+publisher:"Texas A&M University" +contributor:("Girimaji, Sharath")

Texas A&M University

1. Martin, Michael William. Prediction of Damage to Structure resulting from Recirculation of Particles from a Magnetoplasma Spacecraft Engine.

Degree: PhD, Mechanical Engineering, 2014, Texas A&M University

URL: http://hdl.handle.net/1969.1/154205

► A magnetoplasma spacecraft engine, such as the Variable Area Specific Inpulse Magnetoplasma Rocket (VASIMR®), uses magnetic fields and a magnetic nozzle to constrict and accelerate… (more)

▼ A magnetoplasma spacecraft engine, such as the Variable Area Specific Inpulse Magnetoplasma Rocket (VASIMR®), uses magnetic fields and a magnetic nozzle to constrict and accelerate plasma to produce thrust. Most of the ejected plasma particles are expected to detach from the magnetic field lines and escape to provide thrust but some particles may not and could impact the spacecraft structure resulting in surface erosion and electrical charging. The plasma plume for a magnetoplasma engine was modeled computationally and scaled to determine what percentage of particles remained in the magnetic field and the kinetic energy of all impacting particles. Factors such as average particle velocity at the engine exit, magnetic field strength, and plume density distribution (i.e. width) were varied in a full factorial experiment to ascertain the effects of each factor and the important inter-relationships. The results are presented for a generic magnetoplasma engine and for the specific VASIMR® case. Detachment was found to be occurring with 99.42% of particles escaping under the worst conditions and only 0.0172% of particles impacting structure. It was determined that three things led to an increase in the number of impacting particles on spacecraft structure: a stronger magnetic field, a lower exit velocity of particles into the plume, and a wider plume. In addition, there was an “erosion zone” where an increasing particle exit velocity led to more erosion until the number of impacting particles was negligible and erosion dropped significantly. For the specific case under nominal conditions, the erosion rate was 1.386 nm/month of engine operating time on aluminum and 0.611 nm/month on silicon. The electrical charging on spacecraft surfaces was found to be -27.85 V DC, which can be mitigated with current plasma contactor technology or some variant. Therefore, magnetoplasma spacecraft engines can be shown to cause minimal erosion and electrical charging and should be capable of operating safely with current technology by varying the three parameters previously mentioned. Advisors/Committee Members: Lalk, Thomas (advisor), Staack, David (advisor), Morrison, Gerald (committee member), Girimaji, Sharath (committee member).

Subjects/Keywords: VASIMR; magnetoplasma engine; plasma

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APA (6^th Edition):

Martin, M. W. (2014). Prediction of Damage to Structure resulting from Recirculation of Particles from a Magnetoplasma Spacecraft Engine. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/154205

Chicago Manual of Style (16^th Edition):

Martin, Michael William. “Prediction of Damage to Structure resulting from Recirculation of Particles from a Magnetoplasma Spacecraft Engine.” 2014. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/154205.

MLA Handbook (7^th Edition):

Martin, Michael William. “Prediction of Damage to Structure resulting from Recirculation of Particles from a Magnetoplasma Spacecraft Engine.” 2014. Web. 04 Mar 2021.

Vancouver:

Martin MW. Prediction of Damage to Structure resulting from Recirculation of Particles from a Magnetoplasma Spacecraft Engine. [Internet] [Doctoral dissertation]. Texas A&M University; 2014. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/154205.

Council of Science Editors:

Martin MW. Prediction of Damage to Structure resulting from Recirculation of Particles from a Magnetoplasma Spacecraft Engine. [Doctoral Dissertation]. Texas A&M University; 2014. Available from: http://hdl.handle.net/1969.1/154205

Texas A&M University

2. Bertsch, Rebecca Lynne. Rapidly Sheared Compressible Turbulence: Characterization of Different Pressure Regimes and Effect of Thermodynamic Fluctuations.

Degree: MS, Aerospace Engineering, 2011, Texas A&M University

URL: http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8471

► Rapid distortion theory (RDT) is applied to compressible ideal-gas turbulence subjected to homogeneous shear flow. The study examines the linear or rapid processes present in… (more)

Subjects/Keywords: compressible turbulence; rapid distortion theory; linear analysis of turbulence

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APA (6^th Edition):

Bertsch, R. L. (2011). Rapidly Sheared Compressible Turbulence: Characterization of Different Pressure Regimes and Effect of Thermodynamic Fluctuations. (Masters Thesis). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8471

Chicago Manual of Style (16^th Edition):

Bertsch, Rebecca Lynne. “Rapidly Sheared Compressible Turbulence: Characterization of Different Pressure Regimes and Effect of Thermodynamic Fluctuations.” 2011. Masters Thesis, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8471.

MLA Handbook (7^th Edition):

Bertsch, Rebecca Lynne. “Rapidly Sheared Compressible Turbulence: Characterization of Different Pressure Regimes and Effect of Thermodynamic Fluctuations.” 2011. Web. 04 Mar 2021.

Vancouver:

Bertsch RL. Rapidly Sheared Compressible Turbulence: Characterization of Different Pressure Regimes and Effect of Thermodynamic Fluctuations. [Internet] [Masters thesis]. Texas A&M University; 2011. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8471.

Council of Science Editors:

Bertsch RL. Rapidly Sheared Compressible Turbulence: Characterization of Different Pressure Regimes and Effect of Thermodynamic Fluctuations. [Masters Thesis]. Texas A&M University; 2011. Available from: http://hdl.handle.net/1969.1/ETD-TAMU-2010-08-8471

Texas A&M University

3. Razi, Pooyan. Partially-Averaged Navier-Stokes (PANS) Method for Turbulence Simulations: Near-Wall Modeling and Smooth-Surface Separation Computations.

Degree: PhD, Mechanical Engineering, 2016, Texas A&M University

URL: http://hdl.handle.net/1969.1/156797

► In the context of computational fluid dynamics (CFD), accurate simulation of turbulent flows remains a challenging field of research. Although direct numerical simulation (DNS) and… (more)

▼ In the context of computational fluid dynamics (CFD), accurate simulation of turbulent flows remains a challenging field of research. Although direct numerical simulation (DNS) and large-eddy simulation (LES) are able to capture the turbulent flow features to a great extent, they are not viable for complex engineering flows. On the other hand, Reynolds-averaged Navier-Stokes (RANS) models involve too many simplifying assumptions, making them inadequate to capture complex flow features. Variable resolution (VR) bridging methods such as the Partially-averaged Navier-Stokes (PANS) model fill the gap between these two limits by allowing a tunable degree of resolution from RANS to DNS. The goal of this dissertation is to investigate the the PANS model capabilities in providing significant improvement over RANS predictions at slightly higher computational expense and producing LES quality results at significantly lower computational cost. This research work is divided into three main studies. The objective of each study is: (i) investigate the model fidelity at a fixed level of scale resolution (Generation1-PANS/G1-PANS) for smooth surface separation, (ii) derive the PANS closure model in regions of resolution variation (Generation2-PANS/G2-PANS), and (iii) validate G2-PANS model for attached and separated flows. The key contributions of this dissertation are summarized as follows. The turbulence closure model of varying resolution, G2-PANS, is developed by deriving mathematically-consistent commutation residues and using energy conservation principles. The log- layer recovery and accurate computation of Reynolds stress anisotropy is accomplished by transitioning from steady RANS to scaled resolved simulations using the G2-PANS model. This represents a major advantage of PANS as most other hybrid approaches encounter significant errors in the log-layer region. Finally, several smooth-separation flows on the NASA turbulence website have been computed with high degree of accuracy at a significantly reduced computational effort over LES using the G1-PANS and G2-PANS models. These results along with strong theoretical foundations demonstrate that PANS has the potential to become a transformative CFD approach for scale-resolving turbulence simulations. Advisors/Committee Members: Girimaji, Sharath (advisor), Anand, Nagamangala K. (advisor), Handler, Robert (committee member), Annamalai, Kalyan (committee member).

Subjects/Keywords: Turbulence modeling; PANS; Smooth-surface separation; Near-wall modeling

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APA (6^th Edition):

Razi, P. (2016). Partially-Averaged Navier-Stokes (PANS) Method for Turbulence Simulations: Near-Wall Modeling and Smooth-Surface Separation Computations. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/156797

Chicago Manual of Style (16^th Edition):

Razi, Pooyan. “Partially-Averaged Navier-Stokes (PANS) Method for Turbulence Simulations: Near-Wall Modeling and Smooth-Surface Separation Computations.” 2016. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/156797.

MLA Handbook (7^th Edition):

Razi, Pooyan. “Partially-Averaged Navier-Stokes (PANS) Method for Turbulence Simulations: Near-Wall Modeling and Smooth-Surface Separation Computations.” 2016. Web. 04 Mar 2021.

Vancouver:

Razi P. Partially-Averaged Navier-Stokes (PANS) Method for Turbulence Simulations: Near-Wall Modeling and Smooth-Surface Separation Computations. [Internet] [Doctoral dissertation]. Texas A&M University; 2016. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/156797.

Council of Science Editors:

Razi P. Partially-Averaged Navier-Stokes (PANS) Method for Turbulence Simulations: Near-Wall Modeling and Smooth-Surface Separation Computations. [Doctoral Dissertation]. Texas A&M University; 2016. Available from: http://hdl.handle.net/1969.1/156797

Texas A&M University

4. Yu, Dan. State Estimation of Spatio-Temporal Phenomena.

Degree: PhD, Aerospace Engineering, 2016, Texas A&M University

URL: http://hdl.handle.net/1969.1/159046

► This dissertation addresses the state estimation problem of spatio-temporal phenomena which can be modeled by partial differential equations (PDEs), such as pollutant dispersion in the… (more)

▼ This dissertation addresses the state estimation problem of spatio-temporal phenomena which can be modeled by partial differential equations (PDEs), such as pollutant dispersion in the atmosphere. After discretizing the PDE, the dynamical system has a large number of degrees of freedom (DOF). State estimation using Kalman Filter (KF) is computationally intractable, and hence, a reduced order model (ROM) needs to be constructed first. Moreover, the nonlinear terms, external disturbances or unknown boundary conditions can be modeled as unknown inputs, which leads to an unknown input filtering problem. Furthermore, the performance of KF could be improved by placing sensors at feasible locations. Therefore, the sensor scheduling problem to place multiple mobile sensors is of interest. The first part of the dissertation focuses on model reduction for large scale systems with a large number of inputs/outputs. A commonly used model reduction algorithm, the balanced proper orthogonal decomposition (BPOD) algorithm, is not computationally tractable for large systems with a large number of inputs/outputs. Inspired by the BPOD and randomized algorithms, we propose a randomized proper orthogonal decomposition (RPOD) algorithm and a computationally optimal RPOD (RPOD*) algorithm, which construct an ROM to capture the input-output behaviour of the full order model, while reducing the computational cost of BPOD by orders of magnitude. It is demonstrated that the proposed RPOD_ algorithm could construct the ROM in real-time, and the performance of the proposed algorithms on different advection-diffusion equations. Next, we consider the state estimation problem of linear discrete-time systems with unknown inputs which can be treated as a wide-sense stationary process with rational power spectral density, while no other prior information needs to be known. We propose an autoregressive (AR) model based unknown input realization technique which allows us to recover the input statistics from the output data by solving an appropriate least squares problem, then fit an AR model to the recovered input statistics and construct an innovations model of the unknown inputs using the eigensystem realization algorithm. The proposed algorithm outperforms the augmented two-stage Kalman Filter (ASKF) and the unbiased minimum-variance (UMV) algorithm are shown in several examples. Finally, we propose a framework to place multiple mobile sensors to optimize the long-term performance of KF in the estimation of the state of a PDE. The major challenges are that placing multiple sensors is an NP-hard problem, and the optimization problem is non-convex in general. In this dissertation, first, we construct an ROM using RPOD_ algorithm, and then reduce the feasible sensor locations into a subset using the ROM. The Information Space Receding Horizon Control (I-RHC) approach and a modified Monte Carlo Tree Search (MCTS) approach are applied to solve the sensor scheduling problem using the subset. Various applications have been provided to demonstrate the… Advisors/Committee Members: Chakravorty, Suman (advisor), Junkins, John L. (committee member), Girimaji, Sharath (committee member), Darbha, Swaroop (committee member).

Subjects/Keywords: model reduction; spatio-temporal system; sensor placement; unknown input filtering

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

APA (6^th Edition):

Yu, D. (2016). State Estimation of Spatio-Temporal Phenomena. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/159046

Chicago Manual of Style (16^th Edition):

Yu, Dan. “State Estimation of Spatio-Temporal Phenomena.” 2016. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/159046.

MLA Handbook (7^th Edition):

Yu, Dan. “State Estimation of Spatio-Temporal Phenomena.” 2016. Web. 04 Mar 2021.

Vancouver:

Yu D. State Estimation of Spatio-Temporal Phenomena. [Internet] [Doctoral dissertation]. Texas A&M University; 2016. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/159046.

Council of Science Editors:

Yu D. State Estimation of Spatio-Temporal Phenomena. [Doctoral Dissertation]. Texas A&M University; 2016. Available from: http://hdl.handle.net/1969.1/159046

Texas A&M University

5. Castanon Quiroz, Daniel. Solving the MHD Equations in the Presence of Non-Axisymmetric Conductors Using the Fourier-Finite Element Method.

Degree: PhD, Mathematics, 2016, Texas A&M University

URL: http://hdl.handle.net/1969.1/156971

► The research presented in this dissertation focus on the numerical approximation of the magnetohydrodynamic (MHD) equations in the von K´arm´an Sodium (VKS) set-up. These studies… (more)

Subjects/Keywords: Finite Elements; Fourier-Finite Elements; Magnetohydrodynamics; Continuous Lagrange Elements; Nonlinear Dynamo Action

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APA (6^th Edition):

Castanon Quiroz, D. (2016). Solving the MHD Equations in the Presence of Non-Axisymmetric Conductors Using the Fourier-Finite Element Method. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/156971

Chicago Manual of Style (16^th Edition):

Castanon Quiroz, Daniel. “Solving the MHD Equations in the Presence of Non-Axisymmetric Conductors Using the Fourier-Finite Element Method.” 2016. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/156971.

MLA Handbook (7^th Edition):

Castanon Quiroz, Daniel. “Solving the MHD Equations in the Presence of Non-Axisymmetric Conductors Using the Fourier-Finite Element Method.” 2016. Web. 04 Mar 2021.

Vancouver:

Castanon Quiroz D. Solving the MHD Equations in the Presence of Non-Axisymmetric Conductors Using the Fourier-Finite Element Method. [Internet] [Doctoral dissertation]. Texas A&M University; 2016. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/156971.

Council of Science Editors:

Castanon Quiroz D. Solving the MHD Equations in the Presence of Non-Axisymmetric Conductors Using the Fourier-Finite Element Method. [Doctoral Dissertation]. Texas A&M University; 2016. Available from: http://hdl.handle.net/1969.1/156971

Texas A&M University

6. Taneja, Ankita. Consideration of Solar Radiation in Flare Design.

Degree: MS, Chemical Engineering, 2018, Texas A&M University

URL: http://hdl.handle.net/1969.1/173412

► At oil refineries and other chemical processing plants, a flare stack is used to get rid of unwanted or excessive gases and relieve the system… (more)

▼ At oil refineries and other chemical processing plants, a flare stack is used to get rid of unwanted or excessive gases and relieve the system of excess pressure. These gases can be generated during different stages of operation like startup or shutdown, maintenance and process upsets. Since flares handle large amounts of toxic and flammable materials, it makes the flaring operation hazardous. Combustion of huge amount of gases releases heat which is radiated to the atmosphere. Heat radiated from the flare makes it important for siting the flare at a proper location. The heat radiation should not exceed recommended threshold levels so that people on-site and the equipment are not affected. Thus, to have a well-designed flare, knowledge of total radiation emitted from a flare is essential. It will aid in accurately estimating the flare height and the area near the flare, which would sustain high levels of thermal radiation. A common point of contention while calculating radiation level emitted from flare is the decision of including solar radiation (SR) in the calculations. API 521 relegates this decision to the flare design company’s practices. Based on expert judgement, some literature states that for all practical purposes, solar radiation contribution can be discounted. The work performed aims at presenting a framework which quantitatively addresses aforementioned obscurity. The analysis helps flare designers to more objectively decide whether to include SR in their analyses or treat it insignificant contribution. The work studies the various factors that cause variation in SR value: location, time, and orientation of the surface. Considering all these parameters, an appropriate value of SR is chosen as the solar contribution to the thermal radiation from the flare. The effect of SR to the design of the flare is quantified by studying the change in effect distance near the flare and the height of the flare. Consequence analysis software PHAST is used to obtain these calculations. In addition, the outcome that SR inclusion will have on the risk posed by the flare due to thermal radiation on personnel is also examined. This is studied by measuring the change in lethality and heat stress caused by radiation exposure. Advisors/Committee Members: Mannan, M. Sam (advisor), Girimaji, Sharath (committee member), El-Halwagi, Mahmoud (committee member).

Subjects/Keywords: solar radiation; flare design

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APA (6^th Edition):

Taneja, A. (2018). Consideration of Solar Radiation in Flare Design. (Masters Thesis). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/173412

Chicago Manual of Style (16^th Edition):

Taneja, Ankita. “Consideration of Solar Radiation in Flare Design.” 2018. Masters Thesis, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/173412.

MLA Handbook (7^th Edition):

Taneja, Ankita. “Consideration of Solar Radiation in Flare Design.” 2018. Web. 04 Mar 2021.

Vancouver:

Taneja A. Consideration of Solar Radiation in Flare Design. [Internet] [Masters thesis]. Texas A&M University; 2018. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/173412.

Council of Science Editors:

Taneja A. Consideration of Solar Radiation in Flare Design. [Masters Thesis]. Texas A&M University; 2018. Available from: http://hdl.handle.net/1969.1/173412

Texas A&M University

7. Creel, Skylar. An Experimental Study of the Effect of Reshock on the Inclined Interface Richtmyer-Meshkov Instability.

Degree: MS, Mechanical Engineering, 2014, Texas A&M University

URL: http://hdl.handle.net/1969.1/152859

► An experimental study of the Richtmyer-Meshkov instability (RMI) is presented here for the twice-shocked, or reshocked, inclined interface perturbation. Experiment work was conducted in the… (more)

Subjects/Keywords: Shock Tube; Richtmyer-Meshkov Instability; Inclined Interface; Reshock

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APA (6^th Edition):

Creel, S. (2014). An Experimental Study of the Effect of Reshock on the Inclined Interface Richtmyer-Meshkov Instability. (Masters Thesis). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/152859

Chicago Manual of Style (16^th Edition):

Creel, Skylar. “An Experimental Study of the Effect of Reshock on the Inclined Interface Richtmyer-Meshkov Instability.” 2014. Masters Thesis, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/152859.

MLA Handbook (7^th Edition):

Creel, Skylar. “An Experimental Study of the Effect of Reshock on the Inclined Interface Richtmyer-Meshkov Instability.” 2014. Web. 04 Mar 2021.

Vancouver:

Creel S. An Experimental Study of the Effect of Reshock on the Inclined Interface Richtmyer-Meshkov Instability. [Internet] [Masters thesis]. Texas A&M University; 2014. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/152859.

Council of Science Editors:

Creel S. An Experimental Study of the Effect of Reshock on the Inclined Interface Richtmyer-Meshkov Instability. [Masters Thesis]. Texas A&M University; 2014. Available from: http://hdl.handle.net/1969.1/152859

Texas A&M University

8. Bertsch, Rebecca Lynne. Effect of Inhomogeneity and Unsteadiness on the Stability of High-Speed Shear Flows.

Degree: PhD, Aerospace Engineering, 2014, Texas A&M University

URL: http://hdl.handle.net/1969.1/153368

► In hypersonic flows, turbulence critically influences mass and momentum transport, mixing, heat transfer and acoustic noise generation. In contrast to incompressible flow, in high speed… (more)

▼ In hypersonic flows, turbulence critically influences mass and momentum transport, mixing, heat transfer and acoustic noise generation. In contrast to incompressible flow, in high speed flows pressure is a true thermodynamic variable and flowthermodynamic interactions render the investigations extremely challenging. Most studies to date have been performed on steady, uniform or homogeneous shear flows leading to important insight on the flow physics. In most real world applications,flows of practical importance will exhibit unsteadiness and strong inhomogeneity. To date, investigations of unsteadiness and inhomogeneity in high-speed flows are rare. The goal of this dissertation is to study and understand these non-ideal effects when pertinent to shear flows. Towards this goal, we perform three distinct studies: (a) examination of time reversal characteristics of linear inviscid mass, momentum, energy and state equation in compressible flows; (b) Linear analysis (RDT) of compressibility effects on instabilities in temporally periodic (unsteady) homogeneous shear flow; and (c) Numerical investigation of small perturbation evolution in compressible Kolmogorov (inhomogeneous) shear flow. The first study shows that even with the additional governing equations required in the high-speed regime, the inviscid flow field is still reversible. This justifies the use of temporal periodicity to investigate the effect of unsteadiness. The second study presents a detailed analysis of the pressure equation in temporally periodic homogeneous shear flow. The analysis and numerical results show unsteady uniform shear exhibits two stages of evolution due to the changing behavior of pressure. These stages are analogous to the first two stages of evolution established in steady shear. The third stage seen in steady shear is not achieved by periodic shear flow. The final study shows that the evolution of small perturbations in spatially periodic Kolmogorov flow is influenced by: i) the initial compressibility parameter, M_(g0), ii) the initial perturbation orientation, and iii) the stream normal location. Ultimately, the final study supports the postulate that all shear flows exhibit perturbation stability boundary classifications seen in homogeneous shear flows. The findings of this research further our understanding of the effects of unsteadiness and inhomogeneity in realistic flows, which will aid in the development of improved computational tools. Advisors/Committee Members: Girimaji, Sharath (advisor), Bowersox, Rodney (committee member), Donzis, Diego (committee member), Daripa, Prabir (committee member).

Subjects/Keywords: High-speed; compressible; Shear flow; Inhomogeneous; Unsteady

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APA (6^th Edition):

Bertsch, R. L. (2014). Effect of Inhomogeneity and Unsteadiness on the Stability of High-Speed Shear Flows. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/153368

Chicago Manual of Style (16^th Edition):

Bertsch, Rebecca Lynne. “Effect of Inhomogeneity and Unsteadiness on the Stability of High-Speed Shear Flows.” 2014. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/153368.

MLA Handbook (7^th Edition):

Bertsch, Rebecca Lynne. “Effect of Inhomogeneity and Unsteadiness on the Stability of High-Speed Shear Flows.” 2014. Web. 04 Mar 2021.

Vancouver:

Bertsch RL. Effect of Inhomogeneity and Unsteadiness on the Stability of High-Speed Shear Flows. [Internet] [Doctoral dissertation]. Texas A&M University; 2014. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/153368.

Council of Science Editors:

Bertsch RL. Effect of Inhomogeneity and Unsteadiness on the Stability of High-Speed Shear Flows. [Doctoral Dissertation]. Texas A&M University; 2014. Available from: http://hdl.handle.net/1969.1/153368

Texas A&M University

9. Placette, Beth. Effect of Initial Conditions on the Compound Shear- and Buoyancy-driven Mixing.

Degree: MS, Mechanical Engineering, 2012, Texas A&M University

URL: http://hdl.handle.net/1969.1/ETD-TAMU-2012-08-11470

► The effect of initial conditions in combined shear- and buoyancy- driven mixing was investigated through the use of an implicit large eddy simulation code under… (more)

▼ The effect of initial conditions in combined shear- and buoyancy- driven mixing was investigated through the use of an implicit large eddy simulation code under active development at Los Alamos National Laboratory and Texas A&M University. Alterations were done over several months both at Los Alamos National Laboratory and at the Texas A&M University campus, and include a transition from tilted rig to convective channel arrangement, introduction of an inertial reference frame, alteration of boundary conditions, etc. This work resulted in the development of a numerical framework with the capability to model various shear and Atwood number arrangements such as those seen in an inertial confinement fusion environment. In order to validate the code, it was compared to three published experiments, one with Atwood number 0.46 (White et al. 2010), one with high Atwood number 0.6 (Banerjee et al. 2010), and one with very low Atwood number 0.032 (Akula et al. 2012). Upon validating the code, pure Rayleigh-Taylor and pure Kelvin-Helmholtz instabilities were modeled along with five intermediate cases of increasing shear and constant density gradient. Plots of mixing width, Richardson number, growth parameter, and molecular mixing were compared in order to determine at what level of shear the minimum amount of mixing occurs. The results of height gradient and Reynolds number were to previous experiments and theory. The least amount of molecular mixing at the centerline was found to be when the system had a low Atwood number (0.032) and a multimode initial interface perturbation. While the increase in modes of the interface perturbation did not result in a significant change in the growth parameter, the level of molecular mixing at the centerline substantially decreased. As shear was increased in the system, the mixing width and molecular mixing subsequently increased. For this reason, the shear in the system should be eliminated, or at least minimized, if at possible so as to prevent any additional amalgamation in the system. Analysis of the Reynolds number revealed that with an increase in velocity difference between the fluid layers, the value consequently increased. This trend matches with theoretical results as the value is a function of the mixing width and velocity, thus further validating the code. Analysis of the transitional Richardson number revealed that it had a smaller value in the computational case over the experiment, but this fact can be attributed the difference in mixing width between the two methods. The development of the numerical framework with the capability to model various shear and Atwood number arrangements offers the platform for future study of hydrodynamic instabilities. Advisors/Committee Members: Ranjan, Devesh (advisor), Reddy, J. N. (committee member), Girimaji, Sharath (committee member).

Subjects/Keywords: Rayleigh-Taylor; Kelvin-Helmholtz; initial conditions

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APA (6^th Edition):

Placette, B. (2012). Effect of Initial Conditions on the Compound Shear- and Buoyancy-driven Mixing. (Masters Thesis). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/ETD-TAMU-2012-08-11470

Chicago Manual of Style (16^th Edition):

Placette, Beth. “Effect of Initial Conditions on the Compound Shear- and Buoyancy-driven Mixing.” 2012. Masters Thesis, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/ETD-TAMU-2012-08-11470.

MLA Handbook (7^th Edition):

Placette, Beth. “Effect of Initial Conditions on the Compound Shear- and Buoyancy-driven Mixing.” 2012. Web. 04 Mar 2021.

Vancouver:

Placette B. Effect of Initial Conditions on the Compound Shear- and Buoyancy-driven Mixing. [Internet] [Masters thesis]. Texas A&M University; 2012. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/ETD-TAMU-2012-08-11470.

Council of Science Editors:

Placette B. Effect of Initial Conditions on the Compound Shear- and Buoyancy-driven Mixing. [Masters Thesis]. Texas A&M University; 2012. Available from: http://hdl.handle.net/1969.1/ETD-TAMU-2012-08-11470

Texas A&M University

10. Rezvani, Maryam. Bubble Plumes in Crossflow: Laboratory and Field Measurements of Their Fluid Dynamic Properties with Application to Lake Aeration and Management.

Degree: PhD, Civil Engineering, 2016, Texas A&M University

URL: http://hdl.handle.net/1969.1/157046

► This dissertation presents laboratory experiments of bubble plumes in crossflows and field measurements in managed lakes aerated by bubble plumes to better understand the behavior… (more)

▼ This dissertation presents laboratory experiments of bubble plumes in crossflows and field measurements in managed lakes aerated by bubble plumes to better understand the behavior of bubble plumes in natural environments. The laboratory experiments were conducted to investigate the detailed time-average and turbulent fluctuating velocity field in the wake region behind the bubble column and above the separation height, at which fluid entrained at the base of the plume separates from the bubbles. These measurements are important for developing predictive models for bubble plume dynamics and for quantifying their mixing characteristics. Two field campaigns, at Carvins Cove in Virginia and at Lake Hallwil in Switzerland, were conducted to measure the detailed bottom boundary currents and oxygen exchange across the sediment-water interface for different diffuser operations. These lakes have different bubble plume diffuser types, and they span a range of shape, bathymetry, and environmental forcing. These field data are useful to elucidate the physical mechanisms by which currents resulting from both natural forcing (e.g., seiches) and artificial forcing (e.g., bubble plumes) affect oxygen uptake at the sediment-water interface, with the ultimate goal of better management of aeration systems in drinking water reservoirs. Experimental techniques applied in the laboratory experiments include Particle Image Velocimetry (PIV) and Planar Laser Induced Fluorescence (PLIF). Crossflows were generated in two ways: by towing the source and by forcing a recirculation current. A combination of field equipment was used in the field campaigns, including a microprofiler for temperature and oxygen; point and profiling acoustic Doppler velocimeter (ADV); thermistor chains; conductivity, temperature, and depth (CTD) profiles; and a meteorological station. During the field experiments, the bubble plume flow rate was varied to produce different dynamic and chemical conditions in the lakes. The laboratory experiments present a cohesive view of the flow dynamics in the wake of a bubble plume in crossflow. Using the forced and towed plume validates the analogy of the towed plume to that of the real current. The observations showed that no secondary bubble plume forms above the separation height, but rather the bubble column becomes a continuous source of vertical momentum to the wake region. The resulting vertical velocities impart a rising frame of reference on the separated plume so that its trajectory scales like a buoyant jet despite the absence of buoyancy in the separated fluid. Maximum values of the Reynolds stresses and mixing occur at the base of the separated plumes, and the bubble column elevates both the turbulence intensity and the kinetic energy throughout the wake region. The in situ field measurements provide insight into the role of aeration bubble plumes on the oxygen dynamics at the sediment-water interface. Detailed, simultaneous measurements of turbulence and oxygen uptake in the bottom boundary layer allowed the… Advisors/Committee Members: Socolofsky, Scott (advisor), Chang , Kuang-An (committee member), Girimaji, Sharath (committee member), DiMarco, Steve (committee member).

Subjects/Keywords: bubble plumes; crossflow; experimental data; field measurements; lake aeration; PIV; turbulence statistics; fluid dynamics

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APA (6^th Edition):

Rezvani, M. (2016). Bubble Plumes in Crossflow: Laboratory and Field Measurements of Their Fluid Dynamic Properties with Application to Lake Aeration and Management. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/157046

Chicago Manual of Style (16^th Edition):

Rezvani, Maryam. “Bubble Plumes in Crossflow: Laboratory and Field Measurements of Their Fluid Dynamic Properties with Application to Lake Aeration and Management.” 2016. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/157046.

MLA Handbook (7^th Edition):

Rezvani, Maryam. “Bubble Plumes in Crossflow: Laboratory and Field Measurements of Their Fluid Dynamic Properties with Application to Lake Aeration and Management.” 2016. Web. 04 Mar 2021.

Vancouver:

Rezvani M. Bubble Plumes in Crossflow: Laboratory and Field Measurements of Their Fluid Dynamic Properties with Application to Lake Aeration and Management. [Internet] [Doctoral dissertation]. Texas A&M University; 2016. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/157046.

Council of Science Editors:

Rezvani M. Bubble Plumes in Crossflow: Laboratory and Field Measurements of Their Fluid Dynamic Properties with Application to Lake Aeration and Management. [Doctoral Dissertation]. Texas A&M University; 2016. Available from: http://hdl.handle.net/1969.1/157046

Texas A&M University

11. Gomez Elizondo, Carlos Arturo 1981-. Turbulence Modeling for Compressible Shear Flows.

Degree: PhD, Mechanical Engineering, 2012, Texas A&M University

URL: http://hdl.handle.net/1969.1/148160

► Compressibility profoundly affects many aspects of turbulence in high-speed flows - most notably stability characteristics, anisotropy, kinetic-potential energy interchange and spectral cascade rate. Many of… (more)

▼ Compressibility profoundly affects many aspects of turbulence in high-speed flows - most notably stability characteristics, anisotropy, kinetic-potential energy interchange and spectral cascade rate. Many of the features observed in compressible flows are due to the changing nature of pressure. Whereas for incompressible flows pressure merely serves to enforce incompressibility, in compressible flows pressure becomes a thermodynamic variable that introduces a strong coupling between energy, state, and momentum equations. Closure models that attempt to address compressibility effects must begin their development from sound first-principles related to the changing nature of pressure as a flow goes from incompressible to compressible regime. In this thesis, a unified framework is developed for modeling pressure-related compressibility effects by characterizing the role and action of pressure at different speed regimes. Rapid distortion theory is used to examine the physical connection between the various compressibility effects leading to model form suggestions for the pressure-strain correlation, pressure-dilatation and dissipation evolution equation. The pressure-strain correlation closure coefficients are established using fixed point analysis by requiring consistency between model and direct numerical simulation asymptotic behavior in compressible homogeneous shear flow. The closure models are employed to compute high-speed mixing-layers and boundary layers in a differential Reynolds stress modeling solver. The self-similar mixing-layer profile, increased Reynolds stress anisotropy and diminished mixing-layer growth rates with increasing relative Mach number are all well captured. High-speed boundary layer results are also adequately replicated even without the use of advanced thermal-flux models or low Reynolds number corrections. To reduce the computational burden required for differential Reynolds stress calculations, the present compressible pressure-strain correlation model is incorporated into the algebraic modeling framework. The resulting closure is fully explicit, physically realizable, and is a function of mean flow strain rate, rotation rate, turbulent kinetic energy, dissipation rate, and gradient Mach number. The new algebraic model is validated with direct numerical simulations of homogeneous shear flow and experimental data of high-speed mixing-layers. Homogeneous shear flow calculations show that the model captures the asymptotic behavior of direct numerical simulations quite well. Calculations of plane supersonic mixing-layers are performed and comparison with experimental data shows good agreement. Therefore the algebraic model may serve as a surrogate for the more computationally expensive differential Reynolds stress model for flows that permit the weak-equilibrium simplification. Advisors/Committee Members: Duggleby, Andrew (advisor), Girimaji, Sharath (advisor), Annamalai, Kalyan (committee member), Han, Je-Chin (committee member).

Subjects/Keywords: mixing-layer; algebraic Reynolds stress model; pressure-strain correlation; turbulence; compressible

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APA (6^th Edition):

Gomez Elizondo, C. A. 1. (2012). Turbulence Modeling for Compressible Shear Flows. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/148160

Chicago Manual of Style (16^th Edition):

Gomez Elizondo, Carlos Arturo 1981-. “Turbulence Modeling for Compressible Shear Flows.” 2012. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/148160.

MLA Handbook (7^th Edition):

Gomez Elizondo, Carlos Arturo 1981-. “Turbulence Modeling for Compressible Shear Flows.” 2012. Web. 04 Mar 2021.

Vancouver:

Gomez Elizondo CA1. Turbulence Modeling for Compressible Shear Flows. [Internet] [Doctoral dissertation]. Texas A&M University; 2012. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/148160.

Council of Science Editors:

Gomez Elizondo CA1. Turbulence Modeling for Compressible Shear Flows. [Doctoral Dissertation]. Texas A&M University; 2012. Available from: http://hdl.handle.net/1969.1/148160

Texas A&M University

12. Kumar, Gaurav 1984-. Compressible Shear Flow Transition and Turbulence: Enhancement of GKM Numerical Scheme and Simulation/Analysis of Pressure Effects on Flow Stabilization.

Degree: PhD, Aerospace Engineering, 2012, Texas A&M University

URL: http://hdl.handle.net/1969.1/148321

► Despite significant advancements in the understanding of fluid flows, combustion and material technologies, hypersonic flight still presents numerous technological challenges. In hypersonic vehicles turbulence is… (more)

▼ Despite significant advancements in the understanding of fluid flows, combustion and material technologies, hypersonic flight still presents numerous technological challenges. In hypersonic vehicles turbulence is critical in controlling heat generation in the boundary layer, mixing inside the combustor, generation of acoustic noise, and mass flow in the intake. The study of turbulence in highly compressible flows is challenging compared to incompressible due to a drastic change in the behavior of pressure and a relaxation of the incompressibility constraint. In addition fluid flow inside a flight vehicle is complicated by wall-effects, heat generation and complex boundary conditions. Homogeneous shear flow contains most of the relevant physics of boundary and mixing layers without the aforementioned complicating effects. In this work we aim to understand and characterize the role of pressure, velocity-pressure interaction, velocity-thermodynamics interaction in the late-stage transition-to-turbulence regime in a high speed shear dominated flow by studying the evolution of perturbations in in a high Mach number homogeneous shear flow. We use a modal-analysis based approach towards understanding the statistical behavior of turbulence. Individual Fourier waves constituting the initial flow field are studied in isolation and in combination to understand collective statistical behavior. We demonstrate proof of concept of novel acoustic based strategies for controlling the onset of turbulence. Towards this goal we perform direct numerical simulations (DNS) in three studies: (a) development and evaluation of gas kinetic based numerical tool for DNS of compressible turbulence, and perform detailed evaluation of the efficacy of different interpolation schemes in capturing solenoidal and dilatational quantities, (b) modal investigation in the behavior of pressure and isolation of linear, non-linear, inertial and pressure actions, and (c) modal investigation in the possible acoustic based control strategies in homogeneously sheared compressible flows. The findings help to understand the manifestation of the effects of compressibility on transition and turbulence via the velocity-pressure interactions and the action of individual waves. The present study helps towards the design of control mechanisms for compressible turbulence and the development of physically consistent pressure strain correlation models. Advisors/Committee Members: Girimaji, Sharath (advisor), Bowersox, Rodney (committee member), Duggleby, Andrew (committee member), Chen, Hamn-Ching (committee member).

Subjects/Keywords: Modal analysis; Flow control strategies; Homogeneous Shear; Decaying Turbulence; WENO; Gas Kinetic Method

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APA (6^th Edition):

Kumar, G. 1. (2012). Compressible Shear Flow Transition and Turbulence: Enhancement of GKM Numerical Scheme and Simulation/Analysis of Pressure Effects on Flow Stabilization. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/148321

Chicago Manual of Style (16^th Edition):

Kumar, Gaurav 1984-. “Compressible Shear Flow Transition and Turbulence: Enhancement of GKM Numerical Scheme and Simulation/Analysis of Pressure Effects on Flow Stabilization.” 2012. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/148321.

MLA Handbook (7^th Edition):

Kumar, Gaurav 1984-. “Compressible Shear Flow Transition and Turbulence: Enhancement of GKM Numerical Scheme and Simulation/Analysis of Pressure Effects on Flow Stabilization.” 2012. Web. 04 Mar 2021.

Vancouver:

Kumar G1. Compressible Shear Flow Transition and Turbulence: Enhancement of GKM Numerical Scheme and Simulation/Analysis of Pressure Effects on Flow Stabilization. [Internet] [Doctoral dissertation]. Texas A&M University; 2012. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/148321.

Council of Science Editors:

Kumar G1. Compressible Shear Flow Transition and Turbulence: Enhancement of GKM Numerical Scheme and Simulation/Analysis of Pressure Effects on Flow Stabilization. [Doctoral Dissertation]. Texas A&M University; 2012. Available from: http://hdl.handle.net/1969.1/148321

Texas A&M University

13. Semper, Michael Thomas. Examining A Hypersonic Turbulent Boundary Layer at Low Reynolds Number.

Degree: PhD, Aerospace Engineering, 2013, Texas A&M University

URL: http://hdl.handle.net/1969.1/150983

► The purpose of the current study was to answer several questions related to hypersonic, low Reynolds number, turbulent boundary layers, of which available data related… (more)

▼ The purpose of the current study was to answer several questions related to hypersonic, low Reynolds number, turbulent boundary layers, of which available data related to turbulence quantities is scarce. To that end, a unique research facility was created, instrumentation was developed to acquire data in the challenging low Reynolds number (low density) domain, and meaningful data was collected and analyzed. The low Reynolds number nature of the boundary layer (Re_theta = 3700) allows for tangible DNS computations/validations using the current geometry and conditions. The boundary layer examined in this experiment resembled other, higher Reynolds number boundary layers, but also exhibited its own unique characteristics. The Van Driest equivalent velocity scaling method was found to perform well, and the log layer of the law of the wall plot matched expected theory. Noticeably absent from the data was an overlap region between the two layers, which suggests a different profile for the velocity profiles at these low Reynolds number, hypersonic conditions. The low density effects near the wall may be having an effect on the turbulence that modifies this region in a manner not currently anticipated. The Crocco-Busemann relation was found to provide satisfactory results under its general assumptions. When compared to available data, the Morkovin scaled velocity fluctuations fell almost an order of magnitude short. Currently, it is not known if this deficit is due to inadequacies with the Strong Reynolds Analogy, or the Morkovin scaling parameters. The trips seem to promote uniformity across the span of the model, and the data seems to generally be in agreement across the spanwise stations. However, additional information is needed to determine if two-dimensional simulations are sufficient for these boundary layers. When the turbulent boundary layer power spectra is analyzed, the result is found to follow the traditional power law. This result verifies that even at low Reynolds numbers, the length scales still follow the behavior described by Kolmogorov. Moving downstream of the trips, the peak RMS disturbance value grows in amplitude until it reaches a critical value. After this point, the peak begins to decrease in amplitude, but the affected region spreads throughout the boundary layer. Once the influenced region covers a significant portion of the boundary layer, transition occurs. Advisors/Committee Members: Bowersox, Rodney (advisor), Girimaji, Sharath (committee member), North, Simon (committee member), Rediniotis, Othon (committee member).

Subjects/Keywords: hypersonic; turbulent; boundary layer; low Reynolds number; experimental

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APA (6^th Edition):

Semper, M. T. (2013). Examining A Hypersonic Turbulent Boundary Layer at Low Reynolds Number. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/150983

Chicago Manual of Style (16^th Edition):

Semper, Michael Thomas. “Examining A Hypersonic Turbulent Boundary Layer at Low Reynolds Number.” 2013. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/150983.

MLA Handbook (7^th Edition):

Semper, Michael Thomas. “Examining A Hypersonic Turbulent Boundary Layer at Low Reynolds Number.” 2013. Web. 04 Mar 2021.

Vancouver:

Semper MT. Examining A Hypersonic Turbulent Boundary Layer at Low Reynolds Number. [Internet] [Doctoral dissertation]. Texas A&M University; 2013. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/150983.

Council of Science Editors:

Semper MT. Examining A Hypersonic Turbulent Boundary Layer at Low Reynolds Number. [Doctoral Dissertation]. Texas A&M University; 2013. Available from: http://hdl.handle.net/1969.1/150983

Texas A&M University

14. Panickacheril John, John. Universality and Scaling in Compressible Turbulence and Mixing.

Degree: PhD, Aerospace Engineering, 2020, Texas A&M University

URL: http://hdl.handle.net/1969.1/192438

► Compressible turbulence and turbulent mixing play a critical role in diverse systems ranging from engineering devices to astrophysics. Examples include high-speed scram jets, hypersonic flows,… (more)

▼ Compressible turbulence and turbulent mixing play a critical role in diverse systems ranging from engineering devices to astrophysics. Examples include high-speed scram jets, hypersonic flows, combustion and star formation. The phenomenon is poorly understood due to complicated interactions between the compressible (dilatational) and vortical (solenoidal) modes in addition to the coupling of the flow field with thermodynamic variables. Attempts to make progress using traditional governing parameters, namely the Taylor Reynolds number, (Rλ) and the turbulent Mach number, (Mt) have been marred with inconsistencies and conflicting results in the literature. Resolving these discrepancies, further our understanding of this phenomena, develop new turbulence models for actual applications and affect flow control in practical situations are the ultimate objectives of this project. For this, we perform direct numerical simulations for a wide range of forcing conditions using state-of-the-art massively parallel codes that we show to be scalable up to 431200 cores at world-record resolutions. The aggregate database comprises an unprecedented wide range of values of the governing parameters. Through a novel asymptotic theoretical approach and systematic data analysis, we identify a new non-dimensional scaling parameter, δ, the ratio of compressible to vortical strength along with traditional parameters to unravel universal behaviour and scaling laws resolving several major issues currently plaguing the field. This could prove a paradigm shift in how compressible turbulence is studied. We predict the energy distribution across scales of the dilatational part of turbulent kinetic energy by dividing the δ − Mt plane into different physical regimes. These insights are also applied to passive scalar mixing. Although the large-scale of motion of passive scalars is oblivious to the effects of compressibility, it has a strong effect on the smallest scales. With these insights, we successfully parametrize the mixing efficiency in terms of the governing parameters. Our results have major implications in turbulence modeling paving the road towards more accurate, robust and generic models. In order to generate the current unique database, several computational issues had to be addressed, such as IO at scales, the use of accelerators, and the overhead associated with high levels of parallelism. Thus we also contribute towards extending the capabilities of the grand computational challenge of simulating turbulence at realistic conditions seen in nature and engineering applications. Advisors/Committee Members: Donzis, Diego (advisor), Bowersox, Rodney (committee member), Girimaji, Sharath (committee member), Petersen, Eric (committee member).

Subjects/Keywords: Compressible turbulence; Mixing; High performance computing; Direct numerical simulations

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APA (6^th Edition):

Panickacheril John, J. (2020). Universality and Scaling in Compressible Turbulence and Mixing. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/192438

Chicago Manual of Style (16^th Edition):

Panickacheril John, John. “Universality and Scaling in Compressible Turbulence and Mixing.” 2020. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/192438.

MLA Handbook (7^th Edition):

Panickacheril John, John. “Universality and Scaling in Compressible Turbulence and Mixing.” 2020. Web. 04 Mar 2021.

Vancouver:

Panickacheril John J. Universality and Scaling in Compressible Turbulence and Mixing. [Internet] [Doctoral dissertation]. Texas A&M University; 2020. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/192438.

Council of Science Editors:

Panickacheril John J. Universality and Scaling in Compressible Turbulence and Mixing. [Doctoral Dissertation]. Texas A&M University; 2020. Available from: http://hdl.handle.net/1969.1/192438

Texas A&M University

15. Mishra, Aashwin A. A Dynamical Systems Approach Towards Modeling the Rapid Pressure Strain Correlation.

Degree: MS, Aerospace Engineering, 2011, Texas A&M University

URL: http://hdl.handle.net/1969.1/ETD-TAMU-2010-05-8018

► In this study, the behavior of pressure in the Rapid Distortion Limit, along with its concomitant modeling, are addressed. In the first part of the… (more)

▼ In this study, the behavior of pressure in the Rapid Distortion Limit, along with its concomitant modeling, are addressed. In the first part of the work, the role of pressure in the initiation, propagation and suppression of flow instabilities for quadratic flows is analyzed. The paradigm of analysis considers the Reynolds stress transport equations to govern the evolution of a dynamical system, in a state space composed of the Reynolds stress tensor components. This dynamical system is scrutinized via the identification of the invariant sets and the bifurcation analysis. The changing role of pressure in quadratic flows, viz. hyperbolic, shear and elliptic, is established mathematically and the underlying physics is explained. Along the maxim of "understanding before prediction", this allows for a deeper insight into the behavior of pressure, thus aiding in its modeling. The second part of this work deals with Rapid Pressure Strain Correlation modeling in earnest. Based on the comprehension developed in the preceding section, the classical pressure strain correlation modeling approaches are revisited. Their shortcomings, along with their successes, are articulated and explained, mathematically and from the viewpoint of the governing physics. Some of the salient issues addressed include, but are not limited to, the requisite nature of the model, viz. a linear or a nonlinear structure, the success of the extant models for hyperbolic flows, their inability to capture elliptic flows and the use of RDT simulations to validate models. Through this analysis, the schism between mathematical and physical guidelines and the engineering approach, at present, is substantiated. Subsequently, a model is developed that adheres to the classical modeling framework and shows excellent agreement with the RDT simulations. The performance of this model is compared to that of other nominations prevalent in engineering simulations. The work concludes with a summary, pertinent observations and recommendations for future research in the germane field. Advisors/Committee Members: Girimaji, Sharath S. (advisor), Saric, William S. (committee member), Nagy, Tamas K. (committee member), Chen, Hamin C. (committee member).

Subjects/Keywords: Fluid mechanics; Turbulence modeling; second moment closures; pressure strain correlation; rapid distortion theory; dynamical systems

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APA (6^th Edition):

Mishra, A. A. (2011). A Dynamical Systems Approach Towards Modeling the Rapid Pressure Strain Correlation. (Masters Thesis). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/ETD-TAMU-2010-05-8018

Chicago Manual of Style (16^th Edition):

Mishra, Aashwin A. “A Dynamical Systems Approach Towards Modeling the Rapid Pressure Strain Correlation.” 2011. Masters Thesis, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/ETD-TAMU-2010-05-8018.

MLA Handbook (7^th Edition):

Mishra, Aashwin A. “A Dynamical Systems Approach Towards Modeling the Rapid Pressure Strain Correlation.” 2011. Web. 04 Mar 2021.

Vancouver:

Mishra AA. A Dynamical Systems Approach Towards Modeling the Rapid Pressure Strain Correlation. [Internet] [Masters thesis]. Texas A&M University; 2011. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/ETD-TAMU-2010-05-8018.

Council of Science Editors:

Mishra AA. A Dynamical Systems Approach Towards Modeling the Rapid Pressure Strain Correlation. [Masters Thesis]. Texas A&M University; 2011. Available from: http://hdl.handle.net/1969.1/ETD-TAMU-2010-05-8018

Texas A&M University

16. Araya, Daniel. Resistive MHD Simulations of Laminar Round Jets with Application to Magnetic Nozzle Flows.

Degree: MS, Aerospace Engineering, 2012, Texas A&M University

URL: http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10292

► This thesis investigates fundamental flows of resistive magnetohydrodynamics (MHD) by a new numerical tool based on the gas-kinetic method. The motivation for this work stems… (more)

Subjects/Keywords: magnetic nozzle; MHD; gas-kinetic method

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APA (6^th Edition):

Araya, D. (2012). Resistive MHD Simulations of Laminar Round Jets with Application to Magnetic Nozzle Flows. (Masters Thesis). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10292

Chicago Manual of Style (16^th Edition):

Araya, Daniel. “Resistive MHD Simulations of Laminar Round Jets with Application to Magnetic Nozzle Flows.” 2012. Masters Thesis, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10292.

MLA Handbook (7^th Edition):

Araya, Daniel. “Resistive MHD Simulations of Laminar Round Jets with Application to Magnetic Nozzle Flows.” 2012. Web. 04 Mar 2021.

Vancouver:

Araya D. Resistive MHD Simulations of Laminar Round Jets with Application to Magnetic Nozzle Flows. [Internet] [Masters thesis]. Texas A&M University; 2012. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10292.

Council of Science Editors:

Araya D. Resistive MHD Simulations of Laminar Round Jets with Application to Magnetic Nozzle Flows. [Masters Thesis]. Texas A&M University; 2012. Available from: http://hdl.handle.net/1969.1/ETD-TAMU-2011-12-10292

Texas A&M University

17. Konduri, Aditya. Highly Scalable Asynchronous Computing Method for Partial Differential Equations: A Path Towards Exascale.

Degree: PhD, Aerospace Engineering, 2016, Texas A&M University

URL: http://hdl.handle.net/1969.1/156951

► Many natural and engineering systems are governed by nonlinear partial differential equations (PDEs) which result in a multiscale phenomena, e.g. turbulent flows. Numerical simulations of… (more)

Subjects/Keywords: asynchronous computing; computational fluid dynamics; partial differential equations; high performance computing; numerical algorithms

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APA (6^th Edition):

Konduri, A. (2016). Highly Scalable Asynchronous Computing Method for Partial Differential Equations: A Path Towards Exascale. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/156951

Chicago Manual of Style (16^th Edition):

Konduri, Aditya. “Highly Scalable Asynchronous Computing Method for Partial Differential Equations: A Path Towards Exascale.” 2016. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/156951.

MLA Handbook (7^th Edition):

Konduri, Aditya. “Highly Scalable Asynchronous Computing Method for Partial Differential Equations: A Path Towards Exascale.” 2016. Web. 04 Mar 2021.

Vancouver:

Konduri A. Highly Scalable Asynchronous Computing Method for Partial Differential Equations: A Path Towards Exascale. [Internet] [Doctoral dissertation]. Texas A&M University; 2016. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/156951.

Council of Science Editors:

Konduri A. Highly Scalable Asynchronous Computing Method for Partial Differential Equations: A Path Towards Exascale. [Doctoral Dissertation]. Texas A&M University; 2016. Available from: http://hdl.handle.net/1969.1/156951

Texas A&M University

18. Chen, Chang-Hsin. Shock-Turbulence Interactions at High Turbulence Intensities: Theory and Direct Numerical Simulations.

Degree: PhD, Aerospace Engineering, 2018, Texas A&M University

URL: http://hdl.handle.net/1969.1/174324

► The interaction of turbulence with shock waves, while very common in nature and engineered systems, is a very difficult problem from a theoretical, numerical and… (more)

▼ The interaction of turbulence with shock waves, while very common in nature and engineered systems, is a very difficult problem from a theoretical, numerical and experimental perspective. A main challenge comes from the two-way coupling between the shock and turbulence which occurs over a wide range of scales in time and space. As a result, many investigations have resorted to strong simplifications such as the linearization of the governing equations or the assumption of mean conditions across the shock independent of turbulent fluctuations. When the interaction is strong, a condition that is realized when turbulence is relatively intense, much less is known about the behavior of both the shock and turbulence. The focus of this work, thus, is on shock-turbulence interactions (STI) at high turbulent intensities using high-fidelity direct numerical simulations (DNS) that fully resolve the shock. Highly accurate methods are developed to simulate a stationary normal shock as the turbulent flow passes through the domain and used to generate a massive highly resolved database at a wide range of conditions. The numerical study is guided by novel theoretical work that result in analytical expressions for thermodynamic jumps across the shock that, unlike previous results in the literature, depend on turbulence characteristics. Comparison with DNS data shows that these expressions can indeed predict quantitatively a number of statistical variables of interest. The theory also predicts the emergence of new regimes of the interaction which results in distinct amplification or attenuation of different variables depending on governing parameters. This previously unseen behavior is verified against DNS as well. Results on the shock structure are used to validate previous theoretical proposals and extend the analysis to much stronger interactions which leads to the observation of a new regime (a vanished regime in addition to the well-known wrinkled and broken regimes) in which turbulence undergoes a classical spatial decay as it crosses the shock. Finally, the amplification of turbulence across the shock is studied using our DNS results as well as the large collection available in the literature. Disagreements in the literature on Reynolds stresses are resolved by recognizing a special kind of similarity scaling on two different parameters in two different limits. This analysis reconciles apparently contradicting results in the literature. This analysis is extended to other quantities of interest such as enstrophy and mass flux with similar success. Advisors/Committee Members: Donzis, Diego A (advisor), Bowersox, Rodney DW (committee member), Girimaji, Sharath S (committee member), North, Simon W (committee member).

Subjects/Keywords: turbulence; shocks; DNS

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APA (6^th Edition):

Chen, C. (2018). Shock-Turbulence Interactions at High Turbulence Intensities: Theory and Direct Numerical Simulations. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/174324

Chicago Manual of Style (16^th Edition):

Chen, Chang-Hsin. “Shock-Turbulence Interactions at High Turbulence Intensities: Theory and Direct Numerical Simulations.” 2018. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/174324.

MLA Handbook (7^th Edition):

Chen, Chang-Hsin. “Shock-Turbulence Interactions at High Turbulence Intensities: Theory and Direct Numerical Simulations.” 2018. Web. 04 Mar 2021.

Vancouver:

Chen C. Shock-Turbulence Interactions at High Turbulence Intensities: Theory and Direct Numerical Simulations. [Internet] [Doctoral dissertation]. Texas A&M University; 2018. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/174324.

Council of Science Editors:

Chen C. Shock-Turbulence Interactions at High Turbulence Intensities: Theory and Direct Numerical Simulations. [Doctoral Dissertation]. Texas A&M University; 2018. Available from: http://hdl.handle.net/1969.1/174324

Texas A&M University

19. Venugopal, Vishnu. Rarefaction Effects on Thermal Transport and Flow Structures in Cavity Flows.

Degree: PhD, Aerospace Engineering, 2016, Texas A&M University

URL: http://hdl.handle.net/1969.1/158986

► Accurate simulation and modeling the effects of rarefaction on heat and mass transport is of much interest in high-speed flow applications including hypersonic vehicles and… (more)

▼ Accurate simulation and modeling the effects of rarefaction on heat and mass transport is of much interest in high-speed flow applications including hypersonic vehicles and atmospheric re-entry flights. Toward this end, the present work develops numerical schemes appropriate for a wide range of Knudsen numbers and performs analytical investigation of the rarefaction effects. First, the Unified Gas Kinetic Scheme (UGKS) is extended to a wider range of Mach and Knudsen numbers by implementing WENO (Weighted Essentially Non-Oscillatory) interpolation. Direct Simulation Monte Carlo (DSMC) computations are also performed when appropriate for comparison purposes. Though DSMC method is theoretically valid in the entire range of Knudsen numbers (from continuum to free-molecular), real computations with DSMC are limited to rarefied flows as this method demands excessive computational resources to simulate continuum/near-continuum flows. The effect of rarefaction is examined in the canonical lid-driven flows. In particular, the effect of cavity size (cavity aspect ratio), flow speed (lid Mach number) and degree of rarefaction (global Knudsen number) on flow structures and transport properties in the cavity are examined. The simulations are performed at a wide range of flow regimes (a) subsonic incompressible, subsonic compressible and supersonic (b) Knudsen numbers: continuum, near-continuum, transition and highly rarefied regimes. Flow (vortex) structures and thermal transport are characterized as functions of different flow regimes and cavity size. Mechanism of vortex evolution is investigated at a microscopic perspective. Parametric studies followed by careful observations and rigorous analyses reveal important insights to the rarefaction effects on the heat and mass transport behavior of canonical 2D cavity flows. The proposed scheme can extensively be used for fluid flows comprising of large density variations whose length scales extend from a macroscale to a molecular scale. Advisors/Committee Members: Girimaji, Sharath S (advisor), Donzis, Diego A (committee member), Bowersox, Rodney (committee member), Chen, Hamn-Ching (committee member).

Subjects/Keywords: rarefied flows; gas kinetic method; cavity flows; thermodynamic non-equilibrium; thermal transport

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APA (6^th Edition):

Venugopal, V. (2016). Rarefaction Effects on Thermal Transport and Flow Structures in Cavity Flows. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/158986

Chicago Manual of Style (16^th Edition):

Venugopal, Vishnu. “Rarefaction Effects on Thermal Transport and Flow Structures in Cavity Flows.” 2016. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/158986.

MLA Handbook (7^th Edition):

Venugopal, Vishnu. “Rarefaction Effects on Thermal Transport and Flow Structures in Cavity Flows.” 2016. Web. 04 Mar 2021.

Vancouver:

Venugopal V. Rarefaction Effects on Thermal Transport and Flow Structures in Cavity Flows. [Internet] [Doctoral dissertation]. Texas A&M University; 2016. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/158986.

Council of Science Editors:

Venugopal V. Rarefaction Effects on Thermal Transport and Flow Structures in Cavity Flows. [Doctoral Dissertation]. Texas A&M University; 2016. Available from: http://hdl.handle.net/1969.1/158986

Texas A&M University

20. Anderson, Steven Edward. Development of a Coupled Two-Fluid Plasma Gas-Kinetic Scheme (TFPGKS).

Degree: PhD, Aerospace Engineering, 2018, Texas A&M University

URL: http://hdl.handle.net/1969.1/173305

► The study and characterization of plasma flows is of significant interest in many disciplines of engineering and science. Of particular interest is the study and… (more)

▼ The study and characterization of plasma flows is of significant interest in many disciplines of engineering and science. Of particular interest is the study and development of plasma-based electric propulsion devices. Plasma flows can exhibit complex behavior depending upon parameter regime and the interaction with applied and induced electromagnetic fields. Further, due to their typically extreme environments, space plasma flows are difficult to investigate with terrestrial experiments. The complexity of plasma flow governing equations typically renders analytical solutions impossible for all but the simplest problems. Thus, the development of more capable physical models and numerical tools for computer simulation is an important research focus. Over the last two decades, the Gas-Kinetic Scheme (GKS) has been demonstrated to be a highly capable solver for a wide range of gas-dynamics flows, from incompressible to rarefied and hypersonic. Further, it has also been shown to work well for ideal, resistive, and Hall magnetohydrodynamics. This dissertation aims to develop the theoretical framework for a gas-kinetic scheme for a singly-charged ion-electron two-fluid plasma. The approach is to apply a Method-of-Characteristics (MoC) – based solution to the Boltzmann equation for each species with the Bhatnagar-Gross-Krook (BGK) collision operator modeling the species self-collisions. In the Boltzmann-BGK (B-BGK) equation the inter-species collisions are modeled as a resistive force on each species. The derived approximate MoC solution renders the resulting particle characteristic trajectories linear in physical space. To model the non-equilibrium effects of collisions, a Chapman-Enskog (CE) type expansion for each species is performed, which captures Finite-Larmor-Radius (FLR) effects on the stress tensor and the heat flux. To consistently couple the ion and electron fluids to the electromagnetic fields, the Perfectly Hyperbolic Maxwell’s (PHM) equations are used, which incorporate the constraints of Gauss’ Law for the Electric and Magnetic Fields into their temporal evolution. The Two-Fluid Plasma GKS (TFPGKS) scheme is implemented by using Weighted Essentially-Non-Oscillatory (WENO) interpolation for cell interface reconstruction of the flow variables, while a Lax-Friedrichs – type approach is used for the PHM equations. A semi-analytic analysis of the derived fluxes compared to existing models demonstrates the magnetized asymptotic behavior which produces the expected anisotropy in the transport properties. The scheme is benchmarked against analytic solutions for the linearized governing equations. It is further validated against published results for several canonical problems, including the Electromagnetic Shock and Ion Acoustic Solitons. Finally, a parametric study of collisional electromagnetic shocks demonstrates the capabilities of the new TFPGKS scheme over more naive previous implementations. Overall, the work demonstrates the promise of the GKS approach to simulating plasma flows over a wide parameter… Advisors/Committee Members: Girimaji, Sharath S (advisor), Karpetis, Adonios (committee member), Hara, Kentaro (committee member), Staack, David (committee member), Pope, Christopher (committee member).

Subjects/Keywords: gas-kinetic scheme; MHD; two-fluid plasma

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APA (6^th Edition):

Anderson, S. E. (2018). Development of a Coupled Two-Fluid Plasma Gas-Kinetic Scheme (TFPGKS). (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/173305

Chicago Manual of Style (16^th Edition):

Anderson, Steven Edward. “Development of a Coupled Two-Fluid Plasma Gas-Kinetic Scheme (TFPGKS).” 2018. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/173305.

MLA Handbook (7^th Edition):

Anderson, Steven Edward. “Development of a Coupled Two-Fluid Plasma Gas-Kinetic Scheme (TFPGKS).” 2018. Web. 04 Mar 2021.

Vancouver:

Anderson SE. Development of a Coupled Two-Fluid Plasma Gas-Kinetic Scheme (TFPGKS). [Internet] [Doctoral dissertation]. Texas A&M University; 2018. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/173305.

Council of Science Editors:

Anderson SE. Development of a Coupled Two-Fluid Plasma Gas-Kinetic Scheme (TFPGKS). [Doctoral Dissertation]. Texas A&M University; 2018. Available from: http://hdl.handle.net/1969.1/173305

Texas A&M University

21. Jagannathan, Shriram. Reynolds and Mach Number Scaling in Stationary Compressible Turbulence Using Massively Parallel High Resolution Direct Numerical Simulations.

Degree: PhD, Aerospace Engineering, 2014, Texas A&M University

URL: http://hdl.handle.net/1969.1/153329

► Turbulence is the most common state of fluid motion in both natural and engineering systems. Many real world applications depend on our ability to predict… (more)

Subjects/Keywords: Direct Numerical Simulations; DNS; Compressible Turbulence; High performance computing (HPC); isotropic turbulence; stationary turbulence; high resolution

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APA (6^th Edition):

Jagannathan, S. (2014). Reynolds and Mach Number Scaling in Stationary Compressible Turbulence Using Massively Parallel High Resolution Direct Numerical Simulations. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/153329

Chicago Manual of Style (16^th Edition):

Jagannathan, Shriram. “Reynolds and Mach Number Scaling in Stationary Compressible Turbulence Using Massively Parallel High Resolution Direct Numerical Simulations.” 2014. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/153329.

MLA Handbook (7^th Edition):

Jagannathan, Shriram. “Reynolds and Mach Number Scaling in Stationary Compressible Turbulence Using Massively Parallel High Resolution Direct Numerical Simulations.” 2014. Web. 04 Mar 2021.

Vancouver:

Jagannathan S. Reynolds and Mach Number Scaling in Stationary Compressible Turbulence Using Massively Parallel High Resolution Direct Numerical Simulations. [Internet] [Doctoral dissertation]. Texas A&M University; 2014. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/153329.

Council of Science Editors:

Jagannathan S. Reynolds and Mach Number Scaling in Stationary Compressible Turbulence Using Massively Parallel High Resolution Direct Numerical Simulations. [Doctoral Dissertation]. Texas A&M University; 2014. Available from: http://hdl.handle.net/1969.1/153329

Texas A&M University

22. Mishra, Aashwin A. The Art and Science in Modeling the Pressure-Velocity Interactions.

Degree: PhD, Aerospace Engineering, 2014, Texas A&M University

URL: http://hdl.handle.net/1969.1/153358

► The objective of this investigation is to develop a single point model for the global effects of pressure in turbulence, while striking a judicious balance… (more)

Subjects/Keywords: Fluid Mechanics; Turbulence Theory; Hydrodynamic Stability

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APA (6^th Edition):

Mishra, A. A. (2014). The Art and Science in Modeling the Pressure-Velocity Interactions. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/153358

Chicago Manual of Style (16^th Edition):

Mishra, Aashwin A. “The Art and Science in Modeling the Pressure-Velocity Interactions.” 2014. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/153358.

MLA Handbook (7^th Edition):

Mishra, Aashwin A. “The Art and Science in Modeling the Pressure-Velocity Interactions.” 2014. Web. 04 Mar 2021.

Vancouver:

Mishra AA. The Art and Science in Modeling the Pressure-Velocity Interactions. [Internet] [Doctoral dissertation]. Texas A&M University; 2014. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/153358.

Council of Science Editors:

Mishra AA. The Art and Science in Modeling the Pressure-Velocity Interactions. [Doctoral Dissertation]. Texas A&M University; 2014. Available from: http://hdl.handle.net/1969.1/153358

Texas A&M University

23. Cooper, Jacob. Multi-Resolution Simulations of Delta/Diamond Wing Aerodynamics.

Degree: PhD, Aerospace Engineering, 2014, Texas A&M University

URL: http://hdl.handle.net/1969.1/153426

► This dissertation investigates high angle of attack delta wing flow at multiple resolutions of turbulence closure. The work is divided into four studies. The objectives… (more)

▼ This dissertation investigates high angle of attack delta wing flow at multiple resolutions of turbulence closure. The work is divided into four studies. The objectives of each study are: (i) to identify the limits of RANS modeling, (ii) explore the challenges of applying the PANS model to the delta wing flow, (iii) identify the appropriate resolution required to capture specific flow features, and (iv) determine the physical differences between sharp and round leading edge separation. The outcomes from each of these studies are as follows. Steady-state RANS modeling is shown to be adequate for low and moderate angles of attack, except in regions near the point of primary vortex separation. At low Reynolds number the vortex structure on the forward portion of the wing is mostly laminar and must be fully resolved by the grid in order to capture the physics in the aft region. Also at low Reynolds numbers, it is shown that lower resolution simulations perform adequately in capturing important integral flow features such as pressure coefficient and the locations of the vortex separation and attachment lines. High resolution simulations of low Reynolds number flow do resolve more subtle flow features that do not significantly affect the aerodynamic characteristics. The principle advantages of high resolution simulations are most evident at high Reynolds numbers and high angles of attack. The relationship between scale resolution and observed flow features is established. The simulations establish the key flow feature differences between round and sharp leading edge wing at different length scales of motion. Features of interest are the intensity of the vortex structure, the levels of turbulence, surface streamline patterns, and surface pressure coefficient. Differences between the delta and diamond wing shapes are also identified. Advisors/Committee Members: Girimaji, Sharath S (advisor), Cizmas, Paul (committee member), Donzis, Diego (committee member), Chen, Hamn-Ching (committee member).

Subjects/Keywords: delta wing; diamond wing; turbulence model; PANS

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

APA (6^th Edition):

Cooper, J. (2014). Multi-Resolution Simulations of Delta/Diamond Wing Aerodynamics. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/153426

Chicago Manual of Style (16^th Edition):

Cooper, Jacob. “Multi-Resolution Simulations of Delta/Diamond Wing Aerodynamics.” 2014. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/153426.

MLA Handbook (7^th Edition):

Cooper, Jacob. “Multi-Resolution Simulations of Delta/Diamond Wing Aerodynamics.” 2014. Web. 04 Mar 2021.

Vancouver:

Cooper J. Multi-Resolution Simulations of Delta/Diamond Wing Aerodynamics. [Internet] [Doctoral dissertation]. Texas A&M University; 2014. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/153426.

Council of Science Editors:

Cooper J. Multi-Resolution Simulations of Delta/Diamond Wing Aerodynamics. [Doctoral Dissertation]. Texas A&M University; 2014. Available from: http://hdl.handle.net/1969.1/153426

Texas A&M University

24. Mendoza, Nicole Renee. On the Fundamental Unsteady Fluid Dynamics of Shock-Induced Flows through Ducts.

Degree: PhD, Aerospace Engineering, 2013, Texas A&M University

URL: http://hdl.handle.net/1969.1/149437

► Unsteady shock wave propagation through ducts has many applications, ranging from blast wave shelter design to advanced high-speed propulsion systems. The research objective of this… (more)

▼ Unsteady shock wave propagation through ducts has many applications, ranging from blast wave shelter design to advanced high-speed propulsion systems. The research objective of this study was improved fundamental understanding of the transient flow structures during unsteady shock wave propagation through rectangular ducts with varying cross-sectional area. This research focused on the fluid dynamics of the unsteady shock-induced flow fields, with an emphasis placed on understanding and characterizing the mechanisms behind flow compression (wave structures), flow induction (via shock waves), and enhanced mixing (via shock-induced viscous shear layers). A theoretical and numerical (CFD) parametric study was performed, in which the effects of these parameters on the unsteady flow fields were examined: incident shock strength, area ratio, and viscous mode (inviscid, laminar, and turbulent). Two geometries were considered: the backward-facing step (BFS) geometry, which provided a benchmark and conceptual framework, and the splitter plate (SP) geometry, which was a canonical representation of the engine flow path. The theoretical analysis was inviscid, quasi-1D and quasi-steady; and the computational analysis was fully 2D, time-accurate, and viscous. The theory provided the wave patterns and primary wave strengths for the BFS geometry, and the simulations verified the wave patterns and quantified the effects of geometry and viscosity. It was shown that the theoretical wave patterns on the BFS geometry can be used to systematically analyze the transient, 2D, viscous flows on the SP geometry. This work also highlighted the importance and the role of oscillating shock and expansion waves in the development of these unsteady flows. The potential for both upstream and downstream flow induction was addressed. Positive upstream flow induction was not found in this study due to the persistent formation of an upstream-moving shock wave. Enhanced mixing was addressed by examining the evolution of the unsteady shear layer, its instability, and their effects on the flow field. The instability always appeared after the reflected shock interaction, and was exacerbated in the laminar cases and damped out in the turbulent cases. This research provided new understanding of the long-term evolution of these confined flows. Lastly, the turbulent work is one of the few turbulent studies on these flows. Advisors/Committee Members: Bowersox, Rodney DW (advisor), Karpetis, Adonios (advisor), North, Simon (committee member), Girimaji, Sharath (committee member), White, Edward (committee member).

Subjects/Keywords: unsteady fluid dynamics; shock diffraction over convex corners; sudden area enlargement; shock propagation through ducts; shock-induced flows; turbulent

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APA (6^th Edition):

Mendoza, N. R. (2013). On the Fundamental Unsteady Fluid Dynamics of Shock-Induced Flows through Ducts. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/149437

Chicago Manual of Style (16^th Edition):

Mendoza, Nicole Renee. “On the Fundamental Unsteady Fluid Dynamics of Shock-Induced Flows through Ducts.” 2013. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/149437.

MLA Handbook (7^th Edition):

Mendoza, Nicole Renee. “On the Fundamental Unsteady Fluid Dynamics of Shock-Induced Flows through Ducts.” 2013. Web. 04 Mar 2021.

Vancouver:

Mendoza NR. On the Fundamental Unsteady Fluid Dynamics of Shock-Induced Flows through Ducts. [Internet] [Doctoral dissertation]. Texas A&M University; 2013. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/149437.

Council of Science Editors:

Mendoza NR. On the Fundamental Unsteady Fluid Dynamics of Shock-Induced Flows through Ducts. [Doctoral Dissertation]. Texas A&M University; 2013. Available from: http://hdl.handle.net/1969.1/149437

Texas A&M University

25. Reyes, Dasia Ann. Advancing the Theoretical Foundation of the Partially-averaged Navier-Stokes Approach.

Degree: PhD, Aerospace Engineering, 2013, Texas A&M University

URL: http://hdl.handle.net/1969.1/149535

► The goal of this dissertation is to consolidate the theoretical foundation of variable-resolution (VR) methods in general and the partially-averaged Navier-Stokes (PANS) approach in particular.… (more)

▼ The goal of this dissertation is to consolidate the theoretical foundation of variable-resolution (VR) methods in general and the partially-averaged Navier-Stokes (PANS) approach in particular. The accurate simulation of complex turbulent flows remains an outstanding challenge in modern computational fluid dynamics. High- fidelity approaches such as direct numerical simulations (DNS) and large-eddy simulation (LES) are not typically feasible for complex engineering simulations with cur- rent computational technologies. Low-fidelity approaches such as Reynolds-averaged Navier-Stokes (RANS), although widely used, are inherently inadequate for turbulent flows with complex flow features. VR bridging methods fill the gap between DNS and RANS by allowing a tunable degree of resolution ranging from RANS to DNS. While the utility of VR methods is well established, the mathematical foundations and physical characterization require further development. This dissertation focuses on the physical attributes of fluctuations in partially-resolved simulations of turbulence. The specific objectives are to: (i) establish a framework for assessing the physical fidelity of VR methods to examine PANS fluctuations; (ii) investigate PANS simulations subject to multiple resolution changes; (iii) examine turbulent transport closure modeling for partially-resolved fields; (iv) examine the effect of filter control parameters in the limit of spectral cut-off in the dissipative region; and (v) validate low-Reynolds number corrections with RANS for eventual implementation with PANS. While the validation methods are carried out in the context of PANS, they are considered appropriate for all VR bridging methods. The key findings of this dissertation are summarized as follows. The Kolmogorov hypotheses are suitably adapted to describe fluctuations of partially-resolved turbulence fields, and the PANS partially-resolved field is physically consistent with the adapted Kolmogorov hypotheses. PANS adequately recovers the correct energetics in instances of multiple resolution changes. Scaling arguments are used to determine the correct transport closure model for a partially-resolved field in a boundary layer. The need to modify the fε filter control parameter for cut-off in the dissipation range is highlighted. A low-Reynolds number near-wall correction was evaluated on a RANS model with the intent of adapting to it VR methods. Overall, PANS shows promise as a theoretically sound modeling approach, and this work lays the foundation for future PANS investigations. Advisors/Committee Members: Girimaji, Sharath S. (advisor), Daripa, Prabir (committee member), Bowersox, Rodney D. W. (committee member), Cizmas, Paul G. A. (committee member).

Subjects/Keywords: PANS; Turbulence Modeling; Variable Resolution Methods; Bridging Methods

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APA (6^th Edition):

Reyes, D. A. (2013). Advancing the Theoretical Foundation of the Partially-averaged Navier-Stokes Approach. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/149535

Chicago Manual of Style (16^th Edition):

Reyes, Dasia Ann. “Advancing the Theoretical Foundation of the Partially-averaged Navier-Stokes Approach.” 2013. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/149535.

MLA Handbook (7^th Edition):

Reyes, Dasia Ann. “Advancing the Theoretical Foundation of the Partially-averaged Navier-Stokes Approach.” 2013. Web. 04 Mar 2021.

Vancouver:

Reyes DA. Advancing the Theoretical Foundation of the Partially-averaged Navier-Stokes Approach. [Internet] [Doctoral dissertation]. Texas A&M University; 2013. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/149535.

Council of Science Editors:

Reyes DA. Advancing the Theoretical Foundation of the Partially-averaged Navier-Stokes Approach. [Doctoral Dissertation]. Texas A&M University; 2013. Available from: http://hdl.handle.net/1969.1/149535

Texas A&M University

26. Tazraei, Pedram. Advancing Partially-Averaged Navier-Stokes Method in Wall-Bounded and Spatially Evolving Turbulence.

Degree: PhD, Mechanical Engineering, 2020, Texas A&M University

URL: http://hdl.handle.net/1969.1/191887

► Scale-resolving simulations (SRS) of turbulence offer a computationally viable alternative to direct numerical simulations (DNS) and large eddy simulations (LES) for many flows of engineering… (more)

▼ Scale-resolving simulations (SRS) of turbulence offer a computationally viable alternative to direct numerical simulations (DNS) and large eddy simulations (LES) for many flows of engineering interest. SRS seeks to achieve significant computational cost reduction over LES (large eddy simulations) by selective resolution of key coherent structures and modeling the remainder of the flow field using higher fidelity closures. SRS aims to provide significant improvements over Reynolds-averaged Navier-Stokes (RANS) method with only a reasonable increase in computational effort. The objective of this thesis is to advance bridging scale-resolving simulations to a state-of-the-art computational tool for the analysis, comprehension and prediction of turbulent flows of engineering interest. Toward this end, this thesis addresses key challenges facing SRS in near-wall subgrid closures, spatially-evolving flows and transition to turbulence. Scale-resolving simulations can be broadly classified into zonal (Z-SRS) and bridging (B-SRS) approaches. In Z-SRS different subgrid closure methods (e.g., RANS and LES) are used in different parts of the computational domain. One the other hand, B-SRS uses the same closure approach over the entire computational domain. The physical resolution (cut-off scale) of the subgrid model is controlled by changing the closure coefficients in a manner that is consistent with turbulence physics. The partially-averaged Navier-Stokes (PANS) method is a B-SRS approach that employs RANS-type two-equation (or better) closures that are suitably adapted to represent the required degree of spectral resolution. Three studies are undertaken in the thesis to advance PANS in wall-bounded flows with spatially-evolving turbulence and laminar-to-turbulence transition. Although all of the development is in the context of PANS, the findings of the thesis are generally applicable to other SRS methods. In the first study, equilibrium boundary layer (EBL) analysis is performed on the filtered turbulence to drive key closure models for scale resolving simulations (SRS) of turbulence. The objective is to convey the advantages of RANS near-wall closure modeling to SRS methodology. In the context of two-equation SRS turbulence closure, the EBL analysis of filtered-flow fields leads to closure models for turbulent transport of unresolved kinetic energy and dissipation as a function of degree of resolution. The resulting model is then employed to perform SRSPANS computations of a fully developed turbulent channel flow. It is demonstrated that PANS computations yield flow-field statistics that are consistent with filtered-field closure modeling assumptions. (This work has appeared in (1)). The second study aims to enhance the applicability and accuracy of SRS-PANS in fully-developed wall-bounded spatially-evolving turbulent flows. Scale resolving simulations of turbulence that employ two-equation subgrid closures require physically consistent boundary conditions for unresolved kinetic energy and dissipation (or frequency). Hence,… Advisors/Committee Members: Girimaji, Sharath S. (advisor), San Andres, Luis (advisor), Anand, Nagamangala (committee member), Daripa, Prabir (committee member), Donzis, Diego (committee member).

Subjects/Keywords: natural transition over flat plate; turbulent boundary layer; channel flow; wall-bounded turbulent flows; partially-averaged Navier-Stokes method; OpenFOAM; scale-resolving simulations; coherent structures

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APA (6^th Edition):

Tazraei, P. (2020). Advancing Partially-Averaged Navier-Stokes Method in Wall-Bounded and Spatially Evolving Turbulence. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/191887

Chicago Manual of Style (16^th Edition):

Tazraei, Pedram. “Advancing Partially-Averaged Navier-Stokes Method in Wall-Bounded and Spatially Evolving Turbulence.” 2020. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/191887.

MLA Handbook (7^th Edition):

Tazraei, Pedram. “Advancing Partially-Averaged Navier-Stokes Method in Wall-Bounded and Spatially Evolving Turbulence.” 2020. Web. 04 Mar 2021.

Vancouver:

Tazraei P. Advancing Partially-Averaged Navier-Stokes Method in Wall-Bounded and Spatially Evolving Turbulence. [Internet] [Doctoral dissertation]. Texas A&M University; 2020. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/191887.

Council of Science Editors:

Tazraei P. Advancing Partially-Averaged Navier-Stokes Method in Wall-Bounded and Spatially Evolving Turbulence. [Doctoral Dissertation]. Texas A&M University; 2020. Available from: http://hdl.handle.net/1969.1/191887

Texas A&M University

27. Mittal, Ankita. Evolution of Perturbations in High-speed Wall-bounded Flows: Flow-thermodynamic Interactions.

Degree: PhD, Aerospace Engineering, 2020, Texas A&M University

URL: http://hdl.handle.net/1969.1/191778

► The emergence of flow-thermodynamic interactions and dilatational velocity field renders the evolution of perturbations in high Mach number flows significantly different from those in incompressible… (more)

▼ The emergence of flow-thermodynamic interactions and dilatational velocity field renders the evolution of perturbations in high Mach number flows significantly different from those in incompressible flows. These effects have been reasonably well investigated in the linear and fully turbulent regimes however, further research is required to understand the effect of kinetic-internal energy exchange on fundamental nonlinear process of spectral evolution. The primary motivation of this work is to investigate the evolution of perturbations in hypersonic wall bounded Poiseuille flow and establish the effect of compressibility. The work performed addresses three important aspects of computation and prediction of perturbation evolution in high-speed flows: (i) framework for internal energy dynamics, (ii) verification of computational methods based directly on gas kinetic theory and, (iii) physical mechanisms for nonlinear breakdown towards turbulence. Three studies, each addressing the above objectives, are performed which lead to valuable advances in our ability to simulate a wide range of hypersonic flows and improve our understanding of the physical phenomenon occurring in high speed flows. The findings are particularly valuable for the transition phenomenon in hypersonic boundary layers. In the first study, critical mathematical framework to analyze and understand the nonlinear internal-kinetic energy interactions and subsequent spectral energy transfer is developed. The objective is to develop the framework and governing equations needed to analyze internal energy interactions and its spectral distribution in a manner similar to that of kinetic energy analysis. To emulate the role of velocity in kinetic energy analysis, a new variable (ϕ ∼ √p where p is pressure) is introduced to enable the examination of internal energy dynamics. Evolution equations for the mean and fluctuating components of ϕ are derived. These equations enable precise examination of mean–turbulent flow internal energy interactions, internal–kinetic energy exchange and spectral distribution of internal energy. The fundamental nature of flow instability changes with Mach number due to the underlying transformation in the nature of pressure. Therefore, a second study is performed with two-fold objectives, (i) characterize the instability modes in high Mach number Poiseuille flows using linear stability analysis (LSA) and, (ii) perform direct numerical simulations (DNS) of the instability development using a gas-kinetic method (GKM) solver for the purpose of code validation by comparison against LSA results. The LSA and DNS are performed for the case of Poiseuille flow over a range of Mach numbers from moderately supersonic to hypersonic speeds. First, LSA is employed to establish the instability characteristics over the range of Mach numbers. It is exhibited the Mach number range can be divided into different regimes based on the dominant mode type such as first, second or higher modes. Two sets of GKM-DNS are performed to corroborate the LSA… Advisors/Committee Members: Girimaji, Sharath S (advisor), Donzis, Diego (committee member), Karpetis, Adonios (committee member), Guermond, Jean-Luc (committee member).

Subjects/Keywords: Compressible wall-bounded flows; linear stability analysis

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APA (6^th Edition):

Mittal, A. (2020). Evolution of Perturbations in High-speed Wall-bounded Flows: Flow-thermodynamic Interactions. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/191778

Chicago Manual of Style (16^th Edition):

Mittal, Ankita. “Evolution of Perturbations in High-speed Wall-bounded Flows: Flow-thermodynamic Interactions.” 2020. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/191778.

MLA Handbook (7^th Edition):

Mittal, Ankita. “Evolution of Perturbations in High-speed Wall-bounded Flows: Flow-thermodynamic Interactions.” 2020. Web. 04 Mar 2021.

Vancouver:

Mittal A. Evolution of Perturbations in High-speed Wall-bounded Flows: Flow-thermodynamic Interactions. [Internet] [Doctoral dissertation]. Texas A&M University; 2020. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/191778.

Council of Science Editors:

Mittal A. Evolution of Perturbations in High-speed Wall-bounded Flows: Flow-thermodynamic Interactions. [Doctoral Dissertation]. Texas A&M University; 2020. Available from: http://hdl.handle.net/1969.1/191778

Texas A&M University

28. Praturi, Divya Sri. On the Stability of Magnetohydrodynamic Shear Flows: Characterization of Critical Pressure-Velocity-Magnetic-Field Interactions.

Degree: PhD, Aerospace Engineering, 2018, Texas A&M University

URL: http://hdl.handle.net/1969.1/174484

► Plasma shear flows are abundant in nature and frequently encountered in engineering applications. The stability characteristics of plasma shear flows are of much fundamental interest.… (more)

▼ Plasma shear flows are abundant in nature and frequently encountered in engineering applications. The stability characteristics of plasma shear flows are of much fundamental interest. Shear flows are susceptible to various algebraic and modal instabilities, i.e., velocity perturbations grow as a polynomial or an exponential function of time. It is well known in literature that background magnetic field applied along the flow direction and compressibility have a stabilizing influence on these shear instabilities. In this dissertation, a systematic investigation of the stabilization mechanisms is performed. This dissertation consists of three studies, each addressing a different type of free shear layer: Study 1 - homogeneously sheared flows in the incompressible regime; Study 2 - inhomogeneously sheared mixing layers in the incompressible regime; Study 3 - inhomogeneously sheared planar jets in the compressible regime. The common theme of all the studies investigate the nature of pressure-velocity-magnetic-field interactions that influence stabilizing mechanisms. For the case of homogeneous shear investigated in the first study, velocity perturbations in the absence of the magnetic field are susceptible to algebraic instability, i.e., kinetic energy contained in the perturbations (k) grows as, k ~ O(t^n). The stabilizing influence of magnetic field strength and perturbation orientation (β) on the instability is characterized using linear analysis and direct numerical simulations. Linear analysis indicates that the perturbation growth is dependent on the parameter, RvA ≡ VvAk/S, where, VvA, k and S are the Alfvén wave speed, initial wavenumber and mean flow shear, respectively. Analytical solutions for various perturbation energies at extreme RvA regimes – RvA» 1 and RvA « 1 – are derived and compared to numerical simulations. The behavior of perturbations at different RvA regimes and β values is also explicated using numerical simulations. In the second study, a tangent hyperbolic profile is chosen for the mean velocity field. Owing to the presence of an inflection point in the profile, the flow field is subjected to Kelvin-Helmholtz (KH) instability leading to exponential growth of perturbations, i.e., k ~ O(e^t). In the absence of any magnetic field (hydrodynamic limit), the precursor vortices form and roll up into a primary vortex. The primary vortex further entrains fluid leading to the onset of nonlinear asymptotic stage and formation of secondary vortex bands. We investigate the linear and nonlinear effects of magnetic field on this three-stage evolution of KH instability. Flow field features such as circulation, gauge pressure and perturbation energies are utilized to delineate the parameter space into strong, weak and intermediate magnetic-field stabilization regimes. The mechanisms of magnetic field stabilization in each of the three regimes is investigated using direct numerical simulations. In the third study, the evolution of pressure-, kinetic- and magnetic-perturbation energies for the case of… Advisors/Committee Members: Girimaji, Sharath S. (advisor), Donzis, Diego (committee member), Karpetis, Adonios (committee member), Guermond, Jean-Luc (committee member).

Subjects/Keywords: Magnetohydrodynamics; Shear flows

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

APA (6^th Edition):

Praturi, D. S. (2018). On the Stability of Magnetohydrodynamic Shear Flows: Characterization of Critical Pressure-Velocity-Magnetic-Field Interactions. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/174484

Chicago Manual of Style (16^th Edition):

Praturi, Divya Sri. “On the Stability of Magnetohydrodynamic Shear Flows: Characterization of Critical Pressure-Velocity-Magnetic-Field Interactions.” 2018. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/174484.

MLA Handbook (7^th Edition):

Praturi, Divya Sri. “On the Stability of Magnetohydrodynamic Shear Flows: Characterization of Critical Pressure-Velocity-Magnetic-Field Interactions.” 2018. Web. 04 Mar 2021.

Vancouver:

Praturi DS. On the Stability of Magnetohydrodynamic Shear Flows: Characterization of Critical Pressure-Velocity-Magnetic-Field Interactions. [Internet] [Doctoral dissertation]. Texas A&M University; 2018. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/174484.

Council of Science Editors:

Praturi DS. On the Stability of Magnetohydrodynamic Shear Flows: Characterization of Critical Pressure-Velocity-Magnetic-Field Interactions. [Doctoral Dissertation]. Texas A&M University; 2018. Available from: http://hdl.handle.net/1969.1/174484

Texas A&M University

29. Karimi, Mona. Compressibility Effects on the Kelvin-Helmholtz Instability and Mixing Layer Flows.

Degree: PhD, Mechanical Engineering, 2015, Texas A&M University

URL: http://hdl.handle.net/1969.1/161262

► The objective of the thesis is to analyze, understand and explicate the various physical mechanisms underlying the suppression of instability and mixing in compressible mixing… (more)

▼ The objective of the thesis is to analyze, understand and explicate the various physical mechanisms underlying the suppression of instability and mixing in compressible mixing layers. The investigation comprises of three studies which employ linear analysis and Direct Numerical Simulation (DNS). The first study examines the effect of compressibility on the underlying planar Kelvin-Helmholtz (KH) instability. The transformative influence of compressibility on the ubiquitous free shear-flow instability is investigated. This study focuses on the change in the character of pressure from a Lagrange-multiplier in incompressible flows to a thermodynamic variable in compressible flows. Linear analysis reveals that compressibility engenders the formation of a dilatational-interface-layer (DIL) within which the velocity perturbation is wave-like rather than vortical. Inherently unsteady dilatational action is shown to disrupt vortex merging and roll-up leading to suppression of KH instability. The second study examines the effect of perturbation alignment and non-linear interaction on the stability of compressible mixing layers. Linear analysis clearly shows that compressibility effects diminish with increasing obliqueness of the perturbation with respect to the shear plane. Notably, spanwise perturbations are impervious to Mach number effects. The non-linear effects are examined using DNS. It is shown that triadic interactions among the perturbation wavemodes lead to new perturbation wavemodes that are aligned closed to the spanwise directions and hence unstable. The third study examines mixing layer flow structure at various Mach numbers. At low speeds, the mixing layers exhibit strong spanwise rollers and short streamwise ribs. The effect of Mach number on the evolution of structures and the interaction between them are investigated in detail. With increasing Mach numbers, the spanwise rollers are suppressed. In the absence of spanwise rollers, the streamwise ribs align to form streamwise structures. Advisors/Committee Members: Girimaji, Sharath S (advisor), Ranjan, Devesh (advisor), Donzis, Diego A (committee member), Guermond, Jean-Luc (committee member), Petersen, Eric L (committee member), Reed, Helen L (committee member).

Subjects/Keywords: kelvin-Helmholtz instability; comressible mixing layers; shear flows; comressibility

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APA (6^th Edition):

Karimi, M. (2015). Compressibility Effects on the Kelvin-Helmholtz Instability and Mixing Layer Flows. (Doctoral Dissertation). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/161262

Chicago Manual of Style (16^th Edition):

Karimi, Mona. “Compressibility Effects on the Kelvin-Helmholtz Instability and Mixing Layer Flows.” 2015. Doctoral Dissertation, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/161262.

MLA Handbook (7^th Edition):

Karimi, Mona. “Compressibility Effects on the Kelvin-Helmholtz Instability and Mixing Layer Flows.” 2015. Web. 04 Mar 2021.

Vancouver:

Karimi M. Compressibility Effects on the Kelvin-Helmholtz Instability and Mixing Layer Flows. [Internet] [Doctoral dissertation]. Texas A&M University; 2015. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/161262.

Council of Science Editors:

Karimi M. Compressibility Effects on the Kelvin-Helmholtz Instability and Mixing Layer Flows. [Doctoral Dissertation]. Texas A&M University; 2015. Available from: http://hdl.handle.net/1969.1/161262

30. Ebersohn, Frans 1987-. Gas Kinetic Study of Magnetic Field Effects on Plasma Plumes.

Degree: MS, Aerospace Engineering, 2012, Texas A&M University

URL: http://hdl.handle.net/1969.1/148434

► Plasma flow physics in magnetic nozzles must be clearly understood for optimal design of plasma propulsion devices. Toward that end, in this thesis we: i)… (more)

▼ Plasma flow physics in magnetic nozzles must be clearly understood for optimal design of plasma propulsion devices. Toward that end, in this thesis we: i) perform an extensive literature survey of magnetic nozzle physics, ii) assess the validity of magnetohydrodynamics for studying magnetic nozzle physics, and iii) illustrate the effects of the Hall term in simple flows as well as in magnetic nozzle configurations through numerical experiments with the Magneto-Gas Kinetic Method (MGKM). The crucial steps necessary for thrust generation in magnetic nozzles are energy conversion, plasma detachment, and momentum transfer. These three physical phenomena must be understood to optimize magnetic nozzle design. The operating dimensionless parameter ranges of six prominent experiments are considered and the corresponding mechanisms are discussed. An order of magnitude analysis of the governing equations reveal: i) most magnetic nozzles under consideration operate at the edge of the continuum regime rendering continuum-based description and computation valid; ii) in the context of MHD framework, the generalized Ohm’s law must be used to capture all of the relevant physics. This work also continues the development of the Magneto Gas Kinetic Method (MGKM) computational tool. Validation of the solver is performed in shock-tube and Hartmann channel flows in the Hall physics regime. Comparison with theory and available data is made whenever possible. Novel numerical experiments of magnetic nozzle plasma jets in the Hall regime are performed, confirming the theoretically predicted azimuthal rotation of the plasma jet due to Hall physics. The primary conclusion from this work is that the addition of the Hall effect generates helical structures in magnetic nozzle plasma flows. Preliminary results are encouraging for future magnetic nozzle studies and further challenges are identified. Advisors/Committee Members: Girimaji, Sharath S (advisor), Staack, David (advisor), Shebalin, John V (committee member), Richard, Jacques (committee member).

Subjects/Keywords: energy; magneto; method; gas; kinetic; magnetohydrodynamics; Hall; detachment; propulsion; space; nozzle; magnetic; plasma

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

APA (6^th Edition):

Ebersohn, F. 1. (2012). Gas Kinetic Study of Magnetic Field Effects on Plasma Plumes. (Masters Thesis). Texas A&M University. Retrieved from http://hdl.handle.net/1969.1/148434

Chicago Manual of Style (16^th Edition):

Ebersohn, Frans 1987-. “Gas Kinetic Study of Magnetic Field Effects on Plasma Plumes.” 2012. Masters Thesis, Texas A&M University. Accessed March 04, 2021. http://hdl.handle.net/1969.1/148434.

MLA Handbook (7^th Edition):

Ebersohn, Frans 1987-. “Gas Kinetic Study of Magnetic Field Effects on Plasma Plumes.” 2012. Web. 04 Mar 2021.

Vancouver:

Ebersohn F1. Gas Kinetic Study of Magnetic Field Effects on Plasma Plumes. [Internet] [Masters thesis]. Texas A&M University; 2012. [cited 2021 Mar 04]. Available from: http://hdl.handle.net/1969.1/148434.

Council of Science Editors:

Ebersohn F1. Gas Kinetic Study of Magnetic Field Effects on Plasma Plumes. [Masters Thesis]. Texas A&M University; 2012. Available from: http://hdl.handle.net/1969.1/148434

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