MS, University of Cincinnati, 2024, 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 (open full item for complete abstract)

Committee: Daniel Cuppoletti Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Paul Orkwis Ph.D. (Committee Member) Subjects: Aerospace Materials

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)

Committee: Daniel R. Cuppoletti (Committee Chair); Shaaban Abdallah (Committee Member); Paul Orkwis (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics

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

In this dissertation, a series of experiments were carried out to investigate the auto-ignition process of transient fuel jets and sprays issuing into high-temperature, environments. Novel high-speed imaging and laser diagnostic techniques were developed and applied to characterize mixing and turbulent flow conditions prior to and at the onset of ignition. In addition, this research examines the topology and dynamics of ignition kernels as they grow and transition into a stable flame. Research was carried out primarily in canonical atmospheric pressure experiments, but a new high-pressure spray test facility is developed in this work with preliminary measurements presented, demonstrating new experimental capabilities. Specific contributions of this dissertation include: (1) characterization of the transient mixing processes of variable-density atmospheric pressure jets both before and after ignition, (2) determination of the most probable mixing and turbulent flow conditions leading to local auto-ignition, (3) statistical evaluation of the dynamic growth and transport of ignition kernels, (4) construction and characterization of a novel high-pressure, high temperature spray and combustion facility, and (5) demonstration of high-speed mixture fraction measurements in non-reacting and reacting sprays at realistic thermodynamic conditions. First, a series of transient gas-phase fuel jets issuing into a high-temperature, vitiated environment at atmospheric pressure was investigated. A well-known jet-into-hot coflow configuration was utilized with the addition of a fast-acting solenoid valves to achieve pulsed fuel injection in an environment with well-defined boundary conditions. Four test conditions were studied to examine the effects of variations in jet Reynolds number, the fuel mixture composition, and coflow temperature. High-speed laser Rayleigh scattering (LRS) was performed at 10 kHz to measure the mixture fraction and temperature fields from fuel injection (open full item for complete abstract)

Committee: Jeffrey Sutton (Advisor); Seung Hyun Kim (Committee Member); Datta Gaitonde (Committee Member); Igor Adamovich (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

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

Thrust vectoring (TV) is the ability to manipulate the directivity of the primary jet to provide a cross-stream force off the primary jet axis. TV can enable desirable flight regimes such as hyper-maneuverability and short/vertical take-off and landing. Modern conventional TV methods utilize a physical mechanism to mechanically deflect the jet flow and change the thrust direction. This method is both heavy and mechanically complex, especially for an axisymmetric jet. A novel approach to TV is explored in this paper by investigating localized arc filament plasma actuators' (LAFPAs) ability to impart a TV force on a subsonic, axisymmetric jet by attaching the flow to a radially expanding surface (termed “reaction surface”), at the jet exit. LAFPAs will be used to asymmetrically control the entrainment of the jet to provide a deflection of the jet via the conservation of momentum. The deflected jet will then attach to the reaction surface via the Coanda effect. The jet flow was interrogated at baseline and excited cases with a static pressure array located 0.75 jet diameters downstream of the actuators at 70% of the chord of the reaction surface and with cross-stream particle image velocimetry (PIV) located 3 jet diameters downstream of the actuators. Two jet Mach (Mj) values were assessed, Mj = 0.48 and 0.9. The results show that the LAFPAs create a repeatable and significant asymmetric pressure profile trend with respect to excitation frequency. In general, low excitation frequencies provide an asymmetric azimuthal pressure profile that corresponds to a vectored thrust force towards the active actuators, while high excitation frequencies provide an asymmetric azimuthal pressure profile that corresponds to a vectored thrust force away from the active actuators. Cross-stream PIV flow field measurements show that the asymmetry in the azimuthal pressure profile is not as significant as would be desirable for thrust-vectoring applications. However, the PIV results do show (open full item for complete abstract)

Committee: Dr. Nathan Webb (Advisor); Dr. Mo Samimy (Committee Member) Subjects: Aerospace Engineering

Doctor of Philosophy, Case Western Reserve University, 2024, EMC - Mechanical Engineering

The aim of this study is to understand the intricate flow physics and conditions leading to critical heat flux (CHF) inside a horizontally oriented rectangular channel. This study is divided into three parts: design of experimental setup, effect of inlet conditions on critical heat flux and two-phase heat transfer coefficient and understanding the effect of vapor generation on liquid-phase velocity using Particle Image Velocimetry (PIV). The experimental setup allows both upward and downward-facing single-sided heating configurations. Various inlet mass fluxes are examined, along with different levels of inlet sub-cooling. The impact of gravity is studied using flow visualization. During downward facing heating, vapor accumulates along the copper heater wall due to buoyancy effects resulting in notably low CHF and heat transfer values. In contrast, with upward facing heating, buoyancy assists in extraction of vapor from the copper heater wall, facilitating increased liquid contact and higher CHF and heat transfer values. CHF values begin to converge at high inlet mass flux for both orientations, which can be attributed to inertia dominating gravity. Inlet sub-cooling also influences CHF, with highly sub-cooled conditions yielding higher CHF. The impact of orientation and sub-cooled inlet on CHF and heat transfer coefficients are captured. Experimental CHF data was used to validate the Hydrodynamic Instability-Based Model for CHF prediction demonstrating a Mean Absolute Error of 10.8%. Effectively considering gravity forces, heated wall orientation, and flow regimes, the model demonstrates a proficiency in its comprehensive approach. Particle Image Velocimetry (PIV) is utilized to understand the flow physics and the impact of vapor phase on the liquid flow velocity. Four mass flow rates ranging from 5 – 20 g/s with sub-cooled inlet conditions are investigated in a rectangular channel with single-sided heating. Three regions of interest along the heated channel are (open full item for complete abstract)

Committee: Chirag Kharangate (Advisor); Donald Feke (Committee Member); Yasuhiro Kamotani (Committee Member); Steve Hostler (Committee Member) Subjects: Engineering; Experiments; Mechanical Engineering

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

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

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

Master of Science, University of Toledo, 2022, Mechanical Engineering

Inducing a high voltage (in the range of kV) between two proximate electrodes creates a spark, which is known as Corona Discharge. This discharge has the ability to induce a flow (ionic wind) in the medium with which it interacts. Such a flow is what is known as an Electrohydrodynamic flow (EHD), which has found many useful applications. One of its applications is mass-transport/pumping. Such an EHD pump offers many advantages, including high power efficiency and not requiring any mechanical moving parts to operate. Moreover, introducing water vapor into the stream of the ionic wind (i.e., between the two electrodes) allows driving water droplets into certain dielectric liquid. This in turn allows for the creation of emulsions. In order to create such emulsions, an understanding of the electrohydrodynamic (EHD) performance of the corona discharge is crucial. This can lead to better homogeneity and proper water droplet distribution, insuring higher quality and more stable emulsions. This study investigates the pumping performance of an in-house built corona discharge setup for inducing circular motion in the fluid. Silicone oils of different kinematic viscosities are used as the EHD fluid. The EHD performance/fluid characteristics are studied experimentally using particle image velocimetry (PIV) under different types of current (DC and AC). Within DC, a voltage parametric study is performed to investigate the effect of different potential drops on the flow. On the other hand, a frequency parametric study is carried out to highlight the effect of such parameters on the flow under AC conditions.

Committee: Hossein Sojoudi (Committee Chair); George Choueiri (Committee Member); Omid Amili (Committee Co-Chair) Subjects: Fluid Dynamics; Mechanical Engineering

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

Downsizing internal combustion engines along with turbocharging is an effective approach in reducing carbon dioxide emissions from vehicles to combat global warming. A turbocharger comprises a radial turbine driven by exhaust enthalpy flow connected on the same shaft to a centrifugal compressor that provides compressed air to the engine. Under certain engine operating conditions, the turbocharger faces challenges, however, due to instabilities encountered by its centrifugal compressor, primarily stall and surge. While stall adversely affects the compressor's aerodynamic performance and efficiency, surge, which is characterized by large amplitude pressure and flow rate fluctuations, results in drastic deterioration of compressor performance and may lead to complete mechanical failure of the turbocharger. The extremely loud noise (reaching 170 dB) generated during surge is also a major concern. To mitigate these instabilities, it is critical to analyze the flow structures involved in these processes. The present work therefore focuses on developing a thorough characterization of the turbocharger compressor flow field over its entire characteristic map (pressure ratio versus flowrate) using state-of-the-art experimental as well as computational techniques. The turbocharger bench stand at OSU-CAR allowed the isolation of the turbocharger's compressor from the complexities of the engine and provided a simplified bench-top environment for studying the compressor instabilities. The facility was modified by incorporating a stereoscopic particle image velocimetry (SPIV) system that facilitated velocity measurements at the compressor inlet. After integrating all the different components of this system including the laser, chiller, cameras, sheet optics, aerosol generator, laser controller, and timing unit, a methodology for stereoscopic calibration, image acquisition, and optimized post-processing was established. Extensive SPIV measurements were then carried out at the c (open full item for complete abstract)

Committee: Ahmet Selamet (Advisor) Subjects: Aerospace Engineering; Automotive Engineering; Mechanical Engineering

Master of Science in Aerospace Systems Engineering (MSASE), Wright State University, 2021, Mechanical Engineering

The dual-plane airfoil has been adopted in the design of aircraft wings, wind turbine blades, and propellers. The purpose of this research is to investigate the most important design parameters of a dual-plane airfoil model for the best aerodynamic performance, such as gap, stagger, and decalage. The dual-plane airfoil model was designed using the S826 profile. A mechanical mechanism with electrical actuator control is particularly designed to alter the gap and stagger smoothly, as well as the angle of attack (AOA) for each airfoil. It results in a gap range of 1.38c to 2.17c, a stagger range of -0.75c to 1.75c (c is the chord length), an AOA range of -10 to 20 degrees. The decalage angles of 0, 1, and 2 degrees are adopted in the tests for AOA=12 degrees. A low-speed open-circuit wind tunnel at Wright State University is used for the experiment at two Reynolds numbers, 𝑅𝑒=60000, and 𝑅𝑒=100000, respectively. Both airfoils are equipped with 21 pressure tap holes around the airfoil in the middle section. Pressure distribution data around the airfoil is sampled at a rate of 400 Hertz using the DSA 3217 Pressure Scanner. The collected data is processed to calculate the pressure coefficient on the surface of both airfoils. The pressure distribution profiles are generated and compared at various gaps, staggers, and decalages. Lift and drag coefficients are calculated by integrating the pressure distribution over the airfoil. It has been found that both stagger and gap have a significant effect on the pressure distribution at AOA of 12 degrees for the bottom airfoil. A gap ranges from 1.38c to 1.57c can suppress the separation and increase the lift coefficient of the top airfoil at various staggers and decalages. A stagger of 1.75c and negative staggers at a gap of 1.38c can suppress the separation and increase the lift coefficient of the bottom airfoil. Due to boundary layer separation, negative staggers are not effective for 𝑅𝑒=60000. The decalage effect is distinct at (open full item for complete abstract)

Committee: Zifeng Yang Ph.D. (Advisor); Jim Menart Ph.D. (Committee Member); Junghsen Lieh Ph.D. (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

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

Electric Vertical Takeoff and Landing vehicles are poised to bring on-demand flights into cities worldwide, but they must be quiet enough during flight to not disrupt the communities they will operate within. An acoustic analysis framework was developed to evaluate the impact that a ducted rotor would have on the noise generation of an eVTOL. The Overall Sound Pressure Level and Narrowband Spectrum were obtained for sub-scale lab data. The acoustic analysis framework then used this sub-scale data, as well as a simulated flight path, to estimate the Effective Perceived Noise Level and Sound Exposure Level for ground observers. These results were then compared for 2 and 3 bladed, open and ducted rotors operating at conditions up to a tip Mach number of 0.5. The ducted rotor produced less thrust than the open rotor. It was found to broaden rotor tones and increase the broadband noise for both the 2 and 3 bladed configurations. This resulted in higher noise metric values for all ground observers. Additional testing was performed with ground plates installed in the anechoic chamber to evaluate the ground effects. In general this ground effect caused an increase in the rotor tones and the broadband noise. However, the extent of the effect was different for the open and ducted rotors. Particle Image Velocimetry was employed to evaluate the fluid dynamics of both the open and ducted rotors. The flow structures of the open rotor were well defined and demonstrated the noise sources that are most strongly associated with noise generation of rotors. A Scheimpflug adapter was utilized to obtain measurements inside of the duct. Initial measurements proved promising for the flow structures of the ducted rotor. However, further refinements will be necessary to better observe these structures.

Committee: Daniel Cuppoletti Ph.D. (Committee Chair); Ephraim Gutmark Ph.D. (Committee Member); Prashant Khare Ph.D. (Committee Member) Subjects: Aerospace Materials

Doctor of Philosophy, University of Akron, 2021, Mechanical Engineering

The internal behavior of fluid under conditions like natural convection, electro-wetting and coalescence, which are observed in Lab on Chip devices, printing technologies, fluid filtration devices etc., was studied and quantified using the techniques of Particle Image Velocimetry (PIV) through experimental and computational analysis. The experimental analysis was started by a simple case of droplet convection wherein the motion inside the droplet was observed and analyzed using PIV and the particle motion was correlated with the existing engineering models. A computational model was generated using COMSOL multiphysics software to validate the obtained results. The experimental setup was modified to incorporate the physics of Electrowetting (EW). A hypodermic needle was used as an electrode to control the wetting properties of a hydrophobic glass slide by applying an electric potential across the droplet. The experiments were then repeated with changing the electrode orientations from vertical to horizontal with respect to the droplet. The fluid spreading dynamics of the droplet was studied by measuring the particle motion inside the wetting droplet and relating it with its boundary behavior to provide a complete analysis of the same. The observed droplet behavior was compared to a numerical model of an Electrowetting droplet generated using COMSOL multiphysics. The Electrowetting study was urther modified by actuating another droplet along with the original, making them coalesce under the influence of the electric potential. The boundary behavior during coalescence was compared to the naturally driven coalescence of droplets, finding that the electrically driven droplets were faster in actuation velocity and harder to control. The study incorporated the analysis of mixing patterns inside the droplet during coalescence. The experimental results were quantified using PIV and boundary behavior of the droplet after the film drainage was modeled mathematically for furthe (open full item for complete abstract)

Committee: Nicholas G. Garafolo (Advisor); Scott D. Sawyer (Committee Member); Alex Povitsky (Committee Member); George G. Chase (Committee Member); Kevin L. Kreider (Committee Member) Subjects: Fluid Dynamics; Mechanical Engineering

Master of Science in Mechanical Engineering (MSME), Wright State University, 2019, Mechanical Engineering

A primary source of periodic unsteadiness in low-pressure turbines is the wakes shed from upstream blade rows due to the relative motion between adjacent stators and rotors. These periodic perturbations can affect boundary layer transition, secondary flow, and loss generation. In particular, for high-lift front-loaded blades, the secondary flowfield is characterized by strong three-dimensional vortical structures. It is important to understand how these flow features respond to periodic disturbances. A novel approach was taken to generate periodic unsteadiness which captures some of the physics of turbomachinery wakes. Using stationary pneumatic devices, pulsed jets were used to generate disturbances characterized by velocity deficit, elevated turbulence, and spanwise vorticity. Prior to application in a turbine flow environment, the concept was explored in a small developmental wind tunnel using a single device. The disturbance flowfield for different input settings was measured using hot-film anemometry and Particle Image Velocimetry. Insight was also garnered on how to improve later design iterations. With an array of devices installed upstream of a linear cascade of high-lift front-loaded turbine blades, settings were found which produced similar disturbances at varying frequencies that periodically impinged upon the leading-edge region. These settings were used to conduct an in-passage secondary flow study using high-speed Stereoscopic Particle Image Velocimetry. Results demonstrated the application of the periodic unsteadiness generator but found minor changes to the passage vortex. The vortex rotational strength decreased, and migration increased with increased perturbation frequency. Fourier analyses found the PV to be responsive at the actuation frequency with phase-locked ensemble-averaged data revealing that the disturbance periodically caused the PV to lose rotational strength. However, at the tested discrete frequencies, the vortex did not become locked (open full item for complete abstract)

Committee: Mitch Wolff Ph.D. (Advisor); Rolf Sondergaard Ph.D. (Committee Member); Christopher Marks Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering; Experiments; Fluid Dynamics; Mechanical 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 in Mechanical Engineering (MSME), Wright State University, 2018, Mechanical Engineering

Calcific aortic stenosis (CAS) is the most common valvular heart disease and is associated with aortopathy and ventricular dysfunction. Hemodynamic alterations due CAS could affect the aorta lining (endothelium), that is in direct contact with the blood, triggering adverse biological responses that may possibly cause aortic dilation and dissection. Also, CAS could impose excessive ventricular load leading to ventricular wall thickening, thus putting an individual at a higher risk of heart attack or stroke. These pathophysiological effects of CAS are highly dependent on the degree of calcification. However, the impact of CAS development on aorta flow and left ventricular workload remains largely unknown. Hence the objective of this study is to measure experimentally the effect of CAS on aorta hemodynamics using particle image velocimetry; and left ventricular function in terms of left ventricular work, at different stages of calcification. This study will provide insights on aorta flow abnormalities and left ventricular overload, due CAS, which can be linked to aortopathy and heart failure.

Committee: Philippe Sucosky Ph.D., F.A.H.A. (Advisor); George Huang Ph.D. (Committee Member); Zifeng Yang Ph.D. (Committee Member) Subjects: Biomechanics; Fluid Dynamics; Mechanical Engineering; Physiology

PhD, University of Cincinnati, 2018, Engineering and Applied Science: Aerospace Engineering

The operation of gas turbine engines in increasingly harsh environments while constrained by stringent emissions regulations requires multiple advances in combustion technology. This dissertation addresses two different ways to enhance the stability and control of the combustion process under such conditions: the reacting jet in vitiated cross-flow (Part I) and ozone-assisted combustion (Part II). The first chapter of original research (Chapter 4) examines several fundamental aspects of the reacting jet in cross-flow (RJICF). A circular nozzle and high aspect ratio slotted nozzle of identical area were investigated for jet to cross-flow momentum flux ratios ranging from J = 5 to 65 for jet equivalence ratios of up to φj = 5.0. Particle image velocimetry was utilized to study the flow-field and OH* chemiluminescence was used to capture features of the flame behavior. The nozzle geometry was determined to have a significant effect on RJICF flame stability, with substantially expanded blow-out limits for the high aspect ratio slotted nozzle. Enhanced operability of the slotted nozzle is attributed to the substantially larger and stronger recirculation zone on the leeward side of the jet when compared to the circular nozzle. This area is characterized by a more disperse region of elevated vorticity levels, resulting in the entrainment of more hot combustion products with a longer residence time in the recirculation zone, which in turn provides a stronger and more stable ignition source to the oncoming, unburned reactants. The RJICF is a highly dynamic phenomenon, and its unsteady characteristics are discussed in Chapter 5. It is shown that both the non-reacting and reacting flow-fields are characterized by a peak oscillation frequency present in both the streamwise and transverse velocity components. The wake Strouhal numbers (Stw) of the isothermal slotted jet match values of Stw ≈ 0.13 reported in previous studies, whereas under combusting conditions Stw incre (open full item for complete abstract)

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Prashant Khare Ph.D. (Committee Member); Timothy Ombrello Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science, The Ohio State University, 2017, Mechanical Engineering

This thesis utilizes time-resolved particle image velocimetry (PIV) measurements to provide a detailed statistical characterization of the kinematic properties from a set of standard non-premixed flames, which serve as benchmark test cases within the turbulent combustion community. The flames under consideration are the well-characterized DLR CH4/H2/N2 jet flames operating at two Reynolds numbers, DLR A (Re = 15,200) and DLR B (Re = 22,800), where DLR A represents a robust flame condition and DLR B represents a flame near blowout with high degrees of local flame extinction. A qualitative and quantitative comparison between DLR A and DLR B is presented to understand the effect of Reynolds number variations and local flame extinction on turbulence statistics. Detailed data processing techniques to analyze the time-resolved, 2D PIV data have been developed and presented in this work. Radial profiles of the mean and RMS fluctuations of the velocity are presented and results from DLR A agree with previous point-based measurements giving confidence in the measurements and analysis. While the DLR flames are highly utilized test cases, no published velocity data from the DLR B flames is available and thus the current measurements extend the existing data set available for modelers. Probability density functions (PDFs) of various parameters including axial and radial velocity, vorticity, strain rate are presented for both flames. In general, the PDFs for the DLR B flame are much broader than DLR A flame because of the higher Reynolds number of DLR B flame; however, the same general shape is observed across the flames indicating that the high levels of local flame extinction in DLR B does not alter the functional form of the PDFs. Quantities including the mean total strain rate, Reynolds stress and turbulent kinetic energy profiles are computed and properly normalized to show the Reynolds (number) similarity of the jet flames. The observed Reynolds similarity is surprising g (open full item for complete abstract)

Committee: Jeffrey Sutton (Advisor); Seung Hyun Kim (Committee Member) Subjects: Mechanical Engineering

Master of Science (MS), Ohio University, 2017, Mechanical Engineering (Engineering and Technology)

A great many industrial processes involve suspensions of noncolloidal particles in yield stress fluids. Investigating the microstructure is essential allowing the refinement of macroscopic equations for these complex suspensions. The interaction of two particles in a reversing shear flow of complex fluids is a guide to understand the behavior of complex suspensions. In this thesis, we study the hydrodynamic interaction of two small freely-moving spheres in a linear flow field of Newtonian, shear thinning and yield-stress fluids. This thesis includes the literature survey, the experimental procedure and the experimental results. In this study, we perform a series of experiments over a range of shear rates as well as different shear histories using an original apparatus and with the aid of conventional rheometry, Particle Image Velocimetry and Particle Tracking Velocimetry. We show that the Non-Newtonian nature of the suspending fluid strongly affects the shape of particle trajectories and the irreversibility. An important point is that non-Newtonian fluid effects can be varied and unusual. Depending on the shear rate, even a yield stress fluid might show hysteresis, shear banding and elasticity at the local scales that need to be taken into account. The flow field around one particle is studied in different fluids when subjected to shear. The results for one particle are used to describe the two particle interactions afterwards. In addition, we show that how a particle-particle contact and a non-Newtonian behavior result in relative trajectories with fore-aft asymmetries. We present well-resolved velocity and stress fields around the particles. Finally, we discuss that how the relative particle trajectories may affect the microstructure of complex suspensions and consequently the bulk rheology.

Committee: Sarah Hormozi PhD (Advisor); Peter Jung Professor (Committee Member); David Bayless Professor (Committee Member); Sumit Sharma PhD (Committee Member) Subjects: Chemical Engineering; Engineering; Mechanical Engineering; Physics

Doctor of Philosophy (Ph.D.), University of Dayton, 2017, Aerospace Engineering

Cost-effective air-travel is something everyone wishes for when it comes to booking flights. The continued and projected increase in commercial air travel advocates for energy efficient airplanes, reduced carbon footprint, and a strong need to accommodate more airplanes into airports. All of these needs are directly affected by the magnitudes of drag these aircraft experience and the nature of their wingtip vortex. A large portion of the aerodynamic drag results from the airflow rolling from the higher pressure side of the wing to the lower pressure side, causing the wingtip vortices. The generation of this particular drag is inevitable however, a more fundamental understanding of the phenomenon could result in applications whose benefits extend much beyond the relatively minuscule benefits of commonly-used winglets. Maximizing airport efficiency calls for shorter intervals between takeoffs and landings. Wingtip vortices can be hazardous for following aircraft that may fly directly through the high-velocity swirls causing upsets at vulnerably low speeds and altitudes. The vortex system in the near wake is typically more complex since strong vortices tend to continue developing throughout the near wake region. Several chord lengths distance downstream of a wing, the so-called fully rolled up wing wake evolves into a combination of a discrete wingtip vortex pair and a free shear layer. Lift induced drag is generated as a byproduct of downwash induced by the wingtip vortices. The parasite drag results from a combination of form/pressure drag and the upper and lower surface boundary layers. These parasite effects amalgamate to create the free shear layer in the wake. While the wingtip vortices embody a large portion of the total drag at lifting angles, flow properties in the free shear layer also reveal their contribution to the aerodynamic efficiency of the aircraft. Since aircraft rarely cruise at maximum aerodynamic efficiency, a better understanding of the balanc (open full item for complete abstract)

Committee: Aaron Altman (Advisor); Markus Rumpfkeil (Committee Member); Jose Camberos (Committee Member); Wiebke Diestelkamp (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics

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

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

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

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