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2005

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Articles 91 - 120 of 159

Full-Text Articles in Aerospace Engineering

Boundary Layer Flow Control Using Plasma Induced Velocity, Brian E. Balcer Mar 2005

Boundary Layer Flow Control Using Plasma Induced Velocity, Brian E. Balcer

Theses and Dissertations

An examination of the effects of plasma induced velocity on boundary layer flow was conducted. A pair of thin copper film electrodes spanned the test section, oriented at thirty degrees from normal to the free stream flow. An adverse pressure gradient was imposed over the electrode configuration using a pressure coefficient profile similar to that associated with suction side of a Pac-B low pressure turbine blade. In addition, suction was applied to keep flow attached on the upper wall, inducing separation over the electrode. The electrode is supplied by an AC source at three different power levels with the free …

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Experimental Study Of The Subsonic Aerodynamics Of A Blended Wing Body Air Vehicle With A Focus On Rapid Technology Assessment, David A. Gebbie Mar 2005

Experimental Study Of The Subsonic Aerodynamics Of A Blended Wing Body Air Vehicle With A Focus On Rapid Technology Assessment, David A. Gebbie

Theses and Dissertations

The subsonic aerodynamic performance of a blended wing body aircraft constructed using selective laser sintering was assessed in the AFIT low-speed wind tunnel. The scaled-down model of a strike tanker aircraft consisted of a shaped fuselage and sweptback wings. The Reynolds number, based on mean wing chord, during testing was on the order of 105 while the Mach number ranged from 0.10 to 0.20. The model evaluation and analysis process included force and moment measurements acquired from a wind tunnel balance, pressure data measured with 8 taps located on the model’s upper surface, a comparison to computational fluid dynamics (CFD) …

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Mixing Effects Of Pylon-Aided Fuel Injection Located Upstream Of A Flameholding Cavity In Supersonic Flow, Daniel R. Montes Mar 2005

Mixing Effects Of Pylon-Aided Fuel Injection Located Upstream Of A Flameholding Cavity In Supersonic Flow, Daniel R. Montes

Theses and Dissertations

The Air Force Research Lab (AFRL), Propulsion Directorate, Wright-Patterson Air Force Base, Ohio is conducting ongoing research into propulsive efficiency in supersonic ramjet (scramjet) technology. One current focus of this research is the usefulness of flameholding cavities implemented in the supersonic hydrocarbon-fueled combustion chamber. Because good mixing and proper cavity-core interaction lead to more efficient combustion, methods of optimizing fuel/air mixing both within and upstream the cavity are investigated. In a cooperative effort with the Air Force Institute of Technology (AFIT), AFRL provided a supersonic wind tunnel outfitted with an existing cavity design. A circular injection port was placed upstream …

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Parachute Extraction Of A Generic Store From A C-130; A Cfd Proof Of Concept, Stephen C. Platt Mar 2005

Parachute Extraction Of A Generic Store From A C-130; A Cfd Proof Of Concept, Stephen C. Platt

Theses and Dissertations

This thesis encompasses a feasibility analysis of a parachute extracted generic precision guided munition from the cargo bay of a C-130 aircraft in flight. This analysis utilizes the USAF Beggar code and incorporates full physics effects as well as aerodynamic loading assuming an inviscid aircraft and viscous store for a time-accurate solution. Both an immediate and time varying application of the parachute force are utilized as well as two different ordnance body styles at zero and 5 degrees AOA with the store placed on centerline and offset in the cargo bay. The time accurate parachute model is based on empirical …

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Full Capability Formation Flight Control, Ryan K. Osteroos Mar 2005

Full Capability Formation Flight Control, Ryan K. Osteroos

Theses and Dissertations

The subject of automatic formation flight control is of current interest to the development of Unmanned Aerial Vehicles (UAV). Previous control approaches have been refined in this work to allow more robust maneuvering and to include a fourth control parameter. The equations of motion for each aircraft as a point mass, expressed in a wind-axis coordinate system, are coupled into differential equations that model the two aircraft system dynamics. Control laws are developed that include proportional and integral action. Gains are determined based on formation performance. Lead maneuvers are simulated and the controller is gauged on its ability to maintain …

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Computational Aeroelastic Analysis Of Micro Air Vehicle With Experimentally Determined Modes, Joshua A. Stults Mar 2005

Computational Aeroelastic Analysis Of Micro Air Vehicle With Experimentally Determined Modes, Joshua A. Stults

Theses and Dissertations

A computational aeroelastic analysis of a micro air vehicle (MAV) is conducted. This MAV has a 24 inch wing span, and is designed for local area reconnaissance. Wind tunnel data for the MAV with a rigid carbon fiber wing and a flexible carbon fiber ribbed nylon wing are compared to CFD results incorporating static and dynamic deformations. We use laser vibrometry to determine the mode shapes of the flexible wing. From these shapes, CFD grid deformations are calculated as part of a closely-coupled aeroelastic solution method. The accuracy of MAV performance predictions using CFD with and without aeroelastic modeling is …

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Validation Of Turbulence Models In The Beggar Code For Unsteady Flow, Kevin G. Storm Mar 2005

Validation Of Turbulence Models In The Beggar Code For Unsteady Flow, Kevin G. Storm

Theses and Dissertations

Validation of the turbulence models in the CFD code Beggar for unsteady turbulent flow are discussed. Six validation cases of the code are considered, three cases with the intent of validating the code without the turbulence model and three cases to validate the turbulence model itself. Finally, a more realistic simulation of a simplified store is examined. The turbulence models considered are the Baldwin-Lomax, Spalart-Allmaras, and a DES model. The conclusions made deal with necessary prerequisites to properly simulating unsteady turbulent flow and model selection. The prerequisites necessary in the Beggar code are a second order temporal discretization and the …

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Entropy Generation As A Means Of Examining Continuum Breakdown, Christopher R. Schrock Mar 2005

Entropy Generation As A Means Of Examining Continuum Breakdown, Christopher R. Schrock

Theses and Dissertations

To quantify the validity and breakdown of the continuum equations of fluid flow, the concept of entropy generation is examined. This parameter is formulated utilizing statistical mechanics and kinetic theory to avoid the use of equilibrium assumptions. This analysis leads to expressions in terms of energy distribution functions. These results are applied to monatomic and diatomic molecules. A numerical procedure for computing these values using the Direct Simulation Monte Carlo Method (DSMC) is presented. Normal shock waves in argon and nitrogen were simulated at Mach numbers ranging from 1.2 to 10. Results are compared to Navier-Stokes predictions. The Navier-Stokes equations …

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Controlling Sideslip Angle To Reduce The Radar Exposure Of A Tactical, Rotary Winged Uav, Jonathan D. Bulseco Mar 2005

Controlling Sideslip Angle To Reduce The Radar Exposure Of A Tactical, Rotary Winged Uav, Jonathan D. Bulseco

Theses and Dissertations

This work investigates another way of contributing to the radar minimization solution for air vehicles in a threat environment. While much research has been conducted on structural solutions to radar exposure minimization, not much work has been done in the area of using control to continuously assess and present the smallest radar cross section of an air vehicle to oncoming threat radar systems by changing the aircraft's orientation. This work looks at the application of sideslip/beta angle feedback control of an unmanned helicopter to minimize radar cross section exposure in a hostile radar environment. A new way of controlling aircraft …

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The Use Of X-Ray Pulsars For Aiding Gps Satellite Orbit Determination, Dennis W. Woodfork Ii Mar 2005

The Use Of X-Ray Pulsars For Aiding Gps Satellite Orbit Determination, Dennis W. Woodfork Ii

Theses and Dissertations

This research proposes the use of an existing "signal of opportunity" - namely x-ray pulsars - to improve the accuracy and robustness of the GPS satellite and clock estimation algorithm. Improvement in satellite and clock accuracy results in a direct benefit to the user. A simulation has been developed to determine the effects of using x-ray pulsar measurements on the GPS Operational Control Segment. The epoch-specific position, velocity, and clock errors of all GPS satellites in the constellation were estimated using both pseudoranges and time-difference-of-arrival (TDOA) measurements from pulsars. The primary measure of accuracy is a constellation Signal-In-Space Range Error …

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A Redesigned Tail Rotor For Improvement Of Ch-53e High-Altitude Performance, James A. Pritchard Mar 2005

A Redesigned Tail Rotor For Improvement Of Ch-53e High-Altitude Performance, James A. Pritchard

Theses and Dissertations

The Global War on Terror with specific emphasis on the recent military operation in Afghanistan has shown the invaluable contribution that heavy lift helicopters bring to the combatant commander. However, the flight range, altitudes and lift capability required to operate effectively in such an austere environment are pushing the limits of these helicopters. In an attempt to increase the operational capability of the CH-53E, this study will investigate methods for maximizing tail rotor effectiveness at high gross weights and high altitudes. This thesis records an analytical study designed to investigate the intricacies of tail rotor design and, by the computational …

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A Study In Drag Reduction Of Close Formation Flight Accounting For Flight Control Trim Positions And Dissimilar Formations, Michael T. Morgan Mar 2005

A Study In Drag Reduction Of Close Formation Flight Accounting For Flight Control Trim Positions And Dissimilar Formations, Michael T. Morgan

Theses and Dissertations

This thesis further defines the position of greatest fuel savings benefit for the trail aircraft flying in a two-ship formation. The HASC95 vortex lattice code was used for the examination. Investigations of a similar formation of F-16 aircraft and a dissimilar formation of a lead KC-135 aircraft and a trail F-16 aircraft were conducted. The analyses determined the effects of varying airspeed on the optimal position. In addition, flight control surface deflections were taken into account during the analyses. Both investigations trimmed the aircraft in the yaw and roll axes to determine the optimal savings. The similar analysis was conducted …

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Characterization Of Upstream Mixing Cavities And A Downstream Combustion Cavity In Supersonic Flow, Adam P. Quick Mar 2005

Characterization Of Upstream Mixing Cavities And A Downstream Combustion Cavity In Supersonic Flow, Adam P. Quick

Theses and Dissertations

A key area of study in air-breathing hydrocarbon-fueled scramjet combustors is the characterization of cavity-based fuel injection and flame holding. One issue concerns oscillatory disturbances caused by trapped vortices in the main flame holder cavity as a fuel-air mixing enhancement technique. Previous research demonstrates that oscillatory disturbances can be carried downstream via the shear layer and alter the oscillatory characteristics of a downstream cavity. This study investigates the mixing effectiveness of three upstream direct-fueled mixing cavities as well as the effect on the oscillatory behavior of the downstream combustion cavity by the upstream mixing cavity. The three upstream mixing cavities …

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Attitude Model Of A Reaction Wheel/Fixed Thruster Based Satellite Using Telemetry Data, Jason E. Smith Mar 2005

Attitude Model Of A Reaction Wheel/Fixed Thruster Based Satellite Using Telemetry Data, Jason E. Smith

Theses and Dissertations

Attitude determination of satellites is normally the job of inertial instruments, such as gyroscopes, or through sensing instruments, such as star trackers or Global Positioning Satellites (GPS). Satellite health monitoring systems watch and determine if the satellite deviates from its normal operating attitude orientation. Knowing the orientation of a satellite is essential in being able to control it in order to complete the satellite's designated mission. While there are a multitude of ways to determine a satellite's orientation, very little research has been done on determining if the attitude of a satellite can be determined directly from telemetry data of …

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Weight Analysis Of Two-Stage-To-Orbit Reusable Launch Vehicles For Military Applications, Richard A. Caldwell Mar 2005

Weight Analysis Of Two-Stage-To-Orbit Reusable Launch Vehicles For Military Applications, Richard A. Caldwell

Theses and Dissertations

In response to Department of Defense (DoD) requirements for responsive and low-cost space access, this design study provides an objective empty weight analysis of potential reusable launch vehicle (RLV) configurations. Each two-stage-to-orbit (TSTO) RLV has a fixed payload requirement of 20,000 lbf to low Earth orbit. The propulsion systems considered in this study include pure rocket, pure turbine, rocket-based-combined-cycle (RBCC), and turbine-based-combined-cycle (TBCC). The hydrocarbon dual-mode scramjet (DMSJ) engines used in the RBCC and TBCC propulsion systems represent possible applications of the current research being performed in the U.S. Air Force HyTech program. Two sensitivity analyses were then performed on …

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A Numerical Analysis For Passive Attitude Stabilization Using A Tethered Balloon On A Gravity Gradient Satellite, Ernest Matias Maramba Mar 2005

A Numerical Analysis For Passive Attitude Stabilization Using A Tethered Balloon On A Gravity Gradient Satellite, Ernest Matias Maramba

Theses and Dissertations

This research effort analyzes the fundamental dynamics governing a satellite with a gravity gradient boom and a tethered balloon. Satellites that use gravity gradient booms for passive attitude control are characterized by undamped pitch oscillations and no roll control. The tethered balloon acts as a high drag device that accounts for the most drag on the satellite system. By attaching a drag device, the system resists rolling movements while also damping oscillations. This could potentially be a cost effective method for increasing satellite stabilization. The goal of this research is to model the dynamics and determine the feasibility of a …

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Performance Study Of Staging Variable On Two-Stage-To-Orbit Reusable Launch Vehicles, James K. Nilsen Mar 2005

Performance Study Of Staging Variable On Two-Stage-To-Orbit Reusable Launch Vehicles, James K. Nilsen

Theses and Dissertations

The purpose of this research is to investigate the effects of staging variables on Two-Stage-To-Orbit reusable launch vehicles, specifically, the question of what measurable factors play important roles in staging performance. Three different configurations (Rocket-Rocket, Turbojet-Rocket and Turbine Based Combined Cycle-Rocket) were considered. The software, Program to Optimize Simulated Trajectories (POST), was used to analyze these configurations. Vehicle coasting time, staging dynamic pressure and staging Mach number were all varied to determine their influence on the final payload.

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Orbit Estimation Algorithms For A Microsatellite Rendezvous With A Non-Cooperative Target, John P. Heslin Mar 2005

Orbit Estimation Algorithms For A Microsatellite Rendezvous With A Non-Cooperative Target, John P. Heslin

Theses and Dissertations

This study investigated the minimum requirements to establish a satellite tracking system architecture for a microsatellite to rendezvous with a non-cooperative target satellite. A prototype optical tracking system was reviewed with emphasis on a proposed tactical employment that could be used by technologically unsophisticated state or non-state adversaries. With the tracking system architecture selected, simulated tracking data was processed with a Non-Linear Least Squares batch orbit estimation algorithm and a Bayes sequential orbit determination filter to update the target satellite's state vector.

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Technical Feasibility Of Loitering Lighter-Than-Air-Near-Space Maneuvering Vehicles, Eric R. Moomey Mar 2005

Technical Feasibility Of Loitering Lighter-Than-Air-Near-Space Maneuvering Vehicles, Eric R. Moomey

Theses and Dissertations

The near-space region of earth's atmosphere above 20 kilometers altitude is greatly underutilized. Lighter-than-air maneuvering vehicles, or airships, using the principle of buoyancy can take advantage of this region to become potential platforms for precision navigation, environmental monitoring, communication relays, missile warning, surveillance, and weapon delivery. These vehicles purportedly provide persistent coverage over large areas of the earth's surface at substantially lower costs than orbiting satellites. This study investigated the technical requirements to loiter an operational payload within this high altitude region using a lighter-than-air maneuvering platform. A parametric analysis was conducted to identify the critical technologies needed to achieve …

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Modeling And Simulation Of Commercial Satellite Imagery Processes, David A. Shultz Mar 2005

Modeling And Simulation Of Commercial Satellite Imagery Processes, David A. Shultz

Theses and Dissertations

The purpose of this research was to develop a general, statistical model of order-to-delivery times for commercial satellite imagery. The research looked at the current four satellite providers with 3-meter or better imagers in the context of a generalized model of commercial imaging satellite operations. Existing methods use orbit analysis tools to determine the imaging time of a specified target based on defined satellite position and times, but can only develop shortest and longest times to an imaging opportunity. To address the general question of the time it takes to deliver an image for non-specific targets, this research develops a …

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Investigation Of Aerobraking To Return The Space Maneuver Vehicle To Low Earth Orbit From Geotransfer Orbit, Benjamin M. Berlin Mar 2005

Investigation Of Aerobraking To Return The Space Maneuver Vehicle To Low Earth Orbit From Geotransfer Orbit, Benjamin M. Berlin

Theses and Dissertations

This study investigated the use of ballistic and Double-Dip'' aerobraking reentry to return the Space Maneuver Vehicle (SMV) from geotransfer orbit in no more than two atmosphere passes. Lift and drag accelerations were applied to the two-body problem when either of their magnitudes exceeded 1/1000 g. Lift and drag coefficients, along with the SMV model, were taken from Investigation of Atmospheric Reentry for the Space Maneuver Vehicle by Captain McNabb, AFIT/GA/ENY/04-M03. Target perigees were formulated using the two-body problem. The orbit from each target perigee was numerically integrated around a planar earth model using a fourth order Runge-Kutta method. Ballistic …

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Timing Of Increasing Electron Counts From Geosynchronous Orbit To Low Earth Orbit, Kirk M. Olson Mar 2005

Timing Of Increasing Electron Counts From Geosynchronous Orbit To Low Earth Orbit, Kirk M. Olson

Theses and Dissertations

Under certain conditions, high energy electron fluxes can increase over short periods of time in the outer radiation belt and diffuse to low altitudes. Sudden increases of high energy electron densities at low altitudes can drastically damage unsuspecting low-earth-orbit satellites. The progression of electron flux increases from a geosynchronous orbit to low-earth orbit during an electron event is somewhat unknown. If the beginning of electron flux increases at low-earth-orbits could be anticipated, warnings could be issued to space system operators allowing time to take proper measures to protect and minimize satellite damage extending satellite lifetimes and space mission operations. The …

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Fuel-Air Injection Effects On Combustion In Cavity-Based Flameholders In A Supersonic Flow, William H. Allen Jr. Mar 2005

Fuel-Air Injection Effects On Combustion In Cavity-Based Flameholders In A Supersonic Flow, William H. Allen Jr.

Theses and Dissertations

The Air Force Research Lab, Propulsion Directorate, Wright-Patterson Air Force Base, Ohio has studied several designs regarding cavity flameholding for supersonic RAMJET (SCRAMJET) applications. The most recent of these studies have concluded that direct injection of ethylene fuel into the aft cavity ramp produced an efficient, robust flameholder given specific freestream condition and fuel flow rate. The main goals of this experiment are: 1) study the effect on combustion of direct fuel and air injection in the main flameholding cavity and 2) characterization of the operational limits (i.e., sustained combustion limits) over a variety of fuel and air flow rates. …

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Development Of A Higher-Order Upwind Algorithm For Compressible Fluid Flow, Barry A. Croker Mar 2005

Development Of A Higher-Order Upwind Algorithm For Compressible Fluid Flow, Barry A. Croker

Theses and Dissertations

A global fourth-order solution method that incorporates compact differencing with Roe's approximate Riemann solver was investigated. This method was incorporated into a one-dimensional numerical simulation of the compressible Euler equations, and applied to a one-dimensional shock tube problem. The method was also extended to two dimensions, and applied to a two-dimensional shock tube problem and an advecting vortical structure problem on both rectilinear and curvilinear meshes. The results were compared to a third-order Roe scheme and a fourth-order compact difference scheme. An order of accuracy determination showed that it has an order of accuracy somewhere near fourth order, with absolute …

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A Systematic Method For Characterizing The Elastic Properties And Adhesion Of A Thin Polymer Membrane, Bing Feng Ju, Yang Ju, Masumi Saka, Kuo Kang Liu, Kai Tak Wan Mar 2005

A Systematic Method For Characterizing The Elastic Properties And Adhesion Of A Thin Polymer Membrane, Bing Feng Ju, Yang Ju, Masumi Saka, Kuo Kang Liu, Kai Tak Wan

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The elastic properties and adhesion of a thin silicone rubber membrane have been characterized. an effective instrumentation embodying a video-enhanced microscope, which meets force and displacement resolution of 0.1μN and 10 nm, was developed. It provides the capability of simultaneously measuring both the applied force and the resultant displacement of the thin polymer membrane. a linear theoretical elastic solution was applied to quantitatively interpret the measured central deflection of the membrane under a circular concentrical load. Young's modulus of the membrane can be easily determined once the applied force and the central deflection, together with the essential dimensions, are known. …

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Numerical Analysis And Optimization Of The Ultra Compact Combustors, Roger T. Greenwood Mar 2005

Numerical Analysis And Optimization Of The Ultra Compact Combustors, Roger T. Greenwood

Theses and Dissertations

In an effort to increase thrust per weight ratio and decrease pollutant emissions of aero-turbine jet engines, a circumferentially burning Ultra Compact Combustor (UCC) with a Cavity-in-a-Cavity design has been developed. A numerical analysis of this design has been conducted and compared with experimental results. The CFD model has been validated through a wide range of conditions and four alternative physical configurations of the UCC have been modeled. Emissions, combustor efficiencies, temperature and velocity profiles, and pressure drop values were used as comparison parameters. Numerical results indicate that increasing the outflow area will increase the pressure drop over the combustor …

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Maneuver Estimation Model For Relative Orbit Determination, Tara R. Storch Mar 2005

Maneuver Estimation Model For Relative Orbit Determination, Tara R. Storch

Theses and Dissertations

While the use of relative orbit determination has reduced the difficulties inherent in tracking geosynchronous satellites that are in close proximity, the problem is often compounded by stationkeeping operations or unexpected maneuvers. If a maneuver occurs, observations will no longer fit predicted data, increasing the risk of misidentification and cross-tagging. The goal of this research was to develop a model that will estimate the magnitude, direction, and time of a suspected maneuver performed by a collocated satellite in geosynchronous orbit. Relative motion was modelled using Hill's equations, and least squares estimation was employed to create both a linear non-maneuver model …

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Katysat: Kids Aren’T Too Young For Satellites, Robert J. Twiggs, Ben Yuan Feb 2005

Katysat: Kids Aren’T Too Young For Satellites, Robert J. Twiggs, Ben Yuan

Robert "Bob" Twiggs STEM Education Collection

A PowerPoint Presentation created by Professor Bob Twiggs and Bob Yuan titled "Katysat: Kids Aren’t Too Young for Satellites" from February 8, 2005.

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Modelling And Validation Of A Propellant Mixer For Controller Design, Hanz Richter, Enrique Barbieri, Fernando Figueroa Nasa Stennis Space Center Feb 2005

Modelling And Validation Of A Propellant Mixer For Controller Design, Hanz Richter, Enrique Barbieri, Fernando Figueroa Nasa Stennis Space Center

Mechanical Engineering Faculty Publications

A mixing chamber used in rocket engine testing at the NASA Stennis Space Center is modelled by a system of two nonlinear ordinary differential equations. The mixer is used to condition the thermodynamic properties of cryogenic liquid propellant by controlled injection of the same substance in the gaseous phase. The three inputs of the mixer are the positions of the valves regulating the liquid and gas flows at the inlets, and the position of the exit valve regulating the flow of conditioned propellant. Mixer operation during a test requires the regulation of its internal pressure, exit mass flow, and exit …

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Experimental Verification Of The Aerodynamics Of Stream Thrust Probes, Robert S. Hiers Iii, James R. Sirbaugh, Capt Barrett T. Mccann, Russell M. Cummings, Cadet Laura S. Luft, Cadet Dimitrios P. Grillos Jan 2005

Experimental Verification Of The Aerodynamics Of Stream Thrust Probes, Robert S. Hiers Iii, James R. Sirbaugh, Capt Barrett T. Mccann, Russell M. Cummings, Cadet Laura S. Luft, Cadet Dimitrios P. Grillos

Aerospace Engineering

Determining the local stream thrust (a vector quantity) from a measured pitot pressure (a scalar quantity) requires either knowledge of the flow direction or a probe shape that compensates for flow direction. This compensation ideally would make the measured pressure directly proportional to the component of momentum along the probe axis. The flow angle sensitivity required to resolve this component of momentum was previously determined theoretically. A proposed probe nose shape was analyzed using computational fluid dynamics (CFD) and was found to produce a flow angle sensitivity close to the required sensitivity. In the current work, the proposed nose shape …

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