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Lee, Kuan-LinDevelopment of a Compact Thermal Management System Utilizing an Integral Variable Conductance Planar Heat Pipe Radiator for Space Applications
Doctor of Philosophy, Case Western Reserve University, 2017, EMC - Mechanical Engineering
In the present research an innovative space thermal management system is developed utilizing an integral planar variable conductance heat pipe (VCPHP) radiator, which can function reliably over a wide range of environmental conditions. The condenser (or radiator) of this planar shaped heat pipe is self-adjustable, and the evaporator temperature can be stabilized within a tolerable range even when the sink temperature changes significantly. This research includes the design, fabrication and test of four prototype planar heat pipe radiators, which are made with a metallic material and a thermally conductive polymer. The corresponding thermal performance of prototype VCPHPs were measured and analyzed through a benchtop heat pipe-based heat rejection system. To further support the concept, a multi-scale, steady-state heat pipe operation model (SSHPOM), which is able to capture both the thermal and hydrodynamic characteristics of the developed VCPHP radiator was developed. The mathematical model combines a theoretical thin-film evaporation model, a NCG expansion model and 2D steady-state heat transfer analysis. After validation, a feasibility of a large scale VCPHP designed for the Altair Lunar lander mission is predicted via numerical simulations with radiation cooling boundary conditions. Using the mathematical model, the influence of several design parameters can be identified and a maximum heat rejection turn-down ratio of 11.0 is achievable. Furthermore, the vapor-NCG topology within the integral planar heat pipe with a non-uniform heat load is simulated through a volume of fluid (VOF)-based approach.

Committee:

Yasuhiro Kamotani (Advisor); Jaikrishnan Kadambi (Advisor); James T'ien (Committee Member); Chung-Chiun Liu (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

heat pipes; radiator; two-phase heat transfer; space thermal control system

Long, Brandon ScottEffect of Rayleigh-Taylor Instability on Fuel Consumption Rate: A Numerical Investigation
Master of Science (M.S.), University of Dayton, 2017, Aerospace Engineering
An extensive numerical investigation is conducted in order to assess the effect of Rayleigh-Taylor instability on fuel consumption rate (or flame speed). Two geometries are used for this investigation, viz., a high pressure high-g (HPHG) cavity stabilized combustor and a curved duct with a backward facing step. The former geometry is a more practical combustion system that contains liquid fuel injectors with operating conditions that mimic gas turbine cycles, whereas the latter is a canonical combustor used to study turbulent premixed flames. Reynolds averaged Navier-Stokes (RANS) and large eddy simulations (LES) are used. RANS is used for the practical combustor, and both RANS and LES are used for the canonical combustor. The combustion models used are the flamelet generated manifold (FGM) and the two-step species transport for the practical and canonical combustor, respectively. The HPHG combustor is designed to induce bulk rotational flow in the cavity, inducing centrifugal acceleration. The centrifugal force acts from the high-density reactants towards the low-density products creating a Rayleigh-Taylor instability (RTI). Rayleigh-Taylor instabilities are expected to increase the turbulent flame speed and reduce the size of the combustor by increasing the flame wrinkling and/or corrugation. Simulations at two different levels of centrifugal acceleration, and, consequently, dissimilar Rayleigh-Taylor instability were performed. It was found that the nominal g-loads are overestimating the local g-loads from the simulation because thermal expansion is not taken into account. From these simulations it was not possible to discern the effect of RTI on fuel consumption rate due to the complex physical-chemical process inherent to this combustor such as fuel vaporization, molecular mixing, spray-turbulence interaction, turbulence-chemistry interaction, and partial premixing. Therefore, gaseous premixed turbulent flames were simulated in a curved duct with a backward facing step. Two radius of curvature were used, viz., an infinite (straight duct) and a finite radius of curvature (curved duct). These combustors were operated at low and high Reynolds number (3,200 and 32,000). The computational results are compared with broadband chemiluminescence and shadowgraph images reported in the literature for similar conditions and geometries. Both RANS and LES results are in general agreement with measurements. Both experiments and simulations show that increasing the Reynolds number in both straight and curved canonical combustor the flame cannot withstand the Karlovitz number effects and the flame is positioned behind the backward-facing step. In addition, the LES results indicate that at high Reynolds number the flame blows out for the straight channel while it remains stabilized for the curved channel. This result is in agreement with the blowout data reported in the literature. On the other hand, RANS over predict the flame stabilization for the straight channel. Consequently, RANS should not be used in research involving RTI-induced blowout. In conclusion, RTI interacts with a turbulent premixed flame and its overall effect is to extend the conditions under which turbulent premixed flames can be stabilized. This improved flame stabilization is a direct manifestation that the fuel consumption rate (or flame speed) has been enhanced in order for the flame to withstand higher Karlovitz number effects induced by high Reynolds number. However, the mechanism through which RTI works on the turbulent premixed flame is not clear. A new hypothesis is proposed. The increase in RTI should increase the turbulent length scale as well as increase the Karlovitz number. The corrugated flame would withstand the higher Karlovitz number because RTI temporarily and periodically reverses the turbulent energy cascade by minimizing the potential energy of the stratified flow.

Committee:

Scott Stouffer, Ph.D. (Committee Chair); Alejandro Briones, Ph.D. (Committee Member); Brent Rankin, Ph.D. (Committee Member); Jamie Ervin, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Rayleigh-Taylor Instabilities; Fuel Consumption Rate; High Swirl Combustion; High-G Combustion; Backward Facing Step Combustion

Zhu, Yonry RApplications and Modeling of Non-Thermal Plasmas
Bachelor of Science (BS), Ohio University, 2018, Engineering Physics
This thesis focuses on validation of a 0D plasma kinetic model and its subsequent use as an explanatory tool to support the results of hot-fire tests of a plasma assisted rotating detonation combustor. The plasma model predictions showed good agreement with experimentally measured values of various ground state species number densities, vibrationally excited N2 number densities, plasma temperatures, and ignition delay times. Once validated, the plasma model was combined with a ZND detonation model and semi-empirical correlation to determine the effects of a non-thermal plasma on the reduction of the detonation cell size for an H2 - air mixture. The modeling results showed that non-thermal plasma significantly reduces the detonation cell size. This effect is most pronounced at lean conditions, where the model predicted a reduction in cell size by a factor of more than 100. For stoichiometric and rich conditions, the cell size reduction was around a factor of 5. An investigation was conducted to determine the viability of using a non-thermal plasma to expand the operating regime of a rotating detonation combustor. The plasma was produced with a nanosecond pulse generator connected to a ceramic and metal centerbody electrode. Hot-fire testing results showed that the plasma causes detonation onset in conditions that would otherwise not support detonation. This effect was most prominent at near-stoichiometric conditions, with a reduced effect for richer or leaner mixtures.

Committee:

David Burnette (Advisor)

Subjects:

Aerospace Engineering; Mechanical Engineering; Plasma Physics

Keywords:

non-thermal plasma; plasma assisted combustion; nanosecond pulsed plasma; plasma modeling; detonation combustion; rotating detonation combustor; detonation;

Hall, Brenton TaylorUsing the Non-Uniform Dynamic Mode Decomposition to Reduce the Storage Required for PDE Simulations
Master of Mathematical Sciences, The Ohio State University, 2017, Mathematical Sciences
Partial Differential Equation simulations can produce large amounts of data that are very slow to transfer. There have been many model reduction techniques that have been proposed and utilized over the past three decades. Two popular techniques Proper Orthogonal Decomposition and Dynamic Mode Decomposition have some hindrances. Non-Uniform Dynamic Mode Decomposition (NU-DMD), which was introduced in 2015 by Gueniat et al., that overcomes some of these hindrances. In this thesis, the NU-DMD's mathematics are explained in detail, and three versions of the NU-DMD's algorithm are outlined. Furthermore, different numerical experiments were performed on the NU-DMD to ascertain its behavior with repect to errors, memory usage, and computational efficiency. It was shown that the NU-DMD could reduce an advection-diffusion simulation to 6.0075% of its original memory storage size. The NU-DMD was also applied to a computational fluid dynamics simulation of a NASA single-stage compressor rotor, which resulted in a reduced model of the simulation (using only three of the five simulation variables) that used only about 4.67% of the full simulation's storage with an overall average percent error of 8.90%. It was concluded that the NU-DMD, if used appropriately, could be used to possibly reduce a model that uses 400GB of memory to a model that uses as little as 18.67GB with less than 9% error. Further conclusions were made about how to best implement the NU-DMD.

Committee:

Ching-Shan Chou (Advisor); Jen-Ping Chen (Committee Member)

Subjects:

Aerospace Engineering; Applied Mathematics; Computer Science; Mathematics; Mechanical Engineering

Keywords:

Fluid Dynamics; Fluid Flow; Model Reduction; Partial Differential Equations; reducing memory; Dynamic Mode Decomposition; Decomposition; memory; Non-Uniform Dynamic Mode Decomposition

Riley, Zachary BryceInteraction Between Aerothermally Compliant Structures and Boundary-Layer Transition in Hypersonic Flow
Doctor of Philosophy, The Ohio State University, 2016, Aero/Astro Engineering
The use of thin-gauge, light-weight structures in combination with the severe aero-thermodynamic loading makes reusable hypersonic cruise vehicles prone to fluid-thermal-structural interactions. These interactions result in surface perturbations in the form of temperature changes and deformations that alter the stability and eventual transition of the boundary layer. The state of the boundary layer has a significant effect on the aerothermodynamic loads acting on a hypersonic vehicle. The inherent relationship between boundary-layer stability, aerothermodynamic loading, and surface conditions make the interaction between the structural response and boundary-layer transition an important area of study in high-speed flows. The goal of this dissertation is to examine the interaction between boundary layer transition and the response of aerothermally compliant structures. This is carried out by first examining the uncoupled problems of: (1) structural deformation and temperature changes altering boundary-layer stability and (2) the boundary layer state affecting structural response. For the former, the stability of boundary layers developing over geometries that typify the response of surface panels subject to combined aerodynamic and thermal loading is numerically assessed using linear stability theory and the linear parabolized stability equations. Numerous parameters are examined including: deformation direction, deformation location, multiple deformations in series, structural boundary condition, surface temperature, the combined effect of Mach number and altitude, and deformation mode shape. The deformation-induced pressure gradient alters the boundary-layer thickness, which changes the frequency of the most-unstable disturbance. In regions of small boundary-layer growth, the disturbance frequency modulation resulting from a single or multiple panels deformed into the flowfield is found to improve boundary-layer stability and potentially delay transition. For the latter, transitional boundary-layer aerothermodynamic load models are developed and incorporated into a fundamental aerothermoelastic code to examine the impact of transition onset location, transition length and transitional overshoot in heat flux and fluctuating pressure on the response of panels. Results indicate that transitional fluid loading can produce larger thermal gradients, greater peak temperatures, earlier flutter onset, and increased strain energy accumulation as compared to a panel under turbulent loading. Sudden transition, with overshoot in heat flux and fluctuating pressure, occurring near the leading edge of the panel provides the most conservative estimate for determining the life of the structure. Finally, the coupled interaction between boundary-layer transition and structural response is examined by enhancing the aerothermoelastic solver to allow for time-varying transition prediction as a function of the panel deformation and surface temperature. A kriging surrogate is developed to reduce the online computational expense associated with transition prediction within an aerothermoelastic simulation. For the configurations examined in this study, panel deformation has a more dominant effect on boundary-layer stability than surface temperature. Allowing for movement of the transition onset location results in characteristically different panel deformations due to spatial variation in the thermal bending moment. The response of the clamped panel is more sensitive to the transition onset location than the simply-supported panel.

Committee:

Jack McNamara (Advisor); Jeffrey Bons (Committee Member); Datta Gaitonde (Committee Member); Sandip Mazumder (Committee Member); Benjamin Smarslok (Committee Member); S. Michael Spottswood (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

hypersonic; boundary-layer stability; boundary-layer transition; aerothermoelastic; parabolized stability equations; surrogate modeling; kriging

Zhao, YueAutomatic Prevention and Recovery of Aircraft Loss-of-Control by a Hybrid Control Approach
Doctor of Philosophy (PhD), Ohio University, 2016, Electrical Engineering & Computer Science (Engineering and Technology)
In this dissertation, an integrated automatic flight controller for fixed-wing aircraft Loss-of-Control (LOC) Prevention and Recovery (iLOCPR) is designed. The iLOCPR system comprises: (i) a baseline flight controller for six degrees-of-freedom (6DOF) trajectory tracking for nominal flight designed by trajectory linearization, (ii) a bandwidth adaption augmentation to the baseline controller for LOC prevention using the timevarying PD-eigenvalues to trade tracking performance for increased stability margin and robustness in the presence of LOC-prone flight conditions, (iii) a controller reconfiguration for LOC arrest by switching from the trajectory tracking task to the aerodynamic angle tracking in order to recover and maintain healthy flight conditions at the cost of temporarily abandoning the mission trajectory, (iv) a guidance trajectory designer for mission restoration after the successful arrest of a LOC upset, and (v) a supervisory discrete-eventdriven Automatic Flight Management System (AFMS) to autonomously coordinate the control modes (i) - (iv). Theoretical analysis and simulation results are shown for the effectiveness of the proposed methods.

Committee:

Jim Zhu (Advisor); Douglas Lawrence (Committee Member); Frank Van Grass (Committee Member); Robert Williams (Committee Member); Aili Guo (Committee Member); Sergiu Aizicovici (Committee Member)

Subjects:

Aerospace Engineering; Engineering

Keywords:

Aircraft Loss-of-control; hybrid; arrest; prevention; recovery; flight control system; arrest; guidance; trajectory linearization control; switching mode; reconfiguration; bandwidth adaptation; multiple-time-scale nested loop

Stenger, Dillon MichaelDependency of Aluminum Nanoparticle Flash Ignition on Sample Internal Water Content and Aggregation
Master of Science (M.S.), University of Dayton, 2016, Aerospace Engineering
The United States Air Force believes that hypersonic flight opens a multitude of possibilities for the warfighter. One of the main propulsion systems for hypersonic flight is scramjet engines. These engines are currently ignited using a form of electric discharge and a primer fuel. This primer fuel system takes away valuable volume and weight in hypersonic vehicle designs. One alternative ignition method would be the utilization of plasmonic resonance to flash ignite aluminum nanoparticles. This process had been proven multiple times in the past and research has begun on characterizing how this ignition process can be affected. One that has not been researched to date has been how water content and agglomeration affect the energy needed for ignition to be achieved. To understand this functional dependence, aluminum nanoparticles were put through a series of trials with various levels of water content. Samples of particles were heated at 473.15 K to decrease water content and subsequently tested to determine the energy input needed for ignition. To understand the effects of increasing water content, particles were placed in an environment with at least 100% relative humidity for both 48 and 168 hours and then tested to determine the ignition energy needed. The results from the two humidified cases were compared with the data from a control group whose water content was not altered in a controlled manner. It was determined that by humidifying the particles the minimum energy needed for total ignition was lowered by approximately five percent on average while drying the particles increased the energy needed by approximately four percent on average.

Committee:

Aaron Altman, PhD (Advisor); Timothy Ombrello, PhD (Advisor); David Myszka, PhD (Committee Member)

Subjects:

Aerospace Engineering; Engineering; Nanoscience

Keywords:

Aluminum Nanoparticle Flash Ignition; Nanoparticle Aggregation; Nanoparticle Internal Water Content; Alternate Engine Ignition System

Michaels, Simone ColetteDevelopment and Assessment of Artificial Manduca sexta Forewings: How Wing Structure Affects Performance
Master of Sciences (Engineering), Case Western Reserve University, 2016, EMC - Aerospace Engineering
This research presents novel fabrication and testing techniques for artificial insect wings. A series of static and dynamic assessments are designed which allow consistent comparison of small, flexible wings in terms of structure and performance. Locally harvested hawk moths are tested and compared to engineered wings. Data from these experiments shows that the implemented replication method results in artificial wings with comparable properties to that of M. sexta. Flexural stiffness (EI) data shows a considerable difference between the left and right M. sexta wings. Furthermore, EI values on the ventral wing side are found to be consistently higher than the dorsal side. Based on dynamic results, variations in venation structure have the largest impact on lift generation. Lift tests on individual wings and wing sets indicate detrimental effects as a result of wing-wake interaction.

Committee:

Roger Quinn (Advisor); Mark Willis (Committee Member); Richard Bachmann (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Biology; Engineering; Entomology; Mechanical Engineering

Keywords:

Manduca sexta; artificial wings; wing fabrication; biomimicry

Nogar, Stephen MComprehensive Modeling and Control of Flexible Flapping Wing Micro Air Vehicles
Doctor of Philosophy, The Ohio State University, 2015, Aero/Astro Engineering
Flapping wing micro air vehicles hold significant promise due to the potential for improved aerodynamic efficiency, enhanced maneuverability and hover capability compared to fixed and rotary configurations. However, significant technical challenges exist to due the lightweight, highly integrated nature of the vehicle and coupling between the actuators, flexible wings and control system. Experimental and high fidelity analysis has demonstrated that aeroelastic effects can change the effective kinematics of the wing, reducing vehicle stability. However, many control studies for flapping wing vehicles do not consider these effects, and instead validate the control strategy with simple assumptions, including rigid wings, quasi-steady aerodynamics and no consideration of actuator dynamics. A control evaluation model that includes aeroelastic effects and actuator dynamics is developed. The structural model accounts for geometrically nonlinear behavior using an implicit condensation technique and the aerodynamic loads are found using a time accurate approach that includes quasi-steady, rotational, added mass and unsteady effects. Empirically based parameters in the model are fit using data obtained from a higher fidelity solver. The aeroelastic model and its ingredients are compared to experiments and computations using models of higher fidelity, and indicate reasonable agreement. The developed control evaluation model is implemented in a previously published, baseline controller that maintains stability using an asymmetric wingbeat, known as split-cycle, along with changing the flapping frequency and wing bias. The model-based controller determines the control inputs using a cycle-averaged, linear control design model, which assumes a rigid wing and no actuator dynamics. The introduction of unaccounted for dynamics significantly degrades the ability of the controller to track a reference trajectory, and in some cases destabilizes the vehicle. This demonstrates the importance of considering coupled aeroelastic and actuator dynamics in closed-loop control of flapping wings. A controller is developed that decouples the normal form of the vehicle dynamics, which accounts for coupling of the forces and moments acting on the vehicle and enables enhanced tuning capabilities. This controller, using the same control design model as the baseline controller, stabilizes the system despite the uncertainty between the control design and evaluation models. The controller is able to stabilize cases with significant wing flexibility and limited actuator capabilities, despite a reduction in control effectiveness. Additionally, to achieve a minimally actuated vehicle, the wing bias mechanism is removed. Using the same control design methodology, increased performance is observed compared to the baseline controller. However, due to the dependence on the split-cycle mechanism to generate a pitching moment instead of wing bias, the controller is more susceptible to instability from wing flexibility and limited actuator capacity. This work highlights the importance of coupled dynamics in the design and control of flapping wing micro air vehicles. Future enhancements to this work should focus on the reduced order structural and aerodynamics models. Applications include using the developed dynamics model to evaluate other kinematics and control schemes, ultimately enabling improved vehicle and control design.

Committee:

Jack McNamara (Advisor); Andrea Serrani (Advisor); Manoj Srinivasan (Committee Member); Junmin Wang (Committee Member); Michael Oppenheimer (Committee Member); David Doman (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Flapping Wings; Control; Aeroelasticity; Dynamics

Chen, LinMEASUREMENTS OF AUTOCORRELATION FUNCTIONS USING A COMBINATION OF INTRA- AND INTER-PULSES
Master of Science, Miami University, 2015, Computational Science and Engineering
Incoherent scatter radar (ISR) is a versatile tool to study the ionosphere by measuring the autocorrelation function (ACF). Accurate ACF in the E-region is difficult to obtain because the relative short range limits the length of a pulse. The short correlation time of the ionosphere renders the correlation using the pulse-to-pulse technique useless. In the thesis, we study a method that combines intra-pulse and inter-pulse techniques and apply it to the data taken at Arecibo Observatory. We show simultaneously measured ACF’s at short and long lags and summarize the merits of ACF. Applications of ACF and its advantages are discussed. The technique used here will make the derivation of ionosphere parameters more accurate.

Committee:

Qihou Zhou (Advisor); Chi-Hao Cheng (Committee Member); Dmitriy Garmatyuk (Committee Member)

Subjects:

Aeronomy; Aerospace Engineering; Computer Engineering; Computer Science; Earth; Radiology

Keywords:

Incoherent scatter radar; ionosphere; E-region; parameters; autocorrelation function; accurate

Mahmoudi, BehzadInvestigation the Effect of Tribological Coatings: WC/a-C:H and Black Oxide on Micropitting Behavior of SAE52100 Bearing Steel
Doctor of Philosophy, University of Akron, 2015, Civil Engineering
Spherical roller bearings (SRBs) utilized in the gearboxes of wind turbine generators are known to be especially susceptible to premature failure due to low cycle micropitting of the raceways. Micropitting in rolling element bearings is believed to arise from significant roller/raceway sliding in thin film lubrication conditions. Roller/raceway sliding occurs in SRBs as a consequence of their geometry, and almost all the bearings in wind turbine gearboxes operate in thin film (or low lambda) lubrication conditions. There is currently no accepted solution to mitigate micropitting in wind turbine gearboxes that are equipped with SRBs. Since WC/a-C:H coatings on rolling elements have been effectively used to solve wear issues encountered by SRBs in other industrial applications, these coatings have been offered as a solution to low cycle micropitting in wind turbine gearbox SRBs. This research plan has been developed to test the hypothesis that a WC/a-C:H coating will mitigate or eliminate micropitting such as that experienced by SRBs in wind turbine gearboxes. The laboratory tool that is used to create micropitting on test specimens is the PCS Instruments Micropitting Rig (PCS MPR). The MPR is a three-contact disc machine in which there are three rings of equal diameter positioned at 120 degrees apart with a smaller diameter roller located in the middle and in contact with all the rings. This arrangement allows the test roller to be subjected to a large number of rolling contact cycles in a short period of time and hence significantly reduces testing time. At a typical entrainment speed of 3.5m/s, the central test roller will experience approximately one million contact cycles per hour. Since the controls of the PCS MPR allow the speed, slide-roll ratio, temperature, and load to be automatically and independently controlled, the thin film lubrication and slide/roll ratio conditions that generate micropitting on SRBs can be reproduced in the laboratory. Most wind turbine gearboxes operate with a synthetic ISO-320 lubricating oil with anti-wear and extreme pressure additives. However, to ensure thin film lubrication conditions necessary for micropitting experiments were performed on the MPR using an ISO-10 base oil. Baseline tribological testing were performed using untreated SAE 52100 rings and the roller. The targeted surface finish on the rings and the rollers varied from about 0.2 to about 0.6 micrometer Ra, and the entire surface topography was quantified using a Zygo 7300 3D optical profilometer. The sets of roller and rings were tested on the MPR using a range of slide/roll ratios from 0.0 to +/- 10% at contact stresses up to about 3 GPa. The number of cycles needed to generate the onset of micropitting was recorded and some tests were repeated up to three times. Results of micropitting tests on steel/steel, steel/WC/a-C:H and WC/a-C:H/steel contacts were compared with a tribological conversion coating; black oxide. Black oxide is a surface treatment that converts the surface of ferrous alloys to magnetite (Fe3O4). It has been utilized to reduce wear and corrosion of rolling element bearings and gears, and its use has become especially widespread on roller bearings used in the gearboxes of modular wind turbines. It has been reported that black oxide might have a lower friction coefficient than steel, which may reduce shear stresses due to friction, dampen vibrations, or possibly prevent the diffusion of hydrogen.

Committee:

Gary Doll, Professor (Advisor); Evans Ryan, Doctor (Committee Member); Binienda Wieslaw, Doctor (Committee Member); Dong Yalin, Doctor (Committee Member); Menzemer Craig, Doctor (Committee Member); Sancaktar Erol , Doctor (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Materials Science; Mechanical Engineering

Keywords:

DLC coating, Tribology, Bearing, Micropitting, Black Oxide, Surface Fatigue, Frictional Heat, Flash Temprature, Hertzian Contact

Lipkin, IlyaTesting Software Development Project Productivity Model
Doctor of Philosophy in Manufacturing and Technology Management, University of Toledo, 2011, Manufacturing and Technology Management

Software development is an increasingly influential factor in today’s business environment, and a major issue affecting software development is how an organization estimates projects. If the organization underestimates cost, schedule, and quality requirements, the end results will not meet customer needs. On the other hand, if the organization overestimates these criteria, resources that could have been used more profitably will be wasted.

There is no accurate model or measure available that can guide an organization in a quest for software development, with existing estimation models often underestimating software development efforts as much as 500 to 600 percent. To address this issue, existing models usually are calibrated using local data with a small sample size, with resulting estimates not offering improved cost analysis.

This study presents a conceptual model for accurately estimating software development, based on an extensive literature review and theoretical analysis based on Sociotechnical Systems (STS) theory. The conceptual model serves as a solution to bridge organizational and technological factors and is validated using an empirical dataset provided by the DoD.

Practical implications of this study allow for practitioners to concentrate on specific constructs of interest that provide the best value for the least amount of time. This study outlines key contributing constructs that are unique for Software Size E-SLOC, Man-hours Spent, and Quality of the Product, those constructs having the largest contribution to project productivity. This study discusses customer characteristics and provides a framework for a simplified project analysis for source selection evaluation and audit task reviews for the customers and suppliers.

Theoretical contributions of this study provide an initial theory-based hypothesized project productivity model that can be used as a generic overall model across several application domains such as IT, Command and Control, Simulation and etc¿¿¿ This research validates findings from previous work concerning software project productivity and leverages said results in this study. The hypothesized project productivity model provides statistical support and validation of expert opinions used by practitioners in the field of software project estimation.

Committee:

Jeen Su Lim (Committee Chair); James Pope (Committee Member); Michael Mallin (Committee Member); Michael Jakobson (Committee Member); Wilson Rosa (Advisor)

Subjects:

Aerospace Engineering; Armed Forces; Artificial Intelligence; Business Administration; Business Costs; Computer Engineering; Computer Science; Economic Theory; Economics; Electrical Engineering; Engineering; Industrial Engineering; Information Science; Information Systems; Information Technology; Management; Marketing; Mathematics

Keywords:

"Software Estimation"; "Software Cost Model"; "Department of Defense Data"; COCOMO; "Software Project Productivity Model"

Hagerty, PhillipPhysical Vapor Deposition of Materials for Flexible Two Dimensional Electronic Devices
Master of Science (M.S.), University of Dayton, 2016, Chemical Engineering
Molybdenum Disulfide (MoS2) and Tungsten Disulfide (WS2) are two materials in a larger class of materials known as Transition Metal Dichalcogenides (TMDs) that have begun emerge as semiconducting materials. When their horizontal length scale is reduced from bulk to monolayer they demonstrate surprising combinations of properties including a direct electronic band gap and mechanical flexibility. Two dimensional (2D) materials have the potential to revolutionize performance and tailorability of electro-optical devices fabricated entirely from molecularly thin materials. In a departure from traditional exfoliation or high temperature chemical vapor deposition approaches for 2D materials synthesis, novel plasma-based physical vapor (PVD) techniques were used to fabricate uniform films over large areas. This experimental approach allowed unique studies. For example, vapor phase growth allowed systematically variation of the sulfur vacancy concentration in MoS2 and WS2 and subsequent correlation to electronic properties. This effort leads to controlled bottom-up assembly of 2D devices on flexible and standard substrates to experimentally couple the remarkable intrinsic mechanical and electronic properties of ultrathin materials, which are particularly appealing for molecular sensing. The pursuit of an all physical vapor deposited field effect transistor (FET) is the main priority for the 2D materials community as definitive demonstration of the feasibility of physical vapor deposition as a scalable technique for consumer electronics. PVD sputtered Titanium Nitride (TiN) and Tungsten (W) were experimentally characterized as potential back gated materials, Plasma Vapor Deposited (PLD) a-BN was electrically characterized as a uniform ultra-thin low temperature dielectric, and sputtered MoS2 and WS2 were electrically characterized as a semiconductor material. Tungsten deposition methods were previously researched and mimicked for smooth and conductive back gate material depositions. TiN was parameterized and the best room temperature deposition conditions were 70V applied to the sputtering gun with 25 sccm gas flow of 90% N2 and 10% Ar for 60 minutes. The best high temperature depositions were done at 500oC, 70V applied to the sputtering gun with 25 sccm gas flow of 90% N2 and 10% Ar for 30 minutes. Dielectric a-BN electrical characterization began to occur after 6nm which equated to 100 pulses, while 200 pulses equated to 16.5nm thickness. A dielectric constant of 5.90 ± .65 is reported for a-BN for under 20nm thickness. Soft probing techniques by conductively pasted gold wires on the probe tips were required to obtain true electrical measurements of 2D materials in a stacked structure, otherwise scratching would occur and uniformity would cease to exist in the film. Chemical Vapor Deposition (CVD) and mechanical exfoliation have provided the only working TMD semiconductor 2D materials in MOSFET structure to date with lithographic electrical connections. PVD sputtering as a new synthesis method for crystalline TMD with a stoichiometric ratio is achievable over large areas. Though, reduced area depositions are required for doped Silicon and Silicon Oxide (SiO2) based FET structures to limit the chance of encountering a pinhole. With reduced area and stoichiometric enhancement control, sputtered TMD films exhibit high sensitivity to oxygen and are electrically conductive even when exposed to a field effect. Increasing the grain size of the sputtered materials is the next driving force towards a fully recognizable TMD thin film transistor.

Committee:

Christopher Muratore, PhD (Committee Chair); Terrence Murray, PhD (Committee Member); Kevin Myers, DSc (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Electrical Engineering; Engineering; Materials Science

Keywords:

PVD; materials; 2D materials; Nanoelectronics; TMDs; 2D Transistors; Molybdenum Disulfide; MoS2; WS2; Tungsten Disulfide

Thompson, John RyanRELATING MICROSTRUCTURE TO PROCESS VARIABLES IN BEAM-BASED ADDITIVE MANUFACTURING OF INCONEL 718
Master of Science (MS), Wright State University, 2014, Mechanical Engineering
The advancement of laser or electron beam-based additive manufacturing requires the ability to control solidification microstructure. Previous work combined analytical point source solutions and nonlinear thermal finite element analysis (FEA) to explore the effects of deposition process variables on Ti-6Al-4V solidification microstructure. The current work seeks to extend the approach to Inconel 718, with the addition of Cellular Automaton-Finite Element (CAFE) models. Numerical data from finite element results are extracted in order to calculate accurate melt pool geometry, thus leading to corresponding cooling rates and thermal gradients. The CAFE models are used to simulate grain grown and nucleation, providing a link between additive manufacturing process variables (beam power/velocity) and solidification microstructure. Ultimately, a comparison of results between Ti-6Al-4V and Inconel 718 is expected to lay the ground work for the integrated control of melt pool geometry and microstructure in other alloys.

Committee:

Nathan Klingbeil, Ph.D. (Advisor); Raghavan Srinivasan, Ph.D., P.E. (Committee Member); Jaimie Tiley, Ph.D. (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Engineering; Materials Science; Mechanical Engineering

Keywords:

Additive Manufacturing Beam Laser FEA CAFE ProCAST Inconel 718 Ti-6Al-4V melt pool process variables microstructure power velocity gamma prime 3D printing Rosenthal

Stalcup, Erik JamesNumerical Modeling of Upward Flame Spread and Burning of Wavy Thin Solids
Master of Sciences, Case Western Reserve University, EMC - Aerospace Engineering
Flame spread over solid fuels with simple geometries has been extensively studied in the past, but few have investigated the effects of complex fuel geometry. This study uses numerical modeling to analyze the flame spread and burning of wavy (corrugated) thin solids and the effect of varying the wave amplitude. Sensitivity to gas phase chemical kinetics is also analyzed. Fire Dynamics Simulator is utilized for modeling. The simulations are two-dimensional Direct Numerical Simulations including finite-rate combustion, first-order pyrolysis, and gray gas radiation. Changing the fuel structure configuration has a significant effect on all stages of flame spread. Corrugated samples exhibit flame shrinkage and break-up into flamelets, behavior not seen for flat samples. Increasing the corrugation amplitude increases the flame growth rate, decreases the burnout rate, and can suppress flamelet propagation after shrinkage. Faster kinetics result in slightly faster growth and more surviving flamelets. These results qualitatively agreement with experiments.

Committee:

James T'ien (Committee Chair); Joseph Prahl (Committee Member); Yasuhiro Kamotani (Committee Member)

Subjects:

Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

modeling;simulation;numerical modeling;combustion;computational combustion;direct numerical simulation;flame spread;burning;wavy;corrugated;fire dynamics simulator;FDS;fuel structure;fuel geometry;complex geometry;cardboard;

Casaday, Brian PatrickInvestigation of Particle Deposition in Internal Cooling Cavities of a Nozzle Guide Vane
Doctor of Philosophy, The Ohio State University, 2013, Aero/Astro Engineering
Experimental and computational studies were conducted regarding particle deposition in the internal film cooling cavities of nozzle guide vanes. An experimental facility was fabricated to simulate particle deposition on an impingement liner and upstream surface of a nozzle guide vane wall. The facility supplied particle-laden flow at temperatures up to 1000°F (540°C) to a simplified impingement cooling test section. The heated flow passed through a perforated impingement plate and impacted on a heated flat wall. The particle-laden impingement jets resulted in the buildup of deposit cones associated with individual impingement jets. The deposit growth rate increased with increasing temperature and decreasing impinging velocities. For some low flow rates or high flow temperatures, the deposit cones heights spanned the entire gap between the impingement plate and wall, and grew through the impingement holes. For high flow rates, deposit structures were removed by shear forces from the flow. At low temperatures, deposit formed not only as individual cones, but as ridges located at the mid-planes between impinging jets. A computational model was developed to predict the deposit buildup seen in the experiments. The test section geometry and fluid flow from the experiment were replicated computationally and an Eulerian-Lagrangian particle tracking technique was employed. Several particle sticking models were employed and tested for adequacy. Sticking models that accurately predicted locations and rates in external deposition experiments failed to predict certain structures or rates seen in internal applications. A geometry adaptation technique was employed and the effect on deposition prediction was discussed. A new computational sticking model was developed that predicts deposition rates based on the local wall shear. The growth patterns were compared to experiments under different operating conditions. Of all the sticking models employed, the model based on wall shear, in conjunction with geometry adaptation, proved to be the most accurate in predicting the forms of deposit growth. It was the only model that predicted the changing deposition trends based on flow temperature or Reynolds number, and is recommended for further investigation and application in the modeling of deposition in internal cooling cavities.

Committee:

Jeffrey Bons (Advisor); Ali Ameri (Committee Member); Michael Dunn (Committee Member); Datta Gaitonde (Committee Member); Sandip Mazumder (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

particle deposition; turbomachinery; internal cooling, engine fouling

Hahn, Casey BernardDesign and Validation of the New Jet Facility and Anechoic Chamber
Master of Science, The Ohio State University, 2011, Mechanical Engineering

The jet facility and anechoic chamber at the Gas Dynamics and Turbulence Laboratory (GDTL) at The Ohio State University have been redesigned and rebuilt to significantly improve their capabilities. The new jet facility is capable of jets of 2-inch diameter—twice the size of the old jets. The new and much larger anechoic chamber can handle the larger jet and enables the measurements of shock noise generated by the jet of tactical aircraft. Free-field qualification requirements of ISO 3745 standard are met, and the chamber has a cutoff frequency of 160 Hz. A few improvements were incorporated into the new facility including thicker, acoustically-treated walls and an acoustically transparent grating floor above the floor anechoic wedges. Tests showed that very minor variations in the spectra are introduced by the grating floor panels.

Two additional microphones were added to the new facility with three within the upstream region of the acoustic field (a maximum polar angle of 130° compared to the maximum of 90° of the old facility). The radial distances of the microphones were increased, and far-field tests show that the microphones are safely within the far-field of 1-inch and 1.5-inch jets. For a 2-inch jet, some microphones are likely within the transition region of the acoustic field but could be moved farther outward to locate them within the far-field, as there is more room within the chamber. The stagnation chamber diameter was increased from 3.068 inches to 5.047 inches to handle the larger mass flow rate of a 2-inch jet. Initially, spectra suffered from narrowband cavity tones generated by ports upstream. The ports were modified, and a second perforated plate was added to eliminate these tones.

Acoustic data of the new and old jets are compared, and some minor differences in the high frequency content of the spectra are found. Early guesses point to internal rig noise created by flow through the second perforated plate. Work will continue to remove these differences. Finally, PIV results of the old and new jets are compared. The Mach number decay and spreading rates of a new Mach 0.9 jet compare well to an old Mach 0.9 jet. The old Mach 0.9 jets had slightly lower levels of turbulent kinetic energy. A new Mach 1.3 jet compares well with an old Mach 1.3 jet all these statistics.

Committee:

Mo Samimy, PhD (Advisor); Datta Gaitonde, PhD (Committee Member)

Subjects:

Acoustics; Aerospace Engineering; Engineering; Experiments; Fluid Dynamics; Mechanical Engineering

Keywords:

jet facility; anechoic chamber; aeroacoustics

Memory, Curtis L.Turbulent Transition Behavior in a Low Pressure Turbine Subjected to Separated and Attached-Flow Conditions
Doctor of Philosophy, The Ohio State University, 2010, Mechanical Engineering
Various time accurate numerical simulations were conducted on the aft-loaded L1A low pressure turbine airfoil operating at Reynolds numbers presenting with fully-stalled, non-reattaching laminar separation. The numerical solver TURBO was modified from its annular gas turbine simulation configuration to conduct simulations based on a linear cascade wind tunnel facility. Simulation results for the fully separated flow fields revealed various turbulent decay mechanisms. Separated shear layer decay, in the form of vortices forming between the shear layer and the blade wall, was shown to agree with experimental particle image velocimetry (PIV) data in terms of decay vortex size and core vorticity levels. These vortical structures eventually mix into a large recirculation zone which dominates the blade wake. Turbulent wake extent and time-averaged velocity distributions agreed with PIV data. Steady-blowing vortex generating jet (VGJ) flow control was then applied to the flow fields. VGJ-induced streamwise vorticity was only present at blowing ratios above 1.5. VGJs actuated at the point of flow separation on the blade wall were more effective than those actuated downstream, within the separation zone. Pulsed-blowing VGJs at the upstream blade wall position were then actuated at various pulsing frequencies, duty cycles, and blowing ratios. These condition variations yielded differing levels of separation zone mitigation. Pulsed VGJs were shown to be more effective than steady blowing VGJs at conditions of high blowing ratio, high frequency, or high duty cycle, where blowing ratio had the highest level of influence on pulsed jet efficacy. The characteristic "calm zone" following the end of a given VGJ pulse was observed in simulations exhibiting high levels of separation zone mitigation. Numerical velocity fields near the blade wall during this calm zone was shown to be similar to velocity fields observed in PIV data. Instantaneous numerical vorticity fields indicated that the elimination of the separation zone directly downstream of the VGJ hole is a primary indicator of pulsed VGJ efficacy. This indicator was confirmed by numerical time-averaged velocity magnitude rms data in the same region.

Committee:

JenPing Chen, PhD (Advisor); Jeffrey P. Bons, PhD (Committee Member); James W. Gregory, PhD (Committee Member); Mei Zhuang, PhD (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

vortex generating jet; low pressure turbine; direct numeric simulation; steady blowing; pulsed blowing; particle image velocimetry; vortex

Jiang, HuaEffect of Changes in Flow Geometry, Rotation and High Heat Flux on Fluid Dynamics, Heat Transfer and Oxidation/Deposition of Jet Fuels
Doctor of Philosophy (Ph.D.), University of Dayton, 2011, Mechanical Engineering

Jet fuel is used in high-performance military flight vehicles for cooling purposes before combustion. It is desirable to investigate the influence of the flow and heating conditions on fuel heat transfer and thermal stability to develop viable mitigation strategies. Computational fluid dynamics (CFD) simulations and experiments can provide the understanding of the fuel physical phenomena which involves the fluid dynamics, heat transfer and chemical reactions. Three distinct topics are studied: The first topic considers the effect of flow geometry on fuel oxidation and deposition. Experiments and CFD modeling were performed for fuels flowing through heated tubes which have either a sudden expansion or contraction. It was found that the peak deposition occurs near the maximum oxidation rate and excess deposition is formed near the step. This study provides information for the fuel system designer which can help minimize surface deposition due to fuel thermal oxidation.

In the second area of study, the fuel passed heated rotational test articles to investigate the effect of rotation on fuel heat transfer. The coupled effects of centrifugal forces and turbulent flow result in fuel temperatures that increase with rotational speed. This indicates that the convective heat transfer is enhanced as rotational speed increases. This work can assist the understanding of using jet fuel to cool the turbine engine.

In the third segment of research, the fuel was exposed to “rocket-like” conditions. This investigation is to explore the effect of high heat flux and high flow velocity on fuel heat transfer and oxidation/deposition. Simulations show a temperature difference over several hundred degrees in the radial direction within the very thin thermal boundary layer under rapid heating. The fuel contacting the interior wall is locally heated to a supercritical state. As a result, the heat transfer is deteriorated in the supercritical boundary layer. Both simulated and measured deposit profiles show a peak deposit near the end of the heated section. These observations may eventually have an application to the design of high speed supersonic vehicles with improved cooling capabilities.

Committee:

Jamie S. Ervin, PhD (Advisor); Steven Zabarnick, PhD (Committee Co-Chair); Timothy J. Edwards, PhD (Committee Member); Kevin P. Hallinan, PhD (Committee Member)

Subjects:

Aerospace Engineering; Mechanical Engineering

Keywords:

jet fuel; heat transfer deterioration; high heat flux; temperature peak; supercritical; fuel properties; nozzle; sudden expansion/contraction in flow path; fuel deposition; turbulence models; rotation passage; recirculation flow; excess deposition

Rampilla, Lokamanya Siva ManoharA FINITE ELEMENT APPROACH TO STRESS ANALYSIS OF FACE GEARS
Master of Science in Mechanical Engineering, Cleveland State University, 2012, Fenn College of Engineering
Face Gears have alternative gear-teeth configuration compared to Bevel Gears. Face Gear have a standard spur pinion as opposed to a bevel Gear. This work concentrates on modeling of a Face-gear, Meshed with a spur gear, using CAD Software and Finite Elements Analysis. The bending stress developed at the gear teeth is determined. Numerical results are validated using the bending stress developed between two involute spur gears.

Committee:

Majid Rashidi, PhD (Committee Chair); Rama S. R. Gorla, PhD (Committee Member); Asuquo Ebiana, PhD (Committee Member)

Subjects:

Aerospace Engineering; Design; Mechanical Engineering

Keywords:

face gear; Hygear; straight bevel gear; helicopter transmission; analysis

Balagurunathan, JayakishanInvestigation of Ignition Delay Times of Conventional (JP-8) and Synthetic (S-8) Jet Fuels: A Shock Tube Study
Master of Science (M.S.), University of Dayton, 2012, Mechanical Engineering
The global depletion of petroleum-based fuels has led the world to more closely examine alternate fuels. Therefore, alternate fuels produced from feedstocks such as coal, soybeans, palm oil or switch grass through methods such as coal liquefaction, biomass gasification, and Fischer-Tropsch synthesis have been tested. Among these techniques, fuels generated using Fischer-Tropsch technologies are of interest because they produce clean burning hydrocarbons similar to those found in commercial fuels. Therefore, in this study the Fischer-Tropsch derived S-8 fuel was evaluated as a drop-in replacement for the jet fuel JP-8. The jet fuel JP-8 is comprised of n-, iso- and cyclo- alkanes as well as aromatics while the S-8 fuel is primarily comprised of n- and iso- alkanes. The composition of the fuel affects its ignition characteristics chemically and physically by either advancement or delay of time to ignition. Since this study focused on the chemical effects, the fuels were completely pre-vaporized and pre-mixed. A high pressure, high temperature heated single pulse shock tube was used for this study. The shock tube is an established experimental tool used to obtain ignition delay data behind reflected shock waves under operating conditions relevant to modern engines. The experiments were conducted over a temperature range of 1000-1600 K, a pressure of 19±2 atm, equivalence ratios of 0.5, 1 and 3, within a dwell time of 7.6±0.2 ms and an argon dilution of 93% (v/v). Ignition delay times were measured using the signal from the pressure transducer on the end plate with guidance from the optical diagnostic signal. Along with JP-8 and S-8, the ignition delay of n-heptane was also studied. N-heptane was chosen to represent the n-alkanes in the fuels for this study since it was present in both fuels and also to prove the fact that the n-alkanes were rate controlling. The results indicate that both S-8 and JP-8 fuels have similar ignition delays at corresponding equivalence ratios. The fuel-rich mixtures ignited faster at lower temperatures (<1150 K) and the fuel-lean mixtures ignited faster at higher temperatures (>1150 K). In the transition period between lower to higher temperatures (~1100-1200 K), the equivalence ratio had no significant effect on the ignition delay time. The results also show that the ignition delay time measurements of S-8 and JP-8 fuels are similar to the ignition delay of n-heptane at the equivalence ratio of Φ=0.5 and thereby indicate that the n-alkanes present in these fuels controlled the ignition under these conditions. The ignition delay results of S-8 and JP-8 at Φ=3.0 from this study were also compared to prior work (Kahandawala et al., 2008) on 2-methylheptane and n-heptane/toluene (80/20 liquid vol.%), respectively and found to be indistinguishable. This data serves to extend the gas phase ignition delay database for both JP-8 and S-8 and is the first known data taken for both these fuels at higher temperatures (>1000 K) for an equivalence ratio of 3.0 with argon as the diluent gas.

Committee:

Sukh Sidhu, Dr (Committee Chair); Philip Taylor, Dr (Committee Member); Moshan Kahandawala, Dr (Committee Member)

Subjects:

Aerospace Engineering; Aerospace Materials; Alternative Energy; Automotive Engineering; Automotive Materials; Chemical Engineering; Chemistry; Energy; Engineering; Environmental Engineering; Mechanical Engineering; Petroleum Engineering; Technology

Keywords:

Ignition delay; shock tube; S-8; JP-8; Jet fuels; Fuel characteristics; heated shock tube; Fischer-Tropsch; Alternate fuels; alkanes; synthetic fuel; fuel; iso-alkanes; jayakishan balagurunathan

O'Neil, Alanna R.Chemiluminescence and High Speed Imaging of Reacting Film Cooling Layers
Master of Science (M.S.), University of Dayton, 2011, Aerospace Engineering

The demand for more efficient and compact gas turbine engines has resulted in an increase in the operating temperatures and pressures and a decrease in combustor weight and size. These advances may result in incomplete combustion products entering the turbine section. The products can react with the air intended to cool the turbine vanes, and the resulting flame can cause damage to the engine. This study reports chemiluminescence measurements of flames and correlates these to heat release rate and the measured heat flux to a surface. To accomplish this, fuel rich combustion products are generated in a well-stirred reactor. The flow of products is directed over a flat plate with cooling air jets normal to the flow. Chemiluminescence data of the flames is obtained, along with high speed images, and temperature measurements of the flow inside the test section. Three film cooling geometries are studied: normal holes, fan shaped holes, and slot. Measurements are acquired at three equivalence ratios (1.3, 1.4, and 1.5) at three different blowing ratios (M = 1, 4, and 7).

It is found that the rate of heat release from the flame does not always trend the same as the heat transfer to the surface. It is also seen that a large reaction region does not always equate to high heat flux to the surface. If enough cooling air is present the surface is protected from the heat released from the flame.

Committee:

Dilip Ballal, PhD (Committee Chair); Scott Stouffer, PhD (Committee Member); David Blunck, PhD (Committee Member); Sukh Sidhu, PhD (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

Film Cooling; Chemiluminescence; Reacting Boundary Layers; Flames; Image Analysis;

Thake, Michael PatrickInvestigation of a Laminar Airfoil with Flow Control and the Effect of Reynolds Number
Master of Science, The Ohio State University, 2011, Aero/Astro Engineering
Wind tunnel tests are performed on a NACA 643-618 airfoil at Reynolds numbers of 6.4x104, 1.8x105, 1.0x106, and 4.0x106 in order study several aspects of a laminar airfoil. Studies of flow control, separation bubbles and the effect of Reynolds number are the major topics of this effort. The tools used for investigation are surface pressure measurements, wake surveys, particle image velocimetry, hot-film anemometry, surface-oil flow visualization, and infrared imaging in order to view the problem from many angles. Preliminary testing at a Reynolds number of 64,000 determined that four distinct flow regimes exist with respect to angle of attack: weak laminar separation, moderate laminar separation, laminar separation bubble, and strong leading edge laminar separation. A portion of the study investigates the cause of such dynamic flow physics. Attempts are then made to employ flow control to induce or imitate the laminar separation bubble. By creating the laminar separation bubbles, significant lift increase and drag reduction are realized over a broader range of angles of attack. Normal blowing, suction, and zigzag tape are used, which are all well-characterized devices and have the potential to enhance lift and reduce drag. Lift is increased significantly and separation is delayed in three of the four regions as a result of control, where the region of no change is when the laminar separation bubble is already in effect. It is observed that the optimal flow control device changes between regimes because different flow physics are required to induce a change. Studies of Reynolds number scaling found that the lift increased and drag decreased as Reynolds number increased. It is important to note that the laminar separation bubble becomes naturally effective at most angles of attack by a Reynolds number of 180,000. Therefore, the value of flow control diminishes except in regions where strong leading edge separation is the limiting element of the airfoil. This research suggests that the laminar airfoil can be controlled in an energy efficient manner such that high performance is gained across all flight regimes with straightforward actuation.

Committee:

Jeffrey Bons, PhD (Advisor); James Gregory, PhD (Committee Member)

Subjects:

Aerospace Engineering; Engineering

Keywords:

laminar airfoil; aerodynamics; flow control; Reynolds number; separation

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

Kearney-Fischer, Martin A.The Noise Signature and Production Mechanisms of Excited High Speed Jets
Doctor of Philosophy, The Ohio State University, 2011, Mechanical Engineering

Following on previous works showing that jet noise has significant intermittent aspects, the present work assumes that these intermittent events are the dominant feature of jet noise. A definition and method of detection for intermittent noise events are devised and implemented. Using a large experimental database of acoustically subsonic jets with different acoustic Mach numbers (Ma = 0.5 – 0.9), nozzle exit diameters (D = 2.54, 5.08, & 7.62 cm), and jet exit temperature to ambient temperature ratios (ETR = 0.84 – 2.70), these events are extracted from the noise signals measured in the anechoic chamber of the NASA Glenn AeroAcoustic Propulsion Laboratory. It is shown that a signal containing only these events retains all of the important aspects of the acoustic spectrum for jet noise radiating to shallow angles relative to the jet axis, validating the assumption that intermittent events are the essential feature of the peak noise radiation direction. The characteristics of these noise events are analyzed showing that these events can be statistically described in terms of three parameters (the variance of the original signal, the mean width of the events, and the mean time between events) and two universal statistical distribution curves. The variation of these parameters with radiation direction, nozzle diameter, exit velocity, and temperature are discussed.

A second experimental database from the Ohio State University Gas Dynamics and Turbulence Laboratory of far-field acoustic data from an excited subsonic jet with hydrodynamic Mach number of 0.9 (Mj = 0.9) at various total temperature ratios (TTR = 1.0 - 2.5) is analyzed using the same process. In addition to the experimental acoustic database, conclusions and observations from previous works using Localized Arc Filament Plasma Actuators (LAFPAs) are leveraged to inform discussion of the statistical results and their relationship to the jet flow dynamics. Analysis of the excited jet reveals the existence of a resonance condition. When excited at the resonance condition, large amounts of noise amplification can occur – this is associated with each large-scale structure producing a noise event. Conversely, noise reduction occurs when only one noise event occurs per several large-scale structures. One of the important conclusions from these results is that there seems to be a competition for flow energy among neighboring structures that dictates if and how their dynamics will produce noise that radiates to the far-field.

Utilizing the results from both databases, several models for noise sources addressing different aspects of the results are discussed. A simple model for this kind of noise signal is used to derive a relationship between the characteristics of the noise events and the fluctuations in the integrated noise source volume. Based on the known flow-field dynamics and the acoustic results from the excited jet, a hypothetical model of the competition process is described. These various models speculate on the dynamics relating the noise sources to the signal in the far-field and, as such, the present work cannot provide a definitive description of jet noise sources, but can serve as a guide to future exploration.

Committee:

Mo Samimy, PhD (Advisor); Igor Adamovich, PhD (Committee Member); James Bridges, PhD (Committee Member); Michael Dunn, PhD (Committee Member); Walter Lempert, PhD (Committee Member)

Subjects:

Acoustics; Aerospace Engineering; Fluid Dynamics; Mechanical Engineering

Keywords:

Jet Noise; Aeroacoustics; Active Flow Control; Turbulence

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