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Theses and Dissertations

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Articles 31 - 60 of 189

Full-Text Articles in Aerodynamics and Fluid Mechanics

Design And Flight Test Of A Weapons-Cavity Acoustics And Separation Test Bed, Zachary Probst Mar 2016

Design And Flight Test Of A Weapons-Cavity Acoustics And Separation Test Bed, Zachary Probst

Theses and Dissertations

Two very important, and often detrimental, phenomena can occur when an open weapons bay, or more generally-a cavity, is exposed to high-velocity flow. First, a shear layer develops over the cavity, leading to large regions of difficult-to-predict flow. Second, dynamic pressure oscillations are generated within the cavity itself. These two issues can combine to have multiple harmful effects on weapons carriage and employment. This provided motivation for flight tests which quantify forces and moments on a store, mounted at various positions in the cavity, for a variety of flight conditions. Specifically, a low-cost, easily reconfigurable test bed for weapons-cavity research …


Investigation Into Reynolds Number Effects On A Biomimetic Flapping Wing, Daniel K. Hope Mar 2016

Investigation Into Reynolds Number Effects On A Biomimetic Flapping Wing, Daniel K. Hope

Theses and Dissertations

This research investigated how the nature of the wing changed as a function of Reynolds number by measuring the forces produced by wings with varying characteristic lengths, tested at varying air densities. Increasing the wing span increased the overall weight of the wing, which reduced the 1st natural frequency; and did not result in an increase in vertical force over the baseline 50 mm wing. However; if the decrease in natural frequency was counteracted by increasing the thickness of the joint material in the linkage mechanism, vertical force production did increase over the baseline wing planform. Negligible forces and moments …


Analysis Of Hypersonic Vehicle Wakes, Matthew A. Kania Sep 2015

Analysis Of Hypersonic Vehicle Wakes, Matthew A. Kania

Theses and Dissertations

As advancements are made with ballistic missiles, particularly in the area of hypersonic bodies, there is a growing need to advance the methods of detecting these new ballistic weapons. As a result, the National Air and Space Intelligence Center has asked the Air Force Institute of Technology to examine the wake region behind hypersonic bodies. A thorough understanding of the aerothermal phenomena and the chemical reactions occurring in the wake region will enable an advancement of tracking hypersonic bodies. This research examined the wake region behind a hypersonic body using computational fluid dynamics.
This study used Pointwise® to develop a …


Characterization Of A Robotic Manipulator For Dynamic Wind Tunnel Applications, James C. Lancaster Mar 2015

Characterization Of A Robotic Manipulator For Dynamic Wind Tunnel Applications, James C. Lancaster

Theses and Dissertations

The newly acquired 6-DOF Motion Test Apparatus (MTA) was installed to perform dynamic wind tunnel testing in the AFIT Low Speed Wind Tunnel. Several complex motions revealed that the overall performance of the test rig needed improvement especially during small motions. The motions exposed that further enhancements would need to be performed individually for each joint. This research effort focused on the improvement of the MTA wrist roll motor and controller using a pitch oscillation. The controller software was improved using position feedback because the MTA wrist roll motor and controller exhibited reduced signal bias and amplitude attenuation. The enhanced …


Influence Of Mach Number And Dynamic Pressure On Cavity Tones And Freedrop Trajectories, Justin D. Merrick Mar 2014

Influence Of Mach Number And Dynamic Pressure On Cavity Tones And Freedrop Trajectories, Justin D. Merrick

Theses and Dissertations

Weapons release at supersonic speeds from an internal weapons bay is a highly desirable capability. To ensure a successful release at multiple Mach numbers, the aerodynamic environment must be well-understood and repeatable, with a robust system for safe testing of store separation. For this reason, experimental methods were used to investigate the characteristics of a scaled WICS bay with a length-to-depth ratio of 4.5 at multiple Mach numbers and stagnation pressures. Three new nozzles were designed, manufactured, and characterized for the AFIT small supersonic tunnel, yielding freestream Mach numbers of 2.22, 1.84, and 1.43. In addition, a control valve was …


Novel Discretization Schemes For The Numerical Simulation Of Membrane Dynamics, Kyle F. Kolsti Sep 2012

Novel Discretization Schemes For The Numerical Simulation Of Membrane Dynamics, Kyle F. Kolsti

Theses and Dissertations

Motivated by the demands of simulating flapping wings of Micro Air Vehicles, novel numerical methods were developed and evaluated for the dynamic simulation of membranes. For linear membranes, a mixed-form time-continuous Galerkin method was employed using trilinear space-time elements, and the entire space-time domain was discretized and solved simultaneously. For geometrically nonlinear membranes, the model incorporated two new schemes that were independently developed and evaluated. Time marching was performed using quintic Hermite polynomials uniquely determined by end-point jerk constraints. The single-step, implicit scheme was significantly more accurate than the most common Newmark schemes. For a simple harmonic oscillator, the scheme …


The Characterization Of Material Properties And Structural Dynamics Of The Manduca Sexta Forewing For Application To Flapping Wing Micro Air Vehicle Design, Ryan P. O'Hara Sep 2012

The Characterization Of Material Properties And Structural Dynamics Of The Manduca Sexta Forewing For Application To Flapping Wing Micro Air Vehicle Design, Ryan P. O'Hara

Theses and Dissertations

The Manduca Sexta species of moth serves as a source of biological inspiration for the future of micro air vehicle flapping flight. The ability of this species to hover in flapping flight has warranted investigation into the critical material, structural, and geometric properties of the forewing of this biological specimen. A rigorous morphological study of the Manduca Sexta forewing was conducted to characterize the physical and material properties of the biological forewing for the purpose of developing an advanced parametric three dimensional model finite element analysis (FEA) model. This FEA model was tuned to match the experimentally determined structural dynamics …


Freedrop Testing And Cfd Simulation Of Ice Models From A Cavity Into Supersonic Flow, Thomas J. Flora Sep 2012

Freedrop Testing And Cfd Simulation Of Ice Models From A Cavity Into Supersonic Flow, Thomas J. Flora

Theses and Dissertations

Weapon release at supersonic speeds from an internal bay is highly advantageous. For this reason, both experimental and numerical methods were used to investigate store separation from a cavity (L=D=4.5) into Mach 2.94 flow. The experiment used a piezoresistive pressure transducer, Schlieren and high-speed photography for data acquisition. The computational solution used the OVERFLOW solver. A sphere and a Mk-82, scaled to 1:20, were formed using frozen tap water. The sphere model was freedrop tested experimentally and computationally, while the sub-scale store shaped model was freedrop tested experimentally. The total pressure was varied to alter the dynamic response of the …


Evaluation Of The Thorax Of Manduca Sexta For Flapping-Wing Micro Air Vehicle Applications, Alex C. Hollenbeck Mar 2012

Evaluation Of The Thorax Of Manduca Sexta For Flapping-Wing Micro Air Vehicle Applications, Alex C. Hollenbeck

Theses and Dissertations

The tobacco hornworm hawkmoth (Manduca sexta) provides an excellent model from which to garner knowledge pertaining to the development of a Flapping Wing Micro Air Vehicle (FWMAV). Insect-sized FWMAVs will be used by the future warfighter for reconnaissance, nuclear/chemical/biological hazard sensing, and targeting. One of the major challenges facing FWMAV developers is the energetically demanding nature of low Reynolds flapping flight. Investigating the Manduca sexta thorax/wing flapping mechanism as a mechanical system will provide insight into its inherent efficiency. This thesis examined the energetics of the thorax under static loading and dynamic loading using an innovative load-application technique. It was …


Boundary Layer Measurements In The Trisonic Gas-Dynamics Facility Using Particle Image Velocimetry With Co₂ Seeding, Daniel B. Wolfe Mar 2012

Boundary Layer Measurements In The Trisonic Gas-Dynamics Facility Using Particle Image Velocimetry With Co₂ Seeding, Daniel B. Wolfe

Theses and Dissertations

Particle image velocimetry (PIV) is utilized with solid carbon dioxide (CO2) seeding material to conduct boundary layer measurements in the test section of the Air Force Research Laboratory's Trisonic Gas-dynamics Facility (TGF), which has a 24 inch by 24 inch cross-section. Freestream velocity was set at Mach 0.3, Mach 0.5, or Mach 0.8 while stagnation pressure ranged from 500 to 2400 pounds per square foot (psf). High pressure liquid CO2 was directed through expansion nozzles into shroud tubes which led to solidified particles in the wind tunnel stagnation chamber. Two different sets of shroud tubes were used …


Computational Analysis And Characterization Of Rc-135 External Aerodynamics, Michael G. Chenery Mar 2012

Computational Analysis And Characterization Of Rc-135 External Aerodynamics, Michael G. Chenery

Theses and Dissertations

Both the RC-135V/W Rivet Joint (RJ) and the RC-135U Combat Sent (CS) aircraft are United States Air Force (USAF) electronics reconnaissance platforms. The RJ is the USAF's standard airborne signals intelligence (SIGINT) gathering platform, while the CS is designed to collect technical intelligence on adversary radar emitter systems. Both aircraft are extensively modified C-135's characterized by protruding cheek fairings along the sides of the fuselage forward of the wings as well as the addition of numerous antennas along the top and bottom of the fuselage. The major distinguishing feature between the two variants is the nose radome, wherein the RJ …


Validation Of The Chemistry Module For The Euler Solver In Unified Flow Solver, William C. Humphrey Jr. Mar 2012

Validation Of The Chemistry Module For The Euler Solver In Unified Flow Solver, William C. Humphrey Jr.

Theses and Dissertations

In the world of computational fluid dynamics (CFD), three main types of flow regimes exist: continuum, rarified, and free molecular. Of these regimes, the rarified regime is the most difficult to model because the continuum equations don't apply and using the Boltzmann equation is too computationally expensive to use. The Unified Flow Solver (UFS) is currently being developed to solve this problem by using the kinetic continuum Euler equations where valid, and only using the Boltzmann equation where necessary, thus reducing the computational cost. The use of the kinetic Euler equations helps to aid in the coupling of the Euler …


Reynolds Number Effects On Thrust Coefficients And Piv For Flapping Wing Micro Air Vehicles, John P. Tekell Mar 2012

Reynolds Number Effects On Thrust Coefficients And Piv For Flapping Wing Micro Air Vehicles, John P. Tekell

Theses and Dissertations

For the last several years the Air Force Institute of Technology (AFIT) has conducted research in aerodynamics for flapping wing micro air vehicles (MAVs). The focus of this research was to augment this effort by measuring thrust, velocity, and torque in tanks of water and glycerin using a scale and a reaction torque cell. The results for different flapping mechanisms are compared to a rotating propeller with the goal of elucidating the design trade space between rotorcraft and flapping wings at Reynolds numbers less than 100,000. In addition, flow visualization and quantitative velocity data were captured in the wake of …


Coupled Radiation-Gasdynamic Solution Method For Hypersonic Shock Layers In Thermochemical Nonequilibrium, Christopher L. Martin Jr. Dec 2011

Coupled Radiation-Gasdynamic Solution Method For Hypersonic Shock Layers In Thermochemical Nonequilibrium, Christopher L. Martin Jr.

Theses and Dissertations

The purpose of this research was to develop a highly accurate computational method for calculating the nonequilibrium radiative heat transfer within reentry shock layers. The nonequilibrium state of the flowfield was solved using the multispecies multitemperature nonequilibrium flow solver NH7AIR which is capable of separately tracking the vibrational energy of each diatomic species and the energy of the free electrons. The calculation of radiative heat transfer was performed by utilizing the detailed line-by-line spectral radiation solver SPRADIAN. Two radiative transport schemes were implemented in this coupled code. The first scheme was the standard tangent slab solution method. The second scheme …


An Investigation Of Cavity Resonance And Its Relationship To Store Force And Moment Loading, Christopher J. Coley Mar 2011

An Investigation Of Cavity Resonance And Its Relationship To Store Force And Moment Loading, Christopher J. Coley

Theses and Dissertations

A store which is released from an internal bay is subjected to a highly unsteady flowfield which influences the release characteristics for the store. Pressure transducer information is often used to estimate store loading, although no direct correlation between the observed frequencies from the pressure transducers and the store loading has been developed. The relationship between the acoustic modes present in the cavity and the force and moment loading on a store released from a bay are investigated through a CFD study using the OVERFLOW 2.1 solver. The acoustic modes of the cavity are calculated from the pressure fluctuation histories …


Biological Investigation Of The Stimulated Flapping Motions Of The Moth, Manduca Sexta, Travis B. Tubbs Mar 2011

Biological Investigation Of The Stimulated Flapping Motions Of The Moth, Manduca Sexta, Travis B. Tubbs

Theses and Dissertations

No abstract provided.


Particle Size Control For Piv Seeding Using Dry Ice, Brian T. Love Mar 2010

Particle Size Control For Piv Seeding Using Dry Ice, Brian T. Love

Theses and Dissertations

Particle image velocimetry (PIV) has been carried out using solid carbon dioxide (CO2) particles as the seed material to continue the development of clean seeding for use in large-scale, closed-circuit tunnels. Testing occurred in two wind tunnels at subsonic and supersonic speeds using dry ice particles generated by allowing liquefied CO2 to expand from a small diameter injector tube through a larger diameter shroud tube. The particles were injected into the plenum and discrete solid particles, suitable for PIV measurements, were present in the test section. Data on particle size were first collected using a Malvern particle …


A Structural Dynamic Analysis Of A Manduca Sexta Forewing, Travis W. Sims Mar 2010

A Structural Dynamic Analysis Of A Manduca Sexta Forewing, Travis W. Sims

Theses and Dissertations

Micro air vehicles (MAVs) are intended for future intelligence, surveillance, and reconnaissance use. To adequately fulfill a clandestine capacity, MAVs must operate in close proximity to their intended target without eliciting counter-observation. This objective, along with DARPA’s constraint of a sub-15 centimeter span, requires future MAVs to mimic insect appearance and flight characteristics. This thesis describes an experimental method for conducting a structural analysis of a Manduca Sexta (hawkmoth) forewing. Geometry is captured via computed tomography (CT), and frequency data is collected using laser vibrometry in air and vacuum. A finite element (FE) model is constructed using quadratic beams and …


Investigation Of A Novel Compact Vibration Isolation System For Space Applications, Steven D. Miller Mar 2010

Investigation Of A Novel Compact Vibration Isolation System For Space Applications, Steven D. Miller

Theses and Dissertations

A novel compact vibration isolation system was designed, built, and tested for the Space Chromotomography Experiment (CTEx) being built by Air Force Institute of Technology (AFIT) researchers. CTEx is a multifunctional experimental imaging chromotomographic spectrometer designed for flight on the International Space Station (ISS) and is sensitive to jitter caused by vibrations both through the support structure as well as those produced on the optical platform by rotating optical components. CTEx demands a compact and lightweight means of vibration isolation and suppression from the ISS structure. Vibration tests conducted on an initial isolator design resulted in changes in the chosen …


Development Of Morphing Aircraft Structure Using Smp, Soo-Chan Jee Mar 2010

Development Of Morphing Aircraft Structure Using Smp, Soo-Chan Jee

Theses and Dissertations

The U.S Air Force needs new aircraft which provide longer flight time, less fuel consumption, better aerodynamics in order to perform Air Force missions successfully as the mission environment changes rapidly. A morphing wing aircraft is considered as a potential new aircraft for those missions. This thesis explores Shape Memory Polymer (SMP) properties test results and its application for morphing wing skin. Several SMP composite laminates were considered for investigating shape changing characteristics required for morphing skin. The braided composite preforms used in making SMP composites were explored in morphing wing operating system based on the results of property tests. …


Back-Pressure Effect On Shock-Train Location In A Scramjet Engine Isolator, Richard I. Paek Mar 2010

Back-Pressure Effect On Shock-Train Location In A Scramjet Engine Isolator, Richard I. Paek

Theses and Dissertations

The isolator of the scramjet decelerates the incoming high Mach flow to a lower Mach number and stabilizes the flow before it enters the combustor. Because of the unsteady combustion phenomenon and inconsistent completeness of the combustion, pressures within the combustor can vary drastically. These pressure variations can propagate forward and affect the flow field in the isolator - worst case unstarting the inlet. In this research, the shock train location versus the back-pressure is examined experimentally. The back-pressure is artificially created by symmetric (top & bottom) ramps that can close the flow area. Raising/lowering ramps result in higher/lower back-pressure. …


Dive Angle Sensitivity Analysis For Flight Test Safety And Efficiency, Matthew T. Schneider Mar 2010

Dive Angle Sensitivity Analysis For Flight Test Safety And Efficiency, Matthew T. Schneider

Theses and Dissertations

Flutter envelope expansion is one of the most critical types of developmental flight tests. The regions that present the most dangerous flight profiles are those test points in the negative PS realm of the flight envelope. These points develop into high-speed dives and require an accurate predictive model to prevent possible testing accidents. As a flight test is conducted, several conditions such as aircraft weight and ambient air temperature can change, causing a drastic shift in the excess power profiles resulting in significant alteration in the test conditions. Using a dive planning model, a number of parameters were analyzed to …


Cfd Analysis Of Experimental Wing And Winglet For Falconlaunch 8 And The Exfit Program, Benjamin P. Switzer Mar 2010

Cfd Analysis Of Experimental Wing And Winglet For Falconlaunch 8 And The Exfit Program, Benjamin P. Switzer

Theses and Dissertations

Reusable launch vehicles have many benefits over their expendable counterparts. These benefits range from cost reductions to increased functionality of the vehicles. Further research is required in the development of the technology necessary for reusable launch vehicles to come to fruition. The Air Force Institute of Technology’s future involvement in the ExFIT program will entail designing and testing of a new wing tip mounted vertical stabilizer in the hypersonic regime. One proposed venue for experimentation is to utilize the United States Air Force Academy’s FalconLAUNCH Program which annually designs, builds, and launches a sounding rocket capable of reaching hypersonic speeds. …


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 …


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, …


An Investigation Of Shock Wave Physics Via Hybrid Cfd-Bgk Solution Methods For Nonequilibrium Flows, Brook I. Bentley Mar 2009

An Investigation Of Shock Wave Physics Via Hybrid Cfd-Bgk Solution Methods For Nonequilibrium Flows, Brook I. Bentley

Theses and Dissertations

The Unified Flow Solver, a hybrid continuum-rarefied code, is used to investigate the internal structure of a normal shock wave for a Mach range of 1.55 to 9.0 for Argon, and 1.53 to 3.8 for diatomic Nitrogen. Reciprocal shock thickness, density, temperature, heat flux, and the velocity distribution function are calculated for a one-dimensional shock wave and compared with experimental data from Alsmeyer and DSMC results from Bird. Using the Euler, Navier-Stokes, BGK model, and Three-Temperature BGK model schemes, results from UFS compare well with experiment and DSMC. The Euler scheme shows atypical results, possibly resulting from modifications made to …


Least-Squares Finite Element Formulation For Fluid-Structure Interaction, Cody C. Rasmussen Mar 2009

Least-Squares Finite Element Formulation For Fluid-Structure Interaction, Cody C. Rasmussen

Theses and Dissertations

Fluid-structure interaction problems prove difficult due to the coupling between fluid and solid behavior. Typically, different theoretical formulations and numerical methods are used to solve fluid and structural problems separately. The least-squares finite element method is capable of accurately solving both fluid and structural problems. This capability allows for a simultaneously coupled fluid structure interaction formulation using a single variational approach to solve complex and nonlinear aeroelasticity problems. The least-squares finite element method was compared to commonly used methods for both structures and fluids individually. The fluid analysis was compared to finite differencing methods and the structural analysis type compared …


Wind Tunnel Analysis And Flight Test Of A Wing Fence On A T-38, Michael D. Williams Mar 2009

Wind Tunnel Analysis And Flight Test Of A Wing Fence On A T-38, Michael D. Williams

Theses and Dissertations

A low-speed wind tunnel study and flight tests were performed to examine the effects of a wing fence on the T-38A. Wind tunnel results were based upon force and moment data collected with a six-component balance and flow visualization at Reynolds numbers up to 0.3 x 106, based on mean aerodynamic chord. The model did not include the last 7.79 feet of the aircraft, and the engine and exhaust were modeled as through-holes. Five fence geometries, placed at wing station 125 (± 0.825 semispan), were compared. The best performer of these designs, based on drag polar, was the …


Dynamic Supersonic Base Store Ejection Simulation Using Beggar, Michael D. Johnson Dec 2008

Dynamic Supersonic Base Store Ejection Simulation Using Beggar, Michael D. Johnson

Theses and Dissertations

Static and dynamic conditions throughout various aft supersonic store separation events are examined using the Beggar Computational Fluid Dynamics (CFD) code from Air Force SEEK Eagle Office at Eglin Air Force Base, FL. An 8.9 deg half angle sphere cone is used for the carrier vehicle with an identically shaped store stowed within a hollow compartment in the aft section of the carrier body. Dynamic store separation simulations are implemented at a free-stream Mach of 2.9 with a Reynolds number of Re = 6.9 x 106/m referenced against carrier base diameter. Analysis covers multiple dynamic separation events along …