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Air Force Institute of Technology

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Articles 181 - 188 of 188

Full-Text Articles in Aerodynamics and Fluid Mechanics

Computational Investigation Of Circulation Control Turbulence Modeling, T. Bryan Scruggs Dec 1990

Computational Investigation Of Circulation Control Turbulence Modeling, T. Bryan Scruggs

Theses and Dissertations

A computational study of the turbulence model parameters and the effect on the flow field of a circulation control airfoil was conducted. A Beam- Warming algorithm with a modified Baldwin-Lomax turbulence model was used to solve the Navier-Stokes equations. A comparison between the effects of the Bradshaw constant on the flow field about the cylinder and the flow field about an airfoil were to be made. The lack of a steady 'converged' solution for the cylinder precluded the analysis of the flow field about a cylinder. For the airfoil, the separation point moves rearward and an enhanced vortex pattern is …


Analysis Of Hypersonic Blunt-Body Flows Using A Total Variation Diminishing Scheme And The Maccormack Scheme, Montgomery C. Hughson Dec 1990

Analysis Of Hypersonic Blunt-Body Flows Using A Total Variation Diminishing Scheme And The Maccormack Scheme, Montgomery C. Hughson

Theses and Dissertations

An explicit second-order accurate, total variation diminishing (TVD) scheme and the MacCormack scheme are applied to the Euler equations in axisymmetric form to study hypersonic blunt body flows. The modified flux approach of Harten, with modification by Yee, for two-dimensional flows is extended to treat axisymmetric flows. Calculated flow properties for the steady state, blunt body problem such as shock standoff distance, bow shock shape, surface pressure distribution and entropy jump conditions are compared to theory, results from the MacCormack scheme, and experimental data for Mach numbers of 3.0, 4.03, 5.06, 6.03 and 8.1. Additionally, the TVD and MacCormack schemes …


Turbulence Scales In The Passage Of A Linear Turbine Cascade, James L. Acree Dec 1990

Turbulence Scales In The Passage Of A Linear Turbine Cascade, James L. Acree

Theses and Dissertations

Convective heat transfer in a turbine cascade is examined for turbulence effects. Turbulence in the free stream is varied by injection of air through a jet-grid device upstream of the cascade. Pressure and flow patterns on the blade surface, and flow velocity in two components, are examined to determine the effect of the jet-grid. Velocity and velocity fluctuation in two components are measured. Local turbulence scales through the cascade passage are determined, and local turbulent energy dissipation rate is determined. Results indicate injection of air through the jet-grid changes the angle of incidence, and therefore changes the surface pressures and …


An Experimental Study Of A Sting-Mounted Single-Slot Circulation Control Wing, Michael E. Pelletier Dec 1990

An Experimental Study Of A Sting-Mounted Single-Slot Circulation Control Wing, Michael E. Pelletier

Theses and Dissertations

This wind tunnel study investigated the feasibility of using a sting and force balance to measure the aerodynamic forces and moments on a circulation control wing. A 20% this, 8.5% camber, single blowing slot, rectangular wing was designed, built, and tested in the AFIT 5-ft wind tunnel. Lift and drag coefficients were referenced to the stability axis. The Reynolds number for all tests was 950,000; angle of attack was varied from -6 to +6 degrees. Trends in the data were similar to two dimensional data, with the exception of high drag coefficients with increased blowing. Results show it is feasible …


Modelling And Analysis Of Kernel Function And Development Of Equivalent Theodorsen Function For Three-Dimensional Aeroelastic Analysis, John K. Ryder Dec 1990

Modelling And Analysis Of Kernel Function And Development Of Equivalent Theodorsen Function For Three-Dimensional Aeroelastic Analysis, John K. Ryder

Theses and Dissertations

A fractional calculus model is developed for the kernal function under incompressible subsonic flow conditions for rectangular planform airfoils with small aspect ratio. A model valid for restricted regions of the kernel function for compressible subsonic flow conditions is also developed. Additionally, a method for numerically solving the pressure-downwash integral equation for rectangular planform wings of aspect ratio two through ten in incompressible flow is developed. An equivalent Theodorsen function for three- dimensional unsteady flow is developed, enabling the use of simpler two- dimensional aeroelastic equations of motion to fully capture the more complicated three-dimensional effects.


System For Boundary Layer Control Through Pulsed Heating Of A Strip Heater, Milton E. Franke, Lawrence Kudelka Nov 1988

System For Boundary Layer Control Through Pulsed Heating Of A Strip Heater, Milton E. Franke, Lawrence Kudelka

AFIT Patents

A system is described for controlling the transition of laminar/turbulent flow at a surface which comprises a thin narrow strip heater disposed adjacent the surface and extending substantially transversely of the flow of the air stream thereacross, the heater being resiliently held in tension on or in closely spaced relationship to the surface, and a power source operatively connected to the heater for applying pulsed voltage of preselected amplitude and frequency to the heater.


Axisymmetric Thrust Augmenting Ejector With Discrete Primary Air Slot Nozzles, Steven G. Reznick, Milton E. Franke May 1984

Axisymmetric Thrust Augmenting Ejector With Discrete Primary Air Slot Nozzles, Steven G. Reznick, Milton E. Franke

AFIT Patents

A circular thrust augmenting ejector has an annular wall which defines a central passageway and a convergent contoured inlet section, a constant area cylindrical mixing section and a divergent conical diffuser outlet section. The inlet, mixing and outlet sections merge one into the next in axisymmetric serial relationship. The ejector also has a plurality of discrete primary nozzles arranged about the periphery of the annular wall at the entrance to the inlet section thereof for injecting a primary flow of high velocity air into the inlet section and thereby entraining a secondary flow of ambient air into the central passageway …


A Study Of A Wind Tunnel Measurement System For Unsteady Pressures Using Pneumatic Transmission Lines, Mohammed Javed Khan Dec 1978

A Study Of A Wind Tunnel Measurement System For Unsteady Pressures Using Pneumatic Transmission Lines, Mohammed Javed Khan

Theses and Dissertations

The application of pneumatic transmission lines theory to a tube-scanning valve system for unsteady pressure measurements in the AFIT 5-foot wind tunnel is investigated. Transfer gains of various tube-scanning valve configurations were experimentally measured and the validity of a theoretical model verified for a frequency range of 20 Hz to 140 Hz. The selected system having a 0.0625-in. ID flexible tube of 84 in. length connected to a scanning valve was installed in the wind tunnel. Unsteady pressures introduced over an 18 percent airfoil at zero angle of attack were measured with this system. Data were collected for 0, 40, …