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Articles 1 - 12 of 12
Full-Text Articles in Aerodynamics and Fluid Mechanics
Least-Squares, Continuous Sensitivity Analysis For Nonlinear Fluid-Structure Interaction, Douglas P. Wickert
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
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 …
Filtered Rayleigh Scattering Measurements In A Buoyant Flow Field, Steven M. Meents
Filtered Rayleigh Scattering Measurements In A Buoyant Flow Field, Steven M. Meents
Theses and Dissertations
Filtered Rayleigh Scattering (FRS) is a non-intrusive, laser-based flow characterization technique that consists of a narrow linewidth laser, a molecular absorption filter, and a high resolution camera behind the filter to record images. Gases of different species have different molecular scattering cross-sections that become apparent as they pass through the interrogating laser light source, and this difference is used to discriminate between the different gaseous components. This study focuses on the behavior of a buoyant helium jet exiting horizontally into ambient air, and more specifically this jet’s tendency to form side lobes that are discharged from the core fluid under …
Extending Cfd Modeling To Near-Continuum Flows Using Enhanced Thermophysical Modeling, Abram E. Claycomb
Extending Cfd Modeling To Near-Continuum Flows Using Enhanced Thermophysical Modeling, Abram E. Claycomb
Theses and Dissertations
The constitutive relations found in traditional Navier-Stokes-based computational fluid dynamics solvers are known to be limited in altitude. The presence of nonequilibrium phenomena beyond what these methods are able to predict becomes more prevalent at higher altitudes, or increasing Knudsen number. The bulk viscosity, normally assumed to be zero in most computational fluid dynamics applications, is examined as a means of increasing the range of applicability of computational fluid dynamics. The bulk viscosity model used was from recent calculations available in the literature, from a new anisotropic potential energy surface, and is restricted to temperatures below 2000 K. The normal …
Cfd Analysis Of A T-38 Wing Fence, Daniel A. Solfelt
Cfd Analysis Of A T-38 Wing Fence, Daniel A. Solfelt
Theses and Dissertations
A computational study of the effects of a wing fence on the T-38 Talon was performed. RANS simulations were conducted using the CFD solver AVUS to examine the flow around the T-38 and the fence at a Reynolds number of 10 million. The T-38 was modeled as a half aircraft with a symmetry plane down the center line and did not include the empennage. The engine inlet and exhaust were modeled as sink and source boundary conditions using mass flow and pressure specifications. Two fence geometries placed 26" from the wing tip were tested. The first fence, called a simple …
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 …
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 …
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.
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 …
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 …
Validation Of Turbulence Models In The Beggar Code For Unsteady Flow, Kevin G. Storm
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 …
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 …