Doctor of Philosophy, Case Western Reserve University, 2015, Macromolecular Science and Engineering

Computational studies have emerged as a key class of scientific approached to solving different problems of interest in the past few decades. Dissipative Particle Dynamics, DPD, a mesoscale simulation technique based on Molecular Dynamics has been established as a powerful technique in recovering a wide range of physical and chemical processes. Nevertheless, absence of robust bridge between the computational parameters to the physical characteristics of a system has limited applications of DPD. Thus in the second chapter of this dissertation (after a brief introduction and organizational guideline in chapter 1) a systematic study will be presented, providing several routes for setting the simulation parameters based on the real experimental measures. Although computational and theoretical works have always been a crucial areas of research in the rheology society, DPD has not been employed in rheological studies. This is mainly due to the fact that a step-by-step guideline does not exist for rheological measurements in DPD. Another reason for this lack of success in rheological community is that the built-in thermostat in DPD is not capable of providing a stable control over the thermodynamics of the system under flow conditions. Thus, firstly in chapter 3 different methods of viscosity measurement and rheological studies will be discussed in detail, and consequently in chapter 4 a novel thermostat is presented to modify the natural shortcomings of DPD under flow. For decades now, scientists across different disciplines have attempted at identifying the nature of versatile rheological response of colloidal suspensions. Exhibiting Newtonian behavior at very low, shear-thinning at intermediate, and shear-thickening at high flow rates in dense colloidal suspensions exemplifies a broad range of rheological regimes within a simple solid-liquid system. Despite numerous experimental and computational efforts in explaining the underlying mechanism of these behavior, there i (open full item for complete abstract)

Committee: Joao Maia (Advisor); Wnek Gary (Committee Member); Daniel Lacks (Committee Member); Michael Hore (Committee Member) Subjects: Chemical Engineering; Mechanical Engineering; Physics; Polymers

Master of Science (MS), Ohio University, 2024, Chemical Engineering (Engineering and Technology)

The objective of this research is to continue development of the flowtube, a new type of test equipment developed at the ICMT. Baseline testing is commonly used to validate models and ensure understanding of the electrochemical system. Baseline mass transfer experiments were performed using a rotating cylinder electrode (RCE). Baseline corrosion experiments were completed using an RCE as well as a rotating disk electrode (RDE). Mass transfer within the RDE system was also successfully modeled using computational fluid dynamics (CFD) software Ansys Fluent. Experimental and simulated results were validated using well known and accepted correlations. Validation of the CFD simulations is vital because no physical prototype for the flowtube currently exists to compare with the CFD results. The RDE simulations will serve as a baseline to prove that Fluent is capable of performing accurate mass transfer calculations and potentially future corrosion simulations. Current testing apparatuses for flowing environments tend to be large and/or difficult to use in a small-scale lab. To combat this, the flowtube cell can create a controlled single phase flow regime in a glass cell or autoclave and can test 3 samples at one time in its most recent revision. A new revision is currently being created, so the flowtube was modeled using CFD in order to determine how design alterations will affect the flowing environment within the glass cell. The flowtube hydrodynamics have been successfully modeled using Ansys Fluent. This model can illustrate fluid flow in the glass cell around the flowtube apparatus in both steady state and transient conditions. This model will continue to be expanded upon in the future to reflect the design considerations for the next prototype version. Design considerations and their impact on the hydrodynamics of the flowtube system were analyzed through this research.

Committee: Srdjan Nesic (Advisor); Marc Singer (Committee Member); Bruce Brown (Committee Member); Rebecca Barlag (Committee Member) Subjects: Chemical Engineering; Engineering; Fluid Dynamics

Doctor of Philosophy (PhD), Wright State University, 2023, Engineering PhD

In fluid flow experiments, there have been numerous techniques developed over the years to measure velocity. Most popular techniques are non-intrusive such as particle image velocimetry (PIV), but these techniques are not suitable for all applications. For instance, PIV cannot be used in examining in-vivo measurements since the laser is not able to penetrate through the patient, which is why medical applications typically use X-rays. However, the images obtained from X-rays, in particular digital subtraction angiography, are projective images which compress 3D flow features onto a 2D image. Therefore, when intensity techniques, such as optical flow method (OFM), are applied to these images the accuracy of the velocity measurements suffer from 3D effects. To understand the error introduced in using projective images, a vertical square tube chamber was constructed to achieve various water flow rates with variable dye injection points to perform dye visualization velocimetry (DVV). The results from DVV were compared with PIV measurements to quantify the error associated with DVV. Results from DVV were comparable with PIV, but a machine learning correction method, more specifically multilayer perceptron (MLP), was needed to adjust the DVV results. To train the MLP model, CFD simulations were conducted to generate detailed velocity distributions in the tube and projected dye images which would be used for DVV analysis and thus used as input for training. These CFD simulations were compared with PIV measurements and dye visualization images to validate proper boundary conditions and meshing. For the laminar case, MLP reduces the error associated with DVV from 35% down to 6.9%. When MLP was used to correct instantaneous DVV measurements for the turbulence cases, the error decreased from 22% to 9.8% for measurements 20 mm downstream of the dye inlet. For a time-averaged turbulent case, MLP was able to decrease the v-velocity error down to 5% and reduce the error of DVV by 5 (open full item for complete abstract)

Committee: Zifeng Yang Ph.D. (Advisor); George Huang Ph.D. (Committee Member); Philippe Sucosky Ph.D. (Committee Member); Hamed Attariani Ph.D. (Committee Member); Bryan Ludwig M.D. (Committee Member) Subjects: Engineering; Experiments; Mechanical Engineering

Master of Science, The Ohio State University, 2019, Aero/Astro Engineering

This thesis details aeroelastic response prediction of hoods on automobiles in the wake of a leading vehicle. Such conditions can lead to significant hood vibration due to the unsteady loads caused by vortex shedding. A primary focus is the sensitivity of the aeroelastic response to the aerodynamic modeling fidelity. This is assessed by considering both Reynolds-Averaged Navier-Stokes (RANS) and Detached Eddy Simulation (DES) flow models. The aeroelastic analysis is carried out by coupling a commercial computational Fluid dynamics (CFD) solver (StarCCM+) to a commercial computational structural dynamics (CSD) solver (Abaqus). Two different configurations are considered: 1) sedan-sedan and 2) sedan-SUV. This enables the consideration of both varied geometry and structural stiffness on the aeroelastic response. Comparisons between RANS and DES emphasize the importance of turbulence modeling fidelity in order to capture the unsteadiness of the flow and the vibration response of the hood. These comparisons include analysis of the lift forces, pressure loads on the hood, and Power Spectral Density Analysis (PSD) of the flow in the region between the two vehicles. As expected, DES predicts higher frequency content and significantly higher turbulence levels than RANS. Both the sedan and SUV hoods are sensitive to the turbulent fluctuations predicted by DES. The increased levels of turbulence result in up to 40 - 60% higher maximum peak to peak deformation and the excitation of a torsional mode of the hood for the sedan-sedan case. For the more flexible hood configuration (sedan - SUV), these differences are even higher, with maximum peak to peak deformations of up to 17 – 71% higher than the RANS solution.

Committee: Jack McNamara PhD (Advisor); Austin Kimbrell (Committee Member); Mei Zhuang PhD (Committee Member) Subjects: Aerospace Engineering; Automotive Engineering; Engineering

Doctor of Philosophy, The Ohio State University, 2017, Aero/Astro Engineering

Shock-boundary layer interactions (SBLIs) are ubiquitous occurrences in supersonic and hypersonic vehicles and have the tendency to inhibit their structural and aerodynamic performance. For example, in the inlets and isolators of such vehicles, the shock wave generated by one surface interacts with the boundary layer on an adjacent one. They are also present on the exterior of the vehicles, e.g. at the fuselage/vertical stabilizer junctions. These interactions cause unsteady separation, resulting in reduced air in-take efficiency, or unstart in extreme cases; unsteady vortex shedding which yields undesirable broadband noise; and significant pressure fluctuations which compromise the structural integrity of the vehicle and which can lead to loss of control authority. Mitigating these issues is therefore an important part of optimizing aerodynamic and structural design of high speed vehicles. The first step in this respect is obtaining a better understanding of the interaction unsteadiness. Nominally 2-D interactions have been studied extensively and have identified low-frequency shock motions which lead to undesirable pressure loads. The particular frequencies associated with the motions have been characterized using time resolved experiments and computations, and shown to depend on the mean size of the separation. The physical processes responsible for these frequencies are however still under investigation and the physical relationship between the shock motions and pulsations of the separation bubble remains obscure. For flow fields where the shock is swept, a complex 3-D interaction is encountered whose unsteady features are even less well understood. The mean structure of these 3-D interactions has been obtained experimentally and using RANS simulations, and shown to be profoundly different from the 2-D flow field indicating that progress in understanding 2-D interactions cannot be directly translated to 3-D. Specifically, there is no reci (open full item for complete abstract)

Committee: Datta Gaitonde (Advisor); Jen-Ping Chen (Committee Member); Jack McNamara (Committee Member); Mo Samimy (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics

Master of Science in Mechanical Engineering, Cleveland State University, 2016, Washkewicz College of Engineering

Seal whiskers have been found to produce unique wake flow structures that minimize self-induced vibration and reduce drag. The cause of these wake features are due to the peculiar three-dimensional morphology of the whisker surface. The whisker morphology can be described as an elliptical cross section with variation of diameter in the major and minor axis along the length and, angle of incidence, rotation of the elliptical plane with respect to the whisker axis, α at the peak and β at the trough. This research provided a more complete morphology characterization accomplished through CT scanning and analysis of 27 harbor and elephant seal whisker samples. The results of this study confirmed previously reported values and added a characterization of the angle of incidence finding that the majority of angles observed fall within ±5° and exhibit a random variation in magnitude and direction along the whisker length. While the wake effects of several parameters of the whisker morphology have been studied, the effect of the angle of incidence has not been well understood. This research examined the influence of the angle of incidence on the wake flow structure through series of water channel studies. Four models of whisker-like geometries based on the morphology study were tested which isolate the angle of incidence as the only variation between models. The model variations in angle of incidence selected provided a baseline case (α = β = 0°), captured the range of angles observed in nature (α = β = -5°, and α = β = -15°), and investigated the influence of direction of angle of incidence (α = -5°, β = -5°). The wake structure for each seal whisker model was measured through particle image velocimetry (PIV). Angle of incidence was found to influence the wake structure through reorganization of velocity field patterns, reduction of recovery length and modification of magnitude of Tu. The results of this research helped provide a more complete understanding of the seal wh (open full item for complete abstract)

Committee: Wei Zhang PhD (Advisor); Ibrahim Mounir PhD (Committee Member); Shyam Vikram PhD (Committee Member) Subjects: Aerospace Engineering; Aquatic Sciences; Engineering; Fluid Dynamics; Mechanical Engineering

Doctor of Philosophy (PhD), Ohio University, 2015, Biological Sciences (Arts and Sciences)

This study seeks to restore the internal anatomy within the nasal passages of dinosaurs via the use of comparative anatomical methods along with computational fluid dynamic simulations. Nasal airway descriptions and airflow simulations are described for extant birds, crocodylians, and lizards. These descriptions served as a baseline for airflow within the nasal passages of diapsids. The presence of shared airflow and soft-tissue properties found in the nasal passages of extant diapsids, were used to restore soft tissues within the airways of dinosaurs under the assumption that biologically unfeasible airflow patterns (e.g., lack of air movement in olfactory recess) can serve as signals for missing soft tissues. This methodology was tested on several dinosaur taxa. Restored airways in some taxa revealed the potential presence and likely shape of nasal turbinates. Heat transfer efficiency was tested in two dinosaur species with elaborated nasal passages. Results of that analysis revealed that dinosaur noses were efficient heat exchangers that likely played an integral role in maintaining cephalic thermoregulation. Brain cooling via nasal expansion appears to have been necessary for dinosaurs to have achieved their immense body sizes without overheating their brains.

Committee: Lawrence Witmer PhD (Advisor) Subjects: Anatomy and Physiology; Animal Sciences; Biology; Biomechanics; Fluid Dynamics; Paleontology; Scientific Imaging; Zoology

Doctor of Philosophy (PhD), Wright State University, 2015, Engineering PhD

Streamwise vortex-surface interactions can occur in aviation intentionally in the context of formation flight as an energy saving mechanism, unintentionally in wake crossings when aircraft fly in close proximity, and as a consequence of aircraft design through the interaction of fluid dynamics between different aerodynamic surfaces. The bulk of past work on streamwise vortex-surface interactions has focused on steady inviscid analysis for optimizing aerodynamic loads in the context of formation flight or experimental analysis on fin buffeting problems. A fundamental understanding of the viscous and unsteady effects that may occur is both important and currently lacking in the literature. This dissertation seeks to fill this need by using a high-fidelity implicit large-eddy simulation approach coupled with geometrically non-linear finite elements to identify and analyze important physics that may occur. Simple, canonical configurations are employed in order help disentangle the many interrelated factors of a very complex problem. Analysis of a tandem wing configuration elucidated mutual induction between the incident vortex from the leader wing and tip vortex of the follower wing that resulted in a broad taxonomy of flow structure, wake evolution, and unsteady behaviors for several lateral impingement locations. Interaction of an isolated streamwise vortex with a wing revealed a robust helical instability develops when a strong vortex impinges directly with the leading-edge. This spiraling behavior was found to occur as a result of the upstream influence of adverse pressure gradients provided by the wing that drive the vortex into its linearly unstable regime allowing for the growth of shortwave perturbations. Stability can be augmented through vertical positioning of the vortex. A negative offset can enhance stability by providing a stronger adverse pressure gradient while a positive offset exploits a favorable gradient and removes the upstream instability altogethe (open full item for complete abstract)

Committee: George Huang Ph.D. (Advisor); Joseph Shang Ph.D. (Committee Member); Zifeng Yang Ph.D. (Committee Member); Miguel Visbal Ph.D. (Committee Member); Aaron Altman Ph.D. (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

MS, University of Cincinnati, 2006, Engineering : Mechanical Engineering

Hydrofoils are used in maritime applications; such as ships and submarines, for stabilization, maneuvering, etc. In many of these applications, the hydrofoil may experience dynamic motion; an example would be an active-fin ship stabilization system where the hydrofoil oscillates periodically at large angles of attack. Computational Fluid Dynamics (CFD) is used for simulating the flow over an oscillating hydrofoil used in such systems. The CFD simulations for oscillating-hydrofoil flow are used in analysis of performance of the active-fin ship stabilization system. A system model has been created in MATLAB for this purpose. A Proportional Integral Derivative (PID) control system has also been developed to control the fin motion. Simulation of the active-fin ship-stabilization system in MATLAB provides the typical motion experienced by a hydrofoil used in ship stabilization. This motion is fed back to a CFD solver to determine the effect of non-sinusoidal oscillation on Lift, Drag and Moment of the hydrofoil. The aerodynamics of the non-sinusoidally oscillating hydrofoil is analyzed so as to find an optimum pitching motion for the hydrofoil so as to produce higher lift forces and thus provide better performance. Another important aspect which affects the performance of an active-fin ship stabilization system is cavitation occurring in the flow over oscillating hydrofoils. Cavitation occurs because the pressure on the suction side of the hydrofoil falls below the vapor pressure of water. Numerical simulations using Reynolds-averaged Navier-Stokes equations are carried out to analyze the effect of cavitation on the dynamic stall of an oscillating hydrofoil. It was found that the flow physics changes considerably with cavitation. The dynamic stall vortex (DSV) was formed at an angle of attack much smaller than that for the non-cavitating case. The vortical structures were found to be distorted as compared to the non-cavitating case. Cavitation led to large oscillations i (open full item for complete abstract)

Committee: Dr. Urmila Ghia (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2011, Mechanical Engineering

Otitis Media (OM) is a disease that is characterized by inflammation of the Middle Ear (ME) mucosa. This disease is the most frequent reason that children in the US are prescribed antibiotics, accounting for 25% of all prescriptions filled annually. It has been estimated that in the US, an annual health related cost of ~$4 billion is associated with the diagnosis and treatment of OM. Most past studies support a casual role for poor Eustachian Tube (ET) function in the pathogenesis of OM. Therefore, Chapters 2 through 5 focus research on developing new treatments for OM though a better understanding of ET function. The ET is a collapsible airway that connects the Nasopharynx (NP) with the Middle Ear (ME) and is primarily responsible for clearance and pressure regulation of the ME. In Chapters 2 and 3, we use decoupled fluid-structure interaction (FSI) models to simulate ET function. Then in Chapter 4, we then use fully coupled FSI models to better simulate the highly non-linear, transient behavior associated with ET function. During inflammatory OM, the epithelial cells that line the ET lumen can up-regulate the apical expression of mucus glycoproteins. These glycoprotien interactions lead to adhesion forces within the lumen that seals the ET closed, hindering the regulation function of the ET. In Chapter 5 we therefore develop computational models that include these adhesive bonds and investigate how they influence overall ET function. The adhesive forces were first characterized with steered molecular dynamics simulations and then integrated into the tissue scale models. In every case, ET function was shown to be independent of LVPM force magnitudes, while TVPM force magnitudes were always of critical importance. Tissue mechanics, i.e., Young's modulus of both the cartilage and PMT tissue, were also shown to have a significant effect on ET function in all cases. Chapter 5 specifically shows that the ET is highly sensitive to these adhesive forces and different leve (open full item for complete abstract)

Committee: Samir Ghadiali PhD (Advisor); Richard Hart (Committee Member); Alan Litsky (Committee Member); Robert Siston (Committee Member) Subjects: Biomedical Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2005, Mechanical Engineering

The role of compressibility on the convective velocity of large-scale structures in axisymmetric jets is studied using a home-built pulse burst laser system and newly developed high-repetition rate experimental diagnostics. A pulse burst laser system was designed and constructed with the ability to produce a burst of short duration (10 nsec), high energy (order of 10 -100 mJ/pulse) pulses over a ~150 microsecond period with inter-pulse timing as low as 1 microsecond (1 MHz). The application of the pulse burst laser for flow measurements was investigated through the development of MHz rate flow visualization and MHz rate planar Doppler velocimetry (PDV). MHz rate PDV is a spectroscopic technique that produces 28 time-correlated realizations of the velocity over a plane with a maximum repetition rate of up to 1 MHz and accuracies on the order of 5%. Space-time correlations were used to track structures within the flow field and determine their convective velocity. Data produced using flow visualization images agrees with previous research and indicates a strong departure of the convective velocity from theory. Data produced using velocity data, however, shows starkly different trends and does not produce the same measurements of convective velocity. This difference in measurement is attributed to a misinterpretation of the use of space-time correlation for tracking structures. The presence of a distinct boundary between the mixing layer and the jet core as well as the mixing layer and ambient air in the flow visualization data and some of the velocity data leads to a bias in the measurement. The space-time correlation is found to preferentially follow these boundaries, thus leading to faster and/or slower measurements of convective velocity. For the Mach 2.0 jet, velocity data was obtained with seed particles marking the jet core and the mixing layer, but not the ambient air. This lack of velocity measurements on the low-speed side of the jet's mixing layer biased the (open full item for complete abstract)

Committee: Mo Samimy (Advisor) Subjects:

Master of Science, University of Akron, 2013, Mechanical Engineering

Numerical simulations of magnetohydrodynamic (MHD) hypersonic flow are presented for both laminar and turbulent flow over a cylinder and flow entering a scramjet inlet. ANSYS CFX is used to carry out calculations for steady flow at hypersonic speeds (Mach number > 5). The low magnetic Reynolds number (<<1) calculated based on the velocity and length scales in this problem justifies the quasistatic approximation, which assumes negligible effect of velocity on magnetic fields. Therefore the governing equations employed in the simulations are the compressible Navier-Stokes and the energy equations with MHD-related source terms such as Lorentz force and Joule dissipation. Turbulence effects are accounted for when applicable and multiple turbulence models are compared. The results demonstrate the ability of the magnetic field to affect the flowfield, and variables such as location and magnitude of the applied magnetic field are examined. An examination of future work is provided through the implementation of a semi-discrete central scheme in-house code toward the solution of the Orszag-Tang vortex system.

Committee: Abhilash Chandy Dr. (Advisor); Scott Sawyer Dr. (Committee Member); Alex Povitsky Dr. (Committee Member) Subjects: Aerospace Engineering; Engineering; Fluid Dynamics; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2017, Physics

Local momentum anisotropies are large in the early stages of the quark-gluon plasma created in relativistic heavy-ion collisions, due to the extreme difference in the initial longitudinal and transverse expansion rates. In such situations, fluid dynamics derived from an expansion around an isotropic local equilibrium state is bound to break down. Instead, we resum the effects of the slowest nonhydrodynamic degree of freedom (associated with the deviation from momentum isotropy) and include it at leading order, defining a local anisotropic quasi-equilibrium state, thereby treating the longitudinal/transverse pressure anisotropy nonperturbatively. Perturbative transport equations are then derived to deal with the remaining residual momentum anisotropies. This procedure yields a complete transient effective theory called viscous anisotropic hydrodynamics. We then show that the anisotropic hydrodynamic approach, especially after perturbative inclusion of all residual viscous terms, dramatically outperforms viscous hydrodynamics in several simplified situations for which exact solutions exist but which share with realistic expansion scenarios the problem of large dissipative currents. Simulations of the full three-dimensional dynamics of the anisotropic quark-gluon plasma are then presented.

Committee: Ulrich Heinz (Advisor); Michael Lisa (Committee Member); Yuri Kovchegov (Committee Member); Junko Shigemitsu (Committee Member) Subjects: Physics

Doctor of Philosophy, The Ohio State University, 1966, Graduate School

Committee: Not Provided (Other) Subjects: Engineering

Doctor of Philosophy, The Ohio State University, 2016, Aero/Astro Engineering

A novel analysis technique is developed for the time-accurate analysis of noise sources in compressible jet flows. By adopting a Lagrangian point of view, the finite-time Lyapunov exponent (FTLE) method provides a means of linking discrete events in the vicinity of a high-subsonic jet shear layer to aft- and sideline-radiated noise. The FTLE is first validated in the compressible flow regime, as it was originally developed for incompressible flows, where it has shown substantial success in analyzing the dynamics of Lagrangian coherent structures. It is demonstrated by theoretical and numerical experiments that judicious choice of temporal intergration parameters highlights distinct features in the flow field. Due to the non-solenoidal nature of compressible flows, Lagrangian FTLE coefficients computed in forward and backward time can extract wave dynamics from the velocity field in addition to the flow-organizing convective features. Integration time, thus, acts as a pseudo-filter, smoothly separating coherent (convective) structures from propagating waves. Results are confirmed by first examining forward and backward FTLE coefficients for several simple, well-known acoustic fields and in the propagation of a two-dimensional acoustic pulse. Each coefficient is shown to capture a distinct portion of the traveling acoustic waves, with the forward FTLE (sf) focusing on the positive stroke and the negative portion extracted by the backward- integrated (sb) coefficient. Analysis of the mono-chromatic acoustic flow fields shows the peak FTLE magnitudes directly scale with the acoustic frequency and a complete reconstruction of the underlying dilatational field can be achieved by conducting the Lagrangian analysis over a single time step for each time instant. An increase in integration time subsequently leads to both damping and phase-shifting of the resolved acoustic waves as a consequence of the contribution from multiple temporal snapshots. Having established the (open full item for complete abstract)

Committee: Datta Gaitonde (Advisor); Jen-Ping Chen (Committee Member); Mark Lewis (Committee Member); Mohammad Samimy (Committee Member); Mei Zhuang (Committee Member) Subjects: Aerospace Engineering

Master of Science, University of Toledo, 2014, Mechanical Engineering

Helicopters and other Vertical Take-Off or Landing (VTOL) vehicles exhibit an interesting combination of structural dynamic and aerodynamic phenomena which together drive the rotor performance. The combination of factors involved make simulating the rotor a challenging and multidisciplinary effort, and one which is still an active area of interest in the industry because of the money and time it could save during design. Modern tools allow the prediction of rotorcraft physics from first principles. Analysis of the rotor system with this level of accuracy provides the understanding necessary to improve its performance. There has historically been a divide between the comprehensive codes which perform aeroelastic rotor simulations using simplified aerodynamic models, and the very computationally intensive Navier-Stokes Computational Fluid Dynamics (CFD) solvers. As computer resources become more available, efforts have been made to replace the simplified aerodynamics of the comprehensive codes with the more accurate results from a CFD code. The objective of this work is to perform aeroelastic rotorcraft analysis using first-principles simulations for both fluids and structural predictions using tools available at the University of Toledo. Two separate codes are coupled together in both loose coupling (data exchange on a periodic interval) and tight coupling (data exchange each time step) schemes. To allow the coupling to be carried out in a reliable and efficient way, a Fluid-Structure Interaction code was developed which automatically performs primary functions of loose and tight coupling procedures. Flow phenomena such as transonics, dynamic stall, locally reversed flow on a blade, and Blade-Vortex Interaction (BVI) were simulated in this work. Results of the analysis show aerodynamic load improvement due to the inclusion of the CFD-based airloads in the structural dynamics analysis of the Computational Structural Dynamics (CSD) code. Improvements came (open full item for complete abstract)

Committee: Chunhua Sheng Ph.D. (Advisor); Abdeh Afjeh Ph.D. (Committee Member); Ray Hixon Ph.D. (Committee Member); Glenn Lipscomb Ph.D. (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Master of Science in Engineering (MSEgr), Wright State University, 2011, Mechanical Engineering

A high/variable-order numerical simulation procedure for gas dynamics problems was developed to model steep grading physical phenomena. Higher order resolution was achieved using an orthogonal polynomial Gauss-Lobatto grid, adaptive polynomial refinement and artificial diffusion activated by a pressure switch. The method is designed to be computationally stable, accurate, and capable of resolving discontinuities and steep gradients without the use of one-sided reconstructions or reducing to low-order. Solutions to several benchmark gas-dynamics problems were produced including a shock-tube and a shock-entropy wave interaction. The scheme's 1st-order solution was validated in comparison to a 1st-order Roe scheme solution. Higher-order solutions were shown to approach reference values for each problem. Uniform polynomial refinement was shown to be capable of producing increasingly accurate solutions on a very coarse mesh. Adaptive polynomial refinement was employed to selectively refine the solution near steep gradient structures and results were nearly identical to those produced by uniform polynomial refinement. Future work will focus on improvements to the diffusion term, complete extensions to the full compressible Navier-Stokes equations, and multi-dimension formulations.

Committee: George Huang PhD (Advisor); George Huang PhD (Committee Member); Joseph Shang PhD (Committee Member); Miguel Visbal PhD (Committee Member) Subjects: Fluid Dynamics; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2007, Mechanical Engineering

The present research examines the relationship between the large-scale structure dynamics of a jet and the far-field sound. This was achieved by exploring the flowfield and the far field of an axisymmetric Mach 0.9 jet with a Reynolds number of approximately 0.76 million. The jet is controlled by eight plasma actuators, which operate over a large frequency range and have independent phase control allowing excitation of azimuthal modes (m) 0, 1, 2, and 3. The jet's far field is probed with a microphone array positioned at 30 degrees with respect to the downstream jet axis. The array is used to estimate the origin of peak sound events in space, and find the sound pressure level (SPL) and overall sound pressure level (OASPL). The lower forcing Strouhal numbers (StDF's) increase the OASPL and move noise sources upstream while higher StDF's decrease the OASPL and have noise source distributions similar to the baseline jet. The flowfield was investigated using particle image velocimetry (PIV). A Reynolds decomposition of the PIV data emphasized the importance of the streamwise velocity fluctuations for the symmetric azimuthal modes (m = 0 and 2) and the cross-stream velocity fluctuations for the asymmetric azimuthal modes (m = 1 and 3). A proper orthogonal decomposition of the PIV data was performed to extract information about how forcing affects the large-scale flow features and conditionally average the PIV data. When forcing at StD's other than the preferred mode, the conditional-averaged images show large-scale flow features that grow, saturate, and decay closer to the nozzle exit. When exciting a symmetric azimuthal mode, m = 0, near the preferred StDF, the streamwise phase-averaged velocity grows quickly and saturates over a relatively long spatial range. When exciting an asymmetric azimuthal mode, m = 1, near the preferred StDF, the cross-stream phase-averaged velocity grows slowly, saturates, and then decays relatively quickly. The noise source distribution occur (open full item for complete abstract)

Committee: Mo Samimy (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy, Case Western Reserve University, 2006, Mechanical Engineering

A multiphase lattice Boltzmann method (MLBM) based on the HSD model has been adapted for the solution of multiphase fluid dynamics problem. The interactions between particles are expressed through a mean-field approximation and exclusion-volume effect. The behavior of interface is obtained as part of the solution of the lattice Boltzmann equations. No a priori assumptions and artificial treatment are made regarding the shape and dynamic roles of the interface. Interfacial tension dynamics is validated through a series of test running of three-dimensional wave dispersion. The MLBM is also extended to thermal multiphase LBM (TMLBM) which includes the effects of interfacial tension and its dependence on temperature by a hybrid scheme. The key point for this scheme is combining a micro-scale description of the flow with a macroscopic energy transport equation. Applying the TMLBM, a systematic investigation of fluid dynamics in a two-layer immiscible fluid system is undertaken starting with Rayleigh-Benard convection. A parametric study of the effects of thermally induced density change, buoyancy, surface tension variation with temperature on interface dynamics, flow regimes and heat transfer is presented. Further investigation of TMLBM is applied to a two-layer immiscible fluid system with density inversion in which density inverse assumption holds for the lower layer fluid. The evaluation of the effects of density distribution parameter, Rayleigh number, size aspect ratio and Marangoni number on convection flow and heat transfer is presented. Interaction between gravity-induced and vibration-induced thermal convection in a two-layer fluid system has also be studied by TMLBM. The vibrations considered correspond to sinusoidal translations of a rigid cavity at a fixed frequency and is parallel to temperature gradient. The ability of applied vibration to enhance the flow, heat transfer and interface distortion is investigated. Comparisons of two-phase fluid system with si (open full item for complete abstract)

Committee: J. Iwan D. Alexander (Advisor) Subjects:

Master of Science in Aerospace Systems Engineering (MSASE), Wright State University, 2024, Mechanical Engineering

The development of high order numerical schemes has been instrumental in advancing computational fluid dynamics (CFD), particularly for applications requiring high resolution of discontinuities and complex flow phenomena prevalent in high-speed flows. This thesis introduces the Pade-ENO scheme, a high-order method that integrates Essentially Non-Oscillatory (ENO) techniques with compact Pade stencils to achieve superior accuracy, up to 7th order, while maintaining stability in harsh environments. The scheme's performance is evaluated through benchmark tests, including the advection equation, Burgers' equation, and the Euler equations. For high Mach number flows, such as the sod shock tube the Pade-ENO method demonstrates its ability to resolve sharp gradients and discontinuities with no smoothing required. Numerical results highlight the scheme's robustness and its potential as a powerful tool for high-speed aerodynamic simulations, paving the way for future advancements in CFD modeling.

Committee: George Huang Ph.D., P.E. (Advisor); Jose Camberos Ph.D., P.E. (Committee Member); Nicholas Bisek Ph.D. (Committee Member); James Menart Ph.D. (Other) Subjects: Aerospace Engineering; Engineering; Fluid Dynamics; Mathematics; Mechanical Engineering