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Theses and Dissertations

2009

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Articles 1 - 30 of 71

Full-Text Articles in Aerospace Engineering

Laser-Induced Fluorescence And Synthetic Jet Fuel Analysis In The Ultra Compact Combustor, Aaron C. Drenth Dec 2009

Laser-Induced Fluorescence And Synthetic Jet Fuel Analysis In The Ultra Compact Combustor, Aaron C. Drenth

Theses and Dissertations

The Ultra-Compact Combustor (UCC) is currently under investigation at the Air Force Institute of Technology (AFIT) and Air Force Research Laboratory’s Propulsion Directorate. The combustor is a small-scale, axi-symmetric, atmospheric pressure, laboratory combustor with an outer circumferential cavity in which the flame is stabilized by a highly accelerated swirled flow. UCCs will enable aero gas turbine reheat cycle engines and significantly shorten conventional aero gas turbine engines. The experiments of this work utilized the AFIT small-scale combustion diagnostics facility, investigating a sector model of the UCC. The research objectives were to perform an addition to the COAL lab laser diagnostic …


Discrete Film Cooling In A Rocket With Curved Walls, Jonathan F. Mccall Dec 2009

Discrete Film Cooling In A Rocket With Curved Walls, Jonathan F. Mccall

Theses and Dissertations

This study quantified the effects of discrete wall-based film cooling in a rocket with curved walls. Simulations and experiments showed decreasing with wall radius of curvature, holding jet diameter constant, improves net heat flux reduction (NHFR) and adiabatic effectiveness (η) for 90˚ compound injected cylindrical jets, though η is reduced at the highest curvature. NHFR and η improved further with a high favorable stream-wise pressure gradient (K=2.1x10-5) at all tested blowing ratios, but were affected little by a high density ratio (DR=1.76) using carbon dioxide as the coolant. Experiments were run at a Reynolds number of 31K and …


Investigation Into Contact Resistance And Damage Of Metal Contacts Used In Rf-Mems Switches, Kevin W. Gilbert Dec 2009

Investigation Into Contact Resistance And Damage Of Metal Contacts Used In Rf-Mems Switches, Kevin W. Gilbert

Theses and Dissertations

This research examines the physical and electrical processes involved in lifecycle failure of Microelectromechanical (MEMS) Radio-Frequency (RF) cantilever beam ohmic contact switches. Failures of these switches generally occur at the contact, but complete details of performance of microcontacts are difficult to measure and have not been previously reported. This study investigated the mechanics of microcontact behavior by designing and constructing a novel experimental setup. Three representative contact materials of varying microstructure (Au, Au5%Ru, Au4%V2O5) were tested and parameters of contact during cycling were measured. The Au4%V2O5, a dispersion strengthened material developed at …


Fatigue Behavior Of An Advanced Sic/Sic Composite At Elevated Temperature In Air And In Steam, Devon T. Christensen Dec 2009

Fatigue Behavior Of An Advanced Sic/Sic Composite At Elevated Temperature In Air And In Steam, Devon T. Christensen

Theses and Dissertations

The fatigue behavior of an advanced Silicon Carbide/Silicon Carbide (SiC/SiC) ceramic matrix composite (CMC) was investigated at 1200 ˚C in laboratory air and in steam environments. The composite consisted of a SiC matrix reinforced with Boron Nitride (BN) coated Hi-Nicalon fibers woven into eight-harness-satin (8HS) weave plies. Tensile stress-strain behavior and tensile properties were also evaluated at 1200 ˚C. Tension-tension fatigue tests were conducted in both laboratory air and in steam at 1200 ˚C at frequencies of 0.1 Hz, 1.0 Hz, and 10 Hz. The tension-tension fatigue tests had a ratio of minimum stress to maximum stress of R = …


Flow Visualization Study Of Passive Flow Control Features On A Film-Cooled Turbine Blade Leading Edge, Daniel R. Carroll Dec 2009

Flow Visualization Study Of Passive Flow Control Features On A Film-Cooled Turbine Blade Leading Edge, Daniel R. Carroll

Theses and Dissertations

A flow visualization study was conducted on a model of a film-cooled turbine blade leading edge in a closed-loop water channel at ReD = 30k. The model consisted of an 8.89 cm diameter half-cylinder with flat afterbody joined at the ninety degree point. A single radial coolant hole (dc / D = 0.054) drilled 21.5° from the stagnation line, angled 20° to the surface and 90° to the flow direction generated a coolant jet transverse to the freestream. Water channel testing assessed the hydrodynamic effects of 16 passive flow control features, to include a variety of …


Flow Measurements Using Particle Image Velocimetry In The Ultra Compact Combustor, Levi M. Thomas Dec 2009

Flow Measurements Using Particle Image Velocimetry In The Ultra Compact Combustor, Levi M. Thomas

Theses and Dissertations

Velocity measurements were performed using the Particle Image Velocimetry (PIV) technique on the Ultra Compact Combustor (UCC) test rig at the Air Force Institute of Technology (AFIT). Velocity patterns and time-averaged turbulence statistics were calculated for data taken with the UCC burning hydrogen fuel in the straight cavity vane and curved cavity vane configurations. The equivalence ratio was varied from 0.7 to 1.5, while the ratio of cavity air to main air was varied from 5% to 20% in testing performed on the straight vane configuration. Spanwise velocity was observed to decrease linearly with distance from the cavity vane over …


Precision Navigation Using Pre-Georegistered Map Data, Frederick C. Webber Sep 2009

Precision Navigation Using Pre-Georegistered Map Data, Frederick C. Webber

Theses and Dissertations

Navigation performance in small unmanned aerial vehicles (UAVs) is adversely affected by limitations in current sensor technology for small, lightweight sensors. Because most UAVs are equipped with cameras for mission-related purposes, it is advantageous to utilize the camera to improve the navigation solution. This research improves navigation by matching camera images to a priori georegistered image data and combining this update with existing image-aided navigation technology. The georegistration matching is done by projecting the images into the same plane, extracting features using the techniques Scale Invariant Feature Transform (SIFT) [5] and Speeded-Up Robust Features (SURF) [3]. The features are matched …


Least-Squares, Continuous Sensitivity Analysis For Nonlinear Fluid-Structure Interaction, Douglas P. Wickert Sep 2009

Least-Squares, Continuous Sensitivity Analysis For Nonlinear Fluid-Structure Interaction, Douglas P. Wickert

Theses and Dissertations

A least-squares, continuous sensitivity analysis method is developed for transient aeroelastic gust response problems to support computationally efficient analysis and optimization of aeroelastic design problems. A key distinction between the local and total derivative forms of the sensitivity system is introduced. The continuous sensitivity equations and sensitivity boundary conditions are derived in local derivative form which is shown to be superior for several applications. The analysis and sensitivity problems are both posed in a first-order form which is amenable to a solution using the least-squares finite element method. Several example and validation problems are presented and solved, including elasticity, fluid, …


F-16 Ventral Fin Buffet Alleviation Using Piezoelectric Actuators, Joseph S. Browning Sep 2009

F-16 Ventral Fin Buffet Alleviation Using Piezoelectric Actuators, Joseph S. Browning

Theses and Dissertations

Buffet-induced vibrations can have a disastrous impact on aircraft structures. Early attempts at combating buffet vibrations included passive methods such as structural enhancements and leading edge fences. Active methods have shown greater promise, including active airflow control, control surface modulation, and active structural control using piezoelectric actuators. Surface mounted piezoelectric actuators impart directional strain reducing the negative effects associated with harmful vibration. The Block-15 F-16 ventral fin represents an aircraft structure prone to failure when subjected to the buffet field from the wake of a LANTIRN pod. This research takes advantage of the susceptibility to buffet vibration of the Block …


Pulsed Film Cooling On A Turbine Blade Leading Edge, James L. Rutledge Sep 2009

Pulsed Film Cooling On A Turbine Blade Leading Edge, James L. Rutledge

Theses and Dissertations

Unsteadiness in gas turbine film cooling jets may arise due to inherent unsteadiness of the flow through an engine or may be induced as a means of flow control. The traditional technique used to evaluate the performance of a steady film cooling scheme is demonstrated to be insufficient for use with unsteady film cooling and is modified to account for the cross coupling of the time dependent adiabatic effectiveness and heat transfer coefficient. The addition of a single term to the traditional steady form of the net heat flux reduction equation with time averaged quantities accounts for the unsteady effects. …


Alternative Methods To Standby Gain Scheduling Following Air Data System Failure, Matthew W. Coldsnow Sep 2009

Alternative Methods To Standby Gain Scheduling Following Air Data System Failure, Matthew W. Coldsnow

Theses and Dissertations

The United States Air Force has advanced fighter aircraft that lose the ability to operate in a large portion of their operating flight envelope when an air data system failure is experienced. These aircraft are reverted to a fixed set of standby-gains that limit their maneuverability, degrade handling qualities, and increase susceptibility to departure. The purpose of this research was to determine if three alternative methods of standby-gain-scheduling could provide robust control with minimal performance degradation despite the lack of air data. To accomplish this, three methods of standby-gain-scheduling were developed, integrated, and tested in the Infinity Cube simulator at …


The Navigation Potential Of Ground Feature Tracking, Guner Mutlu Sep 2009

The Navigation Potential Of Ground Feature Tracking, Guner Mutlu

Theses and Dissertations

This research effort examines the reduction of error in inertial navigation aided by vision. This is part of an effort focused on navigation in a GPS denied environment. The navigation concept examined here consists of two main steps. First, extract the position of a tracked ground object using vision and geo-locate it in 3 dimensional navigation frame. In this first step multiple positions of the UAV are assumed known; think of a synthetic aperture. The only information about the tracked ground objects/features is the unit vector that points to the objects from the center of the camera. Two such vectors …


Formation Flight Of Earth Satellites On Kam Tori, Christopher T. Craft Aug 2009

Formation Flight Of Earth Satellites On Kam Tori, Christopher T. Craft

Theses and Dissertations

Kolmogorov, Arnold and Moser (KAM) theory provides that orbits of satellites whose dynamics are representable by an integrable Hamiltonian plus a small, real perturbation lie on tori in phase space and remain on the KAM tori for all time, unless acted upon by a non-conservative force. A refined technique for constructing KAM tori for Earth-orbiting satellites is developed and implemented using numerically integrated orbital data for hypothetical satellites and involving methods of Fourier analysis and spectral decomposition. Definition of satellite formations on the KAM tori is performed and analyses conducted to investigate both constellations with large separations and clusters with …


Effects Of Prior Aging At 288°C In Argon Environment On Creep Response Of Carbon Fiber Reinforced Pmr-15 Composite With ±45°Fiber Orientation At 288°C, Tyler F. Gruters Jun 2009

Effects Of Prior Aging At 288°C In Argon Environment On Creep Response Of Carbon Fiber Reinforced Pmr-15 Composite With ±45°Fiber Orientation At 288°C, Tyler F. Gruters

Theses and Dissertations

The creep and recovery response of carbon fiber reinforced PMR-15 composite with a + or - 45 fiber orientation was examined in an argon environment at 288 deg C. Mechanical testing was executed for unaged specimens as well as specimens aged up to 1000 hours. Tensile tests were performed to determine Young's modulus of elasticity and ultimate tensile strength. The creep tests were carried out at stress levels of 30 and 60 MPa. Creep periods of 25 hours were followed by recovery periods of 50 hours at zero stress. Weight loss measurements as a function of aging time were taken …


Aeroelastic Optimization Of Sounding Rocket Fins, Joseph R. Simmons Iii Jun 2009

Aeroelastic Optimization Of Sounding Rocket Fins, Joseph R. Simmons Iii

Theses and Dissertations

This research effort develops a multidisciplinary design tool to optimize sounding rocket fin geometries that minimize the mass of the fins while maintaining aerodynamic performance. This research grew out of a design problem experienced by the US Air Force Academy's Falcon LAUNCH program. The Falcon LAUNCH program is a senior design capstone project during which Air Force Academy cadets design, build and fly a sounding rocket over the course of an academic year. In the Spring of 2007, the Falcon LAUNCH V vehicle experienced a catastrophic failure when three of its four fins sheared off due to flutter. When the …


Cavity Coupled Aeroramp Injector Combustion Study, Dell T. Olmstead Jun 2009

Cavity Coupled Aeroramp Injector Combustion Study, Dell T. Olmstead

Theses and Dissertations

The difficulties with fueling of supersonic combustion ramjet engines with hydrocarbon based fuels presents many challenges that are currently being tackled by the Air Force Research Lab Propulsion Directorate Aerospace Propulsion Division. As the scramjet engine designs are scaled up, the need for a better solution to supersonic mixing has led to the development of many different styles of fuel injection. An aerodynamic ramp injector has been shown to have a quantitative improvement over a physical ramp while still achieving desirable mixing characteristics. The objectives for this research was quantifying the performance and operability implications of replacing four 15 degree …


Performance And Operability Of A Dual Cavity Flame Holder In A Supersonic Combustor, Mackenzie J. Collatz Jun 2009

Performance And Operability Of A Dual Cavity Flame Holder In A Supersonic Combustor, Mackenzie J. Collatz

Theses and Dissertations

The current generation of hydrocarbon fueled scramjet combustors typically requires a flame holding device to facilitate flame ignition and stable combustion. The amount of time available for fuel injection, fuel-air mixing, and combustion is very short, on the order of 1 millisecond. This short dwell time, along with the relatively long ignition delay times of hydrocarbon fuels, makes the flow path and flame holder design extremely important. This study investigates the performance and operability of using a symmetric dual cavity flame holder flow path to stabilize and enhance supersonic combustion. Testing of this flow path configuration, as well as a …


Structural Optimization Of Joined-Wing Beam Model With Bend-Twist Coupling Using Equivalent Static Loads, Nicholas S. Green May 2009

Structural Optimization Of Joined-Wing Beam Model With Bend-Twist Coupling Using Equivalent Static Loads, Nicholas S. Green

Theses and Dissertations

This study is based on the merger of two separate theories to further the efficiency with which joined-wing structural models are designed. The first theory is Geometrically Exact Beam Theory (GEBT). GEBT is a small strain beam theory which is capable of accurately capturing the geometric bend-twist coupling in beam elements that are experiencing large global deformations. This is crucial to the joined-wing problem as it is geometrically nonlinear. The second theory concerns Equivalent Static Loads (ESL). These ESL consist of a load vector that produces the same nodal displacements and rotations as those computed from a pure nonlinear analysis. …


Influence Of Structural Flexibility On Flapping Wing Propulsion, Aaron M. Mcclung Apr 2009

Influence Of Structural Flexibility On Flapping Wing Propulsion, Aaron M. Mcclung

Theses and Dissertations

The inelastic deformation behavior of PMR-15 neat resin, a high-temperature thermoset polymer, was investigated at 288 degrees C. The experimental program was designed to explore the influence of strain rate on tensile loading, unloading, and strain recovery behaviors. In addition, the effect of the prior strain rate on the relaxation response of the material, as well as on the creep behavior following strain controlled loading were examined. The experimental data were modeled with the Viscoplasticity Based on Overstress (VBO) theory. A systematic procedure for determining model parameters was developed and the model was employed to predict the response of the …


Fuel Composition And Performance Analysis Of Endothermically Heated Fuels For Pulse Detonation Engines, Christopher A. Stevens Mar 2009

Fuel Composition And Performance Analysis Of Endothermically Heated Fuels For Pulse Detonation Engines, Christopher A. Stevens

Theses and Dissertations

Waste heat from a pulse detonation engine (PDE) was extracted via concentric, counter flow heat exchangers to produce supercritical pyrolytic conditions for JP-7 and JP-8 fuels. A sampling system and method was utilized to collect samples of reacted fuel to be extracted during steady state operation. Samples were collected over a range of heat exchanger exit temperatures from 820 K (1016° F) to 940 K (1232 degrees F) and for two sets of heat exchangers, one set coated with zeolite catalyst and one set left uncoated. Variation in fuel mass flow rate required the calculation of heat addition as an …


Modeling And Simulation Architecture For Studying Doppler-Based Radar With Complex Environments, Nicholas J. Amato Mar 2009

Modeling And Simulation Architecture For Studying Doppler-Based Radar With Complex Environments, Nicholas J. Amato

Theses and Dissertations

This research effort develops a hybrid large-scale modeling and simulation frame- work that defines the requirements for a program to evaluate radar-aircraft-turbine- clutter interactions. Wind turbines and other moving structures can interfere with a radar’s ability to detect moving aircraft because radar returns from turbines are comparable to those from slow flying aircraft. This interference can lead to aircraft collisions or crashes, reducing the safety for air traffic. Two radar applications, INSSITE and IMOM, were investigated to determine which of the subsystems, in the proposed architecture, are currently available and which need additional development. Current radar applications either delve too …


Reusable Launch Vehicle Design Implications For Regeneration Time, Carlos Alberto Molina Mar 2009

Reusable Launch Vehicle Design Implications For Regeneration Time, Carlos Alberto Molina

Theses and Dissertations

In last few years, the Air Force Research Laboratory sponsored several research projects on a Reusable Launch Vehicles (RLV) whose design, operation, and logistics requirements are intended to be much simpler than for the Space Shuttle. As a part of these efforts, previous researchers developed a model that simulated the post-landing, ground maintenance and prelaunch operations of a RLV in order to evaluate how its design parameters affect the logistics operations. The next logical step is to investigate the effects and interactions of all factors used in the existing simulation model in a single experiment that considers the huge number …


An Experimental Investigation Studying The Influence Of Dimples On A Film Cooled Turbine Blade Leading Edge, Paul G. Frisinger Mar 2009

An Experimental Investigation Studying The Influence Of Dimples On A Film Cooled Turbine Blade Leading Edge, Paul G. Frisinger

Theses and Dissertations

An investigation was conducted to examine the effect of a row of cylindrical surface dimples in reducing the heat load on a turbine blade leading edge model. The models consisted of a foam cylindrical leading edge with a flat afterbody fabricated from Plexiglass. A single coolant hole was located 21.5 degree from the leading edge, angled 20 degree to the surface and 90 degree from the streamwise direction. The leading edge diameter to hole diameter ratio was D/d = 18.7. A row of seven dimples was placed upstream of one of the coolant holes. Infrared thermography techniques were used to …


Performance Enhancements Of Ranging Radio Aided Navigation, Patric J. Ernsberger Mar 2009

Performance Enhancements Of Ranging Radio Aided Navigation, Patric J. Ernsberger

Theses and Dissertations

Determining the position of team members is always useful information, whether it is a team of firefighters fighting a blaze or combatants clearing a building in the field. This information becomes even more decisive for the people responsible for their safety. To accomplish this in areas denied Global Navigation Satellite System (GNSS), such as around buildings or in steep valleys, alternative methods must be used. Radio ranging systems have been a part of the navigation solution for years. They unfortunately have poor performance in certain areas, such as inside buildings, due to multipath and other errors. To improve the position …


Computational Analysis Of Geometric Effects On Strut Induced Mixing In A Scramjet Combustor, Matthew G. Bagg Mar 2009

Computational Analysis Of Geometric Effects On Strut Induced Mixing In A Scramjet Combustor, Matthew G. Bagg

Theses and Dissertations

In order to increase the fuel-air mixing in a scramjet combustion section, the Air Force Institute of Technology and the Air Force Research lab investigated methods to increase the mixing efficiency. Previous experimental work identified the advantages of using a strut upstream of a cavity flame holder to increase the fuel-air mixture. In this paper a computational investigation of strut injectors in a supersonic flow with a cavity flame holder is reported. This research focused on understanding the effect of a change in height and width of the strut upstream of the combustion cavity on the mixing efficiency and pressure …


Effect Of Steam Environment On Creep Behavior Of Nextel720/Alumina-Mullite Ceramic Matrix Composite At Elevated Temperature, Tolga Kutsal Mar 2009

Effect Of Steam Environment On Creep Behavior Of Nextel720/Alumina-Mullite Ceramic Matrix Composite At Elevated Temperature, Tolga Kutsal

Theses and Dissertations

The tensile creep behavior of an oxide-oxide ceramic matrix composite (CMC) was investigated at 1000 and 1100° C in laboratory air and steam. The oxide-oxide CMC studied in this research was Nextel™ 720/alumina-mullite (N720/AM). The composite consists of N720/fibers with 0°/90° fiber orientation and a porous alumina-mullite matrix. Tensile-strain behavior was investigated and tensile properties measured at 900, 1000 and 1100° C. The effect of loading rate on tensile properties of N720/AM ceramic matrix composite at 1100° C in steam was also examined. Creep-rupture tests were performed at 1100° C in laboratory air and steam, and at 1000° C only …


An Engineering Trade Space Analysis For A Space-Based Hyperspectral Chromotomographic Scanner, Phillip Sheirich Mar 2009

An Engineering Trade Space Analysis For A Space-Based Hyperspectral Chromotomographic Scanner, Phillip Sheirich

Theses and Dissertations

Hyperspectroscopy for fast transient events such as battlefield explosions is an undeveloped area of spectral imaging. This thesis is a discussion of issues involved with taking a laboratory design for a rotating prism hyperspectral chromotomographic (CT) instrument and producing a first approximation satellite payload design, operating scheme and trade space analysis to support demonstration of this technology in low-earth orbit. This instrument promises the capability of adding a time dimension to the normal spatial and spectral data produced by most hyperspectral imagers. The ultimate goal is to conduct experiments demonstrating the ultimate viability of spectral definition of transient combustion events …


Critical Design Parameters For Pylon-Aided Gaseous Fuel Injection Upstream Of A Flameholding Cavity, Mitchell R. Pohlman Mar 2009

Critical Design Parameters For Pylon-Aided Gaseous Fuel Injection Upstream Of A Flameholding Cavity, Mitchell R. Pohlman

Theses and Dissertations

The Air Force Institute of Technology and the AFRL are investigating means to increase the efficiency of fuel-air mixing into supersonic flow. Previous work has shown much promise in increasing the penetration and mixing of a fuel-air mixture into the freestream by injecting fuel behind small triangular pylons. Pylon-aided fuel injection has also shown to lift the fuel plume off the combustor floor; this floor-gap prevents the ignition of fuel seeded in the boundary layer. In this paper twenty-one pylons of varying widths, heights, and lengths were examined in four specific test matrices within a CFD environment. Pylons in test …


Satellite Reentry Control Via Surface Area Amplification, Salvador Alemán Mar 2009

Satellite Reentry Control Via Surface Area Amplification, Salvador Alemán

Theses and Dissertations

This project endeavors to find whether it is feasible to use an increase in surface area as a way of increasing the drag on an orbiting object, thus decreasing its orbital lifetime. The surface area increase can be achieved by an apparatus that deploys a balloon. The balloon will act as a parachute that will decrease the potential energy of the object through atmospheric drag. This is most effective by objects that reach the Low Earth altitudes of less than 500 kilometers, where an object is encountering a firmer atmospheric density. The project is carried out through propagating three different …


Near Real-Time Closed-Loop Optimal Control Feedback For Spacecraft Attitude Maneuvers, C. Douglas Mcfarland Mar 2009

Near Real-Time Closed-Loop Optimal Control Feedback For Spacecraft Attitude Maneuvers, C. Douglas Mcfarland

Theses and Dissertations

Optimization of spacecraft attitude maneuvers can significantly reduce attitude control system size and mass, and extend satellite end-of-life. Optimal control theory has been applied to solve a variety of open-loop optimal control problems for terrestrial, air, and space applications. However, general application of real-time optimal controllers on spacecraft for large slew maneuvers has been limited because open-loop control systems are inherently vulnerable to error and the computation necessary to solve for an optimized control solution is resource intensive. This research effort is focused on developing a near real-time optimal control (RTOC) system for spacecraft attitude maneuvers on the Air Force …