Aerodynamics and Fluid Mechanics Commons^™

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

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 …

Tools For Analysis Of Complex Geometries For A Combined Cycle Scram Jet / Rocket, James Moss

Master's Theses - Daytona Beach

A preliminary design for a variable geometry combined cycle supersonic combustion ram jet (SCRAM jet) / rocket was developed. A precise geometry was selected by parametric analysis and the resultant geometry was analyzed using a computational fluid dynamics (CFD) code developed by Dr. Eric Perrell, and modified by, among others, the author.

This paper is broken into several sections discussing, separately, the design innovations used to permit the geometry of the craft to be adjusted to conform to its flight conditions, the 2D analysis tool developed for the parametric analysis, development of the grid for CFD analysis, and modifications made …

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 …

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 …

Adaptive Control Of A Projectile Fin Using Piezoelectric Elastic Beam, Smitha Mani, Sahjendra N. Singh, Surya Kiran Parimi, Woosoon Yim, Mohamed B. Trabia

Mechanical Engineering Faculty Research

No abstract provided.

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

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 …

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 …

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 …

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 …

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) …

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 …

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 …

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 …