Aerodynamics and Fluid Mechanics Commons^™

Design Methodology For Low Speed High Altitude Long Endurance Unmanned Aerial Vehicles, Aaron Altman

Mechanical and Aerospace Engineering Faculty Publications

High Altitude Long Endurance (HALE) Unmanned Aerial Vehicles (UAV's) are increasingly being considered to perform a wide range of tasks. Recent years have seen greater value of UAV's in the military reconnaissance arena, first in the Persian Gulf war, with the use of small UAV's, and more recently over Bosnia with medium sized UAV's.

The NASA ERAST program uses HALE UAV's for environmental sensing and monitoring. The military has investigated using HALE UAV's for Theater Ballistic Missile defense, as well as general battlefield reconnaissance. Proposals have been made to use HALE UAV's for communications relay, long term surveillance (with a …

Vortex Wake And Exhaust Plume Interaction, Including Ground Effect, Ihab Gaber Adam

Mechanical & Aerospace Engineering Theses & Dissertations

Computational modeling and studies of the near-field wake-vortex turbulent flows, far-field turbulent wake-vortex/exhaust-plume interaction for subsonic and High Speed Civil Transport (HSCT) airplane, and wake-vortex/exhaust-plume interaction with the ground are carried out. The three-dimensional, compressible Reynolds-Averaged Navier-Stokes (RANS) equations are solved using the implicit, upwind, Roe-flux-differencing, finite-volume scheme. The turbulence models of Baldwin and Lomax, one-equation model of Spalart and Allmaras and two-equation shear stress transport model of Menter are implemented with the RANS solver for turbulent-flow modeling.

For the near-field study, computations are carried out on a fine grid for a rectangular wing with a NACA-0012 airfoil section and …

Wind Tunnel Testing For Drag Reduction Of An Aircraft Laser Turret, Christopher H. Snyder

Theses and Dissertations

This study investigated the use of aft-mounted fairings and splitter plates to reduce the drag of a half-scale aircraft laser turret. Forces, moments, and pressure distributions were measured in the AFIT 1.5-m (5-ft) wind tunnel at Reynolds numbers between 3x10⁵ and 9x10⁵ based on the turret diameter. Oil traces indicated the nature of the flow near the surface of the unmodified turret and the surrounding area. Tufts placed on the turret, fairings, and splitter plates showed changes in separation regions when configurations were changed. The flow around the turret was characterized by dominant vortices shedding from the top …

The Effect Of Nonvertical Shear On Turbulence In A Stably Stratified Medium, Frank G. Jacobitz, Sutanu Sarkar

School of Engineering: Faculty Scholarship

Direct numerical simulations were performed in order to investigate the evolution of turbulence in a stably stratified fluid forced by nonvertical shear. Past research has been focused on vertical shear flow, and the present work is the first systematic study with vertical and horizontal components of shear. The primary objective of this work was to study the effects of a variation of the angle θ between the direction of stratification and the gradient of the mean streamwise velocity from θ=0, corresponding to the well-studied case of purely vertical shear, to θ=π/2,corresponding to purely horizontal shear. It was observed that the …

The Design And Testing Of An Inlet-Airfoil For A High Altitude Remotely Piloted Aircraft, Preston Bradley Martin

Mechanical & Aerospace Engineering Theses & Dissertations

The following work describes and validates a methodology for the aerodynamic design of a low drag, efficient inlet-airfoil to be used on the cooling installations of a high altitude remotely piloted aircraft. Owing to the primary aircraft design requirement of subsonic endurance at high altitude (85,000 ft), the flight conditions present an aerodynamically unfavorable combination of low chord Reynolds number (500,000) and high subsonic Mach number (0.5). At this flight condition, the inlet-airfoil must meet the heat exchanger cooling flow requirements while maintaining the aerodynamic performance of the airfoil. As a result, the design method is closely coupled with not …

Effect Of High Free Stream Turbulence On Film Cooling Using Double Row Of 30° Slant-Hole Injectors, Lilith I. Sorensen

Theses and Dissertations

In this study free stream turbulence levels from 7.3% to 17.8% are applied to film cooling over a flat plate with two rows of 30° slant holes using a wall jet as the main stream air supply and source of turbulence. Blowing ratios are varied from 0.25 to 2.0 and free stream velocities at injection range from 10 m/s to 85 m/s. A constant density ratio of 1.07 is kept throughout the experiment. Results show that for different magnitudes of blowing ratio free stream turbulence has a different influence on effectiveness. At the forward stations, where blow off was present …

The Influence Of Surface Roughness On Supersonic High Reynolds Number Turbulent Boundary Layer Flow, Robert M. Latin

Theses and Dissertations

A comprehensive study of rough-wall high speed (M=2.9) high Reynolds number (R_e/m = 1.9 x 10⁷) turbulent boundary layer flow was performed consisting of experimental, analytical, and numerical methods. Six wall topologies consisting of a smooth and five rough surfaces (two and three dimensional machined roughness plates; and 80, 36, and 20 grit sand-grain roughened plates) were studied. A confocal laser scan microscope was used to measure the topography of the sand grain roughnesses. The experimental measurement techniques included a convention Pitot pressure probe, laser Doppler velocimetry, hot wire anemometry; color schlieren and laser …

Analysis Of Turbulence Models As Applied To Two- And Three-Dimensional Injection Flows, Clarence R. Chenault

Theses and Dissertations

A steady state solution of the full, three dimensional Favre averaged Navier Stokes equations, coupled with a second order Reynolds stress turbulence model (RSTM) and an eddy viscosity model were used to numerically simulate oblique injection into supersonic flow. Numerical results were compared to experimental data and the turbulence models were evaluated for accurate prediction of thermomechanical mean flow variables, Reynolds stresses, flowfield shock structure and boundary layer phenomena. The RSTM simulation resulted in physically consistent and accurate predictions for the mean flow and turbulent quantities. Simulations with the eddy viscosity model resulted in non-physical and inconsistent turbulence predictions. RSTM …