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)

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

MS, University of Cincinnati, 2021, Engineering and Applied Science: Aerospace Engineering

Using CFD, turbulent Couette flow is investigated in two parts – 1) high-Reynolds number turbulent Couette flow between two flat plates, and 2) turbulent Couette flow over a solid wave – of which, the former is presented as a quintessential foundation to all discussions on high-speed pure shear flow, while the latter, which is a pure shear flow over a wavy surface, is examined as this thesis's major focus to discuss the effects of a stationary wavy bottom surface on turbulent Couette flow. Grid convergence studies are performed for both types of flow, in which the effects of characteristic grid dimensions and inflation layers are documented. Three two-equation turbulence models - Std k-e with Enhanced Wall Functions, the Std k-?, and the k-? SST – are compared against each other, and pitted against formal literature on the subject with the objective to expound on the deliverables of a steady-state RANS (Reynolds Averaged Navier Stokes) simulation of Couette flow at a very high Reynolds number. In the first part, turbulent Couette flow at Re_h = 3,000, 10,133, 21,333, and 51,099 is simulated and studied to assert discussions on a wide range of Reynolds numbers. Core flow velocities, their slopes, wall-bounded velocities, shear stresses, skin-friction coefficient, and turbulent kinetic energies are analyzed. Std k-e applied with enhanced wall functions is consistently found to be in better agreement with previous studies of plane turbulent Couette flow. The results for Re_h = 51,099 are found to be consistent with the trends asserted by literature and validatory computations. Following this, Std k-e with enhanced wall functions is used to simulate the second part of the study. In the second part, turbulent Couette flow over a wavy surface is subjected to a detailed parametric study in which three parameters—Aspect Ratio (AR), Wave Slope (WS), and wavelength based Reynolds number (Re_?) — are independently varied over an order of magnitude to investigate thei (open full item for complete abstract)

Committee: Peter Disimile Ph.D. (Committee Chair); Milind Jog (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Aerospace Materials

Doctor of Philosophy, The Ohio State University, 2019, Aero/Astro Engineering

Recent experimental and computational investigations have provided a comprehensive phenomenological description of unsteadiness in nominally two-dimensional (2-D), spanwise homogeneous shock-wave/turbulent-boundary-layer interactions (STBLIs), including both the impinging-shock and compression-ramp configurations. However, a complete mechanistic description of unsteadiness from an objective dynamical systems perspective has been lacking. Furthermore, the STBLIs encountered in many aerospace applications are fundamentally three-dimensional (3-D), in which the separation structure and topology are profoundly different from those exhibited by 2-D interactions, rendering many of the conclusions derived for the latter inapplicable. This dissertation addresses the main knowledge gaps and advances the understanding of STBLI unsteadiness by providing: (1) an objective mechanistic description of unsteadiness in 2-D interactions, (2) a phenomenological description of unsteadiness in nominally 3-D interactions (swept interactions that are inherently not spanwise homogeneous), including the sharp-fin and swept-compression-ramp configurations, (3) an objective mechanistic description of unsteadiness in these 3-D interactions, and (4) a phenomenological description of unsteadiness in a representative compound 3-D interaction (a double-fin inlet/isolator configuration). The approach employs high-fidelity large-eddy simulations of various 2-D and 3-D STBLIs in the high-supersonic (Mach 2-4) speed regime. Simulation accuracy is ensured through extensive comparison with experimental data obtained from concurrent experimental campaigns at partner institutions. The phenomenological description of unsteadiness is then compiled from various analyses of the resulting, spatiotemporally varying, turbulent flow. These include spectra of the unsteady fluctuations, band-isolated fluctuation dynamics obtained through temporal filtering, reduced-order representations, correlations, and other (open full item for complete abstract)

Committee: Datta Gaitonde PhD (Advisor); Mohammad Samimy PhD (Committee Member); Jen-Ping Chen PhD (Committee Member) Subjects: Aerospace Engineering

Master of Science in Mechanical Engineering (MSME), Wright State University, 2018, Mechanical Engineering

High-lift low-pressure turbine blades produce significant losses at the junction with the endwall. The losses are caused by several complex three-dimensional vortical flow structures, which interact with the blade suction surface boundary layer. This study investigates the unsteady characteristics of these endwall flow structures on a highly loaded research profile and the adjacent endwall using surface-mounted hot-film sensors. Experiments were conducted in a low-speed linear cascade wind tunnel. The front-loaded blade profile was subjected to three different inlet conditions, consisting of two turbulence levels, and three incoming boundary layer thicknesses. Multiple surface-mounted hot-film sensors were installed throughout the passage. This thesis progressed in three stages of research. The first verified that the hot-film sensors could be used to detect flow structures in the cascade. The second used the results from installed hot-films to examine the unsteady characteristics of vortices formed near the leading edge and the propagation of the passage vortex across the passage where it interacts with a corner separation along the suction surface. Simultaneous measurements from the hot-film sensors were analyzed for frequency spectra and time lag in order to provide new insight into the endwall flow dynamics. Finally, signatures from the hot-films were linked to specific flow phenomena through concurrent flow visualization. At each stage of the investigation, results were compared to the results of a numerical simulation.

Committee: Mitch Wolff Ph.D. (Advisor); Rolf Sondergaard Ph.D., P.E. (Committee Member); Christopher Marks Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

Master of Science (MS), Ohio University, 2016, Mechanical Engineering (Engineering and Technology)

Corrosion is a significant issue affecting oil-water transportation pipelines and causing failures. It occurs when the water present in the produced fluids (a mixture of gas and liquid hydrocarbons) comes into contact and reacts with the pipe surface. Preventing direct contact between water and steel surface is key in mitigating corrosion. This can be achieved by ensuring that water is dispersed as droplets in the oil flow. This situation, called dispersed water-in-oil flow, is attained when the specific operating conditions are met. Being able to predict when dispersed water-in-oil flow occurs holds consequently a significant importance in any asset integrity plan. Liquid flow rates and water cut play obviously a crucial role but, more specifically, the prediction of water droplet size and distribution is essential in determining when dispersed water-in-oil flow is stable. This present study focuses on experimental measurements of maximum droplet size and droplet size distribution in water-in-oil dispersion for a wide range of flow conditions. The experimental data are compared with the current prediction models and the effects of turbulent level and water cut on maximum droplet size and droplet size distribution is also studied. Gaps in the current understanding are identified and improvements of the predictions models are then proposed.

Committee: Marc Singer (Advisor); Srdjan Nesic (Committee Member); Sarah Hormozi (Committee Member); Katherine Cimatu (Committee Member) Subjects: Chemical Engineering; Mechanical Engineering

Master of Science, University of Akron, 2016, Mechanical Engineering

Transition to turbulent flow in curved pipe has been well studied through experiments and numerical simulations. Numerical simulations often use helical pipe geometry with infinite length such that the inlet and outlet boundary conditions can be modeled as periodic which reduces computational time. In the present study, we examined a finite length curved pipe with a Poiseuille flow imposed at the inlet and a stress-free boundary condition at the outlet. Direct numerical simulation of the Navier-Stokes equations for rigid walls and a Newtonian fluid was performed using nek5000. Straight extensions were added to the inlet and the outlet such to diminish the impact of boundary conditions on the flow field in the region with curvature. The examined model has a pipe radius of curvature that is three times that of the pipe radius. The model has over 300 million nodes and required an order of magnitude greater computational time when compared to the infinite length curved pipe. Results show that the critical Reynolds number (initiation of instabilities) is greater compared to a straight pipe and occurs near Re=5000-5200. This Re is also larger than the critical Reynolds number typically reported for an infinite length curved pipe (Re= 4200-4300). As expected, flow patterns in the finite length curved pipe were shown to be evolving through the curvature as opposed to that of an infinite length curved pipe where it remains constant. In addition, the initial instabilities observed in the flow did not originate from a Dean flow instability, initiated through secondary flow, but rather were first observed near the outer wall.

Committee: Francis Loth Dr. (Advisor); Paul Fischer Dr. (Advisor); Sergio D. Felicelli Dr. (Committee Member) Subjects: Fluid Dynamics

Master of Science (MS), Ohio University, 2016, Mechanical Engineering (Engineering and Technology)

Corrosion of steel parts is an important problem in the oil and gas industry, both for upstream (from well to refinery environments) and downstream (refinery environment) applications. Water is always present in the reservoir and is carried through the pipelines together with the produced hydrocarbon fluids. In order to transport the oil from the well to the refinery environment, carbon steel pipeline is often the preferred choice of material as it is the most cost-effective and available option. Transportation of oil becomes problematic due to the presence of water in carbon steel pipelines since it causes corrosion. However, corrosion only occurs when liquid water is in direct contact with the steel surface - this scenario is commonly known as water wetting. Several studies have been performed on water wetting in horizontal and inclined pipe flow, and several models have been proposed to estimate the occurrence of water wetting. However, there is still some degree of discrepancy between modeling outcomes, suggesting that the state of understanding of the mechanisms involved is not well defined. Moreover, the available experimental data on water wetting, particularly in inclined oil-water pipe flow, is still scarce and somewhat contradictory, which renders development of physical models difficult. In this research, a comprehensive database of new experimental results was developed. Phase wetting measurements were performed in a 4-inch Internal Diameter flow loop, investigating the effect of pipe inclination, mixture velocity of oil and water and water cut (concentration of water in oil). In addition, the experiments were repeated in a carbon steel and in a polyvinyl chloride test section in order to study the wetting characteristics of the surface. A new phase wetting measurement probe was developed and validated in the flow loop. Based on impedance measurement, this probe showed exceptional capabilities for differentiating oil and water wetting with a great level (open full item for complete abstract)

Committee: Marc Singer (Advisor); Srdjan Nesic (Committee Member); Sarah Hormozi (Committee Member); Katherine Cimatu (Committee Member) Subjects: Engineering; Fluid Dynamics; Mechanical Engineering

MS, University of Cincinnati, 2004, Engineering : Aerospace Engineering

The thrust of this thesis is to introduce and test two Coherent Structures eduction methods utilizing two different databases. The first set of data was collected in the turbulent flow produced by a circular jet that is known to develop high shear layers where large scale coherent structures are usually embedded. The second experiment was conducted on the swirling flow exiting a Triple Annular Research Swirler (TARS). The TARS is used as a fuel injector in a gas turbine combustor simulator and it features three concentric swirling flows that merge into a complex swirling jet. The methods that are exposed in this thesis are the Proper Orthogonal Decomposition (POD) and the Linear Stochastic Estimation (LSE). These techniques that have become more and more famous over the past decades are based on filtering techniques and are built on a solid mathematical background: the POD extracts the most energetic structures from a turbulent flow and essentially relies on projections and linear algebra theory whereas the LSE uses statistical theory to provide an estimate of the instantaneous flow field by reproducing, in space and time, the large-scale coherent structures of the flow using minimum experimental information. The mathematical theory that is needed to understand these techniques has been exposed in a first part and then both POD and LSE were tested and compared for the two databases. Both filtering techniques turned out to be very efficient for extracting Coherent Structures from the turbulent flow fields and for apprehending their dynamic. Although the LSE highly depends on the levels of correlation and consequently raised several issues for the experimental setups, it eventually allowed us reconstructing complete coherent flow fields from the knowledge of only few near-field acoustic signals and provided a tool as powerful in its concept as it is in practice in terms of data reduction.

Committee: Dr. Ephraim Gutmark (Advisor) Subjects: Engineering, Aerospace

Master of Science, The Ohio State University, 2011, Mechanical Engineering

The skin of fast swimming sharks exhibits riblet structures aligned in the direction of flow which are known to reduce skin friction drag in the turbulent flow regime. Structures have been fabricated for study and application which replicate and improve upon the natural shape of the shark skin riblets, providing a maximum drag reduction of nearly 10%. Mechanisms of fluid drag in turbulent flow and riblet-drag reduction theories from experiment and simulation are discussed, a review of riblet performance studies performed is given, and optimal riblet geometries for external flow are defined. A survey of studies experimenting with riblet-topped shark scale replicas is also given. A method for selecting optimal riblet dimensions based on fluid flow characteristics is detailed, and current manufacturing techniques are outlined. The effects of mucus and hydrophobicity are presented. A flow cell has been designed for studying riblet effects in internal rectangular duct flow and is discussed. Data collected using several riblet surfaces fabricated for the flow cell is presented and analyzed. A discussion of the effects of the riblets on fluid flow is given, and conclusions are drawn about the possible benefits of riblets in internal fluid flow.

Committee: Bharat Bhushan (Advisor); Shaurya Prakash (Committee Member) Subjects: Mechanical Engineering

Master of Science (MS), Ohio University, 1983, Mechanical Engineering (Engineering)

An experimental evaluation of enhanced heat exchanger performance from external deluge water augmentation

Committee: Gary Hanson (Advisor) Subjects: Engineering, Mechanical

Doctor of Philosophy, University of Akron, 2013, Mechanical Engineering

Due to their physical properties, gallium nitride crystals are in high demand in applications including light emitting diodes, high power and high frequency devices. One way of growing the crystals is the ammonothermal growth process. The process consists of chemical reactions occurring in reactors under high temperature and high pressure conditions. A basket of gallium nitride nutrient is inserted inside the reactor filled with ammonia and a mineralizer, whereupon gallium nitride is dissolved and transported by natural convection and then deposited onto the seeds. Because the etching and deposition reactions require temperatures in the range of 600 to 1,000 K (620 to 1,340 °F) and pressures in the range of 1,000 to 6,000 bar (14,504 to 87,022 psi), it is impossible to visualize the flow or measure its parameters. This dissertation presents a way to look inside an ammonothermal crystal growth reactor by simulating the process using CFD software. An equivalent reactor and crystal growth environment are created to provide experimental validation. The equivalent reactor respects geometric and dynamic similitude with respect to the actual ammonothermal crystal growth reactor. Experimental temperatures and velocities are recorded and compared with numerical results. Three turbulence models and the laminar model were tested. The laminar and the standard k-omega models performed better compared with experimental results. By simulating an equivalent reactor that allows visualization and measurements, the CFD model was validated. With the validated model, simulations of the actual growth process including mass transfer were performed. The wall temperature profile, the geometry of the nutrient basket, and the baffle were used as parameters to investigate their influence on the deposition rates. The temperatures on the outer walls of the reactor have a great influence on the deposition rate and can lead to etching of the seeds instead of crystal growing. The presence of a ba (open full item for complete abstract)

Committee: Minel Braun Dr. (Advisor); Abhilash Chandy Dr. (Advisor); Alex Povitsky Dr. (Committee Member); Gaurav Mittal Dr. (Committee Member); S. I. Hariharan Dr. (Committee Member); Kevin Kreider Dr. (Committee Member) Subjects: Mechanical Engineering

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

In industries such as mining and powder handling, workers are at risk of exposure to inhaling particulates as the powder can get aerosolized in their work environments. It is critical to characterize the dustiness or propensity of powders to get aerosolized to quantify workers' health risks. The Venturi Dustiness Tester (VDT) is widely used for this purpose. The aerosolization process in this device starts at the powder holding tube, where a dome or hill of powder is exposed to very high flow rate and the aerosol gets sucked into the measurement chamber where it is sampled for dustiness characterization. The process of powder hill aerosolization occurring in VDT is very complex as the obstruction caused by the dome leads to vortex shedding and the shape of the hill changes with aerosolization. To keep the problem tractable, a simplified model problem of flow over a solid hemisphere attached to a horizontal substrate in a rectangular duct is analyzed in this thesis. While this model does not account for changing shape of the hill during the aerosolization process, flow features like vortex shedding and their effect of shear and lift forces acting on the dome surface are captured. This information will be useful in understanding how particulate in a powder hill are likely to be affected by the flow. The flow dynamics in the simplified configuration were explored for different flow speeds, including creeping flow (Re<<1), laminar flow, and turbulent flow using computational fluid dynamics techniques. To obtain the inlet velocity profile to provide the inlet boundary condition for the unsteady simulations of flow over the solid dome, a set of steady-state empty duct simulations were performed first. A grid convergence study was carried out at Re = 1000 to establish grid-independent results for the unsteady simulations. The optimized grid was then used for all Reynolds numbers. In the creeping flow regime, the flow was found to be symmetric around the hemisphere as t (open full item for complete abstract)

Committee: Milind Jog Ph.D. (Committee Chair); Leonid Turkevich Ph.D. (Committee Member); Je-Hyeong Bahk Ph.D. (Committee Member); Urmila Ghia Ph.D. (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2024, Aerospace Engineering

Fluid-Structure Interactions (FSI) are a quintessential multi-disciplinary challenge, where the flowfield is influenced by the structure, and structural deformation is induced by the flow pressure. Computational and experimental research thrusts often seek to answer specific problems for specific configurations, offering observational answers to relatively complex problems. While there is a large body of work on FSI as a whole, the specific coupling mechanisms between the fluid and structural surface in the context of turbulent boundary layers (TBLs) in supersonic flows is an under-explored area of study. This dissertation details progress addressing this gap through cooperative consideration of high-fidelity simulations, classical semi-empirical models, analysis of the governing equations, and data-driven models. Large-Eddy Simulations (LES) of TBLs with static deformations are compared against classical semi-empirical models to characterize applicability to statically deformed surfaces for predicting loads transmitted from the boundary layer to the structure. Additionally, analysis of the governing equations, in conjunction with data-driven modeling, is used to extract a coherent link between structural deformation and the onset of local flow separations. Finally, a parametric study is carried out using Reynolds-Average Navier-Stokes (RANS) and Kriging surrogates to assess the impact of statically deformed surfaces on a downstream ramp. LES indicates that for a variety of deformations sized on the order of the incoming boundary layer, localized flow separation can develop. This leads to important flow modifications that are not readily captured with low-fidelity or semi-empirical models. Motivated by this, a first-order link between local flow separation and structural deformation parameters is established using the Momentum Integral Equation (MIE) combined with data-driven analysis. The curvature of the surface is identified as the dominant structural param (open full item for complete abstract)

Committee: Jack McNamara (Advisor); Datta Gaitonde (Advisor); Scott Peltier (Committee Member); Jen-Ping Chen (Committee Member); Lian Duan (Committee Member) Subjects: Aerospace Engineering

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)

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

Master of Science in Engineering, University of Akron, 2020, Mechanical Engineering

Goodyear unveiled its Eagle 360 concept tires in 2017 and believes that these smart spherical tires, being equipped with sensors and artificial intelligence, will replace the typical cylindrical tires for driverless vehicles. The aerodynamic performance of these tires was not evaluated yet. By understanding the aerodynamic performance of spherical tires, one can improve the fuel consumption and performance of vehicles. The purpose of this research is to study the drag of the smooth and grooved spherical tires and compare their performance to the conventional tires. Using a k-transition turbulence model, the airflow around the spherical tire is analyzed at Re=5.3x105 for numerous setups including isolated stationary tire, isolated rotating tire and moving rotating tire in the presence of rigid ground. Equations of conservation of mass and momentum and turbulence model are discretized using the finite-volume method and solved using second order upwind discretization scheme and SIMPLEC algorithm. All simulations involved in the present study are conducted using ANSYS Fluent software. To validate the approach, the 2-D and 3-D computations for conventional cylindrical tires are conducted and the drag coefficient is compared to prior experimental and computational literature results. The 2-D simulations are conducted for Reynolds numbers ranging from 105 to 106 for several representative configurations, for instance, isolated stationary tire, isolated rotating tire and moving rotating tire with and without wheelhouses (curved and flat) in the presence of road. The 2-D simulations for Reynolds number ranging from 105 to 5x105 are conducted using the k-transition turbulence model and for Reynolds number ranging from 6x105 to 106 with k-ε realizable turbulence model. To avoid numerical divergence, the k-transition turbulence model is solved using SIMPLEC algorithm and k-ε realizable turbulence model with coupled algorithm. 3-D simulations of airflow a (open full item for complete abstract)

Committee: Alex Povitsky (Advisor); Francis Loth (Committee Member); Scott Sawyer (Committee Member) Subjects: Aerospace Engineering; Applied Mathematics; Educational Software; Engineering; Experiments; Fluid Dynamics; Mathematics; Mechanical Engineering; Theoretical Mathematics

MS, University of Cincinnati, 2019, Engineering and Applied Science: Mechanical Engineering

Inhalation exposure of fine and ultrafine particles is a large hazard for individuals working around aerosolized particles. As of yet, there is no clear direct relationship between this inhalation exposure and a material property (dustiness) of the powder. Several methods exist for determining the dustiness of powders: drop test, rotating drum, and Venturi aerosolization. Previous experiments have attempted to correlate the dustiness of a powder and the inhalation exposure of a worker performing activities. Given the wide range of other variables (type of activity, positioning, air flows), it is difficult to isolate the exposure relating purely to dustiness. The National Institute for Occupational Safety and Health (NIOSH) is proposing a series of experiments using simplified work and clean-up activities, designed to remove these sources of variation. This will provide a direct link between the dustiness of a powder and the inhalation exposure of a given task. The studies in this thesis aid in the design of the NIOSH experiments. A series of computational fluid dynamics studies have been conducted as a predictive resource for the proposed NIOSH experimental exposure studies with powders. The simulations reported in this thesis focused on air flowing in a rectangular room past a simplified worker and work table. The dimension of the work space and air flow conditions were chosen to mimic the proposed NIOSH experiments in their ventilation lab. Inhalable and respirable samplers were positioned on the worker. Particles were released above the table surface to follow their movement around the room. The position of the simplified worker around a work table was varied, as well as the location of samplers on the worker's torso. The air flow in the room is significantly perturbed by the presence of the worker and table; a recirculation zone develops downstream of the worker, and vortices are shed downstream of the table legs. The location of the worker ha (open full item for complete abstract)

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

Master of Science in Mechanical Engineering (MSME), Wright State University, 2016, Mechanical Engineering

Improvements in turbine design methods have resulted in the development of blade profiles with both high lift and good Reynolds lapse characteristics. An increase in aerodynamic loading of blades in the low pressure turbine section of aircraft gas turbine engines has the potential to reduce engine weight or increase power extraction. Increased blade loading means larger pressure gradients and increased secondary losses near the endwall. Prior work has emphasized the importance of reducing these losses if highly loaded blades are to be utilized. The present study analyzes the secondary flow field of the front-loaded low-pressure turbine blade designated L2F with and without blade profile contouring at the junction of the blade and endwall. The current work explores the loss production mechanisms inside the low pressure turbine cascade. Stereoscopic particle image velocimetry data, total pressure loss data and oil flow visualization are used to describe the secondary flow field. The flow is analyzed in terms of total pressure loss, vorticity, Q-Criterion, Reynolds' stresses, turbulence intensity and turbulence production. The flow description is then expanded upon using an Implicit Large Eddy Simulation of the flow field. The RANS momentum equations contain terms with static pressure derivatives. With some manipulation these equations can be rearranged to form an equation for the change in total pressure along a streamline as a function of velocity only. After simplifying for the flow field in question the equation can be interpreted as the total pressure transport along a streamline. A comparison of the total pressure transport calculated from the velocity components and the total pressure loss is presented and discussed. Peak values of total pressure transport overlap peak values of total pressure loss through and downstream of the passage suggesting that total pressure transport is a useful tool for localizing and predicting loss origins and loss development using (open full item for complete abstract)

Committee: Mitch Wolff Ph.D. (Advisor); Rolf Sondergaard Ph.D. (Committee Member); Rory Roberts Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering

MS, University of Cincinnati, 2016, Engineering and Applied Science: Aerospace Engineering

An experimental study is first presented on the comparison between two commonly used velocity measurement techniques applied in experimental fluid dynamics: Constant Temperature Anemometry (CTA) and Particle Image Velocimetry (PIV). The comparison is performed in the near-field region of an axisymmetric circular turbulent jet where the flow field contains large scale turbulent structures. The comparison was performed for five Reynolds numbers, based on diameter, between 5,000 and 25,000. The Reynolds numbers selected cover the critical Reynolds number range, 10,000 to 20,000 where the characteristics of the flow transition to a fully developed turbulent mixing layer. A comparison between these two measurement techniques was performed in order to determine the differences between an intrusive (CTA) and non-intrusive (PIV) method when applied to a practical application. The results and observations obtained from the comparison between the two techniques were applied to better characterize the time-averaged characteristics of a single axisymmetric turbulent jet with a Reynolds number of 7,500. The mean and fluctuating velocities, turbulent kinetic energy (TKE), and vorticity were measured as a baseline case. Additionally, smoke visualization was utilized to determine the mixing characteristics of the transient start of an axisymmetric turbulent jet. The shedding frequencies, also known as, the `preferred mode' were investigated for a single jet. Particle Image Velocimetry (PIV) was also utilized to characterize the pre-and post-regions of the interaction region of two axisymmetric, incompressible turbulent jets at included angles: 30, 45, and 60 degrees. The Reynolds number selected (7,500) was within the range of critical Reynolds numbers and the geometrical distance to twin jet impingement, X0, remained constant at 10.33D for each impingement angle. The mean and fluctuating velocities, vorticity, and turbulent kinetic energy (TKE) were measured. Smoke Visual (open full item for complete abstract)

Committee: Peter Disimile Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Milind Jog Ph.D. (Committee Member) Subjects: Aerospace Materials

Doctor of Philosophy, The Ohio State University, 2015, Aero/Astro Engineering

One of the most pervasive threats to aircraft controllability is wing stall, a condition associated with loss of lift due to separation of air flow from the wing surface at high angles of attack. A recognized need for improved upset recovery training in extended-envelope flight simulators is a physical understanding of the post-stall aerodynamic environment, particularly key flow phenomena which influence the vehicle trajectory. Large-scale flow structures known as stall cells, which scale with the wing chord and are spatially-periodic along the span, have been previously observed on post-stall airfoils with trailing-edge separation present. Despite extensive documentation of stall cells in the literature, the physical mechanisms behind their formation and evolution have proven to be elusive. The undertaken study has sought to characterize the inherently turbulent separated flow existing above the wing surface with cell formation present. In particular, the question of how the unsteady separated flow may interact with the wing to produce time-averaged cellular surface patterns is considered. Time-resolved, two-component particle image velocimetry measurements were acquired at the plane of symmetry of a single stall cell formed on an extruded NACA 0015 airfoil model at chord Reynolds number of 560,000 to obtain insight into the time-dependent flow structure. The evolution of flow unsteadiness was analyzed over a static angle-of-attack range covering the narrow post-stall regime in which stall cells have been observed. Spectral analysis of velocity fields acquired near the stall angle confirmed a low-frequency flow oscillation previously detected in pointwise surface measurements by Yon and Katz (1998), corresponding to a Strouhal number of 0.042 based on frontal projected chord height. Probability density functions of the streamwise velocity component were used to estimate the convective speed of this mode at approximately half the free-stream velocity, in (open full item for complete abstract)

Committee: James Gregory Ph.D. (Advisor); Jeffrey Bons Ph.D. (Committee Member); Mo Samimy Ph.D. (Committee Member); Jen-Ping Chen Ph.D. (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics

Master of Science in Engineering, University of Akron, 2015, Chemical Engineering

The internal susceptibility and corrosion of pipelines has widely been minimized by the use of inhibitors which mitigate and control degradation effects due to flow conditions and to aggressive environments created inside the pipeline. However, environmental hazard might constitute a problem due to the chemical substances forming the inhibitors. A very specific application of pipeline integrity occurs in offshore facilities for oil recovery production where a mixture of pressurized water-CO2 is injected to almost depleted oil wells in order to enhance recovery. As CO2 injection is very common in marine environments, the effect of chloride ions is added to the corrosive variables of the system is considered. Environmental aggressiveness is set due to a paired effect of environmental conditions: the formation of carbonic acid in the water-CO2 mixture and the presence of chloride ions as part of the marine environment. Here we aimed to electrochemically characterize a zinc-rich epoxy nanocoating primer (ZREP), as well as a composite variation incorporating carbon nanotubes (CNT-ZREP), on an API X52 pipeline grade steel substrate. A rotating cylinder electrode (RCE) was used to incorporate the flow regime and equivalent shear stress conditions. The selected electrolyte for testing was 3% (wt.) NaCl saturated with CO2. The anti-corrosion properties of these nanocomposite coatings are a result of the combined effects of Zn and C nanoelements, which impart special properties not initially inherent in the matrix or in the nanoelements. The effects of these medium conditions on the performance of the substrate/coating system were characterized in real-time by electrochemical impedance spectroscopy. The damage evolution concept was adopted to analyze the current stages and to propose possible mechanisms for the roles of the CNTs and Zn cathodic in providing enhanced protection to the substrate.

Committee: Homero Castaneda-Lopez Dr. (Advisor); Qixin Zhou Dr. (Committee Member); Rajeev Gupta Dr. (Committee Member) Subjects: Chemical Engineering; Chemistry; Engineering