Search Results (1 - 5 of 5 Results)

Sort By  
Sort Dir
 
Results per page  

Packard, Nathan OwenActive Flow Separation Control of a Laminar Airfoil at Low Reynolds Number
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 pre- and post- leading edge stall; this demarcation enables the utilization of optimal blowing parameters for each circumstance. The range of effectiveness of the employed control algorithm is explored, charting the practicality of the closed-loop control algorithm. To further understand the physical mechanisms inherent in the control process, the transients of the aerodynamic response to flow control are investigated. The on-surface hot-film sensor placed at the leading edge is monitored to understand the time delays and response times associated with the initialization of pulsed normal blowing. The effects of angle of attack and pitch rate on these models are investigated. Black-box models are developed to quantify this response. The sensors at twenty and forty percent chord are also monitored for a further understanding of the transient phenomena.

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

Keywords:

active flow control; experimental fluid dynamics; closed-loop control

Rinehart, Aidan WalkerA Characterization of Seal Whisker Morphology and the Effects of Angle of Incidence on Wake Structure
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 whisker morphology relationship to wake structure and can provide insight into design practices for application of whisker-like geometry to various engineering problems.

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

Keywords:

seal; whisker; PIV; biomimicry; fluid dynamics; particle image velocimetry; bio-engineering; engineering; mechanical engineering; aerospace engineering; experimental fluid dynamics;

Wickizer, Gabriel BenjaminExperimental System Effects on Interfacial Shape and Included Volume in Bubble Growth Studies
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

Keywords:

experimental fluid dynamics;adiabatic single bubble;nucleation and necking;capillary flows;interfacial profile and aspect ratio;flow visualization;

Tomac, Mehmet NazimInternal Fluid Dynamics and Frequency Characteristics of Feedback-Free Fluidic Oscillators
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

Keywords:

experimental fluid dynamics; refractive index matched particle image velocimetry; flow control; flow control actuators; fluidic oscillator; feedback-free fluidic oscillator; jet interactions; jet bifurcations

Sharma, Arvindh RLiquid Jet in Oscillating Crossflow: Characterization of Near-Field and Far-Field Spray Behavior
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 analyzed to quantify spray response. The spray is found to respond to crossflow oscillations by exhibiting a “flapping” behavior in the far-field. The binning method and Mie-scattering intensity image analysis suggest that the spray oscillation decreases with increasing crossflow frequency. The spray width and height fluctuate in the spray cross-section in the presence of crossflow oscillation. The amplitude of spray height fluctuation is higher in low frequency crossflow, and decreases with an increase in frequency. The total Mie-scattering intensity in the cross-section also exhibits a periodic response to crossflow oscillation, suggesting that the droplet characteristics are affected by crossflow fluctuation. The liquid spray near-field and far-field study indicates that the crossflow oscillation frequency plays a large role in determining spray response.

Committee:

Jongguen Lee, Ph.D. (Committee Chair); Milind Jog, Ph.D. (Committee Member); Mark Turner, Sc.D. (Committee Member)

Subjects:

Aerospace Materials

Keywords:

Jet in crossflow;Inlet air modulation;Oscillating crossflow;Liquid spray penetration;Near-field spray;Far-field spray;Aerospace Propulsion;Experimental Fluid Dynamics