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

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

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

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

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

Committee: Mo Samimy (Advisor) Subjects:

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

MS, University of Cincinnati, 2015, Engineering and Applied Science: Aerospace Engineering

An experimental investigation of response characteristics of a liquid jet in oscillating crossflow is undertaken to understand the behavior of a liquid fuel spray in the presence of combustion instabilities. The effect of crossflow oscillations on the liquid jet is studied in the near-field (within x/d˜8) and the far-field (x/d˜50) spray region. Experiments are conducted in bag breakup, multimode and shear breakup regimes by varying crossflow Weber number from 18 to 250, while momentum flux ratio is varied between 10 and 30. The crossflow is modulated in the frequency range of 90 Hz to 450 Hz, with modulation level varying between 5% and 20%, using a mechanical modulating device. High speed shadowgraph is employed to study the near-field and far-field spray movement while intensified high-speed camera images of laser Mie-scattering intensity are utilized in studying the spray cross-section in the far-field. A technique to extract time-varying momentum flux ratio from the windward trajectory of liquid jet in the near-field is developed. The response of near-field spray is quantified in terms of a ratio of the observed momentum flux ratio extracted from a correlation of upper penetration to the expected momentum flux ratio corresponding to the instantaneous crossflow velocity. The liquid jet penetration is found to respond to oscillations in the crossflow at all oscillation frequencies in the near-field. The strength of the response is found to be mainly dependent on the crossflow oscillation frequency, with the strength of response decreasing with increase in frequency. The momentum flux ratio and the modulation level are found to have relatively negligible effects on the level of normalized spray response. The spray response in the far-field is studied by observing the high-speed shadowgraphs and Mie-scattering intensity images at an axial distance of x/d=50. The spray field in the axial location is divided into ten bins and the intensity change in each bin is analy (open full item for complete abstract)

Committee: Jongguen Lee Ph.D. (Committee Chair); Milind Jog Ph.D. (Committee Member); Mark Turner Sc.D. (Committee Member) Subjects: Aerospace Materials

MS, University of Cincinnati, 2012, Engineering and Applied Science: Mechanical Engineering

Measurements in experimental studies of adiabatic single bubble growth dynamics bear the combined effects of both the testing parameters and the test system features. The present study investigates the impact of specific experimental methods and system features, namely gas flow path, system volume, orifice construction, and visualization surface, on the measurement of adiabatic single-bubble growth dynamics at the tip of submerged capillary orifices. The present work jointly focuses on characterization of bubble volume and shape during nucleation and growth. Photos of bubble growth from a 1.75 mm capillary tube orifice were taken for glycerin, water, and 75 wt% aqueous glycerin for system volumes from 0.2 – 301.5 mL over a range of flow rates from 0.01 – 1.6 mL/s, photographed through both planar and curved surfaces. Interfacial aspect ratio and included volume from each system modification were analyzed to determine the effect of system volume and to understand the impact of flow metering on the constant gas flow boundary values in water and aqueous glycerin as well as the influence of curvature in the visualization surface and the effects of liquid viscosity in the presence of these system features. It was found that interfacial aspect ratio decreases with increasing system volume and with decreasing viscosity over the full range of flow rates considered. Additionally, interfacial aspect ratio decreases when a cylindrical visualization surface is used, owing in part to horizontal magnification. Furthermore, it is observed that bubble shape must be treated distinctly from bubble volume when surface curvature is present or system volume is minimized.

Committee: Raj Manglik PhD (Committee Chair); Jude Iroh PhD (Committee Member); Milind Jog PhD (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2012, Aero/Astro Engineering

Detailed investigation of the NACA 643-618 is obtained at a Reynolds number of 6.4x104 and angle of attack sweep of -5° < α < 25°. The baseline flow is characterized by four distinct regimes depending on angle of attack, each exhibiting unique flow behavior. Active flow control is exploited from a row of discrete holes located at five percent chord on the upper surface of the airfoil. Steady normal blowing is employed at four representative angles; blowing ratio is optimized by maximizing the lift coefficient with minimal power requirement. The range of effectiveness of pulsed actuation with varying frequency, duty cycle and blowing ratio is explored. Pulsed blowing successfully reduces separation over a wide range of reduced frequency (0.1-1), blowing ratio (0.5–2), and duty cycle (0.6–50%). A phase-locked investigation, by way of particle image velocimetry, at ten degrees angle of attack illuminates physical mechanisms responsible for separation control of pulsed actuation at a low frequency and duty cycle. Temporal resolution of large structure formation and wake shedding is obtained, revealing a key mechanism for separation control. The Kelvin-Helmholtz instability is identified as responsible for the formation of smaller structures in the separation region which produce favorable momentum transfer, assisting in further thinning the separation region and then fully attaching the boundary layer. Closed-loop separation control of an oscillating NACA 643-618 airfoil at Re = 6.4x104 is investigated in an effort to autonomously minimize control effort while maximizing aerodynamic performance. High response sensing of unsteady flow with on-surface hot-film sensors placed at zero, twenty, and forty percent chord monitors the airfoil performance and determines the necessity of active flow control. Open-loop characterization identified the use of the forty percent sensor as the actuation trigger. Further, the sensor at twenty percent chord is used to distinguish between (open full item for complete abstract)

Committee: Jeffrey Bons Dr. (Advisor); Mohammad Samimy Dr. (Committee Member); Jen-Ping Chen Dr. (Committee Member); Andrea Seranni Dr. (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics

Master of Sciences (Engineering), Case Western Reserve University, 2012, EMC - Aerospace Engineering

The knowledge of the flow field in microchannels is becoming increasingly important with the advent of the ionic wind pump and other microscale heat removal devices. The understanding of this flow field will lead to more effective and improved designs. Non-intrusive microscale particle image velocimetry (PIV) utilizing a microscopic objective lens is used to obtain the velocity field in microchannels. The scales of these channels are similar to those encountered in such devices as the ionic wind pump. Microchannels with dimensions ranging from 0.8 mm to 2 mm are used. Computational fluid dynamics (CFD) models are used to replicate each test, with varying inlet conditions and mesh densities. The CFD flow fields are compared to the PIV results for validation purposes, with relative errors between CFD and PIV typically between 2% and 10%. The agreement between the experimental data and computational results ranged from acceptable to excellent, validating this method. The channel with lowest aspect ratio consistently showed the largest agreement between experimental and numerical values.

Committee: Jaikrishnan R. Kadambi PhD (Advisor); J. Iwan D. Alexander PhD (Committee Member); Vikas Prakash PhD (Committee Member) Subjects: Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2013, Aero/Astro Engineering

In this work, the internal fluid dynamics and frequency characteristics of feedback-free fluidic oscillators are investigated experimentally and numerically. The internal flow field of various scale oscillators was extracted using a refractive index-matched Particle Image Velocimetry (PIV) technique with the help of a PIV phase averaging method and a new sensor setup for simultaneous frequency measurements in refractive index matching fluid. Three different operating regimes (low flow rate, transition and high flow rate regions) and the fluid dynamics of the oscillating behavior in these regimes are revealed with PIV measurements. Flow topologies extracted with PIV measurements differ in these three flow regimes and were found to exhibit various flow features. Frequency measurements were conducted with the use of various experimental techniques including a method that allows non-intrusive measurement. The frequency characteristics were varied depending on properties such as the working fluid, scale and cavity geometry of the fluidic oscillator. Non-dimensional parameters were defined by taking the effects of these variables into account to allow effective comparison of fluidic oscillator designs. Furthermore, 33 modified designs were also tested to provide support for future fluidic oscillator modifications.

Committee: James W. Gregory PhD (Advisor); Mohammad Samimy PhD (Committee Member); Mei Zhuang PhD (Committee Member) Subjects: Aerospace Engineering