Browsing by Subject "transition"
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Item Characterization of Zr-Fe-Cu Alloys for an Inert Matrix Fuel for Nuclear Energy Applications(2013-08-09) Barnhart, Brian A.An ultra-high burnup metallic inert matrix nuclear fuel concept is being characterized and evaluated by Lawrence Livermore National Laboratory based on a metal matrix fuel concept originally developed at the Bochvar Institute in Russia. The concept comprises a dispersion of uranium metal microspheres in a Zr-based alloy matrix that provides thermal bonding between the fuel particles and the cladding material. The objective of this study was to experimentally evaluate both the microstructural and thermophysical properties of Zr-Fe-Cu alloys. The experiments and analyses described were divided into three main parts, nominally based on the analysis methods used to examine the alloys. An Electron Probe Microanalyzer (EPMA) was used to characterize the metallurgical properties of the proposed matrix alloys. The groups of alloys were cast using a high temperature inert atmosphere furnace. The cast alloys showed the expected combination of phases with the exception of the ZrFe2 Laves phase which was predicted for the Zr-12Fe-15Cu1 alloy but was not detected. The Zr-12Fe-5Cu alloy consisted of a Zr solution phase dispersed in a matrix of two different intermetallic phases. The second alloy, Zr-12Fe-10Cu, did not produce a homogenous mixture and consisted of two distinct phase morphologies. The top half of the sample was Zr rich and contained Zr precipitates dispersed in a matrix of intermetallic compounds while the bottom half consisted solely of intermetallic compounds. The third alloy, Zr-12Fe-15Cu, was comprised of four different intermetallic phases three of which had the same apparent Zr_(2)(Fe,Cu) structure but had distinct phase morphologies based on the Backscatter Electron (BSE) images. Upon determining the phase morphologies of each of the fabricated alloys Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA) were used to measure phase transformation and melting temperatures. Little difference was observed between the as-cast and annealed samples. The transitions shifted slightly to higher temperatures and the annealed Zr-12Fe-15Cu alloy only had two transitions compared to three seen in the as-cast samples. Slight changes were observed in the melting temperatures between the as-cast and annealed alloys. Zr-12Fe-5Cu had the largest melting temperature (886.3?C) while Zr-12Fe-10Cu had the smallest melting temperature (870?C). The third alloy, Zr-12Fe-15Cu, had a melting point just below that of Zr-12Fe-5Cu at 882.7?C. Light Flash Analysis (LFA) was implemented to determine the low temperature (20-260?C) thermal diffusivity values of each alloy. The as-cast measurements were more precise than the annealed samples, most likely the result of non-ideal sample integrity prior to loading. Each of the three alloys showed a linear increase in thermal diffusivity over the temperature range. Values for Zr-12Fe-5Cu ranged from 3.54 ? 0.06 mm2/s to 4.42 ? 0.10 mm^(2)/s. The Zr-12Fe-10Cu alloy had maximum and minimum values of 4.19 ? 0.22 mm^(2)/s and 3.17 ? 0.16 mm^(2)/s, respectively. Lastly, Zr-12Fe-15Cu had the largest thermal diffusivity ranging from 3.52 ? 0.15 mm^(2)/s at 20?C to 4.64 ? 0.16 mm_(2)/s at 260?C. Overall, the data from the LFA measurements showed that the Zr-Fe-Cu alloy system had similar diffusivity values compared to other common reactor materials.Item Combined effects of Reynolds number, turbulence intensity and periodic unsteady wake flow conditions on boundary layer development and heat transfer of a low pressure turbine blade(2009-05-15) Ozturk, BurakDetailed experimental investigation has been conducted to provide a detailed insight into the heat transfer and aerodynamic behavior of a separation zone that is generated as a result of boundary layer development along the suction surface of a highly loaded low pressure turbine (LPT) blade. The research experimentally investigates the individual and combined effects of periodic unsteady wake flows and freestream turbulence intensity (Tu) on heat transfer and aerodynamic behavior of the separation zone. Heat transfer experiments were carried out at Reynolds number of 110,000, 150,000, and 250,00 based on the suction surface length and the cascade exit velocity. Aerodynamic experiments were performed at Re = 110,000 and 150,000. For the above Re-numbers, the experimental matrix includes Tus of 1.9%, 3.0%, 8.0%,13.0% and three different unsteady wake frequencies with the steady inlet flow as the reference configuration. Detailed heat transfer and boundary layer measurements are performed with particular attention paid to the heat transfer and aerodynamic behavior of the separation zone at different Tus at steady and periodic unsteady flow conditions. The objectives of the research are (a) to quantify the effect of Tu on the aero-thermal behavior of the separation bubble at steady inlet flow condition, (b) to investigate the combined effects of Tu and the unsteady wake flow on the aero-thermal behavior of the separation bubble, and (c) to provide a complete set of heat transfer and aerodynamic data for numerical simulation that incorporates Navier-Stokes and energy equations. The analysis of the experimental data reveals details of boundary layer separation dynamics which is essential for understanding the physics of the separation phenomenon under periodic unsteady wake flow and different Reynolds number and Tu. To provide a complete picture of the transition process and separation dynamics, extensive intermittency analysis was conducted. Ensemble averaged maximum and minimum intermittency functions were determined leading to the relative intermittency function. In addition, the detailed intermittency analysis reveals that the relative intermittency factor follows a Gaussian distribution confirming the universal character of the relative intermittency function.Item \"Coming To terms\": A grounded theory of dementia caregivers' journeys and expectations of care(2008-02-26) Michael Lawrence Mistric; Judith C. Drew; Thomas Teasdale; Luis Amador; Diane Heliker; Carolyn A. Phillips“Coming to Terms” presents the subjective narratives of family members about what constitutes quality long-term care (LTC) for loved-ones with dementia. It uses those narratives to develop a grounded theory of shared meanings of dementia care that reflects the basic social process by which family members formulate their initial expectations of care delivered in LTC settings.\r\n Family members transition through a five-stage process when dementia affects a loved-one. As they move through these stages, the family members process the realities of dementia and dementia care, grapple with the decision to place their loved-one in a LTC facility, and, ultimately, formulate expectations of the care they want the LTC facility to provide. In essence, family members expect the LTC facility to (1) fulfill their love-one’s basic needs, (2) provide pleasant surroundings, (3) ensure a competent staff, (4) ensure a caring staff, (5) facilitate communication, and (6) practice timely institutional responsiveness. The family members’ expectations not only play a critical role in the initial evaluation of LTC facilities but are also used subsequently to measure the effectiveness of the LTC facility in which the loved-one has actually been placed.\r\n Although the expectations of care described in this study are consistent with the findings of prior studies of expectations of care in other contexts, “Coming to Terms” breaks new ground by illustrating the transitional process through which family members’ expectations of dementia care are germinated, tested, refined, and fully formulated. Rich, descriptive detail informed these results and the participants are acknowledged and appreciated.\r\n The findings of this study can help LTC facilities better understand the issues and concerns of the families whom they serve and aid in the development of LTC policies and procedures that foster greater consumer satisfaction and peace of mind. \r\nItem Compliance and Best Practices in Transition Planning: Effects of Disability and Ethnicity(2011-02-22) Landmark, Leena JoIt is well known that individuals with disabilities have poor postsecondary outcomes. As a result, state and local education agencies are held accountable for the post-school achievements of their students with disabilities. The purposes of this study were (a) to determine the extent to which the transition components of Individualized Education Program (IEP) documents were compliant with the transition requirements of the Individuals with Disabilities Education Improvement Act of 2004 (IDEIA), (b) to determine the extent to which the transition components of the IEP documents provided evidence of best practices, (c) to determine the effects that disability category and ethnicity had on compliance and practices as evidenced in the transition components of the IEP documents, and (d) to determine the relationship between overall compliance and best practices. The sample for the study included 212 secondary students who had a developmental disability, an emotional disorder, or a learning disability and who were African American, Caucasian, or Hispanic. Several types of analyses were conducted including descriptive, multiple logistic regression, and Spearman's rho correlation. The overall level of compliance was 2.03 (SD = 1.238). The range of possible scores was 0 - 5, with 0 indicating that none of the components of compliance were 100 percent compliant, and 5 indicating that all of the components were 100 percent compliant. The overall level of best practices as evidenced in the IEP documents was 4.89 (SD = 1.569). The range of possible scores was 0 - 8, with 0 indicating that there was no evidence of any of the practices in the IEP document, and 8 indicating that evidence of all the practices was found in the IEP document. A student's disability category and ethnicity were found to be influencing characteristics for increasing or decreasing the probability of an IEP document being compliant and/or having evidence of best practices. A statistically significant correlation of r = .429 was found between the overall levels of compliance and best practices, indicating that as the level of compliance increased, so too did the level of best practices evident in the IEP document.Item Design of an Instrumentation System for a Boundary Layer Transition Wing Glove Experiment(2012-08-23) Williams, Thomas 1987-Laminar flow control holds major promise for increasing aircraft efficiency and increasing laminar flow over aerodynamic surfaces could decrease drag by up to 30 percent. The Flight Research Lab at Texas A&M University has studied laminar flow over a wing with 30 degrees of leading edge sweep with Discrete Roughness Elements (DREs) installed and has indicated that DREs can be used to increase laminar flow at Reynolds numbers up to 7.5 million at Mach 0.3. A new project, termed SARGE, has been commissioned in conjunction with NASA for studying DREs on a swept wing glove at conditions relevant to jet transports. The SARGE project must have an instrumentation system capable of accurately measuring flow conditions and transition location on the suction side of the glove. Infrared (IR) thermography has been selected as the primary transition detection tool. A heat transfer analysis has shown that solar radiation will warm the surface of the glove above the adiabatic wall temperature and therefore the laminar region will appear to be warmer. The FLIR SC8000 IR camera has been selected for this application due to its ability to produce high-resolution images in the appropriate IR band. High quality air data is also required for the experiment. A five-hole probe will be used to measure flow angle and velocity near the glove. This instrument will provide meanflow conditions due to its limited frequency response. High quality pressure transducers coupled with careful probe calibration will allow for differential measurements to be made with an uncertainty of +/- 0.03 degrees. Static pressure ports and high frequency response Kulite transducers will also be employed. Hotfilm sensors will be used to verify the state of the boundary layer on the glove through spectral analysis. A unique hotfilm array has been proposed that will enable the measurement of traveling wave vectors through a spectral technique. An experiment on the Flight Research Lab's Cessna O-2 to investigate the veracity of this technique has also been suggested. Thermocouples will also be installed on the glove's surface to monitor temperatures and verify transition location. The layout of the hotfilms and thermocouples is also detailed.Item Laminar-Turbulent Transition Due to 2-D Excrescences at 1% Chord on a Swept Wing(2015-01-22) Crawford, Brian KeithLaminar flow has the potential to dramatically reduce fuel consumption and/or extend the range of modern aircraft. However, before laminar-flow aircraft can be made practical, the effect of surface imperfections must be better understood. Many studies have been performed on the effects of distributed roughness and other types of imperfections. Two-dimensional step excrescences, however have not been studied in significant detail until recently. Two-dimensional steps are common on real aircraft due to practical considerations such as skin-panel junctions, high-lift-device interfaces, deicing mechanisms, etc. Traditionally, these 2-D excrescences have been treated as just another form of roughness; however, the behavior of these steps is fundamentally distinct. The present study tests the effect of 2-D excrescences near 1% chord in order to examine the effects of pressure gradient and curvature. Testing on a 30? swept-wing model is performed in both the flight environment aboard a Cessna O-2A Skymaster, as well as in the Klebanoff-Saric Wind tunnel at Texas A&M University. In both environments, IR thermography is utilized to detect the global laminar?turbulent transition location. In the wind tunnel, a hotwire traverse is also utilized to map out the boundary layer and further measure the influence of these excrescences. Interactions between the crossflow instability and these excrescences are observed. Both critical and subcritical step induced transition behavior is present. Comparisons are made to other contemporary experiments in order to draw conclusions about the influence of pressure gradient, sweep, and curvature on the step-induced transition behavior. The resulting data are intended for use in validating an ongoing companion computational effort.Item Microgravity Flow Regime Transition Modeling(2010-07-14) Shephard, Adam M.Flow regime transitions and the modeling thereof underlie the design of microgravity two-phase systems. Through the use of the zero-g laboratory, microgravity two-phase flows can be studied. Because microgravity two-phase flows exhibit essentially no accelerations (i.e. no buoyancy or gravitational forces), the effects of acceleration on two-phase flow can be decoupled from the effects of other fluid phenomenon. Two-phase systems on earth are understood mostly through empiricisms. Through microgravity two-phase research, a fundamental understanding of two-phase systems can be obtained and applied to both terrestrial systems in space applications. Physically based bubbly-bubbly/slug and bubbly/slug-slug flow regime transition models are introduced in this study. The physical nature of the models demonstrates a new understanding of the governing relationships between coalescence, turbulence, void fraction, boundary layer affects, and the inlet bubble size distribution. Significantly, the new models are dimensionless in addition to being physically derived. New and previous models are evaluated against zero-g data sets. Previous models are not accurate enough for design use. The new models proposed in this study are far more detailed than existing models and are within the precision necessary for most design purposes. Because of the limited data available, further experimental validation is necessary to formally vet the model. Zero-g data set qualification and flight experiment design have not been standardized and as a result, much of the data in the literature can be shown not to represent microgravity conditions. In this study, a set of zero-g quality criteria are developed and used to qualify the data sets available in the literature. The zero-g quality criteria include limitations on buoyancy forces relative to surface tension and inertial forces as well as requirements on acceleration monitoring and flow development length and time. The resulting evaluation of the data sets available in the literature unveils several experiment design shortfalls, which have resulted in data sets being misrepresented as zero-g data sets. The quality standards developed in this study should continue to be improved upon and used in the design of future zero-g fluid experiments. The use of one-g single-phase models in approximating zero-g two-phase experimental data was successfully performed in this study. Specifically the models for pressure drop, friction factor, wall shear, and velocity profile are demonstrated. It is recognized that the mixing apparatus will affect the flow regime transitions, specifically the distribution of bubble sizes that exit the mixing apparatus. Unfortunately, little-to-no information regarding the mixing apparatus used in past experiments can be found in the literature. This will be an area for further developmental research. In summary, the approach to understanding and modeling two-phase phenomenon demonstrated in this study provides tools to future researchers and engineers. Special attention to data qualification and experiment standardization provides a different prospective and interpretation of the currently available data. The physically based and dimensionless modeling demonstrated in this study can be extended to other studies in the field as well as providing a basis for the application of heat transfer modeling to microgravity two-phase systems, specifically boiling and condensation.Item Optical control of nuclear resonant absorption: theory and experiment(Texas A&M University, 2004-09-30) Kolesov, Roman L.Modification of nuclear resonant absorption by means of laser radiation is analyzed both theoretically and experimentally. Theoretical analysis is done on the basis of four-level model of atom. This model includes both electronic and nuclear excitations. It is predicted that under coherent laser driving nuclear resonant Mossbauer absorption can be significantly modified, e.g. new Mossbauer resonances can appear, some of the existing resonances can vanish, both can be Rabi-split, broadened by laser action. In addition, it is predicted that Mossbauer absorption can be completely suppressed due to coherent population trapping. Experimental observation of laser-induced transformations of Mossbauer spectra of 57Fe2+ : MgO is accomplished. New Mossbauer lines appear with laser driving while the existing are broadened. Possible explanations of the observed changes in 57Fe2+ : MgO Mossbauer spectra are population of higher-lying electronic states of iron ion and significant modification of electronic relaxation processes due to modified Jahn-Teller interaction.Item Roughness-induced Transient Growth: Continuous-spectrum Receptivity and Secondary Instability Analysis(2012-07-16) Denissen, Nicholas AllenThis dissertation analyzes the effect of periodic roughness elements on the stability of a flat plate boundary layer. Receptivity data is extracted from direct numerical simulations and experimental data and the results are compared to theoretical predictions. This analysis shows that flow in the immediate vicinity of roughness elements is non-linear; however, the evolution of roughness-induced perturbations is a linear phenomena. New techniques are developed to calculate receptivity information for cases where direct numerical simulations are not yet possible. Additionally, the stability behavior of the roughness wake is analyzed. New instability modes are found, and the effect of boundary layer complexity, perturbation amplitude and other factors are examined. It is shown that the wake is much less stable than optimal perturbation theory predicts, and highlights the importance of receptivity studies. The implication of these results on transition-to-turbulence is discussed, and future work is proposed. TItem Sensitivity of Swept-Wing, Boundary-Layer Transition to Spanwise-Periodic Discrete Roughness Elements(2014-12-12) West, David EdwardMicron-sized, spanwise-periodic, discrete roughness elements (DREs) were applied to and tested on a 30? swept-wing model in order to study their effects on boundary-layer transition in flight where stationary crossflow waves are the dominant instability. Significant improvements have been made to previous flight experiments in order to more reliably determine and control the model angle of attack (AoA) and unit Reynolds number (Re'). These improvements will aid in determining the influence that DREs have on swept-wing, laminar-turbulent transition. Two interchangeable leading-edge surface-roughness configurations were tested: polished and painted. The baseline transition location for the painted leading edge (increased surface roughness) was unexpectedly farther aft than the polished. Transport unit Reynolds numbers were achieved using a Cessna O-2A Skymaster. Infrared thermography, coupled with a post-processing code, was used to globally extract a quantitative boundary-layer transition location. Each DRE configuration was compared to curve-fitted baseline data in order to determine increases or decreases in percent laminar flow while accounting for the influence of small differences in Re' and AoA. Linear Stability Theory (LST) guided the DRE configuration test matrix. In total, 63 flights were completed, where only 30 of those flights resulted in useable data. While the results of this research have not reliably confirmed the use of DREs as a viable laminar flow control technique in the flight environment, it has become clear that significant computational studies, specifically direct numerical simulation (DNS) of these particular DRE configurations and flight conditions, are a necessity in order to better understand the influence that DREs have on laminar-turbulent transition.Item Sensitivity of Swept-Wing, Boundary-Layer Transition to Spanwise-Periodic Discrete Roughness Elements(2014-12-12) West, David EdwardMicron-sized, spanwise-periodic, discrete roughness elements (DREs) were applied to and tested on a 30? swept-wing model in order to study their effects on boundary-layer transition in flight where stationary crossflow waves are the dominant instability. Significant improvements have been made to previous flight experiments in order to more reliably determine and control the model angle of attack (AoA) and unit Reynolds number (Re'). These improvements will aid in determining the influence that DREs have on swept-wing, laminar-turbulent transition. Two interchangeable leading-edge surface-roughness configurations were tested: polished and painted. The baseline transition location for the painted leading edge (increased surface roughness) was unexpectedly farther aft than the polished. Transport unit Reynolds numbers were achieved using a Cessna O-2A Skymaster. Infrared thermography, coupled with a post-processing code, was used to globally extract a quantitative boundary-layer transition location. Each DRE configuration was compared to curve-fitted baseline data in order to determine increases or decreases in percent laminar flow while accounting for the influence of small differences in Re' and AoA. Linear Stability Theory (LST) guided the DRE configuration test matrix. In total, 63 flights were completed, where only 30 of those flights resulted in useable data. While the results of this research have not reliably confirmed the use of DREs as a viable laminar flow control technique in the flight environment, it has become clear that significant computational studies, specifically direct numerical simulation (DNS) of these particular DRE configurations and flight conditions, are a necessity in order to better understand the influence that DREs have on laminar-turbulent transition.Item Session 4A | Vireo Users Group Birds-of-a-Feather(Texas Digital Library, 2022-05-26) Mumma, Courtney; Peterson, BillieThis is an opportunity for Vireo users to come together to talk about their transitions and plans for Vireo 4. There will be ample opportunity to ask questions of the lead developers at TDL as well as the leaders of the Vireo User Group’s Steering Committee.