Master of Science in Engineering, University of Akron, 2025, Mechanical Engineering

This thesis investigates the nonlinear dynamics of self-phoretic spheroidal microswimmers near planar boundaries, focusing on the emergence and structure of limit cycles in their configuration space. Active particles—microscale entities capable of self-propulsion via conversion of environmental energy—exhibit rich behaviors when confined or interacting with boundaries. Among these, self-phoretic colloids represent a particularly versatile class whose motion arises from surface gradients in chemical or thermal fields. We explore how two design parameters—the particle's aspect ratio and the distribution of surface phoretic mobility—govern the nature of their trajectories, fixed points, and periodic orbits. Employing boundary element simulations across a wide parameter space, we characterize the velocity fields in configuration space defined by particle orientation and height above the wall. A combination of coarse and fine grids, along with linear and cubic interpolation schemes, is used to extract robust dynamical trajectories. Fixed points are identified by solving for vanishing linear and angular velocities, and their stability is assessed via local flow structures. In the intermediate range of aspect ratios, we observe the birth of stable and unstable limit cycles, whose nature is mapped using data from the Poincare maps. These cycles emerge through bifurcations in the dynamics as the particle geometry and surface mobility are tuned. Our results reveal a rich phase diagram: below a critical aspect ratio, only unstable fixed points are observed; above another threshold, only stable ones remain. In between, limit cycles emerge—first stable, then unstable—with a region of coexistence demarcated by clear topological transitions in phase portraits. We further show how increasing surface mobility enlarges the size of stable cycles and shrinks unstable ones, leading to their eventual disappearance. Finally, we demonstrate that the physical displacement of these swi (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2025, Mathematics

This thesis consists of two self-contained works on nonlinear differential equations arising in models of multilayer channel flows. In Chapter 2 we consider the linear stability of traveling waves in a thin-film model for two-fluid Couette flow when a thin layer of the more viscous fluid resides next to the stationary wall. We prove that in a neighborhood of a bifurcation point from a flat state, characterized by a positive integer kb, the principal branch (kb = 1) is spectrally stable while all other branches (kb > 1) are spectrally unstable. For larger amplitude traveling waves, we establish a number of conditional theorems where the conditions were checked with help of computer assist for a set of parameter values. Using these theorems, we rigorously confirm earlier numerical evidence (D. Papageorgiou & S. Tanveer, Proc. Roy. Soc. Lond. A, doi:10.1098/rspa.2019.0367) on stability and instability of traveling waves over a range of parameters. In Chapter 3 we study traveling front solutions for a coupled system of PDEs with quadratic nonlinearity which models a stratified three-layer channel flow down an inclined channel. We prove a set of conditional theorems for the existence of traveling fronts, whose conditions have been verified through computer assist in the case of second-order dissipation in a number of examples. For fourth-order dissipation, which is appropriate when surface tension is included while inertia and density stratification are absent, we prove conditional theorems as well, though we still have to check that conditions are applicable.

Master of Science, Miami University, 2025, Mechanical Engineering

In this work, twenty vertical aluminum plates were fabricated with micro-channel features and tested to evaluate their defrosting effectiveness. Manufacturing techniques included the use of micro-milling, fluorosilane surface coatings, and/or silica nanospring (SN) mats. Given the intended application was heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems, striking a balance between defrosting performance and manufacturing cost was a primary focus. Minimizing the cost was achieved by mitigating the “edge effect” through strategically-located micro-channels. The “edge effect” refers to a phenomenon where droplets cling to the bottom edge of vertical surfaces during defrosting and are not removed. Although full-plate SN coatings were observed to have defrosting percentages as high as 90.3%, their current cost is likely prohibitive for HVAC&R applications. In contrast, micro-channels located at the bottom of vertical surfaces coupled with a fluorosilane coating proved to be a promising balance between performance and cost. By treating only the bottom edge of the plate, manufacturing times were significantly reduced, and the defrosting performance remained comparable to fully-treated plates. General observations about surface defrosting performance in terms of efficiency metrics were also outlined and discussed.

Doctor of Philosophy, Case Western Reserve University, 2025, EMC - Aerospace Engineering

Hypersonic stagnation point injection (SPI) experiments are performed using a 7◦ half-angle cone with a 19 mm radius spherical nose and a single, 1.93 mm radius sonic jet in the center of the model directed in to a Mach 6 quiet and a Mach 5.8 noisy air free stream. Injected gases include air, argon, helium, CO2, and SF6. The primary data consists of high-speed schlieren imaging at 76 kHz. Spectral analyses of the schlieren data is used to observe and define three key modes fundamental to the motions of the flow structures: (1) the longitudinal mode, (2) the vortex-coupled mode, and (3) the vortex-shedding mode. The proper orthogonal decomposition (POD) is used to track the mode energy fractions as a function of thrust coefficient while the dynamic mode decomposition (DMD) is used to gain insight into the nature of the motions present in each mode. The spectral proper orthogonal decomposition (SPOD) is used to probe specific frequencies present in the jet reservoir pressure and other spectra. As the thrust coefficient increases, the longitudinal mode becomes the dominant visible motion and the highest energy POD mode while the vortex-coupled mode becomes less energetic. The wavenumber of the Kelvin-Helmholtz instability (KHI) along the contact surface is shown to increase with thrust coefficient and under noisy flow conditions, and is shown to depend on the molar mass and speed of sound of the injected gas. This work provides the first hypersonic SPI experimental data and analyses on how different modes evolve with varying thrust coefficient and injected gas and the first observations and characterization of the KHI in an SPI flow.

Doctor of Philosophy, Case Western Reserve University, 2025, EMC - Aerospace Engineering

The ill-posed inverse problem of optical flow generally entails minimizing a weighted sum of two terms – fidelity and regularization – and the weights in the sum are parameters that require manual tuning based on the properties of both the flow and the particle images. This manual tuning has historically been a consistent challenge that has limited the general applicability of OFV for experimental data, as the calculated velocity field is sensitive to the value of the weights. This work proposes a hierarchical model for the weighting parameters in the framework of a maximum a posteriori (MAP)-based Bayesian optimization approach. The classical Lagrange multiplier weighting parameter is replaced with a new, less-sensitive parameter that can be predetermined from experimental images. The resulting method is tested on three different synthetic PIV datasets and on experimental particle images. The method is found to be capable of self-adjusting the local weights of the optimization process in real-time while simultaneously determining the velocity field, leading to an optimally regularized estimate of the velocity field without requiring any dataset specific manual tuning of the parameters. The presented approach is the first truly general, parameter-free optical flow method for PIV images. The method with automatic locally varying regularization (wOFV★) is found to be at least 15% more accurate than state-of-the-art cross-correlation for non-wall-bounded flows with at least an 8-fold increase in spatial resolution. The developed method is freely available as a part of the PIVlab package. The work also extends wOFV methods further to wall-bounded flows where near-wall measurements are notoriously difficult. Two different approaches to applying OFV methods to wall-bounded flows are proposed. It is found that with the wall extension strategy, the OFV methods can successfully resolves the near-wall profile with enhanced accuracy compared to the other velocimetry methods, (open full item for complete abstract)

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.

Doctor of Philosophy, The Ohio State University, 2025, Electrical and Computer Engineering

Power electronics converters that use wide-bandgap (WBG) semiconductors have become prevalent in transportation electrification and consumer electronics due to their compactness and high power efficiency. However, small semiconductor die size and increased device power capacity pose challenges in circuit design, especially in thermal management, which requires innovative cooling solutions to handle the higher heat flux. Effective thermal management is vital for ensuring performance, reliability, and efficiency. Research has focused on advanced cooling techniques, such as phase-change cooling and micro-scale channel cold plates, across different industries. Despite their benefits, these approaches often struggle with complexity, cost, and efficiency. A promising solution is the use of liquid metal coolants with Magnetohydrodynamic (MHD) pumps, which have shown potential in improving thermal efficiency while reducing power demands. The efficacy of liquid metal-based cooling has been proved in power module thermal management and electronics thermal switches. Both experimental and numerical studies underscore the benefits, citing notable enhancements in thermal efficiency and great reductions in power requirements. This research introduces and validates novel circuit-integrated liquid metal-based cooling systems for high power density converters using WBG devices. Following a review of high-performance thermal solutions, particularly liquid metal cooling in electronics, an innovative system design is presented. This system integrates two types of MHD pumps, rigorously analyzed through numerical calculations and finite element analysis (FEA) simulations. At its core, the MHD pump is embedded directly within the circuit's dc input bus or magnetic components, eliminating the need for external power supplies and allowing for the replacement of permanent magnets with soft magnetic materials, greatly enhancing efficiency. Additionally, the system autonomously adjusts (open full item for complete abstract)

MS, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

Validation of a novel impulse-density formulation of the incompressible Navier-Stokes equations utilizing the Helmholtz decomposition is presented. This formulation transforms the primitive velocity-pressure variables into an equal number of gauge variables, effectively eliminating the need for the primitive pressure and satisfying the requirements of the nonlinear, incompressible Navier-Stokes model in both two and three dimensions. As validation, comparisons are made with historical lid-driven cavity benchmark results, and the analytical Taylor-Green and Lamb-Oseen vortices are modeled numerically. The proposed method offers several advantages, including the resolution of numerical challenges associated with the primitive pressure, and allowing the use of simple, intuitive boundary conditions. However, it demands fine spatial discretization in certain scenarios, especially at moderate and higher Reynolds numbers, which is a notable limitation. The new impulse-density formulation offers a promising approach for academic research in simulating incompressible viscous flows.

Master of Science, Miami University, 2025, Mechanical and Manufacturing Engineering

Reduced order modeling (ROM) methods, such as those based upon Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD), offer data-based turbulence modeling with potential applications for flow control. While these models are often cheaper than numerical approaches, their results require validation with source data. Within the literature, the metrics and standards used to validate these models are often inconsistent. Chabot (2014) produced a data-driven framework for validating these ROMs that used surrogate Markov models (SMMs) to compare how the system dynamics evolved rather than how any single metric evolved. These SMMs were constructed by clustering the flow data into different states of suitably similar flow fields, and the Markov model then mapped how likely each state was to transition into another. While this method was successful, there persisted an amount of uncertainty in how the outlier states within this clustering scheme were determined. Additionally, the study only examined the application of this procedure to POD-Galerkin ROMs. This study aims to tie the outlier state determination directly to the models' parent data. The study will also apply this procedure to ROMs generated from DMD to investigate how this framework's effectiveness carries over to different classes of ROMs.

Master of Sciences (Engineering), Case Western Reserve University, 2025, EMC - Mechanical Engineering

Particle Image Velocimetry (PIV) is a technique that allows velocity measurements of a 2D plane of a fluid flow by illuminating seeding particles in the fluid with a laser sheet. However, the use of laser is often costly, introduces complexity, and poses a challenge in near-wall measurements due to light scattering from surfaces. Particle shadow velocimetry (PSV) is a novel velocimetry technique with the potential of being a low-cost, laser-free alternative to the established PIV technique. It works by tracking shadows cast by the seeding particles on an illuminated background. Little is known about the accuracy of this technique validated against PIV. This study starts by characterization the performance of this technique, presents results from two experiments using both PIV and PSV on the same plane, and discusses its advantages and potential applications.

Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Mechanical Engineering

Water scarcity is a growing challenge worldwide, resulting from increased population growth, industrial practices, and shifting climates. Researchers have been studying reliable, efficient, and cost effective, ways and techniques to obtain high quality fresh water using both a renewable and clean energy source such as power from solar energy or solar thermal concentration. Independent, self-operated, and low maintenance systems are highly desired for desalination systems. Deployable, solar-thermal desalination systems are promising technologies for promoting water security and sustainable community development in remote or storm-damaged coastal regions. However, these systems produce less distillate per unit energy input compared to industrial- scale desalination systems. The introduction of novel, metallic wicks in these systems increases distillate efficiency by generating an evaporation interface. It is proposed that metallic wicks with optimized micro-structure porous properties, i.e. porosity, permeability, capillary pressure, etc., will further increase distillate yields in capillary-driven desalination modules. Recent studies have demonstrated the potential of metallic wicks for increased distillate production at low-temperature (< 60 °C) operation. Many other studies assessed the quality of the distilled water, but they did not evaluate the salt accumulated at the water- vapor interface within the wick resulted from the evaporation. Another important issue that impacts the passive flow resulted from the wicking action is the dry-out that might occur within the metallic wick in the porous medium due to the evaporation process. A two-dimensional, steady-state heat and mass transfer study was performed to investigate the impact of various microstructure properties such as porosity and permeability, and environmental conditions such as solar irradiation on the distillate yield, wick dry-out, and salt diffusion/precipitation within candidate porous media struct (open full item for complete abstract)

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.

Master of Science, Miami University, 2024, Mechanical and Manufacturing Engineering

In this work, the heat transfer performance of chemically functionalized, double growth silica nanospring coated aluminum tubes during methanol condensation experiments is investigated. Tube sets were coated in a fluorosilane compound via liquid immersion, and then a Krytox oil was used to create a slippery liquid infused porous surface (SLIPS). Heat transfer performance of each tube was evaluated by conducting condensation experiments in a vacuum chamber with saturated methanol. Experimental data were collected for methanol with each set of tubes for subcooling degrees of 0.5°C, 1.0°C, 1.5°C, 2.0°C, 2.5°C, 3.0°C, 4.0°C, 5.0°C, and 7.0°C with cooling water flowing at volumetric flow rates ranging from 1.5 LPM to 4.0 LPM. At 0.5°C subcooling and 1.5 LPM, the surface coating combination of the fluorosilane and Krytox GPL103 oil was found to outperform the baseline, bare uncoated tubes by 94.2% on average. Additionally, all SLIPS coatings maintained their dropwise condensation behavior without reverting back to filmwise condensation during the entire testing period (i.e. > 16 hours). While heat transfer performance showed a slight increase at low degrees of subcooling and low flow rates, further testing is still needed to test the long-term durability and efficacy of this coating technology at higher flow rates.

Doctor of Philosophy, Case Western Reserve University, 2024, Macromolecular Science and Engineering

Extensional flows control a variety of industrial processes that involve spraying, printing, and droplet deposition. Within these applications, polymers are used as rheology modifiers to control the flow and droplet breakup, properties which are largely dictated by the polymer's architecture. For example, high molecular weight polymers are often used because of the backbone's ability to deform under stress adds elasticity to solutions. But, by modifying the architecture of a polymer, these elastic contributions can be significantly altered. We have studied the extensional flows of graft polymers as a function of side chain density and length, and liquid crystalline rigid rods using drop-on-substrate rheology (DOSR), a technique that offers strong insights into the fluid dynamics of non-Newtonian droplet breakup. To understand the effects of polymer backbone extension and graft density on extensional flows, polyacrylamide-graft-poly(ethylene glycol) amine (PAM-g-PEGa) was synthesized at grafting densities of 2.5%, 5.5%, 8%, and 30% and characterized via NMR and light scattering. DOSR was then used to determine the extensional relaxation times as a function of concentration for each polymer. We find that as a function of grafting density, the trend in relaxation times is nonmonotonic. At low grafting densities, the viscous friction of the added side chains counteracts the effects of backbone extension, whereas at higher grafting densities, the effects of the extended backbone dominate extensional flow properties. In the continuation of our study of graft polymers in extensional flows, PAM-g-PEGa with varying side chain lengths at a fixed grafting density were also investigated. The trend in relaxation times were also found to be non-monotonic. In contrast to flexible PAM-g-PEGa, poly(γ-benzyl-L-glutamate) (PBLG) forms rigid rods. This conformation allows for PBLG to develop cholesteric liquid crystalline phases at high volume fractions, which can also be used (open full item for complete abstract)

Doctor of Philosophy, University of Toledo, 2024, Mechanical Engineering

Particle-laden flows, characterized by the motion of discrete solid particles or droplets within a continuous carrier medium, are ubiquitous in various fields, spanning from environmental phenomena to industrial processes. Understanding these complex flows, particularly within intricate biological systems such as the human aorta, presents significant challenges and opportunities in fundamental and applied research. This study investigates the passive control of the fate of embolic particles in the aorta grafted with the cannula of a left ventricular assist device (LVAD). An LVAD is a mechanical heart-assist pump that is used for severe heart failure patients awaiting heart transplants or as a permanent therapy. A risk factor with this type of device is the transport of blood clots (formed in the left ventricle or within the pump) to the brain vasculature bed, leading to an ischemic stroke event. Previous studies have highlighted the influence of the cannula-aorta graft angle on hemodynamics and particle trajectories. However, there have been inconsistencies across numerical simulations, as well as a sore lack of experimental validations. This has served as the motivation for this dissertation to design and develop a robust experimental-based framework to study the transport of inertial particles in a biofluidic setting. The framework has been complemented by high-fidelity computational studies. For the geometry, four patient-specific cases as well as two idealized aortic computer-aided design (CAD) models have been developed and used for experimental and numerical analyses. The idealized model development process integrates statistical data from the literature alongside morphological parameters extracted from the recruited patients' models. A set of experimental studies is conducted to investigate the dynamics and trajectories of particles within the developed aortic models. Water has been used as the working fluid at two target flow rates o (open full item for complete abstract)

Doctor of Philosophy, University of Akron, 2024, Electrical Engineering

Researchers worldwide are fervently working on developing efficient, lightweight, and compact electric machines across various industries to meet the growing demands of today's world. To achieve these goals, a holistic system-level approach is necessary, moving beyond motor design alone. In the heating, ventilation, and air conditioning (HVAC) industry, where motor-driven compressors are extensively used, optimizing overall system efficiency is paramount. Recent advancements are focused on integrating the motor directly into the compressor housing, resulting in a more streamlined, cost-effective, and energy-efficient system. Radial-flux induction machines used in HVAC systems are less efficient than advanced permanent magnet (PM) machines. Axial-flux machines (AFMs) offer superior torque and power density but face adoption challenges due to cost and infrastructure. AFMs are well-suited for space-constrained applications like electric vehicles. Their planar design and adjustable airgaps provide advantages over radial-flux machines (RFMs). This dissertation proposes integrating the compressor impeller into the rotor of an electric motor for centrifugal motor-compressor systems in HVAC. The ideal motor for this integration is determined to be the axial-flux permanent magnet (AFPM) motor. While the Slotted version of this motor fits the design requirements, this study proposes the use of a Slotless structure due to its ease of manufacturability and smooth torque performance with a dual Slotless stator and single Coreless rotor (SL-AFPM) motor. Foremost, the research compares SL-AFPM with its counterpart, the Slotted axial-flux permanent magnet (S-AFPM) motor, focusing on two different slot/pole configurations. The study aims to explore the full potential of both designs while disregarding their application in integrated motor-compressor systems and associated limitations. The findings reveal that the SL-AFPM motor has smoother torque quality. Although the SL-AFPM (open full item for complete abstract)

MS, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

Liquid-vapor phase change is a key to modeling countless multiphase flows, notably in the storage of cryogenic propellants during long-term space missions. Although recent studies have progressed our understanding of the physics of phase change, reliable models to compute the interphase mass transfer remain elusive, and popular phase change models rely heavily on tuning coefficients to model the phase change mass transfer. Large inconsistencies in the phase change calculations occur due to the unpredictable nature of these tuning coefficients. In this work, several pieces of the kinetic phase change mechanism are used from other studies to build a new computational routine capable of modeling kinetic phase change without the need for tuning parameters. A common problem with implementing kinetic phase change models is the need for values of the accommodation coefficient. This problem is solved by using a transition state theory-based model to compute the accommodation coefficient as a function of the liquid and vapor densities. Vapor temperature is found to play a critical role in the accurate prediction of phase change rates. Errors as large as one order of magnitude are seen for deviations as small as 0.1% in the values of the vapor temperature. Accurate modeling of phase change rates requires vapor temperature within the Knudsen layer to be used as inputs to the kinetic models. Due to the inability of macro-scale computational fluid dynamics (CFD) models to capture temperature gradients in the Knudsen layer, a new parameter, γ, is introduced to approximate the Knudsen layer vapor temperature. This new computational routine is implemented within Ansys Fluent™ with the help of User-Defined Functions (UDFs). CFD simulations are used to recreate phase change experiments from recent studies involving Hydrogen and Methane. Data from the CFD simulations are used to correlate γ to the evaporation rate. A function to calculate γ using the area-averaged phase change molar f (open full item for complete abstract)

MS, University of Cincinnati, 0, Engineering and Applied Science: Aerospace Engineering

This study underlines the impact of the flow structures on the internal flow field through shape-transitioning ducts with global favorable pressure gradients and local adverse pressure gradients, local to the shape-transitioning geometries. Results are evaluated for convergence apropos of acquisition frequency. This thesis presents preliminary results of flow structure measurement by introducing the structures with a cylindrical bluff body in the cross flow. Structure transport through the two duct configurations studied includes the free jet of a convergent nozzle and through a shape-transitioning nozzle. Particle Image Velocimetry (PIV) was employed in data acquisition considering its substantial spatiotemporal resolution necessary. Findings show that the free jet results are characterized by high-velocity jets, detached velocity deficit region at the tailing edge of the cylinder, and strong velocity gradients due to the shear layers formed between the wake, the jets, and the ambient. On the contrary, flow through the shape transitioning or favorable pressure gradient (FPG) nozzle reflects a well-behaved flow with a low-velocity region attached to the cylinder in most cases. The outcome difference primarily stems from the velocity experienced at the cylinder in each case. An examination of convergence, considering the acquiring frequency of the flow field data, unveiled a weighty impact of acquisition frequency on the results of turbulent flow fields. The ensemble average of the results based on the mathematical computation using analytical methods in the time domain revealed an overall comparable trend in results with notable distinctions in the near wake region. Convergence dependence of results on flow essence emerged with a comparison of the running averages at a point within and outside the wake. In conclusion, it was established that a smaller subset of image pairs drawn from a universal set is ample for effectively capturing the physics of the flow fiel (open full item for complete abstract)

Master of Science in Engineering, University of Akron, 2024, Mechanical Engineering

The world of manufacturing, especially of steel and steel-based products, uses metalworking operations such as grinding, cutting, turning, milling, drilling etc. These machines in their day-to-day operations, use coolants to remove residual heat on metal surfaces to eradicate heat related fatigues, surface, and sub-surface cracks. Hence, the application technique of coolant has significance among engineers and researchers. Our research focuses on solving a particular problem related to the performance of liquid coolant jets. In many of these industrial coolant operations, challenges are faced to put the jet in a precise spot on the workpiece. Also, if there are cavitations inside the liquid jet and the stream is more like a spray than in a ‘coherent' mode, it cannot penetrate the rotating air boundary layer around the grinding wheel or in some cases, rotating workpiece. These situations can be ameliorated by a longer coherent coolant jet. As opposed to spray type jets, a coherent stream can offer higher liquid volume in a smaller cross-sectional area which in general is able to remove heat in higher efficiency. In this thesis, we simulate liquid jet flows of different density in ambient quiescent air to see how the jet develops and breaks due to surface tension and shear forces. We observe how different designs of nozzles produce coherent jets of different lengths before their breakup and how they interact with a rotating grinding wheel. Another prospect of this thesis can be design and study of a newly proposed technique of nozzle with peripheral jets compared to the existing designs. Commercial software Ansys FLUENT with the license provided by the University of Akron has been used to perform the simulations. We compare our results with existing experimental and analytical data to validate the numerical model used. This comparison confirms that numerical simulations are accurate and can be trusted while keeping in mind that some physical phenomena that is obser (open full item for complete abstract)

Master of Science, The Ohio State University, 2024, Aerospace Engineering

The high-speed flight environment entails a wide array of physical phenomena including compressible turbulence, shock-wave boundary layer interactions, and intense aero-thermodynamics. A fundamental understanding of the physics governing these phenomena is of prime relevance to the airframe design, surface material selection, and aerodynamic performance of hypersonic flight vehicles. As such, benchmark datasets which allow for global field analyses of the dynamics of hypersonic turbulence are the subject of a multitude of recent academic studies. The present work leverages modern computational hardware to perform massive-scale direct numerical simulations (DNS) of spatially evolving turbulent boundary layers. The computational approach taken in this work helps to overcome some of the challenges that are faced when experimentally investigating high-speed turbulent boundary layers such as insufficient near-wall resolution, freestream acoustic perturbations, and repeatability. Reynolds-Averaged Navier-Stokes (RANS) simulations are also leveraged to assess the typical assumptions made when developing compressible turbulence models. Modern turbulence models for compressible boundary layers are largely based upon extensions of incompressible models and thus do not uniquely consider the intrinsic hypersonic phenomena outlined above. This discrepancy leads to inaccurate predictions of vital design quantities and overly conservative vehicle designs. Due to its relative affordability, RANS is likely to remain the preferred design tool in real-world applications. It is therefore essential to analyze the predictions made by commonly used RANS models and compare them with high-fidelity data. This manuscript presents two DNS datasets of a Mach 4.9 turbulent boundary layer under cold-wall conditions (T_w/T_r = 0.60). In the first simulation, the zero-pressure-gradient (ZPG) turbulent boundary layer is spatially developed to a friction Reynolds number Re_𝜏 ~ 2500, which is (open full item for complete abstract)