In this dissertation, Immersed Boundary Method (IBM) is evaluated in ribbed duct geometries to show the potential of simulating complex geometry with a simple structured grid. IBM is first investigated in well-accepted benchmark cases: channel flow and pipe flow with circular cross-section. IBM captures all the flow features with very good accuracy in these two cases. Then a two side ribbed duct geometry is test using IBM at Reynolds number of 20,000 under fully developed assumption. The IBM results agrees well with body conforming grid predictions. A one side ribbed duct geometry is also tested at a bulk Reynolds number of 1.5⨉10⁴. Three cases have been examined for this geometry: a stationary case; a case of positive rotation at a rotation number (Ro=ΩDₕ/U) of 0.3 (destabilizing); and a case of negative rotation at Ro= -0.3 (stabilizing). Time averaged mean, turbulent quantities are presented, together with heat transfer. The overall good agreement between IBM, BCG and experimental results suggests that IBM is a promising method to apply to complex blade geometries. Due to the disadvantage of IBM that it requires large amount of cells to resolve the boundary near the immersed surface, wall modeled LES (WMLES) is evaluated in the final part of this thesis. WMLES is used for simulating turbulent flow in a developing staggered ribbed U-bend duct. Three cases have been tested at a bulk Reynolds number of 10⁵: a stationary case; a positive rotation case at a rotation number Ro=0.2; and a negative rotation case at Ro=-0.2. Coriolis force effects are included in the calculation to evaluate the wall model under the influence of these effects which are known to affect shear layer turbulence production on the leading and trailing sides of the duct. Wall model LES prediction shows good agreement with experimental data. / Master of Science

Kamala Harris made history on November 7, 2020, when she was elected as the first female Vice President of the United States. In addition to being the first woman, she became the first African-American and Indian-American to attain this position. As a result, the media had to grapple with how to cover her historic campaign from the moment she was announced as the vice-presidential selection. This qualitative thematic analysis examined The New York Times and The Wall Street Journal's coverage of her campaign with significant analysis on important events such as the initial buzz surrounding her selection, the convention speech, and the vice-presidential debate. Specifically, this study examines 70 news articles total from both newspapers from August 11-November 3, 2020 to determine the recurring themes from her coverage. Results indicated that although traditional media frames and themes were not a significant focus, Harris's intersectionality brought about a new set of frames to explore, with subtle differences between the two newspapers. Implications of these results and future considerations for the media are discussed. / Master of Arts / Kamala Harris made history on November 7, 2020, when she was elected as the first female Vice President of the United States. In addition to being the first woman, she became the first African-American and Indian-American to attain this position. Throughout her campaign, the media had to learn how to cover an historic candidate effectively, since this moment had no precedent. This thesis chose to explore The New York Times and The Wall Street Journal's coverage of her campaign because of their influence in shaping the news around the country and they both represent different sides of the political spectrum. Important events that are covered include the initial announcement, the convention speech, and the vice-presidential debate. This study looks to determine if the stereotypical frames that the media places on female candidates are still seen with Harris. Results indicated that although traditional media stereotypes were not a significant focus, Harris's identity brought about a new set of themes to analyze, with each paper focusing on different aspects. Implications of these results and future considerations for the media are discussed.

This study explores the potential of the naphthalene sublimation technique to be used to analyze the manner in which surfaces regress, specifically focusing on the effect that skin friction has on regression and vice versa. For this experimentation, a flat steel plate installed with three skin friction sensors was coated with naphthalene via a mechanized sprayer and was installed in the wall of the Ahmic Aerospace Turbulent Boundary Layer Research supersonic wind tunnel. The plate and sensor configuration was subjected to three subsequent tunnel runs at Mach 2.31. This process was repeated at plenum pressures of 0.35 MPa and 0.69 MPa, which correspond to Reynolds Numbers of 1.4x10^7/m and 2.8x10^7/m. Between the first and final run, a -4.7% and -3.7% percent change in the coefficient of friction was seen at the 0.35 MPa and 0.69 MPa plenum conditions, respectively. Images of the plate taken before and after each run qualitatively indicate continual naphthalene regression with each subsequent tunnel run. This decrease in the coefficient of friction was attributed in part to the regression of the naphthalene coating, indicating that this method has the potential to be used to study the interaction between skin friction and regressing surfaces. Additionally, this study showed that it is certainly possible to measure skin friction with sensors where both the head of the movable sensor element and the surrounding wall is coated with sprayed naphthalene. / Master of Science / This study explores the potential of using an experimental method to better understand how surfaces recede when subjected to moving air. A chemical called naphthalene was used because naphthalene naturally recedes very easily, unlike many other materials which a researcher would want to study the receding behavior of, making it an ideal choice for this study. Sensors made to detect the amount of force generated by flowing air over a surface were installed into a flat metal plate. The plate was coated with naphthalene and installed into the wall of a wind tunnel, which generates airflow over the plate to simulate flight conditions. Three separate and sequential airflow runs over the plate were conducted. This process was repeated under two different air conditions. In both conditions, a decrease in the amount of force due to the air moving over the plate was detected as subsequent runs were conducted and the naphthalene receded. This indicates the method has the potential to be used to study how other surfaces recede when subjected to moving air.

This investigation concerns the design, build, and testing of a new class of skin friction sensor capable of performing favorably in high-speed, high-enthalpy flow conditions, such as that found in atmospheric re-entry vehicles, scramjets, jet engines, material testing, and industrial processes. Fully understanding and optimizing these complex flows requires an understanding of aerodynamic properties at high enthalpies, which, in turn, requires numerical and analytical modeling as well as reliable diagnostic instrumentation. Skin friction is a key quantity in assessing the overall flight and engine performance, and also plays an important role in identifying and correcting problem areas. The sensor design is founded on a direct-measuring, cantilever arrangement. The design incorporates two fundamental types of materials in regards to thermal conductivity and voltage resistivity properties. The non-conducting material distinction greatly deters the effect of heat soak and prevents EMI transmission throughout the sensor. Four custom fabricated metal-foil strain gauges are arranged in a Wheatstone bridge configuration to increase sensitivity and to provide further compensation for sensitivity effects. The sensor is actively cooled via a copper water channel to minimize the temperature gradient across the electronic systems. The design offers a unique immunity to many of the interfering influences found in complex, high-speed, high-enthalpy flows that would otherwise overshadow the desired wall shear measurement. The need to develop an encompassing design methodology was recognized and became a principal focus of this research effort. The sensor design was developed through a refined, multi-disciplinary approach. Concepts were matured through an extensive and iterative program of evolving key performance parameters. Extensive use of finite element analysis (FEA) was critical to the design and analysis of the sensor. A software package was developed to utilize the powerful advantage of FEA methods and optimization techniques over the traditional trial and error methods. Each sensor endured a thorough series of calibrations designed to systematically evaluate individual aspects of its functionality in static, dynamic, pressure, and thermal responses. Bench-test facilities at Virginia Tech (VT) and Air Force Research Laboratory (AFRL) further characterized the design vibrational effects and electromagnetic interference countermeasure effectiveness. Through iterations of past designs, sources of error have been identified, controlled, and minimized. The total uncertainty of the skin friction sensor measurement capability was determined to be ±8.7% at 95% confidence and remained fairly independent of each test facility. A rigorous, multi-step approach was developed to systematically test the skin friction sensor in various facilities, where flow enthalpy and run duration were progressively increased. Initial validation testing was conducted at the VT Hypersonic Tunnel. Testing at AFRL was first performed in the RC-19 facility under high-temperature, mixing flow conditions. Final testing was conducted under simulated scramjet flight conditions in the AFRL RC-18 facility. Performance of the skin friction sensors was thoroughly analyzed across all three facilities. The flow stagnation enthalpies upward of 1053 kJ/kg (453 Btu/lbm) were tested. A nominal Mach 2.0 to 3.0 flow speed range was studied and stagnation pressure ranged from 172 to 995 kPa (25 to 144 psia). Wall shear was measured between 94 and 750 Pa (1.96 and 15.7 psf). Multiple entries were conducted at each condition with good repeatability at ±5% variation. The sensor was also able to clearly indicate the transient flow conditions of a full scramjet combustion operability cycle to include shock train movement and backflow along the isolator wall. The measured experimental wall shear data demonstrated good agreement with simple, flat-plate analytical estimations and historic data (where available). Numerical CFD predictions of the scramjet flow path gave favorable results for steady cold and hot flow conditions, but had to be refined to handle the various fueling injection schemes with burning in the downstream combustor and surface roughness models. In comparing CFD wall shear predictions to the experimental measurements, in a few cases, the sensor measurement was adversely affected by shock and complex flow interaction. This made comparisons difficult for these cases. The sensor maintained full functionality under sustained high-enthalpy conditions. No degradation in performance was noted over the course of the tests. This dissertation research and development program has proven successful in advancing the development of a skin friction sensor for applications in high-speed, high-enthalpy flows. The sensor was systematically tested in relevant, high-fidelity laboratory environments to demonstrate its technology readiness and to successfully achieve a technology readiness level (TRL) 6 milestone. The instrumentation technology is currently being transitioned from laboratory development to the end users in the hypersonic test community. / Ph. D.

Heat transfer experiments were done on a flat plate to study the effect of internal counter-flow backside cooling on adiabatic film cooling effectiveness and heat transfer coefficient. In addition, the effects of density ratio (DR), blowing ratio (BR), diagonal length over diameter (L/D) ratio, and Reynolds number were studied using this new configuration. The results are compared to a conventional plenum fed case. Data were collected up to X/D =23 where X=0 at the holes, an S/D = 1.65 and L/D=1,2. Testing was done at low L/D ratios since short holes are normally found in double wall cooling applications in turbine components. A DR of 2 was used in order to simulate engine-like conditions and this was compared to a DR of 0.92 since relevant research is done at similar low DR. The BR range of 0.5 to 1.5 was chosen to simulate turbine conditions as well. In addition, previous research shows that peak effectiveness is found within this range. Infrared (IR) thermography was used to capture temperature contours on the surface of interest and the images were calibrated using a thermocouple and data analyzed through MATLAB software. A heated secondary fluid was used as 'coolant' in the present study. A steady state heat transfer model was used to perform the data reduction procedure. Results show that backside cooling configuration has a higher adiabatic film cooling effectiveness when compared to plenum fed configurations at the same conditions. In addition, the trend for effectiveness with varying BR is reversed when compared with traditional plenum fed cases. Yarn flow visualization tests show that flow exiting the holes in the backside cooling configuration is significantly different when compared to flow exiting the plenum fed holes. We hypothesize that backside cooling configuration has flow exiting the holes in various directions, including laterally, and behaving similar to slot film cooling, explaining the differences in trends. Increasing DR at constant BR shows an increase in adiabatic effectiveness and HTC in both backside cooling and plenum fed configurations due to the decreased momentum of the coolant, making film attachment to the surface more probable. The effects of L/D ratio in this study were negligible since both ratios used were small. This shows that the coolant flow is still underdeveloped at both L/D ratios. The study also showed that increasing turbulence through increasing Reynolds number decreased adiabatic effectiveness. / MS / Gas turbine engines are used for multiple applications for power (power plants) or thrust (aircraft propulsion). Engine efficiency is correlated with higher working temperatures, which exceed the melting points of the materials being used. Therefore, more efficient cooling techniques are needed in order to protect the engine turbine components, such as blades and vanes. Relatively cooler air is bypassed from the compressor to the turbine section to cool the turbine components from the high temperatures. The air flows through the turbine components and out through machined holes referred to as film cooling holes. A protective layer, or film, protects the external region of the blade or vane. Previous research has found that the geometry of the airfoils used and the flow conditions play a major role in heat transfer. Most of the relevant research use a model that contains one-sided heat transfer. The present study focuses on combined backside and film cooling heat transfer, with different geometries and flow conditions, using a steady-state model for the data reduction procedure.

This work seeks a sense of confrontation through constructing walls against the mountain landscape. The thesis document demonstrates this confrontation through four schemes: a bridging wall with courtyards and tower (70 ft in height), a concrete wall (80 ft in height), a fabric wall (80 ft in height), a steel skeleton wall (120 ft in height), and a solid wall with steel plates (24 ft in height). The surfaces color in all schemes is similar, but material means change with each scheme. All walls are designed to be built on the mountain lake of San Bernardino Pass in Switzerland. The document contains pencil and charcoal drawings, sketches, soft pastels drawings, digital projections, and model photographs. / Master of Architecture

The flow of jets in confining enclosures has significant application in many engineering processes. In particular, two jet flows have been studied; the impingement of axisymmetric jets in a confined space and a turbulent inlet wall jet in a confining enclosure. The impingement of axisymmetric jets in a cavity has been examined using flow visualization, laser Doppler anemometry, and numerical simulations. When the flow field was examined under various geometrical and fluid parameters several flow regions were found, depending on the geometrical and fluid parameters. Initially, a steady flow field existed for all arrangements for Red < ~90 but subsequent increments in the fluid velocity caused an oscillating flow field to emerge. The onset of the oscillations and the upper limit of finite oscillations were found to be a function of the nozzle diameter to chamber dimension ratio. Although steady numerical simulations predicted the steady flow field well, steady simulations of the oscillating flow field over-predicted the peak axial velocities. The oscillating flow field is considered to be a class of self-sustaining oscillations where instabilities in the jet shear layer are amplified because of feed back from pressure disturbances in the impingement region. The turbulent wall jet in a cavity has been studied using flow visualization, laser Doppler anemometry (LDA), particle streak velocimetry (PSV) and numerical simulations. Instantaneous PSV measurements agreed well with time averaged LDA measurements. Two dimensional simulations using an algebraic stress turbulence model (ASM) were in better agreement with the experimental data than two and three dimensional simulations using a k - ε turbulence model in the wall jet region. A wall jet growth rate was found to be 54% higher than a wall jet in stagnant surroundings due to the enclosure boundaries. / Thesis / Doctor of Philosophy (PhD)

In this thesis, the benefits of boundary layer control (BLC) in improving aerodynamic performance and engine stability were examined in a compact, serpentine inlet exhibiting flow separation. A 1/14-scale turbofan engine simulator provided the flow through the inlet. The inlet's mass flow was measured to be 759 scfm (0.939 lbm/s) with an average throat Mach number of 0.23 when the simulator speed was 40 krpm. Boundary layer suction, blowing, and their combination were used to minimize the inlet's flow separation. The effectiveness of the suction alone and the blowing alone was shown to be approximately equivalent, and the effectiveness of the combined use of both was seen to be better than either one by itself. With blowing and suction flowrates around 1% of the simulator's core flow, the inlet's distortion was lowered by 40.5% (from 1.55% to 0.922%) while the pressure recovery was raised by 9.7% (from 87.2% to 95.6%). With its reduction in distortion, BLC was shown to allow the simulator to steadily operate in a range that would have otherwise been unstable. Minimizing the flow separation within the inlet was shown to directly relate to measurements from flush-mounted microphones along the inlet wall: as the exit distortion decreased the microphone spectrum also decreased in magnitude. The strong relationship between the aerodynamic profiles and the microphone signal suggests that microphones may be used in an active flow control scheme, where the BLC effort can be tailored for different engine operating conditions. Unfortunately, the sensing scheme used in this experiment showed the microphone signal to continue to decrease even when the separation is overly compensated; therefore refinements must be made before it would be practical in a real application. / Master of Science

This project focuses on the wall as a cross-axis form, one which gives an order to the landscape and a reference for the rest of the building to be set against. The intersections of these walls produce four corners housing four pavilions for dwelling. As the walls extend over the landscape, it culminates with a tower, a dwelling space for a guest, overlooking the surrounding landscape. / Master of Architecture

The presence of roughness on a surface subject to high Reynolds number flows promotes the formation of a turbulent boundary layer and the generation of a fluctuating pressure field imposed on the surface. While numerous studies have investigated the wall pressure fluctuations over zero-pressure gradient smooth walls, few studies have examined the effects of surface roughness on the wall pressure field. Additionally, due to the difficulties in obtaining high Reynolds number flows over fully rough surfaces in laboratory settings, an even fewer number of studies have investigated this phenomenon under flow conditions predicted to be fully free of transitional effects that would ensure similarity laws could be observed. This study presents the efforts to scale and describe the wall pressure spectrum of a rough wall, high Reynolds number turbulent boundary layer free of transitional effects. Measurements were taken in the Virginia Tech Stability Wind Tunnel for both smooth and rough walls. A deterministic roughness fetch composed of 3-mm hemispheres arranged in a 16.5-mm square array was used for the rough surface. Smooth and rough wall flows were examined achieving Reynolds numbers up to Re_θ = 68700 and Re_θ = 80200 respectively, with the rough wall flows reaching roughness based Reynolds numbers up to k_g⁺ = 507 with a simultaneous blockage ratio of δ/k_g = 76. A new roughness based inner variable scaling is proposed that provides a much more complete collapse of the rough wall pressure spectra than previous scales had provided over a large range of Reynolds numbers and roughness configurations. This scaling implies the presence of two separate time scales associated with the near wall turbulence structure generation. A clearly defined overlap region was observed for the rough wall surface pressure spectra displaying a frequency dependence of Ï ^-1.33, believed to be a function of the surface roughness configuration and its associated transport of turbulent energy. The rough wall pressure spectra were shown to decay more rapidly, but based on the same function as what defined the smooth wall decay. / Master of Science