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Articles 1 - 15 of 15
Full-Text Articles in Engineering
Effects Of High Freestream Turbulence And Conduction On Film Cooling Effectiveness Of Shaped Holes, Richard A. Macias Jr.
Effects Of High Freestream Turbulence And Conduction On Film Cooling Effectiveness Of Shaped Holes, Richard A. Macias Jr.
Theses and Dissertations
With technological advancements allowing higher turbine temperatures, film cooling continues to be an important research area. The Film Cooling Rig (FCR) was fitted with a turbulence generator to vary freestream turbulence intensity and length scale, enabling the effects of high freestream turbulence on overall effectiveness to be studied. A cylindrical hole and laidback fan-shaped hole were investigated over a range of Advective Capacity Ratio (ACR) for freestream turbulence intensities of 2%, 10%, and 15%. For a given ACR, increasing the turbulence intensity resulted in lower overall effectiveness values due to the larger heat transfer coefficient that comes from turbulent ow. …
Three-Dimensional Wall Effects In A Scramjet Cavity Flameholder, Evan P. Oren
Three-Dimensional Wall Effects In A Scramjet Cavity Flameholder, Evan P. Oren
Theses and Dissertations
Scramjets, or supersonic combustion ramjets, are a key component for the development of powered hypersonic vehicles. The flameholding strategy used in this engine creates a recirculation region by creating a cavity in one side of the combustor. This highly unsteady region is difficult to interrogate through conventional means. A novel optical observation technique called hyperspectral imaging has been developed to examine the scramjet combustion chamber. The hyperspectral camera is capable of generating an interferogram at hundreds to thousands of wavelengths. These data are integrated across the line-of-sight with no information on three-dimensional (3D) location of origin. A model must be …
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 …
Performance-Metric Driven Atmospheric Compensation For Robust Free-Space Laser Communication, Peter N. Crabtree
Performance-Metric Driven Atmospheric Compensation For Robust Free-Space Laser Communication, Peter N. Crabtree
Theses and Dissertations
The effect of turbulence on laser propagation is a significant challenge to current electro-optical systems. While atmospheric compensation techniques in space object imaging and high-energy laser weapons have been thoroughly investigated, optimizing these techniques for Laser Communication (LaserCom) has not been examined to the same degree. Average Strehl ratio is the typical design metric for current atmospheric compensation systems. However, fade probability is the relevant metric for LaserCom. This difference motivated the investigation into metric-driven atmospheric compensation. Metric-based tracking techniques for fade mitigation is the first major focus of this research. In a moderate range air-to-air scenario, focal plane spot …
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 …
Computational Fluid Dynamics Investigation Of Vortex Breakdown For A Delta Wing At High Angle Of Attack, Jacob A. Freeman
Computational Fluid Dynamics Investigation Of Vortex Breakdown For A Delta Wing At High Angle Of Attack, Jacob A. Freeman
Theses and Dissertations
Using the commercially available FLUENT 3-D flow field solver, this research effort investigated vortex breakdown over a delta wing at high angle of attack (α) in preparation for investigation of active control of vortex breakdown using steady, along- core blowing. A flat delta-shaped half-wing with sharp leading edge and sweep angle of 60° was modeled at α=18° in a wind tunnel at Mach 0.04 and Reynolds number of 3.4 x 105. A hybrid (combination of structured and unstructured) numerical mesh was generated to accommodate blowing ports on the wing surface. Results for cases without and with along-core blowing …
The Combined Effects Of Freestream Turbulence, Pressure Gradients, And Surface Roughness On Turbine Aerodynamics, Christine P. Ellering
The Combined Effects Of Freestream Turbulence, Pressure Gradients, And Surface Roughness On Turbine Aerodynamics, Christine P. Ellering
Theses and Dissertations
This work used scaled facsimiles of real turbine blade surfaces to characterize correlations between turbine blade roughness, freestream turbulence, pressure gradients and skin friction (Cf). Addition of roughness caused Cf to increase: up to 300% for the roughest surface. Addition of freestream turbulence resulted in 125% increase for the same surface. The combined effects showed increases up to 380%. Although decreasing roughness, freestream turbulence, and Reynolds number resulted in less dramatic results, it was concluded that the Cf increases due to combined effects were consistently higher than their corresponding sum of the parts. The combined effects of roughness and pressure …
Effect Of High Free Stream Turbulence On Film Cooling Using Double Row Of 30° Slant-Hole Injectors, Lilith I. Sorensen
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 …
Analysis Of Turbulence Models As Applied To Two- And Three-Dimensional Injection Flows, Clarence R. Chenault
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 …
Atmospheric Induced Errors In Space-Time Adaptive Processing, Vinod D. Naga
Atmospheric Induced Errors In Space-Time Adaptive Processing, Vinod D. Naga
Theses and Dissertations
This thesis examines the effects of atmospheric turbulence-induced phase perturbations on the performance of ground-based Space-Time Adaptive Processing (STAP) systems. Both Fully Adaptive Joint Domain Optimum and Partially Adaptive Factored-Time Space processing methods are examined. This thesis concentrates on the turbulence effects on STAP applied to ground-based arrays. This thesis further focuses on the capability of STAP to resolve targets at low elevation angles in the presence of turbulence. Only clutter interference and receiver noise are considered. Turbulence effects on the EM phase-front are calculated for turbulence strength Cn(2) values ranging from 5.0 x 10(exp -14) m-2/3 to 5.0 x …
Atmospheric Turbulence Scintillation Effects On Wavefront Tilt Estimation, James A. Louthain
Atmospheric Turbulence Scintillation Effects On Wavefront Tilt Estimation, James A. Louthain
Theses and Dissertations
A new atmospheric turbulence screen generator is developed for use in performance calculations of adaptive optics systems valid over a wide range of atmospheric turbulence parameters. The screen generator accounts for diffraction effects caused by weak turbulence and incorporates the phase, amplitude, and cross statistics of the perturbed optical field. The wavefront's phase and amplitude perturbations are taken from the correlation functions developed by Lee and Harp and the cross correlation of the phase and amplitude derived in this thesis. The screen generator uses a modal representation to perform a Fourier series expansion of the wavefront phase and amplitude over …
Experimental Investigation Of Non-Adiabatic Supersonic Slot Injection Into A Supersonic Cross-Flow, Kelly C. Tucker
Experimental Investigation Of Non-Adiabatic Supersonic Slot Injection Into A Supersonic Cross-Flow, Kelly C. Tucker
Theses and Dissertations
Turbulence and mean flow measurements were acquired downstream of a normal, supersonic (M=1.6), two-dimensional, slot injection into Mach 3.0 flow (Re/m = 15x106). Two non-adiabatic cases Ti/T∞ = 1.11 and Ti/T∞ = 0.93) were studied. Multiple overheat anemometry and conventional mean flow analysis, as well as shadowgraph and schlieren photography, were utilized to study the turbulent mixing layer. The mean flow data included the Pitot, cone-static, and Mach number profiles. The measured turbulence data included shear stresses, mass flux, total temperature turbulence intensities, and turbulent heat fluxes. The temperature and density variation …
Flow Visualization Of A Turbulent Shear Flow Using An Optical Wavefront Sensor, Daniel W. Jewell
Flow Visualization Of A Turbulent Shear Flow Using An Optical Wavefront Sensor, Daniel W. Jewell
Theses and Dissertations
The research reported here investigated the use of a shearing interferometer (SI) wavefront sensor to determine the effects of shear-layer turbulence on an optical wavefront. A collimated helium-neon laser beam was propagated through a plane shear-layer produced by mixing helium and nitrogen at different velocities. Since the gases have different indices of refraction, the optical wavefront was distorted by different amounts by each gas. The SI measured the wavefront slope across the sampled area of the wavefront. The shear-layer was viewed from two orthogonal directions. This document contains shadow graphs, interference patterns imaged by each of the SI's six cameras, …
Experimental Investigation Of The Effects Of Blowing Ratio Parameter On Heat Transfer To A Film-Cooled Flat Plate, Marco R. Valencia
Experimental Investigation Of The Effects Of Blowing Ratio Parameter On Heat Transfer To A Film-Cooled Flat Plate, Marco R. Valencia
Theses and Dissertations
The effects of blowing ratio on film cooling effectiveness were investigated. Two round-nosed test plates were used. One made of aluminum and the second of corian (low thermal conductivity). Injection at 35 degrees in the downstream direction was studied. Helium was mixed with air to produce a density ratio (coolant to mainstream) of 1.6 and 2.0, while the blowing ratio varied from 0.3 to 2.2. Surface temperature was measured by thin film gages located up to a nondimensional downstream distance X/D of 30. Two injection regimes, weak and strong, were found. In the weak regime, film cooling reduced gage heat …
System For Boundary Layer Control Through Pulsed Heating Of A Strip Heater, Milton E. Franke, Lawrence Kudelka
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.