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1. Gandhi, Kandukuri Diffusion and chemical reaction of a liquid in laminar flow between parallel plates /

Master of Science, The Ohio State University, 1965, Graduate School

Committee: Not Provided (Other) Subjects:

2. Cretcher, Charles The pressure rise associated with shock-induced laminar boundary layer separation /

Master of Science, The Ohio State University, 1963, Graduate School

Committee: Not Provided (Other) Subjects:

3. De Laney, Robert An analysis of the effects of an applied electric field on heat transfer to an ionized dense gas in laminar pipe flow /

Master of Science, The Ohio State University, 1967, Graduate School

Committee: Not Provided (Other) Subjects:

4. Eiswirth, Edward A study of shock tube generated conical flowfields /

Master of Science, The Ohio State University, 1969, Graduate School

Committee: Not Provided (Other) Subjects:

5. Jones, Kenneth Experimental study of the boundary layer flow on a hovering helicopter rotor using flow visualization /

Master of Science, The Ohio State University, 1968, Graduate School

Committee: Not Provided (Other) Subjects:

6. Kerestes, Jared Using Unsupervised Machine Learning to Reduce the Energy Requirements of Active Flow Control

Doctor of Philosophy (PhD), Wright State University, 2024, Engineering PhD

It is generally accepted that there exist two types of laminar separation bubbles (LSBs): short and long. The process by which a short LSB transitions to a long LSB is known as bursting. In this research, large eddy simulations (LES) are used to study the evolution of an LSB that develops along the suction surface of the L3FHW-LS at low Reynolds numbers. The L3FHW-LS is a new high-lift, high-work low-pressure turbine (LPT) blade designed at the Air Force Research Laboratory. The LSB is shown to burst over a critical range of Reynolds numbers. Bursting is discussed at length and its effect on transition, vortex shedding, and profile loss development are analyzed in depth. The results of these analyses make one point very clear: the effects of bursting are non-trivial. That is, long LSBs are not just longer versions of short LSBs. They are phenomena unto themselves, distinct from short LSBs in terms of their vortex dynamics, profile loss footprint, time-averaged topology, etc. This work culminates in a demonstration of how, with the aid of unsupervised machine learning, these differences can be leveraged to reduce the energy requirements of steady vortex generator jets (VGJs). Relative to pulsed VGJs, steady VGJs require significantly more energy to be effective but are more realistic to implement in actual application. By tailoring VGJ actuation to LSB type (i.e., actuating differently in response to a long LSB than to a short LSB), it is shown that significant energy savings can be realized.

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Committee: Mitch Wolff Ph.D. (Advisor); George Huang Ph.D. (Committee Member); John Clark Ph.D. (Committee Member); Christopher Marks Ph.D. (Committee Member) Subjects: Fluid Dynamics

7. Goparaju, Hemanth Numerical Investigation of Fundamental Mechanisms in Hypersonic Transition to Turbulence

Doctor of Philosophy, The Ohio State University, 2022, Aerospace Engineering

Laminar-to-turbulent transition estimation is one of the key challenges in designing hypersonic vehicles, primarily due to uncertainties in the disturbance environment and the enormous parametric space involved. A comprehensive understanding of the underlying physical processes is lacking, hindering the development of efficient control strategies. In particular, the role of leading-edge bluntness during various stages of transition remains unresolved, which is of practical relevance. This thesis documents a series of five complementary numerical studies aimed at understanding the laminar-to-turbulent transition process on hypersonic flat plates with varying leading edge bluntness. Direct numerical simulations are used to accurately resolve the spatio-temporal scales of the flows. These are complemented with physics and data-driven techniques to gain insight into the flow fields. The first study investigates the role of leading-edge bluntness in the receptivity of broadband freestream disturbances and their linear amplification mechanisms. At small nose radii, the disturbances trigger Mack modes, whose growth rate reduces with increasing bluntness. After a critical radius, waves of a different class with predominant support in the entropy layer are amplified. With increasing bluntness, the amplification rates of these disturbances increase. In the second study, the laminar-to-turbulent transition on a sharp flat plate is examined with stochastic freestream forcing. Second-mode waves are most amplified, followed by their fundamental resonance and finally the onset of turbulence. During various stages of the transition, acoustic and vortical dissipation dominate the wall heating, and near-wall streaks enhance the skin-friction. The third study scrutinizes the characteristics of the late stages of transition by triggering an isolated bypassed turbulent spot on a hypersonic flat plate, and examines its evolution with the momentum potential theory. Mack (open full item for complete abstract)

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Committee: Datta Gaitonde Prof (Advisor); Jack McNamara Prof (Committee Member); Lian Duan Prof (Committee Member) Subjects: Aerospace Engineering

8. Hirt, David Numerical Studies of Natural Convection in Laterally Heated Vertical Cylindrical Reactors: Characteristic Length, Heat Transfer Correlation, and Flow Regimes Defined

Doctor of Philosophy, University of Akron, 2022, Mechanical Engineering

Natural convection in laterally heated vertical cylindrical enclosures (LHVCE) has been studied in the past; however, few studies have thoroughly investigated the characteristic length scales. The studied parameters of this enclosure included: the heated and cooled length, diameter, aspect ratio, hot cold wall temperature difference, and the fluid properties. The characteristic length and form of two correction functions were derived from a logical set of assumptions based upon the enclosure configuration. Utilizing the derived dimensionless functions and length scale in conjunction with numerical simulation results, a best fit correlation was formed. The correlation, a first of its kind for this geometry, successfully predicted heat transfer and the flow regime changes from laminar to turbulence. The correlation and the underlying foundation from which it was formed showed to be in agreement with other similar studies. This study then proceeded from enclosures to internal reactor configurations containing baffles. The baffles were grouped into three geometries: rings, single hole openings, and a uniquely shaped (flow enhancing) baffle. The dimensions of each baffle were parametrically varied, typically by scaling the openings; and the velocity and temperature contour results of the simulations are presented. It was found that the central hole and shaped baffle exhibited more desirable flow patterns and thermal environments than the ring baffles. The final portion of the study investigated the effect of the porous media within the enclosure. The porous media cannot be studied independently, thus, two baffles from the previous investigation were utilized for the porous media. Three porous media configurations were studied: homogenous block, extruded concentric rings, and disks. Each of the basic configurations were laid out with a set of scaling parameters and were simulated parametrically in conjunction with the two baffles. The resistance of the porous media was (open full item for complete abstract)

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Committee: Nicholas Garafolo (Advisor); Minel Braun (Advisor); Sergio Felicelli (Committee Chair); Alex Povitsky (Committee Member); Scott Sawyer (Committee Member); Kevin Kreider (Committee Member); Edward Evans (Committee Member) Subjects: Engineering

9. Jana Maiti, Chandrima Numerical Characterization of Turbulence-driven Secondary Motions in Fully-developed Single-phase and Stratified Flow in Rectangular Ducts

PhD, University of Cincinnati, 2021, Engineering and Applied Science: Mechanical Engineering

The pivot of this dissertation is the numerical analysis of turbulence-driven secondary motions in rectangular ducts, fully and partially filled with water. Flow through horizontal ducts are characterized by a unique flow pattern known as secondary flow of the second kind or ‘Nikuradse' flow who first discovered them in 1926, while working under Prandtl. The secondary flows are 1-2% of the axial flow and are in addition, and perpendicular, to the axial flow. Despite their weak strength, the secondary motions significantly influence stress distribution and scalar transport such as heat transfer. The mean secondary flow consists of four pairs of counter-rotating vortices, anti-symmetric about the diagonal bisector and each pair is flanked by a shear layer on the intersecting side walls. Turbulence-driven secondary flow in straight ducts appears only above a critical Reynolds number. These are absent in the laminar regime. From this perspective, the aim of the present study is to investigate the appearance and evolution of turbulence-driven secondary motions in a square cross-section duct near the transition, and explore their asymptotic behavior for high Reynolds number, Re. We perform a numerical experiment which involves calculating the flow in a square duct over100=Re=50,000. At a critical Reynolds number Rec = 704, the flow becomes turbulent, with the pressure drop, dp/dx, discontinuously increasing and a weak cross-flow discontinuously developing. The cross-flow may be quantified by the circulation in each octant of the duct. For Re > 2500, the bulk Nikuradse vortex contributes ~ 9/5 and the wall vorticity ~ -4/5 to the circulation. A sub-class of turbulent duct flow is turbulent flow through open ducts or partially-filled ducts. Flow through an open or partially-filled duct is characterized by the presence of an air-water interface interacting with a solid wall, forming a mixed-boundary corner. A novel feature of the mixed-boundary corner i (open full item for complete abstract)

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Committee: Urmila Ghia Ph.D. (Committee Chair); Leonid Turkevich (Committee Member); Milind Jog Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Mechanical Engineering

10. Sharma, Anshu Numerical Investigation of a Swirl Induced Flameless Combustor for Gas Turbine Applications

MS, University of Cincinnati, 2020, Engineering and Applied Science: Aerospace Engineering

With increasing air traffic and energy requirements; and the fast deteriorating environment, time to explore new, greener and efficient combustion techniques is now. Flameless combustion (FC) is one such regime, being investigated for applications to of Gas Turbines. It is characterized by presence of well distributed reaction zones, absence of temperature peaks and a strong turbulence-chemistry interaction. High levels of turbulence facilitating faster mixing compared to the reaction rates, oxidizer at temperature higher than the auto-ignition temperature of the air-fuel mixture, low equivalence ratios (φ) are some pre-requisites to obtaining FC. High efficiency, low NOx, low combustion noise and improved stability are some advantages of FC, which have been established through experimental and numerical studies. The study outlined here is a continuation of previous FC studies carried out at the Gas Dynamics and Propulsion Lab (GDPL), University of Cincinnati where the distributed vortex burner, designed to operate at typical gas turbine conditions was found to exhibit FC at lean operating conditions. The current study aims to scale down this burner while retaining FC characteristics. Additonally, three new designs, C2B, C3B and C9B,were proposed to improve fuel entrainment in the central recirculation zone (CRZ) with non-intrusive fuel injection tubes while retaining flameless characteristics. These designs differ only in the angle and location of fuel injection. For this study, non-reacting and reacting flow simulations were carried out using STAR-CCM+. Turbulence was modeled using the Realizable k-ε model while complex chemistry Laminar Flame Concept (LFC) approach was used for transport of chemical species simulation. San Diego mechanism with 57 species and 268 reactions was used to provide a high-fidelity chemistry model for the combustion of gaseous Propane. The choice of numerical models was validated against experimental data from GDPL and was foun (open full item for complete abstract)

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Committee: Ephraim Gutmark Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Rodrigo Villalva Gomez Ph.D. (Committee Member) Subjects: Aerospace Materials

11. Enayati, Hooman NUMERICAL FLOW AND THERMAL SIMULATIONS OF NATURAL CONVECTION FLOW IN LATERALLY-HEATED CYLINDRICAL ENCLOSURES FOR CRYSTAL GROWTH

Doctor of Philosophy, University of Akron, 2019, Mechanical Engineering

Light industry has been revolutionized by using light emitting diodes, high power, and high-frequency devices. The base of this revolution relies on the usage of crystals such as gallium nitride (GaN). There are three main crystal growth techniques; Hydride Vapor Phase Epitaxy (HVPE), Amonothermal Crystal Growth and Solution Growth. Ammmonothermal crystal growth is the most effective method for growing high-quality GaN crystals. Gallium nitride crystals are dissolved and transported by natural convection and then deposited on the seeds in the reactor in a process that requires high temperatures (315C to 760C), as well as high-pressure environments (1000 to 3000 atm). Fluid flow study in such a domain is expensive and has its own experimental difficulties. Yet, experimental results are essentials to validate the numerical simulations. The first part of the present work, aims at establishing the threshold parameters for dynamic and geometric similitude (based on the Rayleigh number (Ra)), for natural convection in a cylindrical enclosure heated laterally. Ra considered for this purpose spanned a range between 750 and 8.8e8, where the characteristic length, L, used in its definition is represented by the ratio of cylindrical enclosure's volume to its lateral surface area (R/2). The commercial CFD code, ANSYS FLUENT is used to model a 2-D axisymmetric cylindrical geometry using the laminar and k-w SST turbulent solvers. When comparatively analyzed, the results allowed conclusions associating values of the Ra to flow development from laminar to transitional and to turbulent flow. The next part of the present work aims to investigate the effects of using different RANS models (k-e and k-w), in ANSYS FLUENT, on the fluid and thermal maps for a fixed Ra of 8.8e6, with similar thermal and geometrical boundary conditions using the 2-D axisymmetric model. The results will provide an overall insight into the differences and how a new turbulent model can potentially change (open full item for complete abstract)

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Committee: Minel. J. Braun PhD (Advisor); Alex Povitsky PhD (Committee Member); Scott Sawyer PhD (Committee Member); George Chase PhD (Committee Member); Kevin. L. Kreider PhD (Committee Member) Subjects: Mechanical Engineering

12. Hirt, David Parametric Study via Numerical Simulations of Natural Convection in Laterally Heated Cylindrical Enclosures: Investigating Characteristic Length

Master of Science, University of Akron, 2018, Mechanical Engineering

This study numerically investigates the laterally heated vertical cylinder and the length scale associated with this reactor. For natural convection the important dimensionless characteristic is the Rayleigh number, which predicts the flow regime as laminar, transitional, or turbulent. The Rayleigh number is useful as a design tool for scaling a reactor. Up to this point the associated length scale has been assumed as various definitions of length and diameter and has not yet been thoroughly investigated. The current assumed definitions for the length scale: height, diameter, and volume to lateral surface area, are directly studied in a multi-dimensional (2D and 3D) numerical parametric study involving these length scales and aspect ratio (height/diameter). Other important characteristics such as the ratio of heating to cooling and thickness of the divider (insulator) between heating and cooling are also studied. The study begins with turbulent transient 2D axisymmetric simulations and proceeds to turbulent transient 3D simulations then compares the 3D and 2D simulations. Finally, 2D and 3D laminar simulations are investigated. Presented are the results of the fluid flow speeds, thermal environments, flow patterns, boundary layer thickness, boundary layer velocity, and normal probability density functions which provide a unique way of studying how the Rayleigh number is influenced by variables. The numerical simulations are examined for spatial step, time step, and relative convergence by a mesh study, time step study, and thermal analysis, respectively. The turbulence model used (k-ω SST) is based on recent published studies. All simulations were conducted with the commercially available software ANSYS FLUENT. Findings are discussed when they prove significant, and aid in developing a fundamental understanding of the physics occurring inside this reactor setup. The results indicate that the current the length scales assumed for this reactor are incorrec (open full item for complete abstract)

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Committee: Braun Minel J (Advisor); Nicholas Garafolo G (Committee Member); Scott Sawyer (Committee Member); Abhilash Chandy J (Other) Subjects: Mechanical Engineering

13. Palakurthi, Nithin Kumar Aerodynamics of Particle Detachment from Surfaces: A Numerical Study

MS, University of Cincinnati, 2017, Engineering and Applied Science: Mechanical Engineering

Understanding particle detachment from surfaces is necessary to better characterize dust generation and entrainment in large scale industries (such as metallurgical and foundry facilities, or in clean room settings, semiconductor device fabrication) and in health care, such as the desired inhalation of pharmaceuticals or the unwanted respiratory exposure to small particles (e.g. asbestos). The present work explores aerodynamics of a particle resting on a flat and non-flat surface subjected to fluid flows. Since many of the difficulties and results of the full 3D problem are manifest in the two-dimensions (2D), as a first step (2D) simulations are conducted in a parallel plate channel, where we approximate the particle as a cylinder. Next, in three-dimensions (3D), particle is represented as a sphere in a parallel plate channel. In both 2D and 3D cases, to model the particle just touching the surface leads to singularity in grid generation; we have addressed this issue with two concurrent approaches. In the first approach, the particle is located at various finite distances from the surface; results are then extrapolated to zero height (particle just touching the surface). In the second approach, the bottom of the particle is embedded into the surface at different depths; again, results are extrapolated to zero embedding depth. To study aerodynamics of the particle on a non-flat surface (Wedge and Cone), test particle is positioned at various axial (2D & 3D) and azimuthal (3D) locations on the wedge/cone. The cylinder diameter, wedge height and angles are varied to understand their effect on lift, drag and moment experienced by the test cylinder. Flow is assumed to be steady, laminar and incompressible. Simulations are carried out for a range of Reynolds numbers 1 < Re < 2000. A fully-developed velocity profile is specified at inlet of the domain. The computational domain is discretized using structured and hybrid grids taking into account the boundary layer physi (open full item for complete abstract)

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Committee: David Thompson Ph.D. (Committee Chair); Urmila Ghia Ph.D. (Committee Member); Kirti Ghia Ph.D. (Committee Member); Leonid Turkevich Ph.D. (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering