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Articles 61 - 90 of 171
Full-Text Articles in Engineering
Cfd Investigation Of Effect Of Depth To Diameter Ratio On Dimple Flow // Computational Fluid Dynamics Investigation Of Effect Of Depth To Diameter Ratio On Dimple Flow Dynamics, Robert B. Etter
Theses and Dissertations
This study aimed to further the understanding of laminar flow through a dimple with the goal of mitigating flow separation. Dimples of various depth to diameter ratios (0.05, 0.15) were examined for three different dimple diameters and chordwise locations, corresponding to diameter based (ReD) and chordwise location based (Rex) Reynolds number combinations of ReD 20500\Rex 5000, ReD 20500 Rex 77000, and ReD 9000 Rex 21000. For the last combination, a dimple of depth to diameter ratio of 0.25 was also examined. The dimples were placed in a flat plate located in a diverging channel causing an adverse pressure gradient encouraging …
A Comparison Of Film Cooling Techniques In A High Speed, True Scale, Fully Cooled Turbine Vane Ring, Michael J. Umholtz
A Comparison Of Film Cooling Techniques In A High Speed, True Scale, Fully Cooled Turbine Vane Ring, Michael J. Umholtz
Theses and Dissertations
An effort was undertaken to understand the impact of different film cooling configurations in a true scale turbine vane for three proprietary airfoil designs. The measurements for this study were taken at the United States Air Force Turbine Research Facility (TRF). The TRF enabled heat transfer data to be obtained on full scale turbine hardware under realistic engine conditions. The surface heat flux of the turbine blades was analyzed using the impulse response method. The overall effectiveness was compared between airfoil types at 60% span over varying streamwise locations on both suction and pressure surfaces. Using an approximated massflow, a …
Cfd Investigation Of Flow Past Idealized Engine Nacelle Clutter /// Computational Fluid Dynamics Investigation Of Flow Past Idealized Engine Nacelle Clutter, Matthew S. Caspers
Cfd Investigation Of Flow Past Idealized Engine Nacelle Clutter /// Computational Fluid Dynamics Investigation Of Flow Past Idealized Engine Nacelle Clutter, Matthew S. Caspers
Theses and Dissertations
This research modeled low-speed flow past idealized engine nacelle clutter in support of aircraft re suppression research. The idealized clutter was comprised of three vertical rows of staggered circular cylinders approximating typical nacelle obstructions such as fuel lines and wire bundles. Single-phase, Detached-Eddy Simulations (DES) were conducted using the commercial CFD solver, Fluent™, to resolve the flow-field dynamics inside the clutter element and determine mechanisms accounting for the failure of suppressant spray droplets from traversing the array under low-speed, free-stream conditions (ReD = 1, 575). The numerical models provided no evidence that span-wise vorticity or non-uniform shedding was responsible for …
Filtered Rayleigh Scattering Measurements In A Bouyant Flowfield, Christopher C. Mcgaha
Filtered Rayleigh Scattering Measurements In A Bouyant Flowfield, Christopher C. Mcgaha
Theses and Dissertations
Filtered Rayleigh Scattering (FRS) is a non-intrusive technique for studying flowfields. Molecular scattering provides the signal to the camera, and the difference in molecular cross section can be used to discriminate between unmixed gaseous components. The focus of this research is to document the behavior of a horizontal buoyant jet using FRS. A helium jet of precisely controlled mass flow rate is injected into a standard room temperature environment, and FRS provides the means to measure its core trajectory and mixing rate. Trajectory analysis, conducted with consideration of the Reynolds number and Grashof number, can be used to compare these …
Experimental Investigation Of Oblique Wing Aerodynamics At Low Speed, Matthew J. Dillsaver
Experimental Investigation Of Oblique Wing Aerodynamics At Low Speed, Matthew J. Dillsaver
Theses and Dissertations
In an effort to increase the range of missiles and guided bombs, the USAF is looking at options for new wing configurations. One such configuration being considered is oblique wings. An oblique wing is a wing that pivots about a point on the aircraft fuselage thereby having one side swept forward and the other swept aft. Additional interest is looking at a wing only configuration that also rotates with one wing tip forward of the other. Studies have shown that this configuration can provide less drag for a given lift at both supersonic cruise and subsonic loiter conditions. This experiment …
Experimental Characterization Of Turbulent Flow Around Cylinder Arrays, Adam D. Harder
Experimental Characterization Of Turbulent Flow Around Cylinder Arrays, Adam D. Harder
Theses and Dissertations
This research was done as part of an effort to develop alternative fire suppressant technologies for aircraft engine nacelles. A circular cylinder array was designed, built, and placed in the AFIT roll-around low speed wind tunnel to model generic clutter inside an engine nacelle. A turbulence grid was fabricated to enable measurements of the effects of turbulence level, independent of airspeed, on the flow over different model configurations. The wind tunnel test section was 12 inches wide x 12 inches high x 24 inches long. Pressure differential measurements were taken on various cylinder configurations. The configurations included one cylinder as …
Demonstration Of Clean Particle Seeding For Particle Image Velocimetry In A Closed Circuit Supersonic Wind Tunnel, Charles M. Mcniel
Demonstration Of Clean Particle Seeding For Particle Image Velocimetry In A Closed Circuit Supersonic Wind Tunnel, Charles M. Mcniel
Theses and Dissertations
The purpose of this research was to determine whether solid carbon dioxide (CO2) particles might provide a satisfactory, and cleaner, alternative to traditional seed material for Particle Image Velocimetry (PIV) for use in a closed circuit supersonic wind tunnel. The Air Force Institute of Technology (AFIT) closed circuit pressure-vacuum supersonic wind tunnel was utilized, which achieves a nominal Mach number of Mach 2.9 in a 2.5 inch by 2.5 inch square test section. CO2 was dispensed into the flow as a liquid from a standard compressed gas liquid tank through two different injector styles at two injection …
The Aerodynamic Performance Of The 24 Inch Houck Configuration, Michael M. Walker
The Aerodynamic Performance Of The 24 Inch Houck Configuration, Michael M. Walker
Theses and Dissertations
Fuel efficiency of aircraft is of great importance to the military and private sector. A more efficient wing design for UAVs would lead to improvements in mission support while reducing fuel costs for the Air Force. An experimental investigation of one candidate design, the Houck Aircraft Configuration, has been conducted in the AFIT low speed wind tunnel. This aircraft shares similarities to other joined-wing aircraft, but includes curved flow-guides of varying spanwise camber connecting the upper and lower wingtips. Experimental results that the addition of flow guides on the 24" Houck Configuration results in a 2.5% reduction in L/D(sub max) …
Quantifying Non-Equilibrium In Hypersonic Flows Using Entropy Generation, Ryan W. Carr
Quantifying Non-Equilibrium In Hypersonic Flows Using Entropy Generation, Ryan W. Carr
Theses and Dissertations
The constitutive relations traditionally used for finding shear stress and heat flux in a fluid become invalid in non-equilibrium flow. Their derivation from kinetic theory only demonstrates they are valid only for small deviations from equilibrium. Because it is fundamentally linked to non-equilibrium, entropy generation is used to investigate the limits of the continuum constitutive relations. However, the continuum equations are inherently limited to near equilibrium conditions due to the constitutive relations; thus kinetic theory must be used as a basis for comparison. Direct Simulation Monte Carlo (DSMC), a particle method alternative to continuum methods, is based on kinetic theory …
Three Component Velocity Measurements In The Tip Vortex Of A Micro-Air-Vehicle, Hong-Joon Park
Three Component Velocity Measurements In The Tip Vortex Of A Micro-Air-Vehicle, Hong-Joon Park
Theses and Dissertations
The purpose of this research was to improve the MAV that will be used for battle damage assessment and reconnaissance or local surveillance through the experiments in AFIT wind tunnel. The experiments were performed to investigate the wing displacement and wing tip vortex interaction. To conduct the experiments, telescopic survey tool and tri-axial hot-wire anemometer was utilized. The results indicate that wing tip displacement of the flexible wing was approximately 8 times that of the rigid wing in an unstalled condition and data suggests that flexible wing has a denser core-distribution of velocity within the wing tip vortex and delays …
Particle Image Velocimetry Using A Novel, Non-Intrusive Particle Seeding, Charles J. Delapp Ii
Particle Image Velocimetry Using A Novel, Non-Intrusive Particle Seeding, Charles J. Delapp Ii
Theses and Dissertations
The purpose of this research effort was to study the use of non-intrusive particle seeding for Particle Image Velocimetry (PIV). Current seeding material and techniques involve the use of either solid particles or liquid mixtures which can contaminate or damage closed circuit wind tunnels, and in some cases can introduce a potential fire or explosive hazard. The proposed method is based on creating seed particles utilizing Carbon Dioxide (CO2). The CO2 would be dispensed into the flow as a liquid, immediately condensing to solid seed particles as they leave the spray nozzle. The advantage of using these particles is that …
A Wind Tunnel Investigation Of Joined Wing Scissor Morphing, Christopher C. Dike
A Wind Tunnel Investigation Of Joined Wing Scissor Morphing, Christopher C. Dike
Theses and Dissertations
The Air Force Research Laboratory's Munitions Directorate has been looking to extend the range of its small smart bomb. Corneille [6] has conducted tests to determine the aerodynamic characteristics of joined wings on a missile and determine if joined wings are more beneficial than a single wing configuration. The concept of retrofitting wings on the bomb introduced an interesting problem: storage before deployment. This study conducted steady-state low speed wind tunnel testing of a joined wing configuration that morphed from a compact configuration for storage to a full extension. These steady-state tests examine differing sweep angles of the same joined …
Characterizing A Co-Flow Nozzle For Use In A Filtered Rayleigh Scattering System, David S. Miceli
Characterizing A Co-Flow Nozzle For Use In A Filtered Rayleigh Scattering System, David S. Miceli
Theses and Dissertations
Research was conducted on the flow field exiting a co-annular flow nozzle for use in filtered Rayleigh scattering flow visualizations. More specifically, the flow visualizations were of the flow field exiting a coflow nozzle and illuminated by a tunable, nominal 4.2 watt narrow line width Argon laser operating at 514.5nm. ND:YAG lasers are typically used in this application, but some of the properties of a tunable Argon laser make it an attractive alternative. Before generating flow visualizations, the coflow nozzle was characterized both experimentally and computationally. Due to a flow asymmetry in the outer annulus flow field, the nozzle was …
Experimental Investigation Of The Aerodynamic Ground Effect Of A Tailless Lambda-Shaped Ucav With Wing Flaps, Jason T. Mostaccio
Experimental Investigation Of The Aerodynamic Ground Effect Of A Tailless Lambda-Shaped Ucav With Wing Flaps, Jason T. Mostaccio
Theses and Dissertations
This experimental study adequately identified the ground effect region of a lambda-shaped unmanned combat air vehicle (UCAV). The lambda planform used in this study was originally tested in a previous experiment to determine the stability and control characteristics generated out-of-ground-effect. The following study extends the existing database by analyzing the inherent aerodynamic behavior that is produced by employing trailing edge flap deflections while flying in-ground-effect (IGE). To accomplish this objective, static ground effect tests were performed in the AFIT 3? x 3? subsonic wind tunnel where a ground plane was used to simulate the forces and moments on the UCAV …
Dynamic Nonlinear Bending And Torsion Of A Cantilever Beam, Michael S. Whiting
Dynamic Nonlinear Bending And Torsion Of A Cantilever Beam, Michael S. Whiting
Theses and Dissertations
This effort sought to measure the dynamic nonlinear bending and torsion response of a cantilever beam. The natural frequencies of a cantilever beam in both chord and flap directions were measured at different static root pitch angles with varying levels of weights attached at the free end. The results were compared with previous experimentation to validate the data and testing procedures while lowering the associated error bands. Additionally, methodology for measuring mode shapes was set forth and mode shapes were measured for a few test cases with zero degrees of root pitch.
Free Flight Store Simulation Using Beggar, Judson T. Babcock
Free Flight Store Simulation Using Beggar, Judson T. Babcock
Theses and Dissertations
The complete numerical solution of the airflow around a store in extended free flight is of particular importance to the United States Air Force. Beggar is the primary Computational Fluid Dynamics (CFD) program used by the USAF to obtain solutions for store separations. However, Beggar's ability to simulate a store in free flight is limited because the store must fall through a static background mesh, eventually reaching a point where the solution will fail. The length of any free flight simulation is consequently limited by the height of the background mesh. Code modifications are made to Beggar to remove this …
Spatially-Resolved Temperature Diagnostic For Supersonic Flow Using Cross-Beam Doppler-Limited Laser Saturation Spectroscopy, Grady T. Phillips
Spatially-Resolved Temperature Diagnostic For Supersonic Flow Using Cross-Beam Doppler-Limited Laser Saturation Spectroscopy, Grady T. Phillips
Theses and Dissertations
Optical techniques for measuring the temperature in three-dimensional supersonic reactive flows have typically depended on lineshape measurements using single-beam laser absorption spectroscopy. However, absorption over extended path lengths in flows with symmetric, turbulent eddies can lead to systematically high extracted temperatures due to Doppler shifts resulting from flow along the absorption path. To eliminate these problems, Cross-Beam Saturation Absorption Spectroscopy (CBSAS) and Cross-Beam Inter-Modulated Fluorescence (CBIMF) have been developed which utilize two crossed and nearly copropogating laser beams.to record the spectral signal of an I2 ro-vibrational line in a small three-dimensional volume using a tunable CW dye laser. Temperature …
Cfd Investigation Of The Flow Dynamics Inside A Spherical Surface Indentation, Robert C. Vincent
Cfd Investigation Of The Flow Dynamics Inside A Spherical Surface Indentation, Robert C. Vincent
Theses and Dissertations
This study aims to identify the flow structure inside and around a dimple surface indentation that passively reduces flow separation, and to generate characterization parameters for the effectiveness of the aforementioned flow structure in boundary layer separation control. In this study the surface indentation is cut into a flat plate in a diverging channel that creates an adverse pressure gradient. In the baseline flat plate conditions, the shedding vortices formed by the pressure gradient create an oscillating pressure field in the dimple. This geometry has been chosen to simulate the adverse pressure gradient present in the flow regime found on …
Store Separations From A Supersonic Cone, Richard J. Simko
Store Separations From A Supersonic Cone, Richard J. Simko
Theses and Dissertations
The purpose of this research was to analyze the environment a store would travel through if ejected from a supersonic cone. This was done using the Beggar Computational Fluid Dynamics (CFD) code from the Air Force SEEK Eagle Office at Eglin Air Force Base, FL. CFD simulations were compared to experimental results from a previous AFIT thesis and conclusions were drawn based on whether or not the current wind tunnel setup at AFIT is capable of performing analyses of supersonic store separations. Also included in this research is a study of supersonic base pressure profiles, near-wake velocity profiles, wind tunnel …
Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein
Macroscopic Computational Model Of Dielectric Barrier Discharge Plasma Actuators, Timothy R. Klein
Theses and Dissertations
Recent progress in the generation and sustainment of gas discharges at atmospheric pressure has energized research in the field of plasma-aerodynamics. Plasma actuators are promising devices that achieve flow control with no moving parts, do not alter the airfoil shape and place no parts in the flow. The operation of a plasma actuator is examined using a macroscopic (force and power addition) computational fluid dynamic model of a dielectric barrier discharge, DBD, in Fluent. A parametric approach is adopted to survey the range of requisite magnitudes of momentum and energy delivered to the flow field and to identify the effects …
Dynamic Aeroelastic Analysis Of Wing/Store Configurations, Gregory H. Parker
Dynamic Aeroelastic Analysis Of Wing/Store Configurations, Gregory H. Parker
Theses and Dissertations
Limit-cycle oscillation, or LCO, is an aeroelastic phenomenon characterized by limited amplitude, self-sustaining oscillations produced by fluid-structure interactions. In order to study this phenomenon, code was developed to interface a modal structural model with a commercial computational fluid dynamics program. LCO was simulated for a rectangular wing, referred to as the Goland+ wing. It was determined that the aerodynamic nonlinearity responsible for LCO in the Goland+ wing was the combination of strong trailing-edge and lambda shocks which periodically appear and disappear. This mechanism limited the flow of energy into the structure which quenched the growth of the flutter, resulting …
Wind Tunnel Study Of Interference Effects Relating To Aft Supersonic Ejection Of A Store, Timothy P. Jung
Wind Tunnel Study Of Interference Effects Relating To Aft Supersonic Ejection Of A Store, Timothy P. Jung
Theses and Dissertations
An investigation into the issues surrounding the release of a store into a supersonic wake was conducted. A 10-degree half-angle cone was used to model the carrier vehicle as well as the store. The store was 42% than the vehicle. The experiments were conducted at a freestream Mach number of 2.93 and at zero degrees angle of attack. This study analyzed the effects of a support or strut mounted under the wind tunnel model. Research was conducted on the effects of a store at various positions in the wake, as well as the effects of a rear cavity in the …
The Effect Of Aerodynamic Surfaces Versus Thrust Maneuvers On Reentry Vehicles, Meredith M. Albrecht
The Effect Of Aerodynamic Surfaces Versus Thrust Maneuvers On Reentry Vehicles, Meredith M. Albrecht
Theses and Dissertations
This research effort analyzes the effect of aerodynamic surfaces versus thrust maneuvers on a reentry vehicle. At high altitudes the effect of aerodynamic surfaces on the reentry vehicle is small due to low atmospheric density; however as the vehicle reaches lower altitudes a lift maneuver is very successful in deflecting the vehicle and creating a large impact footprint. When a continuous thrust maneuver is input in the place of a lift maneuver the results are very similar at the highest maneuver altitudes, although the impact footprint shrinks rapidly as the maneuver altitude decreases. Additionally, when the thrust maneuver is along …
Effects Of Boundary Layer Flow Control Using Plasma Actuator Discharges, Jeffrey M. Newcamp
Effects Of Boundary Layer Flow Control Using Plasma Actuator Discharges, Jeffrey M. Newcamp
Theses and Dissertations
This study addresses the usage and effects of atmospheric plasma discharges on the near wall flow conditions for a Pak-B low-pressure turbine blade. A plasma actuator was built normal to the freestream flow in a low-speed wind tunnel. The test section of the wind tunnel had a contoured upper wall geometry designed to mimic the suction side of a Pak-B turbine blade. A high frequency ac voltage source supplied three voltages in the kilovolt range at four Reynolds numbers in the experiment, between 10,000 and 103,000. The effect of the plasma on the near-wall boundary layer conditions was evaluated at …
Experimental Investigation Into The Aerodynamic Ground Effect Of A Tailless Chevron-Shaped Ucav, Brett L. Jones
Experimental Investigation Into The Aerodynamic Ground Effect Of A Tailless Chevron-Shaped Ucav, Brett L. Jones
Theses and Dissertations
This experimental study adequately identified the ground effect region of an unmanned combat air vehicle (UCAV). The AFIT 3' x 3' low-speed wind tunnel and a ground plane were used to simulate the forces and moments on a UCAV model in ground effect. The chevron planform used in this study was originally tested for stability and control and the following extends the already existing database to include ground effects. The ground plane was a flat plate mounted with cylindrical legs. To expand the capabilities of the AFIT 3' x 3' low-speed wind tunnel, hot-wire measurements and flow visualization revealed an …
Boundary Layer Control Of A Circular Cylinder Using A Synthetic Jet, Christopher K. Smith
Boundary Layer Control Of A Circular Cylinder Using A Synthetic Jet, Christopher K. Smith
Theses and Dissertations
Active control of flow around a circular cylinder at a sub-critical Reynolds number was studied experimentally. The flow was controlled by using a synthetic jet which ran span wise along the cylinder and emanated radially from the cylinder. The experiments were conducted over a two dimensional cylinder in a water tunnel at a Reynolds number of approximately 5800. Seven different jet locations and seven different jet oscillation frequencies were examined. Particle image velocimetry (PIV) was used for flow visualization. The synthetic jet proved to delay flow separation at a wide range of locations and oscillation frequencies. The greatest positive effect …
Boundary Layer Flow Control Using Plasma Induced Velocity, Brian E. Balcer
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 …
Development Of A Higher-Order Upwind Algorithm For Compressible Fluid Flow, Barry A. Croker
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 …
Experimental Study Of The Subsonic Aerodynamics Of A Blended Wing Body Air Vehicle With A Focus On Rapid Technology Assessment, David A. Gebbie
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) …
Characterization Of Upstream Mixing Cavities And A Downstream Combustion Cavity In Supersonic Flow, Adam P. Quick
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 …