutants, vapor droplets, fuel/oxidizer, etc. is of critical importance. To understand and hence develop proper predictive tools for such transported entities, it is necessary to understand turbulence from a Lagrangian perspective (of an observer moving with the flow), including the interaction between turbulent transport and molecular diffusion. Usually, in both direct numerical simulations (DNS) and experiments, a population of fluid particles is tracked forward in time (forward tracking) from specified initial conditions to understand how a cloud of material spreads in a turbulent flow. However the process of turbulent mixing occurs when material located at different regions at previous times is brought together at a later time. In such a scenario, it is more important to track the particles backward in time (backward tracking). Backward tracking is also important from a modeling perspective, which would help address questions about the dynamical origins of a patch of contaminant material, or a highly convoluted multi-particle cluster. Furthermore, it can also be shown that the n-th moment of a passive scalar field can be directly related to the backward in time statistics of an n-particle cluster. Although conceptually simple, backward tracking is very difficult to accomplish due to time irreversibility of Navier-Stokes equations, and thus not very well understood in literature. In this work, we use DNS of stationary isotropic turbulence to investigate the process of backward and forward dispersion using state of the art computing facilities. A new massively parallel computational framework has been developed to enable particle tracking in DNS at Petascale problem sizes, performing up to 40X faster than the previous implementation. We have also implemented an efficient and statistically robust approach to extract backward and forward statistics via the post-processing of trajectory data stored in DNS of fluid particles and diffusing molecules (that undergo Brownian motion relative to the fluid). Detailed results are first obtained for pairs of fluid particles. An important consequence of applying Kolmogorov’s similarity hypotheses to Lagrangian statistics of particle pairs is the universal t3 scaling (Richardson’s scaling) at intermediate times. Backward dispersion is found to be faster at intermediate times resulting in a higher Richardson constant, though the scaling is not as robust as in forward dispersion. Extensions to higher-order moments of the separation are also addressed. Statistics of the trajectories of molecules taken singly and in pairs are investigated. The separation statistics of molecular pairs exhibit more robust Richardson scaling compared to fluid particles. An important innovation in this work is to demonstrate explicitly the… Advisors/Committee Members: Yeung, Pui-Kuen (advisor), Ruffin, Stephen (committee member), Menon, Suresh (committee member), Chow, Edmond (committee member), Webster, Donald (committee member).

Subjects/Keywords: Turbulent dispersion; Turbulent mixing; Direct numerical simulations; High performance computing

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APA (6^th Edition):

Buaria, D. (2016). Lagrangian investigations of turbulent dispersion and mixing using petascale computing. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/58572

Chicago Manual of Style (16^th Edition):

Buaria, Dhawal. “Lagrangian investigations of turbulent dispersion and mixing using petascale computing.” 2016. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/58572.

MLA Handbook (7^th Edition):

Buaria, Dhawal. “Lagrangian investigations of turbulent dispersion and mixing using petascale computing.” 2016. Web. 22 Jan 2021.

Vancouver:

Buaria D. Lagrangian investigations of turbulent dispersion and mixing using petascale computing. [Internet] [Doctoral dissertation]. Georgia Tech; 2016. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/58572.

Council of Science Editors:

Buaria D. Lagrangian investigations of turbulent dispersion and mixing using petascale computing. [Doctoral Dissertation]. Georgia Tech; 2016. Available from: http://hdl.handle.net/1853/58572

Georgia Tech

9. 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

10. Marshall, Andrew. Turbulent flame propagation characteristics of high hydrogen content fuels.

Degree: PhD, Mechanical Engineering, 2015, Georgia Tech

URL: http://hdl.handle.net/1853/53859

► Increasingly stringent pollution and emission controls have caused a rise in the use of combustors operating under lean, premixed conditions. Operating lean (excess air) lowers… (more)

▼ Increasingly stringent pollution and emission controls have caused a rise in the use of combustors operating under lean, premixed conditions. Operating lean (excess air) lowers the level of nitrous oxides (NOx) emitted to the environment. In addition, concerns over climate change due to increased carbon dioxide (CO2) emissions and the need for energy independence in the United States have spurred interest in developing combustors capable of operating with a wide range of fuel compositions. One method to decrease the carbon footprint of modern combustors is the use of high hydrogen content (HHC) fuels. The objective of this research is to develop tools to better understand the physics of turbulent flame propagation in highly stretch sensitive premixed flames in order to predict their behavior at conditions realistic to the environment of gas turbine combustors. This thesis presents the results of an experimental study into the flame propagation characteristics of highly stretch-sensitive, turbulent premixed flames generated in a low swirl burner (LSB). This study uses a scaling law, developed in an earlier thesis from leading point concepts for turbulent premixed flames, to collapse turbulent flame speed data over a wide range of conditions. The flow and flame structure are characterized using high speed particle image velocimetry (PIV) over a wide range of fuel compositions, mean flow velocities, and turbulence levels. The first part of this study looks at turbulent flame speeds for these mixtures and applies the previously developed leading points scaling model in order to test its validity in an alternate geometry. The model was found to collapse the turbulent flame speed data over a wide range of fuel compositions and turbulence levels, giving merit to the leading points model as a method that can produce meaningful results with different geometries and turbulent flame speed definitions. The second part of this thesis examines flame front topologies and stretch statistics of these highly stretch sensitive, turbulent premixed flames. Instantaneous flame front locations and local flow velocities are used to calculate flame curvatures and tangential strain rates. Statistics of these two quantities are calculated both over the entire flame surface and also conditioned at the leading points of the flames. Results presented do not support the arguments made in the development of the leading points model. Only minor effects of fuel composition are noted on curvature statistics, which are mostly dominated by the turbulence. There is a stronger sensitivity for tangential strain rate statistics, however, time-averaged values are still well below the values hypothesized from the leading points model. The results of this study emphasize the importance of local flame topology measurements towards the development of predictive models of the turbulent flame speed. Advisors/Committee Members: Lieuwen, Tim C. (advisor), Seitzman, Jerry (committee member), Menon, Suresh (committee member), Genzale, Caroline (committee member), Zinn, Ben T. (committee member).

Subjects/Keywords: Turbulent flames; Premixed flames; Turbulent flame speed; High hydrogen; Stretch effects; Curvature; Tangential strain rate; Leading points; Fuel effects; Low swirl burner; Particle image velocimetry; Flame topology

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APA (6^th Edition):

Marshall, A. (2015). Turbulent flame propagation characteristics of high hydrogen content fuels. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/53859

Chicago Manual of Style (16^th Edition):

Marshall, Andrew. “Turbulent flame propagation characteristics of high hydrogen content fuels.” 2015. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/53859.

MLA Handbook (7^th Edition):

Marshall, Andrew. “Turbulent flame propagation characteristics of high hydrogen content fuels.” 2015. Web. 22 Jan 2021.

Vancouver:

Marshall A. Turbulent flame propagation characteristics of high hydrogen content fuels. [Internet] [Doctoral dissertation]. Georgia Tech; 2015. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/53859.

Council of Science Editors:

Marshall A. Turbulent flame propagation characteristics of high hydrogen content fuels. [Doctoral Dissertation]. Georgia Tech; 2015. Available from: http://hdl.handle.net/1853/53859

Georgia Tech

11. Schulz, Joseph C. A study of magnetoplasmadynamic effects in turbulent supersonic flows with application to detonation and explosion.

Degree: PhD, Aerospace Engineering, 2015, Georgia Tech

URL: http://hdl.handle.net/1853/53971

► Explosions are a common phenomena in the Universe. Beginning with the Big Bang, one could say the history of the Universe is narrated by a… (more)

Subjects/Keywords: Magnetohydrodynamics; Detonation; Fluid instability; Numerical methods

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APA (6^th Edition):

Schulz, J. C. (2015). A study of magnetoplasmadynamic effects in turbulent supersonic flows with application to detonation and explosion. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/53971

Chicago Manual of Style (16^th Edition):

Schulz, Joseph C. “A study of magnetoplasmadynamic effects in turbulent supersonic flows with application to detonation and explosion.” 2015. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/53971.

MLA Handbook (7^th Edition):

Schulz, Joseph C. “A study of magnetoplasmadynamic effects in turbulent supersonic flows with application to detonation and explosion.” 2015. Web. 22 Jan 2021.

Vancouver:

Schulz JC. A study of magnetoplasmadynamic effects in turbulent supersonic flows with application to detonation and explosion. [Internet] [Doctoral dissertation]. Georgia Tech; 2015. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/53971.

Council of Science Editors:

Schulz JC. A study of magnetoplasmadynamic effects in turbulent supersonic flows with application to detonation and explosion. [Doctoral Dissertation]. Georgia Tech; 2015. Available from: http://hdl.handle.net/1853/53971

Georgia Tech

12. Gottiparthi, Kalyana Chakravarthi. A study of dispersion and combustion of particle clouds in post-detonation flows.

Degree: PhD, Aerospace Engineering, 2015, Georgia Tech

URL: http://hdl.handle.net/1853/53972

► Augmentation of the impact of an explosive is routinely achieved by packing metal particles in the explosive charge. When detonated, the particles in the charge… (more)

Subjects/Keywords: Detonation; Explosion; Dense flow; Eulerian-Eulerian; Eulerian-Lagrangian

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APA (6^th Edition):

Gottiparthi, K. C. (2015). A study of dispersion and combustion of particle clouds in post-detonation flows. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/53972

Chicago Manual of Style (16^th Edition):

Gottiparthi, Kalyana Chakravarthi. “A study of dispersion and combustion of particle clouds in post-detonation flows.” 2015. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/53972.

MLA Handbook (7^th Edition):

Gottiparthi, Kalyana Chakravarthi. “A study of dispersion and combustion of particle clouds in post-detonation flows.” 2015. Web. 22 Jan 2021.

Vancouver:

Gottiparthi KC. A study of dispersion and combustion of particle clouds in post-detonation flows. [Internet] [Doctoral dissertation]. Georgia Tech; 2015. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/53972.

Council of Science Editors:

Gottiparthi KC. A study of dispersion and combustion of particle clouds in post-detonation flows. [Doctoral Dissertation]. Georgia Tech; 2015. Available from: http://hdl.handle.net/1853/53972

Georgia Tech

13. Quinlan, John Mathew. Investigation of driving mechanisms of combustion instabilities in liquid rocket engines via the dynamic mode decomposition.

Degree: PhD, Aerospace Engineering, 2015, Georgia Tech

URL: http://hdl.handle.net/1853/54343

► Combustion instability due to feedback coupling between unsteady heat release and natural acoustic modes can cause catastrophic failure in liquid rocket engines and to predict… (more)

▼ Combustion instability due to feedback coupling between unsteady heat release and natural acoustic modes can cause catastrophic failure in liquid rocket engines and to predict and prevent these instabilities the mechanisms that drive them must be further elucidated. With this goal in mind, the objective of this thesis was to develop techniques that improve the understanding of the specific underlying physical processes involved in these driving mechanisms. In particular, this work sought to develop a small-scale, optically accessible liquid rocket engine simulator and to apply modern, high-speed diagnostic techniques to characterize the reacting flow and acoustic field within the simulator. Specifically, high-speed (10 kHz), simultaneous data were acquired while the simulator was experiencing a 170 Hz combustion instability using particle image velocimetry, OH planar laser induced fluorescence, CH* chemiluminescence, and dynamic pressure measurements. In addition, this work sought to develop approaches to reduce the large quantities of data acquired, extracting key physical phenomena involved in the driving mechanisms. The initial data reduction approach was chosen based on the fact that the combustion instability problem is often simplified to the point that it can be characterized by an approximately linear constant coefficient system of equations. Consistent with this simplification, the experimental data were analyzed by the dynamic mode decomposition method. The developed approach to apply the dynamic mode decomposition to simultaneously acquired data located a coupled hydrodynamic/combustion/acoustic mode at 1017 Hz. On the other hand, the dynamic mode decomposition's assumed constant operator approach failed to locate any modes of interest near 170 Hz. This led to the development of two new data analysis techniques based on the dynamic mode decomposition and Floquet theory that assume that the experiment is governed by a linear, periodic system of equations. The new periodic-operator data analysis techniques, the Floquet decomposition and the ensemble Floquet decomposition, approximate, from experimental data, the largest moduli Floquet multipliers, which determine the stability of the periodic solution trajectory of the system. The unstable experiment dataset was analyzed with these techniques and the ensemble Floquet decomposition analysis found a large modulus Floquet multiplier and associated mode with a frequency of 169.6 Hz. Furthermore, the approximate Rayleigh criterion indicated that this mode was unstable with respect to combustion instability. Overall, based on the positive finding that the ensemble Floquet decomposition was able to locate an unstable combustion mode at 170 Hz when the operator's time period was set to 1 ms, suggests that the dynamic mode decomposition based 1017 Hz mode parametrically forces the 170 Hz mode, resulting in what could be characterized as a parametric combustion instability. Advisors/Committee Members: Zinn, Ben T. (advisor), Dieci, Luca (committee member), Lieuwen, Tim (committee member), Menon, Suresh (committee member), Seitzman, Jerry M. (committee member).

Subjects/Keywords: CI; LRE; DMD; Floquet; Floquet decomposition; FD; EFD; POD; Combustion; Stability; Instability; Acoustic; Liquid rocket; Dynamic mode decomposition; Ensemble floquet decomposition; Periodic; Vibrations; Time-varying; Eigenvalues

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APA (6^th Edition):

Quinlan, J. M. (2015). Investigation of driving mechanisms of combustion instabilities in liquid rocket engines via the dynamic mode decomposition. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/54343

Chicago Manual of Style (16^th Edition):

Quinlan, John Mathew. “Investigation of driving mechanisms of combustion instabilities in liquid rocket engines via the dynamic mode decomposition.” 2015. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/54343.

MLA Handbook (7^th Edition):

Quinlan, John Mathew. “Investigation of driving mechanisms of combustion instabilities in liquid rocket engines via the dynamic mode decomposition.” 2015. Web. 22 Jan 2021.

Vancouver:

Quinlan JM. Investigation of driving mechanisms of combustion instabilities in liquid rocket engines via the dynamic mode decomposition. [Internet] [Doctoral dissertation]. Georgia Tech; 2015. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/54343.

Council of Science Editors:

Quinlan JM. Investigation of driving mechanisms of combustion instabilities in liquid rocket engines via the dynamic mode decomposition. [Doctoral Dissertation]. Georgia Tech; 2015. Available from: http://hdl.handle.net/1853/54343

Georgia Tech

14. Caruso, Natalie R. S. Facility effects on Helicon ion thruster operation.

Degree: PhD, Aerospace Engineering, 2016, Georgia Tech

URL: http://hdl.handle.net/1853/55014

► In order to enable comparison of Helicon ion thruster performance across different vacuum test facilities, an understanding of the effect of operating pressure on plasma… (more)

Subjects/Keywords: Helicon ion thruster; MadHeX; Facility effects; Neutral ingestion; Magnetic nozzle; Plasma; Electric propulsion

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APA (6^th Edition):

Caruso, N. R. S. (2016). Facility effects on Helicon ion thruster operation. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/55014

Chicago Manual of Style (16^th Edition):

Caruso, Natalie R S. “Facility effects on Helicon ion thruster operation.” 2016. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/55014.

MLA Handbook (7^th Edition):

Caruso, Natalie R S. “Facility effects on Helicon ion thruster operation.” 2016. Web. 22 Jan 2021.

Vancouver:

Caruso NRS. Facility effects on Helicon ion thruster operation. [Internet] [Doctoral dissertation]. Georgia Tech; 2016. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/55014.

Council of Science Editors:

Caruso NRS. Facility effects on Helicon ion thruster operation. [Doctoral Dissertation]. Georgia Tech; 2016. Available from: http://hdl.handle.net/1853/55014

Georgia Tech

15. Smith, Andrew Gerard. Simulations of vitiated bluff body stabilized flames.

Degree: PhD, Aerospace Engineering, 2016, Georgia Tech

URL: http://hdl.handle.net/1853/55582

► Bluff bodies have a wide range of applications where low-cost, light weight methods are needed to stabilize flames in high-speed flow. The principles of bluff… (more)

▼ Bluff bodies have a wide range of applications where low-cost, light weight methods are needed to stabilize flames in high-speed flow. The principles of bluff body flame stabilization are straightforward, but many details are not understood; this is especially true in vitiated environments where measurements are difficult to obtain. Most work has focused on premixed flames but changing application requirements are now driving studies on non-premixed gaseous and spray flames. This thesis aims to improve the understanding of vitiated, bluff body stabilized flames, specifically on non-premixed, spray flames, through the use of Large Eddy Simulation (LES). The single flameholder facility at Georgia Tech was chosen as the basis for the simulations in this thesis. The flameholder was a rectangular bluff body with an aerodynamic leading edge with discrete liquid fuel injectors embedded just upstream of the trailing edge in a configuration described as “close-coupled.” The liquid phase was modeled using a Lagrangian particle approach where discrete fuel droplets were injected into the domain. Experimental data was used to tune model parameters as well as the stripped droplet velocities and sizes. The discharge coefficient needed to be taken into account to achieve the correct fuel jet penetration. The experiments were conducted over a range of global equivalence ratios; lean equivalence ratios, φ global ≈ 0.5, exhibited symmetric flame shedding and conversely large scale sinusoidal B ́ernard/von-K ́arm ́an shedding was observed when the equiva- lence ratio was near unity. Reacting flow LES were computed at these two fuel flow rates to improve understanding of the different flame dynamics. LES were first com- pleted using a quasi-laminar subgrid turbulence-chemistry interaction model. Span- wise averaging of instantaneous and time-averaged LES results were compared with experimental high- and low-speed imaging and showed the LES was in qualitative agreement at both fuel flow rates. At phi_global ≈ 0.5, the fuel jet did not penetrate as far into the crossflow compared to phi_global ≈ 0.95 and thus more fuel was delivered to the shear layers of the bluff body resulting in higher heat release in the shear layers for the low fuel flow rate. The heat release damped the large sinusoidal structures via gas expansion and baroclinic torque generation. Higher fuel jet penetration in the phi_global ≈ 0.95 case meant less fuel was delivered to the shear layers and so less heat release occurred directly behind the bluff body so the large scale sinusoidal shedding was not damped. The impact of the subgrid turbulence-chemistry interaction model on the flame dynamics was tested by comparing the quasi-laminar LES with LES using the subgrid linear eddy model (LEMLES). The flame structure predicted with LEMLES matched that of the quasi-laminar LES, at both fuel flow rates in the near- field behind the bluff body but deviated farther downstream. A flame edge analysis showed little sensitivity to the choice of… Advisors/Committee Members: Menon, Suresh (advisor), Seitzman, Jerry (committee member), Lovett, Jeffery (committee member), Sankar, Lakshmi (committee member), Jagoda, Jechiel (committee member).

Subjects/Keywords: LES; Bluff body; Combustion

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APA (6^th Edition):

Smith, A. G. (2016). Simulations of vitiated bluff body stabilized flames. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/55582

Chicago Manual of Style (16^th Edition):

Smith, Andrew Gerard. “Simulations of vitiated bluff body stabilized flames.” 2016. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/55582.

MLA Handbook (7^th Edition):

Smith, Andrew Gerard. “Simulations of vitiated bluff body stabilized flames.” 2016. Web. 22 Jan 2021.

Vancouver:

Smith AG. Simulations of vitiated bluff body stabilized flames. [Internet] [Doctoral dissertation]. Georgia Tech; 2016. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/55582.

Council of Science Editors:

Smith AG. Simulations of vitiated bluff body stabilized flames. [Doctoral Dissertation]. Georgia Tech; 2016. Available from: http://hdl.handle.net/1853/55582

16. Gallagher, Timothy. Towards multi-scale reacting fluid-structure interaction: micro-scale structural modeling.

Degree: MS, Aerospace Engineering, 2015, Georgia Tech

URL: http://hdl.handle.net/1853/53483

► The fluid-structure interaction of reacting materials requires computational models capable of resolving the wide range of scales present in both the condensed phase energetic materials… (more)

Subjects/Keywords: Explosives simulation

10 more images…

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APA (6^th Edition):

Gallagher, T. (2015). Towards multi-scale reacting fluid-structure interaction: micro-scale structural modeling. (Masters Thesis). Georgia Tech. Retrieved from http://hdl.handle.net/1853/53483

Chicago Manual of Style (16^th Edition):

Gallagher, Timothy. “Towards multi-scale reacting fluid-structure interaction: micro-scale structural modeling.” 2015. Masters Thesis, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/53483.

MLA Handbook (7^th Edition):

Gallagher, Timothy. “Towards multi-scale reacting fluid-structure interaction: micro-scale structural modeling.” 2015. Web. 22 Jan 2021.

Vancouver:

Gallagher T. Towards multi-scale reacting fluid-structure interaction: micro-scale structural modeling. [Internet] [Masters thesis]. Georgia Tech; 2015. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/53483.

Council of Science Editors:

Gallagher T. Towards multi-scale reacting fluid-structure interaction: micro-scale structural modeling. [Masters Thesis]. Georgia Tech; 2015. Available from: http://hdl.handle.net/1853/53483

17. Pasumarti, Venkata-Ramya. Large eddy simulation of heated pulsed jets in high speed turbulent crossflow.

Degree: MS, Aerospace Engineering, 2010, Georgia Tech

URL: http://hdl.handle.net/1853/37291

► The jet-in-crossflow problem has been extensively studied, mainly because of its applications in film cooling and injector designs. It has been established that in low-speed… (more)

Subjects/Keywords: LES; Jet in crossflow; Jet scaling; Compressible flow; Turbulent flow; Fluid dynamics; Eddies

11 more images…

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APA (6^th Edition):

Pasumarti, V. (2010). Large eddy simulation of heated pulsed jets in high speed turbulent crossflow. (Masters Thesis). Georgia Tech. Retrieved from http://hdl.handle.net/1853/37291

Chicago Manual of Style (16^th Edition):

Pasumarti, Venkata-Ramya. “Large eddy simulation of heated pulsed jets in high speed turbulent crossflow.” 2010. Masters Thesis, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/37291.

MLA Handbook (7^th Edition):

Pasumarti, Venkata-Ramya. “Large eddy simulation of heated pulsed jets in high speed turbulent crossflow.” 2010. Web. 22 Jan 2021.

Vancouver:

Pasumarti V. Large eddy simulation of heated pulsed jets in high speed turbulent crossflow. [Internet] [Masters thesis]. Georgia Tech; 2010. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/37291.

Council of Science Editors:

Pasumarti V. Large eddy simulation of heated pulsed jets in high speed turbulent crossflow. [Masters Thesis]. Georgia Tech; 2010. Available from: http://hdl.handle.net/1853/37291

18. Gryngarten, Leandro Damian. Multi-phase flows using discontinuous Galerkin methods.

Degree: PhD, Aerospace Engineering, 2012, Georgia Tech

URL: http://hdl.handle.net/1853/45824

► This thesis is concerned with the development of numerical techniques to simulate compressible multi-phase flows, in particular a high-accuracy numerical approach with mesh adaptivity. The… (more)

▼ This thesis is concerned with the development of numerical techniques to simulate compressible multi-phase flows, in particular a high-accuracy numerical approach with mesh adaptivity. The Discontinuous Galerkin (DG) method was chosen as the framework for this work for being characterized for its high-order of accuracy -thus low numerical diffusion- and being compatible with mesh adaptivity due to its locality. A DG solver named DiGGIT (Discontinuous Galerkin at the Georgia Institute of Technology) has been developed and several aspects of the method have been studied. The Local Discontinuous Galerkin (LDG) method -an extension of DG for equations with high-order derivatives- was extended to solve multiphase flows using Diffused Interface Methods (DIM). This multi-phase model includes the convection of the volume fraction, which is treated as a Hamilton-Jacobi equation. This is the first study, to the author's knowledge, in which the volume fraction of a DIM is solved using the DG and the LDG methods. The formulation is independent of the Equation of State (EOS) and it can differ for each phase. This allows for a more accurate representation of the different fluids by using cubic EOSs, like the Peng-Robinson and the van der Waals models. Surface tension is modeled with a new numerical technique appropriate for LDG. Spurious oscillations due to surface tension are common to all the capturing schemes, and this new approach presents oscillations comparable in magnitude to the most common schemes. The moment limiter (ML) was generalized for non-uniform grids with hanging nodes that result from adaptive mesh refinement (AMR). The effect of characteristic, primitive, or conservative decomposition in the limiting stage was studied. The characteristic option cannot be used with the ML in multi-dimensions. In general, primitive variable decomposition is a better option than with conservative variables, particularly for multiphase flows, since the former type of decomposition reduces the numerical oscillations at material discontinuities. An additional limiting technique was introduced for DIM to preserve positivity while minimizing the numerical diffusion, which is especially important at the interface. The accuracy-preserving total variation diminishing (AP-TVD) marker for ``troubled-cell' detection, which uses an averaged-derivative basis, was modified to use the Legendre polynomial basis. Given that the latest basis is generally used for DG, the new approach avoids transforming to the averaged-derivative basis, what results in a more efficient technique. Furthermore, a new error estimator was proposed to determine where to refine or coarsen the grid. This estimator was compared against other estimator used in the literature and it showed an improved performance. In order to provide equal order of accuracy in time as in space, the commonly used 3rd-order TVD Runge-Kutta (RK) scheme in the DG method was replaced in some cases by the Spectral Deferred Correction (SDC) technique. High orders in time were shown to only be… Advisors/Committee Members: Menon, Suresh (Committee Chair), Liu, Yingjie (Committee Member), Ruffin, Stephen (Committee Member), Sankar, Lakshmi (Committee Member), Smith, Marilyn (Committee Member).

Subjects/Keywords: Computational fluid dynamics; Multi-fluid; Multi-phase; Discontinuous Galerking; Fluid dynamics; Numerical analysis; Navier-Stokes equations Numerical solutions; Simulation methods; Mathematical models

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APA (6^th Edition):

Gryngarten, L. D. (2012). Multi-phase flows using discontinuous Galerkin methods. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/45824

Chicago Manual of Style (16^th Edition):

Gryngarten, Leandro Damian. “Multi-phase flows using discontinuous Galerkin methods.” 2012. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/45824.

MLA Handbook (7^th Edition):

Gryngarten, Leandro Damian. “Multi-phase flows using discontinuous Galerkin methods.” 2012. Web. 22 Jan 2021.

Vancouver:

Gryngarten LD. Multi-phase flows using discontinuous Galerkin methods. [Internet] [Doctoral dissertation]. Georgia Tech; 2012. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/45824.

Council of Science Editors:

Gryngarten LD. Multi-phase flows using discontinuous Galerkin methods. [Doctoral Dissertation]. Georgia Tech; 2012. Available from: http://hdl.handle.net/1853/45824

19. Periagaram, Karthik Balasubramanian. Determination of flame characteristics in a low swirl burner at gas turbine conditions through reaction zone imaging.

Degree: PhD, Aerospace Engineering, 2012, Georgia Tech

URL: http://hdl.handle.net/1853/45828

► This thesis explores the effects of operating parameters on the location and shape of lifted flames in a Low Swirl Burner (LSB). In addition, it… (more)

▼ This thesis explores the effects of operating parameters on the location and shape of lifted flames in a Low Swirl Burner (LSB). In addition, it details the development and analysis of a CH PLIF imaging system for visualizing flames in lean combustion systems. The LSB is studied at atmospheric pressure using LDV and CH PLIF. CH* chemiluminescence is used for high pressure flame imaging. A four-level model of the fluorescing CH system is developed to predict the signal intensity in hydrocarbon flames. Results from imaging an atmospheric pressure laminar flame are used to validate the behavior of the signal intensity as predicted by the model. The results show that the fluorescence signal is greatly reduced at high pressure due to the decreased number of CH molecules and the increased collisional quenching rate. This restricts the use of this technique to increasingly narrow equivalence ratio ranges at high pressures. The limitation is somewhat alleviated by increasing the preheat temperature of the reactant mixture. The signal levels from high hydrogen-content syngas mixtures doped with methane are found to be high enough to make CH PLIF a feasible diagnostic to study such flames. Finally, the model predicts that signal levels are unlikely to be significantly affected by the presence of strain in the flow field, as long as the flames are not close to extinction. The results from the LSB flame investigation reveal that combustor provides reasonably robust flame stabilization at low and moderate values of combustor pressure and reference velocities. However, at very high velocities and pressures, the balance between the reactant velocity and the turbulent flame speed shifts in favor of the former resulting in the flame moving downstream. The extent of this movement is small, but indicates a tendency towards blow off at higher pressures and velocities that may be encountered in real world gas turbine applications. There is an increased tendency of relatively fuel-rich flames to behave like attached flames at high pressure. These results raise interesting questions about turbulent combustion at high pressure as well as provide usable data to gas turbine combustor designers by highlighting potential problems. Advisors/Committee Members: Seitzman, Jerry (Committee Chair), Genzale, Caroline (Committee Member), Jagoda, Jeff (Committee Member), Lieuwen, Tim (Committee Member), Menon, Suresh (Committee Member).

Subjects/Keywords: Chemkin; LIF modeling; LSB; CH PLIF; Swirl combustor; Combustion engineering; Combustion; Flame stability; Gas-turbines

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APA (6^th Edition):

Periagaram, K. B. (2012). Determination of flame characteristics in a low swirl burner at gas turbine conditions through reaction zone imaging. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/45828

Chicago Manual of Style (16^th Edition):

Periagaram, Karthik Balasubramanian. “Determination of flame characteristics in a low swirl burner at gas turbine conditions through reaction zone imaging.” 2012. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/45828.

MLA Handbook (7^th Edition):

Periagaram, Karthik Balasubramanian. “Determination of flame characteristics in a low swirl burner at gas turbine conditions through reaction zone imaging.” 2012. Web. 22 Jan 2021.

Vancouver:

Periagaram KB. Determination of flame characteristics in a low swirl burner at gas turbine conditions through reaction zone imaging. [Internet] [Doctoral dissertation]. Georgia Tech; 2012. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/45828.

Council of Science Editors:

Periagaram KB. Determination of flame characteristics in a low swirl burner at gas turbine conditions through reaction zone imaging. [Doctoral Dissertation]. Georgia Tech; 2012. Available from: http://hdl.handle.net/1853/45828

20. 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

21. Kim, Jaecheol. The role of radicals supplied directly and indirectly on ignition.

Degree: PhD, Aerospace Engineering, 2014, Georgia Tech

URL: http://hdl.handle.net/1853/53001

► The ignition process is a critical consideration for combustion devices. External energy transfer to the combustor is required for ignition in common combustion systems. There… (more)

▼ The ignition process is a critical consideration for combustion devices. External energy transfer to the combustor is required for ignition in common combustion systems. There are many ways to deposit energy into the flow but a standard method is a spark discharge because it is simple, compact, and reliable. Sparks can be categorized as either inductive or capacitive sparks that use a coil or an electrical resonance circuit with capacitor, respectively, to amplify the voltage. The creation of a successful ignition event depends on the spark energy deposited into the flow, the initial composition, pressure, temperature, turbulence level of flow etc. The deposited energy by the spark into the flow is critical for estimation of initial energy available for ignition of the mixture. Therefore, the electrical characteristics of the sparks were investigated under various flow conditions. Then measurements of deposited energy into the flow were conducted using a very accurate experimental procedure that was developed in this research. The results showed considerable electric energy losses to the electrodes for the relatively long, inductive sparks. However, the short, capacitive spark deposits electric energy into the flow with minimal loss (above 90% deposition efficiency). In addition, the characteristics of inductive spark are affected by flow velocity and by the existence of a flame. However, variations in the flow conditions do not affect the characteristics of the capacitive spark such as voltage-current time trace and energy deposition efficiency. Two ignition systems using above mentioned two spark types were developed. First, the capacitive spark energy was directly deposited into the premixed flow. Most researchers have not concentrated on the early initiation process but on the flame growth. Therefore, the generated kernel formed by the energy deposition was observed and characterized using optical methods, immediately following the spark. In addition, the mixing effect for this ignition kernel with surrounding gas was simulated using a numerical method. Based on the time trace of the OH* chemiluminescence, the reaction starts with the discharge and it is continuous until combustion begins. This means that in the presence of a high density spark in premixed flow, there exists no traditional delay as defined by other researchers for auto ignition. A simple Radical Jet Generator (RJG) was developed that is able to ignite and stabilize a flame in a high-speed flow. The inductive spark initiates the combustion in the RJG chamber. The RJG then injects the partially-burned products carrying large amounts of heat and radicals into a rapidly moving flammable main stream. Then it ignites and stabilizes a flame. The RJG requires low levels of electrical power as long as the flow velocity is relatively low since most of the radicals are produced by the incomplete combustion in its chamber. The importance of radicals was analyzed by RJG experiments and numerical methods. The reaction zone for RJG using a rich mixture was… Advisors/Committee Members: Jagoda, Jeff (advisor), Seitzman, Jerry (committee member), Scarborough, David (committee member), Menon, Suresh (committee member), Choi, Woong-sik (committee member).

Subjects/Keywords: High energy; OH chemiluminescence;

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APA (6^th Edition):

Kim, J. (2014). The role of radicals supplied directly and indirectly on ignition. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/53001

Chicago Manual of Style (16^th Edition):

Kim, Jaecheol. “The role of radicals supplied directly and indirectly on ignition.” 2014. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/53001.

MLA Handbook (7^th Edition):

Kim, Jaecheol. “The role of radicals supplied directly and indirectly on ignition.” 2014. Web. 22 Jan 2021.

Vancouver:

Kim J. The role of radicals supplied directly and indirectly on ignition. [Internet] [Doctoral dissertation]. Georgia Tech; 2014. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/53001.

Council of Science Editors:

Kim J. The role of radicals supplied directly and indirectly on ignition. [Doctoral Dissertation]. Georgia Tech; 2014. Available from: http://hdl.handle.net/1853/53001

22. Sforzo, Brandon Anthony. High energy spark ignition in non-premixed flowing combustors.

Degree: PhD, Aerospace Engineering, 2014, Georgia Tech

URL: http://hdl.handle.net/1853/53014

► In many practical combustion devices, including those used in gas turbine engines for aircraft and power generation, a high energy spark kernel is necessary to… (more)

▼ In many practical combustion devices, including those used in gas turbine engines for aircraft and power generation, a high energy spark kernel is necessary to reliably ignite the turbulently flowing flammable gases. Complicating matters, the spark kernel is sometimes generated in a region where a non-flammable mixture is present, or where there is no fuel at all. This requires the spark kernel to travel to a flammable region before rapid combustion can begin in non-premixed or stratified flows. This transit time allows for chemical reactions to take place within the kernel as well as mixing with surrounding gases. Despite these demanding conditions, the majority of research in ignition has been for low energy sparks and premixed conditions, not resembling those found in many combustion devices. Similarly, there is little work addressing this issue of spark kernel evolution in the non-premixed flowing environment, and none available that control the time allowed for transit. The goal of this thesis is to understand the development of a spark kernel issued into a non-premixed flow and the sensitivities of the ignition process. To this effect, a stratified flow facility for ignition experiments has been fabricated utilizing a high speed schlieren and emission imaging system for visualizing the kernel motion and ignition success. Additionally, OH chemiluminescence and CH PLIF were used to track chemical species during the ignition process. This facility is also used to control the important variables regarding the flow and spark kernel interaction to quantify the influence on ignition probability. A reduced order model employing a perfectly stirred reactor (PSR) has also been developed based on experimental observations of the entrainment of fluid into the evolving kernel. The simulations provide additional insight to the chemical development in the kernel under different input conditions. This model was enhanced by introducing random perturbations to the input variables, mimicking a practical situation. A computationally efficient support vector machine was trained to replicate the numerical model outputs and predict ignition probabilities for nominal input conditions, providing comparison to experimental results. Experimental and numerical results show that initial mixing with non-flammable fluid quickly reduces the ability for the kernel to ignite the flammable flow, resulting in a strong influence of the inlet temperature and the kernel transit time on the probability of ignition. Once the kernel reaches the flammable mixture, entrainment of this flow occurs, which requires on the order of a vortex turn-over time before chemistry can begin. Initial chemical reactions include endothermic fuel decomposition, further reducing the kernel temperature prior to heat release, creating a competition between the cooling effect of additional mass entrainment and the delayed heat release reactions. CH PLIF results show that flame chemistry is initially confined to a thin region that corresponds to the… Advisors/Committee Members: Seitzman, Jerry (advisor), Jagoda, Jeff (committee member), Menon, Suresh (committee member), Sun, Wenting (committee member), McKinney, Randal (committee member).

Subjects/Keywords: Ignition; Combustion; Experimental; Numerical; Gas turbines

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APA (6^th Edition):

Sforzo, B. A. (2014). High energy spark ignition in non-premixed flowing combustors. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/53014

Chicago Manual of Style (16^th Edition):

Sforzo, Brandon Anthony. “High energy spark ignition in non-premixed flowing combustors.” 2014. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/53014.

MLA Handbook (7^th Edition):

Sforzo, Brandon Anthony. “High energy spark ignition in non-premixed flowing combustors.” 2014. Web. 22 Jan 2021.

Vancouver:

Sforzo BA. High energy spark ignition in non-premixed flowing combustors. [Internet] [Doctoral dissertation]. Georgia Tech; 2014. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/53014.

Council of Science Editors:

Sforzo BA. High energy spark ignition in non-premixed flowing combustors. [Doctoral Dissertation]. Georgia Tech; 2014. Available from: http://hdl.handle.net/1853/53014

23. Gopala, Yogish. Breakup characteristics of a liquid jet in subsonic crossflow.

Degree: PhD, Aerospace Engineering, 2012, Georgia Tech

URL: http://hdl.handle.net/1853/44741

► This thesis describes an experimental investigation of the breakup processes involved in the formation of a spray created by a liquid jet injected into a… (more)

▼ This thesis describes an experimental investigation of the breakup processes involved in the formation of a spray created by a liquid jet injected into a gaseous crossflow. This work is motivated by the utilization of this method to inject fuel in combustors and afterburners of airplane engines. This study aims to develop better understanding of the spray breakup processes and provide better experimental inputs to improve the fidelity of numerical models. This work adresses two key research areas: determining the time required for a liquid column to break up in the crossflow (i.e., primary breakup time) and the effect of injector geometry on spray properties. A new diagnostic technique, the liquid jet light guiding technique that utilizes ability of the liquid jet to act as a waveguide for laser light was developed to determine the location where the liquid column breaks up, in order to obtain the primary breakup time. This study found that the liquid jet Reynolds number was an important factor that governed the primary breakup time and improved the existing correlation. Optical diagnostic techniques such as Phase Doppler Particle Analyzer, Liquid Jet Light Guiding Technique, Particle Image Velocimetry and Imaging techniques were employed to measure the spray properties that include spray penetration, droplet sizes and velocities, velocity field on the surface of the liquid jet and the location of the primary breakup time. These properties were measured for two injectors: one with a sharp transition and the other with a smooth transition. It was found that the spray created by the injector with a sharp transition forms large irregular structures while one with smooth transition produces a smooth liquid jet. The spray transition creates a spray that penetrates deeper into the crossflow, breakup up earlier and produces larger droplets. Additionally, this study reports the phenomenon of the liquid jet splitting into two or more jets in sprays created by the injector with a smooth transition. Advisors/Committee Members: Zinn, Ben (Committee Chair), Genzale, Caroline (Committee Member), Lubarsky, Eugene (Committee Member), Menon, Suresh (Committee Member), Seitzman, Jerry (Committee Member).

Subjects/Keywords: Sharp edged orifice; Primary breakup; Column breakup point; Jet in crossflow; Round edged orifice; Airplanes Motors; Reynolds number; Fluid mechanics

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APA (6^th Edition):

Gopala, Y. (2012). Breakup characteristics of a liquid jet in subsonic crossflow. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/44741

Chicago Manual of Style (16^th Edition):

Gopala, Yogish. “Breakup characteristics of a liquid jet in subsonic crossflow.” 2012. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/44741.

MLA Handbook (7^th Edition):

Gopala, Yogish. “Breakup characteristics of a liquid jet in subsonic crossflow.” 2012. Web. 22 Jan 2021.

Vancouver:

Gopala Y. Breakup characteristics of a liquid jet in subsonic crossflow. [Internet] [Doctoral dissertation]. Georgia Tech; 2012. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/44741.

Council of Science Editors:

Gopala Y. Breakup characteristics of a liquid jet in subsonic crossflow. [Doctoral Dissertation]. Georgia Tech; 2012. Available from: http://hdl.handle.net/1853/44741

24. Balakrishnan, Kaushik. On the high fidelity simulation of chemical explosions and their interaction with solid particle clouds.

Degree: PhD, Aerospace Engineering, 2010, Georgia Tech

URL: http://hdl.handle.net/1853/34672

► High explosive charges when detonated ensue in a flow field characterized by several physical phenomena that include blast wave propagation, hydrodynamic instabilities, real gas effects,… (more)

▼ High explosive charges when detonated ensue in a flow field characterized by several physical phenomena that include blast wave propagation, hydrodynamic instabilities, real gas effects, fluid mixing and afterburn effects. Solid metal particles are often added to explosives to augment the total impulsive loading, either through direct bombardment if inert, or through afterburn energy release if reactive. These multiphase explosive charges, termed as heterogeneous explosives, are of interest from a scientific perspective as they involve the confluence and interplay of various additional physical phenomena such as shock-particle interaction, particle dispersion, ignition, and inter-phase mass, momentum and energy transfer. In the current research effort, chemical explosions in multiphase environments are investigated using a robust, state-of-the-art Eulerian-gas, Lagrangian-solid methodology that can handle both the dense and dilute particle regimes. Explosions into ambient air as well as into aluminum particle clouds are investigated, and hydrodynamic instabilities such as Rayleigh- Taylor and Richtmyer-Meshkov result in a mixing layer where the detonation products mix with the air and afterburn. The particles in the ambient cloud, when present, are observed to pick up significant amounts of momentum and heat from the gas, and thereafter disperse, ignite and burn. The amount of mixing and afterburn are observed to be independent of particle size, but dependent on the particle mass loading and cloud dimensions. Due to fast response times, small particles are observed to cluster as they interact with the vortex rings in the mixing layer, which leads to their preferential ignition/ combustion. The total deliverable impulsive loading from heterogeneous explosive charges containing inert steel particles is estimated for a suite of operating parameters and compared, and it is demonstrated that heterogeneous explosive charges deliver a higher near-field impulse than homogeneous explosive charges containing the same mass of the high explosive. Furthermore, particles are observed to introduce significant amounts of hydrodynamic instabilities in the mixing layer, resulting in augmented fluctuation intensities and fireball size, and different growth rates for heterogeneous explosions compared to homogeneous explosions. For aluminized explosions, the particles are observed to burn in two regimes, and the average particle velocities at late times are observed to be independent of the initial solid volume fraction in the explosive charge. Overall, this thesis provides useful insights on the role played by solid particles in chemical explosions. Advisors/Committee Members: Menon, Suresh (Committee Chair), Jagoda, Jeff (Committee Member), Ruffin, Stephen (Committee Member), Thadhani, Naresh (Committee Member), Walker, Mitchell (Committee Member).

Subjects/Keywords: Richtmyer-Meshkov instability; Rayleigh-Taylor instability; Aluminum combustion; Turbulent mixing; Explosions; Navier-Stokes equations; Hydrodynamics; Multiphase flow; Fluid dynamics

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APA (6^th Edition):

Balakrishnan, K. (2010). On the high fidelity simulation of chemical explosions and their interaction with solid particle clouds. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/34672

Chicago Manual of Style (16^th Edition):

Balakrishnan, Kaushik. “On the high fidelity simulation of chemical explosions and their interaction with solid particle clouds.” 2010. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/34672.

MLA Handbook (7^th Edition):

Balakrishnan, Kaushik. “On the high fidelity simulation of chemical explosions and their interaction with solid particle clouds.” 2010. Web. 22 Jan 2021.

Vancouver:

Balakrishnan K. On the high fidelity simulation of chemical explosions and their interaction with solid particle clouds. [Internet] [Doctoral dissertation]. Georgia Tech; 2010. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/34672.

Council of Science Editors:

Balakrishnan K. On the high fidelity simulation of chemical explosions and their interaction with solid particle clouds. [Doctoral Dissertation]. Georgia Tech; 2010. Available from: http://hdl.handle.net/1853/34672

25. Genin, Franklin Marie. Study of compressible turbulent flows in supersonic environment by large-eddy simulation.

Degree: PhD, Aerospace Engineering, 2009, Georgia Tech

URL: http://hdl.handle.net/1853/28085

► A Large-Eddy Simulation (LES) methodology adapted to the resolution of high Reynolds number turbulent flows in supersonic conditions was proposed and developed. A novel numerical… (more)

Subjects/Keywords: Hybrid numerical scheme; Compressible turbulence; LDKM closure; Eddies; Computer simulation; Combustion; Turbulence

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APA (6^th Edition):

Genin, F. M. (2009). Study of compressible turbulent flows in supersonic environment by large-eddy simulation. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/28085

Chicago Manual of Style (16^th Edition):

Genin, Franklin Marie. “Study of compressible turbulent flows in supersonic environment by large-eddy simulation.” 2009. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/28085.

MLA Handbook (7^th Edition):

Genin, Franklin Marie. “Study of compressible turbulent flows in supersonic environment by large-eddy simulation.” 2009. Web. 22 Jan 2021.

Vancouver:

Genin FM. Study of compressible turbulent flows in supersonic environment by large-eddy simulation. [Internet] [Doctoral dissertation]. Georgia Tech; 2009. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/28085.

Council of Science Editors:

Genin FM. Study of compressible turbulent flows in supersonic environment by large-eddy simulation. [Doctoral Dissertation]. Georgia Tech; 2009. Available from: http://hdl.handle.net/1853/28085

26. Axdahl, Erik Lee. A study of premixed, shock-induced combustion with application to hypervelocity flight.

Degree: PhD, Aerospace Engineering, 2013, Georgia Tech

URL: http://hdl.handle.net/1853/50290

► One of the current goals of research in hypersonic, airbreathing propulsion is access to higher Mach numbers. A strong driver of this goal is the… (more)

Subjects/Keywords: PMSIC; Combustion; Hypervelocity; Hypersonic; Injection; Hypersonic planes; Aerodynamics, Hypersonic; Combustion; Mach number; Aerodynamics; Aerodynamics, Supersonic; Airplanes Scramjet engines

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APA (6^th Edition):

Axdahl, E. L. (2013). A study of premixed, shock-induced combustion with application to hypervelocity flight. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/50290

Chicago Manual of Style (16^th Edition):

Axdahl, Erik Lee. “A study of premixed, shock-induced combustion with application to hypervelocity flight.” 2013. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/50290.

MLA Handbook (7^th Edition):

Axdahl, Erik Lee. “A study of premixed, shock-induced combustion with application to hypervelocity flight.” 2013. Web. 22 Jan 2021.

Vancouver:

Axdahl EL. A study of premixed, shock-induced combustion with application to hypervelocity flight. [Internet] [Doctoral dissertation]. Georgia Tech; 2013. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/50290.

Council of Science Editors:

Axdahl EL. A study of premixed, shock-induced combustion with application to hypervelocity flight. [Doctoral Dissertation]. Georgia Tech; 2013. Available from: http://hdl.handle.net/1853/50290

27. 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

28. Emerson, Benjamin L. Dynamical characteristics of reacting bluff body wakes.

Degree: PhD, Aerospace Engineering, 2013, Georgia Tech

URL: http://hdl.handle.net/1853/49073

► Combustion instability plagues the combustion community in a wide range of applications. This un-solved problem is especially prevalent and expensive in aerospace propulsion and ground… (more)

▼ Combustion instability plagues the combustion community in a wide range of applications. This un-solved problem is especially prevalent and expensive in aerospace propulsion and ground power generation. The challenges associated with understanding and predicting combustion instability lie in the flame response to the acoustic field. One of the more complicated flame response mechanisms is the velocity coupled flame response, where the flame responds dynamically to the acoustic velocity as well as the vortically induced velocity field excited by the acoustics. This vortically induced, or hydrodynamic, velocity field holds critical importance to the flame response but is computationally expensive to predict, often requiring high fidelity CFD computations. Furthermore, its behavior can be a strong function of the numerous flow parameters that change over the operability map of a combustor. This research focuses on a nominally two dimensional bluff body combustor, which has rich hydrodynamic stability behavior with a manageable number of stability parameters. The work focuses first on experimentally characterizing the dynamical flow and flame behavior. Next, the research shifts focus toward hydrodynamic stability theory, using it to explain the physical phenomena observed in the experimental work. Additionally, the hydrodynamic stability work shows how the use of simple, model analysis can identify the important stability parameters and elucidate their governing physical roles. Finally, the research explores the forced response of the flow and flame while systematically varying the underlying hydrodynamic stability characteristics. In the case of longitudinal combustion instability of highly preheated bluff body combustors, it shows that conditions where an acoustic mode frequency equals the hydrodynamic global mode frequency are not especially dangerous from a combustion instability standpoint, and may actually have a reduced heat release response. This demonstrates the very non-intuitive role that the natural hydrodynamic flow stability plays in the forced heat release response of the flame. For the fluid mechanics community, this work contributes to the detailed understanding of both unforced and forced bluff body combustor dynamics, and shows how each is influenced by the underlying hydrodynamics. In particular, it emphasizes the role of the density-shear layer offset, and shows how its extreme sensitivity leads to complicated flow dynamics. For the flow-combustor community as a whole, the work reviews a pre-existing method to obtain the important flow stability parameters, and demonstrates a novel way to link those parameters to the governing flow physics. For the combustion instability community, this thesis emphasizes the importance of the hydrodynamic stability characteristics of the flow, and concludes by offering a paradigm for consideration of the hydrodynamics in a combustion instability problem. Advisors/Committee Members: Lieuwen, Timothy C. (advisor), Seitzman, Jerry (committee member), Menon, Suresh (committee member), Jagoda, Jechiel (committee member), Glezer, Ari (committee member).

Subjects/Keywords: Combustion; Bluff body; Hydrodynamics; Combustion instability; Thermoacoustics; Wakes (Fluid dynamics); Aerodynamics; Combustion Stability; Flame; Hydrodyamics

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

APA (6^th Edition):

Emerson, B. L. (2013). Dynamical characteristics of reacting bluff body wakes. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/49073

Chicago Manual of Style (16^th Edition):

Emerson, Benjamin L. “Dynamical characteristics of reacting bluff body wakes.” 2013. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/49073.

MLA Handbook (7^th Edition):

Emerson, Benjamin L. “Dynamical characteristics of reacting bluff body wakes.” 2013. Web. 22 Jan 2021.

Vancouver:

Emerson BL. Dynamical characteristics of reacting bluff body wakes. [Internet] [Doctoral dissertation]. Georgia Tech; 2013. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/49073.

Council of Science Editors:

Emerson BL. Dynamical characteristics of reacting bluff body wakes. [Doctoral Dissertation]. Georgia Tech; 2013. Available from: http://hdl.handle.net/1853/49073

29. 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

30. Dasgupta, Debolina. Turbulence-chemistry interactions for lean premixed flames.

Degree: PhD, Aerospace Engineering, 2018, Georgia Tech

URL: http://hdl.handle.net/1853/60746

► Turbulent combustion, particularly premixed combustion has great practical importance due to their extensive industrial usage in gas turbines, internal combustion engines etc. However, the physics… (more)

▼ Turbulent combustion, particularly premixed combustion has great practical importance due to their extensive industrial usage in gas turbines, internal combustion engines etc. However, the physics governing the inherent multi- scale interactions of turbulence, flow-field and chemistry is not yet well established. A complete understanding of each of these interactions and their coupling is essential for the development of models that can aid simulations of realistic engines (using Large Eddy Simulations (LES) or Reynolds averaged Navier-Stokes equations (RANS). Particularly, understanding the flame structure and its stabilization requires an understanding of the turbulence-chemistry interactions. This can manifest itself in many different forms. For example, flame wrinkling gives rise to flame stretch that can modify the local temperature and species concentrations in turn altering the local chemistry. Also, the smaller eddies in a turbulent flow can penetrate into the preheat and reaction zones changing the species’ gradients within the flame. The influence of turbulence on chemistry can be analyzed in two different ways: firstly, a “global” analysis which investigates the direct impact of turbulence on the chemical pathways (a series of elementary reactions involved in the fuel oxidation process) and secondly, a “local” analysis which investigates the influence of turbulence on the chemical flame structure (i.e. species and reaction rate profiles). To understand these influences of turbulence, this work performs Direct Numerical Simulations (DNS) for lean premixed flames involving three fuels: hydrogen, methane and n-dodecane. A “global” analysis using different metrics such as heat release and species consumption/production is performed to quantify the changes in the chemical pathways. This analysis is performed for the metrics averaged over the entire flame and conditioned on local flame features such as fuel consumption, curvature etc. The results are also compared and contrasted with simple laminar flame models such as unstretched flames, stretched flames and perfectly stirred reactors. In general, the laminar models provide a good estimate for the chemical pathways for these key metrics suggesting turbulence does not have a significant impact on the fuel oxidation pathways. However, this is not true for the reaction rate and species profiles across the flame. Conditional means of these quantities are calculated to identify the “local” influence of turbulence on chemistry. These conditional means are also compared with laminar unstretched and stretched flames to identify regions of good agreement and deviation. The laminar calculations are performed using two different transport models; firstly, the mixture-averaged transport wherein every species diffuses into the mixture with its molecular diffusivity and secondly, Le=1 transport wherein the mass diffusivity of every species is equal to the thermal diffusivity of the mixture eliminating effects of preferential and differential diffusion. Le=1 is considered the… Advisors/Committee Members: Lieuwen, Tim (advisor), Oefelein, Joseph (committee member), Menon, Suresh (committee member), Sun, Wenting (committee member), Sievers, Carsten (committee member).

Subjects/Keywords: Premixed flames; Turbulent combustion; Turbulence-chemistry interactions; Combustion modeling; Numerical combustion

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

APA (6^th Edition):

Dasgupta, D. (2018). Turbulence-chemistry interactions for lean premixed flames. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/60746

Chicago Manual of Style (16^th Edition):

Dasgupta, Debolina. “Turbulence-chemistry interactions for lean premixed flames.” 2018. Doctoral Dissertation, Georgia Tech. Accessed January 22, 2021. http://hdl.handle.net/1853/60746.

MLA Handbook (7^th Edition):

Dasgupta, Debolina. “Turbulence-chemistry interactions for lean premixed flames.” 2018. Web. 22 Jan 2021.

Vancouver:

Dasgupta D. Turbulence-chemistry interactions for lean premixed flames. [Internet] [Doctoral dissertation]. Georgia Tech; 2018. [cited 2021 Jan 22]. Available from: http://hdl.handle.net/1853/60746.

Council of Science Editors:

Dasgupta D. Turbulence-chemistry interactions for lean premixed flames. [Doctoral Dissertation]. Georgia Tech; 2018. Available from: http://hdl.handle.net/1853/60746

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