+publisher:"Georgia Tech" +contributor:("Oefelein, Joseph")

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 March 04, 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. 04 Mar 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 Mar 04]. 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. Wei, Sheng. Effect of jet fuel composition on forced ignition in gas turbine combustors.

Degree: PhD, Aerospace Engineering, 2019, Georgia Tech

URL: http://hdl.handle.net/1853/61204

► The rapid growth in the aviation industry means increasing consumption of jet fuels, which is leading to greater interest in alternate and sustainable fuel sources.… (more)

▼ The rapid growth in the aviation industry means increasing consumption of jet fuels, which is leading to greater interest in alternate and sustainable fuel sources. The overall properties of these alternative fuels can be designed to meet existing standards. Nevertheless, the compositional differences between alternative and conventional fuels can lead to important variations in chemical and physical properties that impact engine performance. For example, ignition is of paramount importance to ensure reliable operation, especially in extreme conditions like cold starts and high altitude relights. For aircraft engines, ignition is the process of creating self-sustaining flames starting with a high-temperature source located near a combustor liner. This thesis is devoted to studying the differences in ignition behavior due to the variations in fuel composition. Fuel variations in ignition are studied in a well-characterized test facility that is readily amenable to modeling and simulation. The experiments employ a sunken-fire ignitor, like those typically employed in aircraft engines, operating at 15 Hz with ~1.25J spark energy. Performance differences among fuels are characterized through their ignition probabilities. To understand both the chemical and physical fuel effects on ignition, both prevaporized fuels and liquid fuel sprays are examined. The purpose of prevaporizing the fuel is to remove the process of liquid to gas transition and to focus on combustion chemistry alone. In the forced ignition of liquid fuel sprays, which mimics the situation encountered in aviation gas turbine engines, both physical and chemical properties of the fuel are relevant. Statistically significant differences between fuel ignition probabilities are observed. The droplet heating time is shown to correlate well with ignition probability. A particle Doppler phase analyzer (PDPA) is used to study droplet size distribution near the ignitor. These droplet distribution measurements can be useful for future CFD modeling. In addition to differentiating fuel performances through ignition probability, advanced diagnostic techniques are employed to understand the evolution of a spark kernels as it interacts with combustible mixtures. These techniques include high speed OH planar laser induced fluorescence, OH* chemiluminescence, and schlieren imaging. The results reveal the entrainment of ambient fluid into the convecting spark kernel, the decomposition of vaporized jet fuel in the high temperature kernel, and the transition from local “hot spots” within the spark kernel to a self-sustaining flame. In addition to the experiments, reduced order modeling is used to better understand the physics and chemistry of ignition for both prevaporized and liquid fuels. Chemical differences are found to depend on the relative distribution between intermediate breakdown products (e.g., ethylene, propene and isobutene) from the parent fuels, as these intermediates have drastically different chemical rates as a function of temperature. The energy transfer… Advisors/Committee Members: Seitzman, Jerry (advisor), Jagoda, Jechiel (committee member), Sun, Wenting (committee member), Oefelein, Joseph (committee member), Ranjan, Devesh (committee member).

Subjects/Keywords: Ignition; Combustion

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APA (6^th Edition):

Wei, S. (2019). Effect of jet fuel composition on forced ignition in gas turbine combustors. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/61204

Chicago Manual of Style (16^th Edition):

Wei, Sheng. “Effect of jet fuel composition on forced ignition in gas turbine combustors.” 2019. Doctoral Dissertation, Georgia Tech. Accessed March 04, 2021. http://hdl.handle.net/1853/61204.

MLA Handbook (7^th Edition):

Wei, Sheng. “Effect of jet fuel composition on forced ignition in gas turbine combustors.” 2019. Web. 04 Mar 2021.

Vancouver:

Wei S. Effect of jet fuel composition on forced ignition in gas turbine combustors. [Internet] [Doctoral dissertation]. Georgia Tech; 2019. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1853/61204.

Council of Science Editors:

Wei S. Effect of jet fuel composition on forced ignition in gas turbine combustors. [Doctoral Dissertation]. Georgia Tech; 2019. Available from: http://hdl.handle.net/1853/61204

Georgia Tech

3. Kim, Sayop. Advancing turbulent spray and combustion models for compression ignition engine simulations.

Degree: PhD, Aerospace Engineering, 2019, Georgia Tech

URL: http://hdl.handle.net/1853/61216

► This thesis seeks to investigate the turbulent mixing influence on spray atomization and combustion processes encountered in compression ignition diesel engines. Despite greater thermal efficiency… (more)

▼ This thesis seeks to investigate the turbulent mixing influence on spray atomization and combustion processes encountered in compression ignition diesel engines. Despite greater thermal efficiency of diesel engine than spark ignition engine, the nature of stratified air-fuel mixture and non-premixed flame gives rise to unacceptable levels of nitrogen oxides (NOx) and particulate matter (PM), thus the use of diesel engines has often been limited to heavy-duty vehicle and industrial power sources. However, recent advancement in diesel engine combustion strategies, e.g. low temperature combustion (LTC), has demonstrated promising pathways towards improvement in the engine-out pollutants. Therefore, particularly in the effort of computer-aided engine design tasks, such a new engine design concept requires more accurate modeling techniques applicable over a broader range of engine operating conditions than those of conventional engine strategies. In the notion of challenges in new engine operating conditions, this thesis aims to present successful implementation of improvement in numerical modeling techniques in high-pressure spray atomization and resulting turbulent spray flame of interest. Three-dimensional Computational Fluid Dynamics (CFD) in in-cylinder turbu- lent combustion is considered an integral part of engine design progress, but rather a cost-prohibitive to apply over a broad range of engine relevant conditions. In spite of successful use of existing spray atomization modeling, prior researchers have pointed out some degree of failure in LTC targeted injection strategies. Furthermore, finite rate and strong nonlinearity of chemistry influenced by local turbulent mixing still re- main in challenges to account for in cost-efficient CFD analysis. In this context, a new attempt of hybrid spray primary breakup modeling is presented and demonstrated in successful application aimed at LTC technique. In addition, the Representative Interactive Flamelets (RIF) model with aid of multi-flamelets approach is extensively assessed in terms of predictive capability against classical combustion model. The combustion model employed in this study are fully examined in the general diesel combustion metric, e.g., ignition delay and flame lift-off length as well as newly sug- gested test metric, combustion recession. The combustion recession has been recently idenfied, but still remain largely unknown. Since the governing physics of this phenomenon is characterized by turbulent mixing coupled with finite rate chemistry, this can be considered as a relevant test metric for turbulent combustion models. In addition, very recent experimental studies have introduced a new non-sooting diesel combustion technique by manipulating direct injection method. The ducted fuel injection (DFI) has thus been demonstrated with its potential of low soot emissions. Knowing that the duct equipped ahead of injector nozzle was identifed to enhance turbulent mixing, investigations of DFI combustion may prove the effectiveness of turbulece-chemistry… Advisors/Committee Members: Genzale, Caroline (advisor), Jagoda, Jechiel (advisor), Oefelein, Joseph (committee member), Sun, Wenting (committee member), Alexeev, Alexander (committee member), Lucchini, Tommaso (committee member).

Subjects/Keywords: Diesel engine; CFD; Spray modeling; Turbulence-chemistry interaction; Combustion modeling

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APA (6^th Edition):

Kim, S. (2019). Advancing turbulent spray and combustion models for compression ignition engine simulations. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/61216

Chicago Manual of Style (16^th Edition):

Kim, Sayop. “Advancing turbulent spray and combustion models for compression ignition engine simulations.” 2019. Doctoral Dissertation, Georgia Tech. Accessed March 04, 2021. http://hdl.handle.net/1853/61216.

MLA Handbook (7^th Edition):

Kim, Sayop. “Advancing turbulent spray and combustion models for compression ignition engine simulations.” 2019. Web. 04 Mar 2021.

Vancouver:

Kim S. Advancing turbulent spray and combustion models for compression ignition engine simulations. [Internet] [Doctoral dissertation]. Georgia Tech; 2019. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1853/61216.

Council of Science Editors:

Kim S. Advancing turbulent spray and combustion models for compression ignition engine simulations. [Doctoral Dissertation]. Georgia Tech; 2019. Available from: http://hdl.handle.net/1853/61216

Georgia Tech

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

Degree: PhD, Aerospace Engineering, 2018, Georgia Tech

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

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

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

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

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APA (6^th Edition):

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

Chicago Manual of Style (16^th Edition):

Chang, Yu-Hung. “High-fidelity emulation of spatiotemporally evolving flow dynamics.” 2018. Doctoral Dissertation, Georgia Tech. Accessed March 04, 2021. http://hdl.handle.net/1853/60842.

MLA Handbook (7^th Edition):

Chang, Yu-Hung. “High-fidelity emulation of spatiotemporally evolving flow dynamics.” 2018. Web. 04 Mar 2021.

Vancouver:

Chang Y. High-fidelity emulation of spatiotemporally evolving flow dynamics. [Internet] [Doctoral dissertation]. Georgia Tech; 2018. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1853/60842.

Council of Science Editors:

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

Georgia Tech

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

Degree: PhD, Aerospace Engineering, 2019, Georgia Tech

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

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

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

Subjects/Keywords: Large Eddy simulation; Emulation

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APA (6^th Edition):

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

Chicago Manual of Style (16^th Edition):

Li, Yixing. “High-fidelity numerical simulation and emulation of bi-fluid swirl injector flow and combustion dynamics.” 2019. Doctoral Dissertation, Georgia Tech. Accessed March 04, 2021. http://hdl.handle.net/1853/61698.

MLA Handbook (7^th Edition):

Li, Yixing. “High-fidelity numerical simulation and emulation of bi-fluid swirl injector flow and combustion dynamics.” 2019. Web. 04 Mar 2021.

Vancouver:

Li Y. High-fidelity numerical simulation and emulation of bi-fluid swirl injector flow and combustion dynamics. [Internet] [Doctoral dissertation]. Georgia Tech; 2019. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1853/61698.

Council of Science Editors:

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

6. Zhai, Xiaomeng. Studies of turbulence structure using well-resolved simulations with and without effects of a magnetic field.

Degree: PhD, Aerospace Engineering, 2018, Georgia Tech

URL: http://hdl.handle.net/1853/61192

► This thesis presents results from a large-scale computational study motivated to advance understanding of turbulence structure in isotropic turbulence as well as in magnetohydrodynamic (MHD)… (more)

Subjects/Keywords: Turbulence; Magnetohydrodynamics; Large-scale computing

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APA (6^th Edition):

Zhai, X. (2018). Studies of turbulence structure using well-resolved simulations with and without effects of a magnetic field. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/61192

Chicago Manual of Style (16^th Edition):

Zhai, Xiaomeng. “Studies of turbulence structure using well-resolved simulations with and without effects of a magnetic field.” 2018. Doctoral Dissertation, Georgia Tech. Accessed March 04, 2021. http://hdl.handle.net/1853/61192.

MLA Handbook (7^th Edition):

Zhai, Xiaomeng. “Studies of turbulence structure using well-resolved simulations with and without effects of a magnetic field.” 2018. Web. 04 Mar 2021.

Vancouver:

Zhai X. Studies of turbulence structure using well-resolved simulations with and without effects of a magnetic field. [Internet] [Doctoral dissertation]. Georgia Tech; 2018. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1853/61192.

Council of Science Editors:

Zhai X. Studies of turbulence structure using well-resolved simulations with and without effects of a magnetic field. [Doctoral Dissertation]. Georgia Tech; 2018. Available from: http://hdl.handle.net/1853/61192

Georgia Tech

7. Carter, John. Statistical and temporal analysis of shock-driven instability through simultaneous density and velocity measurements.

Degree: PhD, Mechanical Engineering, 2020, Georgia Tech

URL: http://hdl.handle.net/1853/63573

► The effects of initial conditions (single- and multi-mode) and nondimensional density ratio (Atwood number, A) on dynamics of mixing in Richtmyer – Meshkov Instability evolution are… (more)

Subjects/Keywords: Richtmyer Meshkov instability; Shock driven instability; Turbulence

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APA (6^th Edition):

Carter, J. (2020). Statistical and temporal analysis of shock-driven instability through simultaneous density and velocity measurements. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/63573

Chicago Manual of Style (16^th Edition):

Carter, John. “Statistical and temporal analysis of shock-driven instability through simultaneous density and velocity measurements.” 2020. Doctoral Dissertation, Georgia Tech. Accessed March 04, 2021. http://hdl.handle.net/1853/63573.

MLA Handbook (7^th Edition):

Carter, John. “Statistical and temporal analysis of shock-driven instability through simultaneous density and velocity measurements.” 2020. Web. 04 Mar 2021.

Vancouver:

Carter J. Statistical and temporal analysis of shock-driven instability through simultaneous density and velocity measurements. [Internet] [Doctoral dissertation]. Georgia Tech; 2020. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1853/63573.

Council of Science Editors:

Carter J. Statistical and temporal analysis of shock-driven instability through simultaneous density and velocity measurements. [Doctoral Dissertation]. Georgia Tech; 2020. Available from: http://hdl.handle.net/1853/63573

8. 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 March 04, 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. 04 Mar 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 Mar 04]. 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

9. 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 (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 March 04, 2021. http://hdl.handle.net/1853/60746.

MLA Handbook (7^th Edition):

Dasgupta, Debolina. “Turbulence-chemistry interactions for lean premixed flames.” 2018. Web. 04 Mar 2021.

Vancouver:

Dasgupta D. Turbulence-chemistry interactions for lean premixed flames. [Internet] [Doctoral dissertation]. Georgia Tech; 2018. [cited 2021 Mar 04]. 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

10. Williams, Aimee. The role of droplets in the autoignition of a polydisperse Jet-A spray in vitiated co-flow.

Degree: PhD, Aerospace Engineering, 2019, Georgia Tech

URL: http://hdl.handle.net/1853/61748

► The objective of this study is to understand the underlying mechanisms of autoignition of a polydisperse fuel spray. Understanding and predicting autoignition of fuel sprays… (more)

▼ The objective of this study is to understand the underlying mechanisms of autoignition of a polydisperse fuel spray. Understanding and predicting autoignition of fuel sprays is important to the design of modern gas turbine engines, especially in the interest of developing a flame-holder-less afterburner concept. In this system, liquid fuel is injected into a high temperature, flowing, vitiated air flow. Previous studies of fuel spray autoignition have suggested multiple mechanisms for a fuel spray to autoignite, including single droplet and droplet cloud ignition behavior. The majority of liquid-fueled autoignition studies have been parametric in nature and describe the overall effect of droplet size, equivalence ratio, turbulence intensity, etc. on ignition delay time but do not investigate the phenomena controlling the local behavior of autoignition kernel formation and growth. Autoignition studies of cold gaseous fuel jets in hot oxidizer cross flows have shown the importance of local mixture fraction. A test facility was developed that is capable of reproducing flow conditions in an aero-engine reheat combustor. Fuel is injected using a reproduction of a commercially available spray nozzle installed on an aerodynamically shaped body centered in the flow by three aerodynamic pylons. High speed chemiluminescence and UV PLIF were used to determine the dependence of the locations where autoignition kernels form, upon the flow temperature and velocity. Analysis of the scatter in the time-resolved ignition locations revealed the importance of temperature fluctuations in the vitiated flow. Specifically, the most upstream ignition locations likely correspond to the hottest and, therefore, most reactive fluid packets. The distribution of the fuel spray was found to affect the appearance of most upstream autoignition kernels. A near stationary (on average) flame was found to exist at high co-flow temperatures, being stabilized by autoignition as distinct kernels were formed upstream of the main flame region. Advisors/Committee Members: Seitzman, Jerry (advisor), Zinn, Ben T. (advisor), Jagoda, Jechiel (committee member), Oefelein, Joseph (committee member), Lovett, Jeffrey (committee member).

Subjects/Keywords: Autoignition; Fuel spray; PLIF; High-speed chemiluminscence; Jet-A spray

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APA (6^th Edition):

Williams, A. (2019). The role of droplets in the autoignition of a polydisperse Jet-A spray in vitiated co-flow. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/61748

Chicago Manual of Style (16^th Edition):

Williams, Aimee. “The role of droplets in the autoignition of a polydisperse Jet-A spray in vitiated co-flow.” 2019. Doctoral Dissertation, Georgia Tech. Accessed March 04, 2021. http://hdl.handle.net/1853/61748.

MLA Handbook (7^th Edition):

Williams, Aimee. “The role of droplets in the autoignition of a polydisperse Jet-A spray in vitiated co-flow.” 2019. Web. 04 Mar 2021.

Vancouver:

Williams A. The role of droplets in the autoignition of a polydisperse Jet-A spray in vitiated co-flow. [Internet] [Doctoral dissertation]. Georgia Tech; 2019. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1853/61748.

Council of Science Editors:

Williams A. The role of droplets in the autoignition of a polydisperse Jet-A spray in vitiated co-flow. [Doctoral Dissertation]. Georgia Tech; 2019. Available from: http://hdl.handle.net/1853/61748

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

Degree: PhD, Aerospace Engineering, 2018, Georgia Tech

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

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

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

Subjects/Keywords: Emulation; Combustion response

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APA (6^th Edition):

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

Chicago Manual of Style (16^th Edition):

Yeh, Shiang-Ting. “Common proper orthogonal decomposition-based emulation and system identification for model-based analysis of combustion dynamics.” 2018. Doctoral Dissertation, Georgia Tech. Accessed March 04, 2021. http://hdl.handle.net/1853/59965.

MLA Handbook (7^th Edition):

Yeh, Shiang-Ting. “Common proper orthogonal decomposition-based emulation and system identification for model-based analysis of combustion dynamics.” 2018. Web. 04 Mar 2021.

Vancouver:

Yeh S. Common proper orthogonal decomposition-based emulation and system identification for model-based analysis of combustion dynamics. [Internet] [Doctoral dissertation]. Georgia Tech; 2018. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1853/59965.

Council of Science Editors:

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

12. Rock, Nicholas. Lean blowout sensitivities of complex liquid fuels.

Degree: PhD, Aerospace Engineering, 2019, Georgia Tech

URL: http://hdl.handle.net/1853/61726

► Lean blowout is a process whereby a previously stable flame is either extinguished or convected out of its combustor. In aviation applications, blowout is a… (more)

▼ Lean blowout is a process whereby a previously stable flame is either extinguished or convected out of its combustor. In aviation applications, blowout is a direct threat to passenger safety and it therefore sets operational limits on a combustor. Understanding the blowout problem is a key prerequisite to the deployment of alternative aviation fuels, as these fuels are expected to have comparable flame stability characteristics as traditional jet fuels. The objective of this work is to identify the fuel properties that govern lean blowout and to characterize their effect on the physics involved in the blowout process. The blowout performance of 18 different liquid fuels were experimentally compared in an aircraft relevant combustor. These experiments were repeated at 3 different air inlet temperatures, 300 K, 450 K, and 550 K, in order to vary the effect of fuel physical properties. Custom fuels were introduced that were specifically designed to decouple interrelated fuel properties and to accentuate the significance of preferential vaporization on lean blowout. The methodology that was used clearly demonstrated differences in the equivalence ratio at blowout between fuels, and a multiple linear regression analysis was performed to determine the relative contributions of each of the fuel properties. This work also characterizes the effect of fuel composition on the processes that precede blowout of the flame, thereby providing an explanation for why certain fuel properties govern lean blowout boundaries. By quantifying the time variation of flame luminosity and extinction “events” as a function of blowout proximity, it was demonstrated that local extinction processes are operative in and lead to blowout in spray flames. In addition, high speed imaging was used to analyze the space-time evolution of the most upstream point of the flame near blowout. Fast motion of these points upstream relative to the flow velocity was interpreted as flame re-ignition. These re-ignition processes become manifest when the stability of the flame is severely threatened by local extinction and often allow for recoveries that extend flame burning. Fuel composition was shown to have a clear effect on a flame’s propensity for extinction and re-ignition. Advisors/Committee Members: Lieuwen, Timothy C. (advisor), Seitzman, Jerry (committee member), Menon, Suresh (committee member), Oefelein, Joseph (committee member), Colket, Meredith (Med) B. (committee member).

Subjects/Keywords: Lean blowout; Alternative jet fuels; Extinction and re-ignition

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

APA (6^th Edition):

Rock, N. (2019). Lean blowout sensitivities of complex liquid fuels. (Doctoral Dissertation). Georgia Tech. Retrieved from http://hdl.handle.net/1853/61726

Chicago Manual of Style (16^th Edition):

Rock, Nicholas. “Lean blowout sensitivities of complex liquid fuels.” 2019. Doctoral Dissertation, Georgia Tech. Accessed March 04, 2021. http://hdl.handle.net/1853/61726.

MLA Handbook (7^th Edition):

Rock, Nicholas. “Lean blowout sensitivities of complex liquid fuels.” 2019. Web. 04 Mar 2021.

Vancouver:

Rock N. Lean blowout sensitivities of complex liquid fuels. [Internet] [Doctoral dissertation]. Georgia Tech; 2019. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1853/61726.

Council of Science Editors:

Rock N. Lean blowout sensitivities of complex liquid fuels. [Doctoral Dissertation]. Georgia Tech; 2019. Available from: http://hdl.handle.net/1853/61726

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