Vineyards are often grown in semi-arid climates, such as California’s central valley, where water resources can be limited. Summer weather conditions result in high water use by these plants. For wine grapes, a high-value commodity, there are known benefits to fruit quality in irrigating grapevines with slightly below optimum for the plant. Growers would like to be able to precisely irrigate without overusing water or overstressing the vines. This calls for improving ways to monitor vineyard water use by estimating the combined soil evaporation and plant transpiration known as evapotranspiration (ET). A computer model developed by the USDA called the Two-Source Energy Balance model (TSEB) can estimate ET through satellite or aircraft measurements of land surface temperature. The model has been successful for simple, uniform vegetation such as maize, soybeans, and grasslands. The ability of TSEB to estimate vineyard ET has been tested through a field experiment called the Grape Remote sensing, Atmospheric Profile,& Evapotranspiration eXperiment or GRAPEX. Water is primarily transported away from the ground and plants by turbulent swirls in the wind. Models such as TSEB assume these swirls occur in a consistent manner over a few minutes to hours. Yet, interactions between the wind, the complex vineyard canopy, and heating near the ground can cause them to be episodic or intermittent. There are questions of if and how intermittent water vapor transport might happen in vineyards, and whether the TSEB model will still estimate ET well in such cases. In this study wind, humidity, air temperature, and surface temperatures are used to examine when intermittent behavior occurs, how it affects ET from the vineyard canopy, and how TSEB performs for intermittent versus more steady conditions. Results show that intermittent turbulence significantly alters the microclimate in the vineyard canopy compared to more ideal, steady behavior. The TSEB model was successful but showed reduced ability to estimate ET during times of intermittent behavior. The knowledge gained is an important step toward using TSEB as a powerful tool for sustainable water management, not only in vineyards, but other cash crops with complicated canopies such as orchards, as well as natural ecosystems.

<p>The hydrologic cycle may be described in essence as the process of water rising and falling in its various phases between land and atmosphere. In this minimal description of the hydrologic cycle two features come into focus: intermittency and irreversibility. In this dissertation intermittency and irreversibility are investigated broadly in the soil-plant-atmosphere system. The theory of intermittency and irreversibility is addressed here in three ways: (1) through its effect on components of the soil-plant-atmosphere system, (2) through development of a measure of the degree of irreversibility in time-series, and (3) by the investigation of the dynamical sources of this intermittency. First, soil infiltration and spring frost risk are treated as two examples of hydrologic intermittency with very different characters and implications for the soil plant system. An investigation of the water budget in simplified soil moisture models reveals that simple bucket models of infiltration perform well against more accurate representation of intra-storm infiltration dynamics in determining the surface water partitioning. Damaging spring frost is presented as a ``biologically-defined extreme event'' and thus as a more subtle form of hydrologic intermittency. This work represents the first theoretical development of a biologically-defined extreme and highlights the importance of the interplay between daily temperature mean and variance in determining the changes in damaging frost risk in a warming climate. Second, a statistical measure of directionality/asymmetry is developed for stationary time-series based on analogies with the theory of nonequilibrium thermodynamics. This measure is then applied to a set of DNA sequences as an example of a discrete sequence with limited state-space. The DNA sequences are found to be statistically asymmetric and further that the local degree of asymmetry is a reliable indicator of the coding/noncoding status of the DNA segment. Third, the phenomenology of rainfall occurrence is compared with canonical examples of dynamical intermittency to determine whether these simple dynamical features may display a dominant signature in rainfall processes. Summer convective rainfall is found to be broadly consistent with Type-III intermittency. Following on this result we studied daytime atmospheric boundary layer dynamics with a view toward developing simplified models that may further elucidate the interaction the interaction between land surface conditions and convective rainfall triggering.</p> / Dissertation

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A systematic approach of testing and validating transition models is developed and employed in testing of a recently developed transition model. The testing methodology uses efficient computational tools and a wide range of test cases. The computational tools include a boundary layer code, single zone Navier Stokes solver, and a multi-block Navier Stokes solver which uses MPI and is capable of handling complex geometries and moving grids. Test cases include simple flat plate experiments, cascade experiments, and unsteady wake/blade interaction experiments. The test cases are used to test the predicting capabilities of the transition model under various effects such as free stream turbulence intensity, Reynolds number variations, pressure gradient, flow separation, and unsteady wake/blade interaction. Using the above test cases and computational tools a method is developed to validate transition models. The transition model is first implemented in boundary layer code and tested for simple flat plate cases. Then the transition model is implemented in single zone Navier Stokes solver and tested for hysteresis effects for flat plate cases. Finally the transition model is implemented in multi zone Navier Stokes solver and tested for compressor and turbine cascade cases followed by unsteady wake/blade interaction experiments. Using the method developed a new correlation based transition model (Menter et al. 2004) which uses local variables is tested and validated. The new model predicted good results for high free stream turbulence and high Reynolds number cases. For low free stream turbulence and low Reynolds number cases, the results were satisfactory.

Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisors: Jack S. Turner and Dean J. Driebe. Vita. Includes bibliographical references and index.

Theory of turbulence at small scales plays a fundamental role in modeling turbulence and in retrieving information from physical measurements of turbulent flows. A systematic methodology based on direct numerical simulations of turbulent flows is developed to investigate universality of small scale turbulence. Understanding characteristics of the small scale intermittency in turbulent flows and the accuracy of the models, measurements, and theories in predicting it are the main objectives. The research is designed to address two central questions; 1) possible effects of large scale anisotropies on the small scale turbulence and 2) potential biases in characterizing small scale turbulence due to the nature of the quantities used to extract the information, known as surrogates. Direct numerical simulations of forced, isotropic homogeneous turbulence with extraordinarily fine spatial resolution on a periodic box up to 4096 × 4096 × 4096 grid points are analyzed first, to provide a clear insight to the small scale turbulence in the absence of large scale anisotropy. Direct numerical simulations of forced, homogeneous and axisymmetric density stratified flows on a periodic box up to 4096 × 4096 × 2048 grid points with the buoyancy Reynolds number ranging from 10 to 220 are considered next. Different levels of density stratification in the vertical direction cause different levels of large scale anisotropy in the flows. These unique simulations provide a clear picture of turbulent structures over an extensive range of scales. The dissipation rate of turbulent kinetic energy is chosen as the main descriptor of small scale structures. A comprehensive study on surrogates of energy dissipation rate is conducted to identify the best descriptor of the small scale turbulence based on easily measured quantities in physical experiments. In particular, the one-dimensional longitudinal and transverse surrogates, as well as a surrogate based on the asymmetric part of the strain rate tensor, are considered.The statistical analysis of local and locally averaged energy dissipation rate indicates that the small scale intermittency manifested in the energy dissipation rate is universal with intermittency exponent of μ = 0.25 ± 0.05, independent of flow conditions and measurement methods. In contrary, the general shape of the probability density functions of energy dissipation rate is strongly skewed to reflect all the existing dynamics in the flow. The surrogates are fundamentally different than the energy dissipation rate. The longitudinal and transverse surrogates overestimate the intermittency exponent by factors of 1.5 and 2.2, respectively. The scale dependency of the moments of locally averaged energy dissipation rate is proposed as a powerful technique to identify the dominant dynamics of the complex flows for a specific range of scales in physical space. Specifically, for the stratified turbulence, this method suggests a superposition of patches of three-dimensional turbulence superimposed on the background semi two-dimensional stratified flow.

Eight roughness configurations in Clemson boundary layer wind tunnel are presented. For these configurations, flow parameters such as turbulent intensities, integral length scales, large- and small- scale turbulence, and spectra of velocity components of the wind are obtained and studied to the simulated turbulence. At the same time, new analyzing tools, orthogonal wavelet techniques, are applied to provide additional information in time domain. This makes it possible to study the intermittency event, one important characteristic associated with pressure peak activities in turbulence. Three parameters, scale energy, intermittency factor and intermittency energy are defined. Variation of these quantities as a result of different configuration is discussed. Finally, the corresponding variations in measured pressure peaks in relation with the variations of configuration as well as with the intermittency parameters are investigated. The work here is of important significance for future wind tunnel and field data comparison, and this could help to find the best simulation among all configurations. / Master of Science

No description available.

No presente trabalho, três tipos de fotocatalisadores híbridos nanométricos, CdS, CdS/TiO2, e CdS/TiO2/SiO2, foram preparados e utilizados em três aplicações fotoquímicas: fotodegradação macro e microscópica de um corante, fotólise da água para geração de H2 com acompanhamento via espectrometria de massas in situ e estudo de uma reação redox via microscopia de fluorescência de campo largo. As análises por microscopia eletrônica de varredura (MEV) e de transmissão (MET) apresentaram esferas de sílica com diâmetro em torno de 300 nm e nanopartículas de CdS e TiO2 com diâmetro da ordem de 5 nm e com alta aglomeração. O recobrimento da sílica com TiO2 e CdS não foi uniforme, resultando em \"ilhas\" preferencialmente isoladas. Apesar da morfologia heterogênea, os fotocatalisadores foram eficientes na degradação da safranina O, apresentando cinética de 1ª ordem em relação à concentração do corante. No que se refere à fotólise da água, o sistema ternário (CdS/TiO2/SiO2) apresentou a maior taxa de produção de H2 (0,79 mmol h-1 g-1), o que indica maior eficiência na transferência ou injeção de carga entre CdS e TiO2, devido ao melhor contato entre os dois semicondutores na superfície das nanopartículas (NPs) de sílica. Esse sistema também foi o mais eficiente na fotorredução do corante não fluorescente resazurina no corante fluorescente resorufina, acompanhada através de medidas de intermitência de fluorescência utilizando microscopia de fluorescência de campo largo. Em geral, os sistemas após adição do corante apresentaram intermitência de fluorescência mais lenta, com maiores tempos de relaxação de off. A fotorredução do corante estabeleceu um método interessante para o mapeamento das regiões de injeção de carga CdS/TiO2, inicialmente escuras e a seguir com alta intensidade de emissão. / In the present work, three types of nanosized hybrid photocatalysts, CdS, CdS/TiO2 and CdS/TiO2/SiO2, were synthesized and used in three photochemical applications: macro and microscopic photodegradation of a dye, photolysis of water to generate H2 monitored by in situ mass spectrometry and study of a redox reaction by wide-field fluorescence microscopy. Scanning (SEM) and transmission (TEM) electronic microscopies showed quasi-monodispersed silica spheres with a diameter of about 300 nm and CdS and TiO2 nanoparticles with a diameter of approximately 5 nm highly agglomerated. The coating of the silica with CdS and TiO2 was not uniform, resulting in \"islands\" preferentially isolated. Despite the heterogeneous morphology of the photocatalysts, they were efficient in the degradation of a safranine O solution, showing kinetics of first order with respect to dye concentration. With regard to water photolysis, the ternary system (CdS/TiO2/SiO2) showed the highest rate of H2 production (0.79 mmol g-1 h-1) , which indicates more efficient charge transfer or injection between CdS and TiO2 due to better contact between the two semiconductors on the surface of the silica nanoparticles (NPs). This system also was the most efficient photocatalyst in the photorreduction of the nonfluorescent dye resazurin into the fluorescent dye resorufin, monitored by fluorescence intermittency measurements using wide-field microscopy. In general, the systems after adding the dye presented slower fluorescence intermittency, with higher times of off relaxation. The photoreduction of the dye provided an interesting method for mapping the regions of CdS/TiO2 charge injection, initially dark and then with high emission intensity.

The steady flow aerodynamics of a cascade of compressor airfoils is computed using a two-dimensional thin layer Navier-Stokes flow solver. The Dhawan and Narasimha transition model and Mayle‟s transition length model were implemented in this flow solver so that transition from laminar to turbulent flow could be included in the computations. A method to speed up the convergence of the fully turbulent calculations has been introduced. In addition, the effect of turbulence production formulations and including streamline curvature correction in the Spalart-Allmaras turbulence model on the transition calculations is studied. These transitional calculations are correlated with the low and high incidence angle experimental data from the NASA-GRC Transonic Flutter Cascade. Including the transitional flow showed a trendwise improvement in the correlation of the computational predictions with the pressure distribution experimental data at the high incidence angle condition where a large separation bubble existed in the leading edge region of the suction surface.