Дисертації з теми "Atmospheric wind tunnel"

To benefit from strong winds, an increasing number of wind turbines are placed in complex terrains. But complex terrains means complex flows and difficult wind resource assessment. This study proposed to use wind tunnel modelling to evaluate the wind in a complex topography. The goal of this study is to evaluate the possibilities of wind resources assessment by wind tunnel modelling and to quantify the important modelling parameters. The lower part of the atmosphere, the atmospheric boundary layer (ABL) is defined by a velocity and a turbulence gradient. The ABL is reproduced in the wind tunnel by placing obstacles and roughness elements of different size representative to the type of terrain desired. The flow produced in the wind tunnel is validated against field data and a wise choice of the obstacles is discussed to reproduce the desired wind profile. The right reproduction of the inflow conditions is found to be the most important parameter to reproduce. The choice of the area to reproduce around a site in usually difficult to make in order to keep a low scaling factor and to account for the surrounding topography. A series of tests on simplified hills helps the experimentalist in this choice by enlightening the longitudinal and vertical extension of the wake downstream different hills shapes. Finally, two complex topographies are studied in two wind tunnels, the Bolund hill in Denmark and the Alaiz mountain in Spain. The results are giving good results, 5 to 10 %, for predicting the wind speed but more scatter is observed for the modelling of the turbulence, up to 100 %. The laboratory simulation of atmospheric flows proves to be a demanding but reliable tool for the prediction of the mean wind speed in complex terrain.

PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
A questão da poluição ambiental está recebendo cada vez mais importância. Por esse motivo, os estudos relacionados a processos de dispersão de poluentes estão ganhando cada vez mais destaques. Como estudos em campo são mais custosos, os estudos realizados em laboratório, com modelos reduzidos, estão sendo mais aplicáveis, uma vez que permitem análises de problemas específicos. Este trabalho tem como objetivo realizar um estudo exploratório em um túnel de vento do comportamento de uma pluma emitida por uma chaminé, que permita modificações nas condições de velocidade e temperatura da pluma. Para isso, foi realizada a reprodução da camada limite atmosférica, através do Método de Irwin, simulando um ambiente suburbano, em que o perfil de velocidades média foi medido com a técnica de Anemometria de Fio Quente. Foram realizados ensaios para três condições do escoamento principal e levantados os perfis de velocidade e intensidade turbulenta à jusante da chaminé. Foi realizado um estudo da inclinação da pluma, tanto pela influência da velocidade, quanto pela diferença de temperatura da pluma em relação à do escoamento principal, que foi variada em 10 e 20 graus Celsius. As análises de concentração foram possíveis através das imagens obtidas com a técnica de Velocimetria por Imagem de Partículas. Foram feitas análises do perfil de concentração a diferentes posições a sotavento da chaminé e o coeficiente de dispersão vertical obtido foi comparado com diversas literaturas conhecidas.
Environmental pollution issue is becoming increasingly important. For this reason, studies related to processes of atmospheric dispersion of pollutants are gaining prominence. Since studies in situ are expensive, laboratory studies with reduced models are useful, since specific problem can be investigated. The present work performs an experimental study, in a wind tunnel, evaluating the behavior of a plume generated by a chimney. For this, the reproduction of the atmospheric boundary layer was made, using the Irwin method, simulating a suburban environment, in which the mean velocity profile was measured with the Hot Wire Anemometry technique. Tests were performed for three main flow conditions and the profiles of velocity and turbulent intensity were made upstream of the stack. A study of the bent of the plume was made, both by the influence of the velocity, and by the temperature difference between the plume and the main flow, that was varied at 10 and 20 degrees Celsius. The concentration analyzes were possible through the images obtained with the Particle Image Velocimetry technique. Concentration profile analyzes were performed at different leeward positions of the chimney and the vertical dispersion coefficient obtained was compared with several known literatures.

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

The vortex wake characteristics of aircraft during landing and take-off are of interest in connection with both the safety of following aircraft penetrating the vortex and the dispersion of engine exhaust plumes. A series of measurements were carried out in an Atmospheric Boundary Layer Wind Tunnel (ABLWT) to identify and characterise both the mean and turbulent flow field of a pair of wake vortices in ground proximity. Cont/d.

There has been much success in atmospheric boundary layer simulation with medium sized closed-circuit wind tunnels with test section dimensions of approximately 1 x 1 m. However, smaller, blower-type wind tunnels are more common in university laboratories due to the lower cost and smaller space requirements. A small size, open flow wind tunnel with a 1 x 1 foot test section was modified to simulate the atmospheric boundary layer with a combination of upstream spires and cubic roughness elements. The primitive spire geometry detailed in the literature was found to yield poor agreement with the power law velocity profile of interest, and a novel iterative algorithm was developed to produce nonlinear spire geometry. The geometry generated by the algorithm was tested in the wind tunnel and found to simulate the desired velocity profile based on a Hellman exponent of 0.20 with a high degree of agreement, having a maximum velocity error of 4%. This confirmed the suitability of small-sized wind tunnels for simulating the atmospheric boundary layer.

Aerogeradores, ou turbinas eólicas, são máquinas instaladas em grandes parques eólicos que convertem a energia cinética do vento em energia elétrica. A definição da separação e da interação entre máquinas é um fator fundamental de análise durante a fase de projeto, pois os chamados efeitos de esteira podem inviabilizar o desenvolvimento de um parque eólico. Em geral, a esteira de um aerogerador está caracterizada por um significativo déficit de velocidade e uma intensificação dos níveis de turbulência, o que ocasiona a diminuição da eficiência aerodinâmica e a redução da vida útil das máquinas localizadas a sotavento. Embora existam diferentes pesquisas destinadas à compreensão e previsão dos efeitos de esteira, o problema permanece como uma questão desafiadora que exige a adoção de ferramentas de alta precisão para sua identificação. Este trabalho apresenta uma metodologia experimental em túnel de vento, para a caracterização e avaliação do campo de escoamento na esteira aerodinâmica de um modelo reduzido, sob diferentes condições de escoamento incidente. Especificamente, investiga-se a influência da turbulência atmosférica para quatro perfis de escoamento: i) uniforme-suave; ii) uniforme-turbulento; iii) lei potencial com expoente α = 0,11; iv) lei potencial com expoente α = 0,23. Todos os casos foram conduzidos sob condições de estratificação neutra, e foi utilizado anemômetro de fio-quente para efetivar as medições dos perfis de velocidade média e intensidade da turbulência, em diferentes posições da esteira. Os resultados mostraram diferenças substanciais no comportamento dos perfis de esteira, em função dos níveis de turbulência incidente. Particularmente, observou-se que o incremento da turbulência atmosférica reduz o déficit de velocidade e promove uma maior mistura turbulenta, o que acelera a dissipação dos efeitos de esteira. Assim, a metodologia experimental em túnel de vento evidencia-se como uma importante ferramenta de análise que possibilita amplo espectro para a investigação, precisão e confiabilidade de projetos eólicos.
Wind turbines are machines installed in large wind farms to convert the wind's kinetic energy into electrical power. For an optimal wind farm siting, it is necessary to take into account the interaction between wind turbine wakes. In general, wake effects are associated with velocity deficit and enhanced turbulence intensity. This may reduce the aerodynamic efficiency and lifetime of downwind turbines, making the project unfeasible. Several experimental and numerical studies have been conducted to unravel the behavior of wind turbine wakes under different inflow conditions. However, current wind farm siting tools are incapable of accurately predicting and assessing its effects. This document presents an experimental methodology in the wind tunnel to survey the influence of the atmospheric turbulence on the wake flow field of a wind turbine model. Specifically, four different flow conditions were investigated: i) uniform-laminar; ii) uniform-turbulent; iii) power law exponent α = 0.11; iv) power law exponent α = 0.23. All cases were developed under neutrally stratified conditions. Hot-wire anemometry was used to obtain high-resolution measurements of the mean velocity and turbulence intensity profiles at different downwind positions. Results show that different turbulence intensity levels of the incoming flow lead to substantial differences in the spatial distribution of the wakes. Particularly, higher ambient turbulence promotes a faster wake recovery and lower velocity deficit. In conclusion, the use of wind tunnel experiments is a trustworthy alternative that brings precision and reliability to wind projects.

The threshold friction velocities of potential dust sources in the US Southwest were measured in the field using a Portable Wind Tunnel, which is based on the Desert Research Institute's Portable In-Situ Wind Erosion Laboratory (PI-SWERL). A mix of both disturbed and undisturbed surfaces were included in this study. It was found that disturbed surfaces, such as those at the Iron King Mine tailings site, which is part of the EPA's Superfund program and contains surface concentrations of arsenic and lead reaching as high as 0.5% (w/w), had lower threshold friction velocities (0.32 m s⁻¹ to 0.40 m s⁻¹) in comparison to those of undisturbed surfaces (0.48 to 0.61 m s⁻¹). Surface characteristics, such as particle size distribution, had effects on the threshold friction velocity (smaller grain sized distributions resulted in lower threshold friction velocities). Overall, the threshold friction velocities of disturbed surfaces were within the range of natural wind conditions, indicating that surfaces disturbed by human activity are more prone to causing windblown dust.

The Martian atmosphere is of great scientific interest, both because of its similarity to Earth’s atmosphere, and because of its relevance to exploration of Mars. Although satellite instruments have provided a wealth of atmospheric data, they have provided little information about the atmospheric boundary layer. Conditions in the lowest few metres of the Martian atmosphere are perhaps the most directly interesting to humans, as this is the portion of our own atmosphere with which we have the most contact. In this thesis is described the design, calibration and operations planning for a new wind sensor for use on Mars. This sensor is lighter and smaller than previous Mars wind sensors. At the time of writing, the wind sensor is on its way to Mars as part of the science payload of Beagle 2, a small exobiology lander due to arrive in December 2003. The Beagle 2 wind sensor (B2WS) is a hot-film anemometer. Three platinum films are equally spaced around the surface of a vertical cylinder. A known current is dissipated in each film, heating the film 40-80°C above the ambient gas temperature. The film temperature is obtained by measuring its resistance. An effective heat transfer coefficient is then calculated for each film. A novel scheme has been developed which allows calculation of a wind vector from the differences between these heat transfer coefficients, rather than from their average. This makes the measured wind vector less prone to common-mode errors such as uncertainties in air temperature or sky temperature. The sensor was calibrated in a low density wind tunnel, optimised to provide stable winds of air or carbon dioxide at Martian pressures (5 – 10 mbar) and speeds (0.5 – 30 m/s). The flow field in the test section was calculated using analytical and finite element modelling techniques, and validated experimentally using a pitot probe. This facility’s stability and accuracy represent a significant improvement over previous calibration facilities. An analytical model of heat flow in the sensor has been developed in order to permit correction for conditions which may be encountered on Mars, but were not tested for in the wind tunnel. The wind sensor’s performance in a real Martian atmosphere is simulated using wind and temperature data from a previous Mars lander. The position of the wind sensor position at the end of Beagle 2's motorised arm allows several new possibilities for wind measurement on Mars that were unavailable in previous missions. The height of the wind and air temperature sensors can be adjusted to any height between 20 and 95 cm above the ground. The temperature sensor can be scanned horizontally and vertically above the lander to study convective updrafts above the heated lander. Planned operations sequences on Mars are discussed.

Lors des rentrées atmosphériques, les processus thermochimiques hors équilibre dans la couche de choc limitent la fiabilité des prédictions aérothermiques. Afin d'améliorer l'exactitude de ces prévisions, des modèles cinétiques sont actuellement développés. Ces modèles sont expérimentalement évalués à l'aide d'expériences dans lesquelles un départ à l'équilibre thermodynamique est caractérisé. Pour cette raison, le présent travail est consacré à la caractérisation du déséquilibre thermodynamique au sein d'écoulements réactifs à haute enthalpie. La plupart des études expérimentales dédiées à la validation de modèles cinétiques à haute température emploient des installations communément appelées tubes à choc. Nous évaluons ici la possibilité de générer un départ significatif à l'équilibre thermodynamique dans des écoulements plasma stationnaires, incluant des jets supersoniques dans lesquels le déséquilibre vibrationnel est fortement attendu. Des diagnostics spectroscopiques appropriés ont été appliqués, permettant de futures comparaisons avec des descriptions microscopiques issue de modèles théoriques
During planetary atmospheric entries, thermochemical non-equilibrium processes in the shock layer limit the reliability of aerothermal environment prediction. To improve prediction accuracy, non-equilibrium kinetic models are being developed. These models are experimentally assessed through the comparison with well characterized non-equilibrium experiments. For this purpose, the present work is dedicated to the thermodynamic characterization of non-equilibrium in high enthalpy reactive flows. Conversely to common studies that employ short duration facilities to investigate shock layer kinetics, we will assess the possibility of producing significant departure from equilibrium using radio-frequency and microwave stationary plasma flows, including supersonic plasma flows where vibrational non-equilibrium is strongly expected. Suitable spectroscopic diagnostics have been applied allowing future comparisons to be made between the microscopic description of the experiments and theoretical non-equilibrium models

O estudo experimental dos processos de dispersão atmosférica de poluentes permite a análise de problemas específicos e a avaliação dos modelos teórico-numéricos. Os custos da experimentação de campo conduzem à realização de estudos de laboratório em modelos reduzidos. Este trabalho tem por objetivo principal a reprodução dos ventos atmosféricos e dos processos de dispersão em escala reduzida em túnel de vento. Foram estabelecidos os requerimentos gerais de modelagem para os diversos problemas relacionados com o estudo experimental da dispersão de poluentes atmosféricos, incluindo a simulação da camada limite atmosférica e da fonte de emissão. A partir desta análise, foram desenvolvidos e avaliados diversos modelos experimentais dos ventos turbulentos na camada limite atmosférica neutral utilizando velocidades médias muito baixas que permitam cumprir os requerimentos de semelhança do processo de dispersão. As simulações incluem ventos turbulentos sobre terrenos homogêneos a diferentes escalas. Na avaliação experimental foram utilizados dados da literatura e comparações diretas com resultados de campo para a condição de atmosfera em estabilidade neutra. Foram estudados escoamentos turbulentos mais complexos nas proximidades de um modelo simples de uma edificação e em um entorno urbano não homogêneo. Para os estudos da difusão atmosférica, foi estabelecida a prioridade da modelagem de problemas locais de dispersão. Foi modelada uma fonte de emissão pontual de baixa altura representativa de uma chaminé que permita a modificação das condições de empuxo da pluma. A análise do processo de dispersão e das concentrações foi realizada considerando diversas configurações que incluem a fonte de emissão isolada num escoamento homogêneo, a consideração dos efeitos da esteira próxima ao modelo de uma edificação, e finalmente de um terreno urbano não homogêneo. Foram determinadas as concentrações médias e as flutuações de concentração na pluma. Estes resultados permitiram obter os campos de concentração e, a partir das funções de densidade de probabilidade e funções de densidade espectral, analisar as zonas de intermitência no campo de concentração. Comparações com resultados da literatura e com modelos teóricos complementam o estudo realizado. É dada ênfase na análise das flutuações de concentração e na intermitência dos processos de dispersão, dada a importância do seu conhecimento para o desenvolvimento de modelos bem como à escassa informação experimental na bibliografia. Os resultados deste trabalho permitem estabelecer a viabilidade da simulação da camada atmosférica neutral e dos estudos de dispersão em túnel de vento, determinando vantagens e limitações dos modelos reduzidos. A influência das características do escoamento turbulento, das configurações próximas do terreno e das características da emissão no processo de dispersão foi estudada. Finalmente, são analisadas as condições de intermitência associadas aos escoamentos turbulentos e, em particular, aos campos de concentração próximos a uma fonte de emissão.
The experimental study of the pollutant dispersion processes allows the analysis of specific problems as well as the evaluation of theoretical models. The costs related to full scale measurements make the experimental studies over reduced scaled models a better research tool. This work has the aim of modeling some kinds of atmospheric winds and related dispersion processes in wind tunnels. The general modeling laws related to the experimental study of pollutants dispersion were followed, including the boundary layer simulation and the emission source. Several experimental models of the turbulent winds in neutral boundary layers were developed and evaluated by using very low wind velocities, allowing the fulfillment of the similitude laws of the dispersion process. The simulations include turbulent winds over homogeneous terrains at different scales. Literature data were used in the experimental evaluation as well as direct comparisons with field results for the atmosphere under neutral stability conditions. Also, more complex turbulent flows were studied in the close proximities of a simple building model in a non homogeneous surrounding. For the atmospheric diffusion studies, it was decided to model local dispersion situations. A single, punctual type of emission source was modeled, representing the conditions at a low height chimney and allowing the modification of the plume buoyancy conditions. The analysis of the dispersion process and concentrations was performed under several configurations including the isolated source emission in a homogeneous flow, the consideration of the wake effects close to a building model, and finally of a non homogeneous urban terrain. The mean and fluctuating components of the plume concentration were obtained. These results allowed the characterization of the concentration fields. From the probability and spectral density functions it was possible to analyze the intermittence of the concentration field. Comparisons with literature results and with theoretical models complement the study. Special care is taken in the analysis of the fluctuations of the concentration and in the intermittence of the dispersion processes, due to its importance to the development of theoretical models as well as the lack of experimental information in the open literature.

A estrutura do vento varia de acordo com as características do terreno e com a rugosidade da superfície terrestre, desacelerando proporcionalmente sua intensidade de acordo com a proximidade do solo, o que determina a constituição da camada limite atmosférica (C.L.A.). As características do escoamento sobre e no entorno de características topográficas obtusas tais como morros são de grande interesse em muitas aplicações, especialmente aquelas ligadas à engenharia de vento. Esta pesquisa foca a investigação da C.L.A. sobre terrenos complexos, analisando a estrutura do escoamento turbulento, a separação e a recomposição do mesmo. Para tanto, dois métodos são empregados e comparados na presente investigação para identificar a influência da orografia complexa sobre o escoamento do vento: padrões ou códigos de carga de vento e análises experimentais em túnel de vento. Nove modelos experimentais de morros isolados, sendo quatro simétricos bidimensionais, quatro simétricos tridimensionais e um assimétrico, todos com a consideração de dois tipos de terreno, categoria I – plano e categorias III-IV – medianamente rugosas são analisados. A partir de uma simulação experimental da camada limite em túnel de vento, é possível parametrizar os efeitos do vento sobre terrenos complexos (MILLER, 1995). A definição de variáveis, tais como: o perfil de velocidade do vento, a intensidade de turbulência, os efeitos topográficos na velocidade do vento constituem-se em elementos fundamentais para cálculos estruturais de edificações situadas no entorno. Foram desenvolvidas simulações experimentais no túnel de vento de camada limite Prof. Joaquim Blessmann, da Universidade Federal do Rio Grande do Sul. Na superfície do modelo assimétrico, na radial principal do mesmo, foram localizados nove perfis de medição, contendo cada um, vinte alturas de investigação. Os demais modelos tiveram como foco de análise o cume dos mesmos, também com perfis definidos nas mesmas alturas. As medições da velocidade do vento e da intensidade da turbulência foram procedidas por um sistema de anemometria de fio quente. Os dados obtidos em túnel de vento foram confrontados com expressões empíricas calculadas para os mesmos pontos segundo cinco códigos ou padrões de carga de vento, pontuando também as correlações entre os mesmos e entre estes com a norma brasileira NBR 6123 (1988). Os modelos, códigos ou padrões analisados foram: Jackson e Hunt (1975) e Davenport, Surry e Lemelin (1988), models e as normas a seguir nominadas:Norma Brasileira: cargas de vento em Edificações - NBR 6123 (1988); European Standard:Eurocode1: Basis of Design and Actions on Structures, CEN TC 250: 2002; Australian/New Zealand Standard: Minimum Design Loads on Structures, AS/NZS 1170.2: 2002; Architectural Institute of Japan AIJ: 2004; American Society of Civil Engineering Standard, ASCE 7-95 (ASCE 7-95), Minimum Design Loads for Buildings and Other Structures;National Building Code of Canada, 2005, (NRCC 2005). Além do estudo comparativo acerca da resposta estimada pelos códigos nominados, esta pesquisa constitui-se em um banco de dados de medições em pontos localizados nos morros nominados, em túnel de vento. O comparativo entre os padrões mostra a inexistência de uma harmonização entre os mesmos para a consideração dos parâmetros a serem empregues para o cálculo de cargas de vento. Estas diferenças na definição dos parâmetros básicos para o carregamento de vento em estruturas determinam grandes dificuldades na unificação de formatos recomendados na previsão das cargas de vento. Comparativamente aos dados experimentais, os padrões, em geral, mostram-se conservadores para os dois tipos de morros analisados, simétrico e assimétrico, para os dois tipos de terreno, tanto considerando-se análises em 2D ou 3D.
The structure of the wind varies with the characteristics of the terrain and roughness land surface, slowing its intensity proportionally according to the surrounding terrain, which determines the onset of boundary layer (ABL). The characteristics of the flow over and around topographic features such as hills are of great interest in many applications, especially those related to wind engineering. From an experimental simulation of the boundary layer wind tunnel, it is possible to parameterize the effects of wind over complex terrain (MILLER, 1995). The definition of variables, such as the profile of wind speed, the turbulence intensity, the topographic effects on wind speed are key elements in structural calculations for buildings situated around the area. This research focuses on the investigation of the ABL complex terrain conditions, analyzing the structure of turbulent flow and characterization of separation and reattachment of the flow. Experimental simulations were developed in the wind tunnel of the atmospheric boundary layer Prof. Joaquim Blessmann, Federal University of Rio Grande do Sul in nine models of hills, four symmetrical two-dimensional, four- symmetrical threedimensional and one asymmetrical, all considering two types of terrain, category I - plan and Category III-IV- moderately rough. The surface of the asymmetric model was measured in nine profiles ploted on the main radial of the hill, with twenty heights each, and the other models were examined at top of the hill. The measurements were performed with a system of hot wire anemometry to measure the wind velocity and intensity of turbulence. The identification of the data obtained in the wind tunnel were confronted with empirical expressions for the same points, in order to establish the correlations between patterns and among these with NBR 6123 (1988). Two models and five codes of wind loads are analyzed: Jackson and Hunt (1975) and e Davenport, Surry e Lemelin (1988) Models and Brazilian Association of Technical Standards: Wind Load on Buildings, NBR 6123 (1988); European Standard: Eurocode1: Basis of Design and Actions on Structures, CEN TC 250: 2002; Australian/New Zealand Standard: Minimum Design Loads on Structures, AS/NZS 1170.2: 2002; Architectural Institute of Japan AIJ: 2004; American Society of Civil Engineering Standard, ASCE 7-95 (ASCE 7-95), Minimum Design Loads for Buildings and Other Structures; National Building Code of Canada, 2005, (NRCC 2005) codes. This study focuses not only the comparison of the response estimated by international codes nominees, but also a data bank of wind tunnel data to validate this tool based on empirical expressions. The comparison of the patterns shows a lack of consideration for international harmonization of the parameters to be employed for the calculations of wind loads. These differences in defining the basic parameters for the wind loading on structures determines difficulties to unify the formats recommended in the prediction of wind loads. Compared to the experimental data, the patterns will generally show up conservative for both types of mounts analyzed, symmetrical and asymmetrical, for both types of terrain, both considering 2D or 3D.

La décarbonation du secteur de l'énergie est un défi majeur de notre époque. Les énergies renouvelables offrent une solution viable. L'éolien offshore peut contribuer à une grande partie de la demande énergétique. Pour accéder à l'importanteressource éolienne en mer, il est nécessaire d'installer des éoliennes flottantes. Comme la technologie est encore à l'état préindustriel, plusieurs questions restent à résoudre. En utilisant la modélisation physique à une échelleréduite, cette thèse vise à étudier le comportement instationnaire et le développement du sillage d’un modèle simplifié d’éolienne. Le modèle est placé dans une soufflerie atmosphérique et soumis à une gamme de mouvements idéalisés et réalistes. Les valeurs de vitesse moyenne restent globalement inchangées mais l’intensité de turbulence et l’énergie cinétique turbulente (TKE) sont modifiées. Le bilan TKE révèle que la production et la dissipation turbulentes sont augmentées avec l'introduction du mouvement de vague idéalisé. Les spectres d'énergie de l'écoulement sont affectés par l'introduction du mouvement. Un mouvement idéalisé à fréquence unique entraîne une signature claire dans les spectres d'énergie du sillage. Un déplacement vers des fréquences plus élevées peut être observé pour plusieurs régimes de mouvement. Un mouvement réaliste à 3 degrés de liberté affecte le sillage différemment d'un mouvement idéalisé à 3 degrés de liberté
Decarbonising the energy sector is a major challenge of our times. Renewable energies offer a viable solution. Offshore windalone can contribute a large portion of the energy demand. To access the large wind resource further offshore floating wind turbines are necessary. Floating offshore wind turbines (FOWTs) are a potential source for increased offshore energy production. As the technology is still in a pre-industrial state several questionsremain to be addressed. Using physical modelling at a reduced scale, this thesis aims to investigate the unsteady behaviour and the development of the wake in a simplified FOWT model. The model is placed in an atmospheric wind tunnel and subjected to a. range of idealised and realistic motions. Each degree of freedom is studied separately and all three degrees of freedom (Dof) together. The effects of induced sinusoidal surge motion on the characteristics of the model’s wake up to 8D downstream are studied. The results show globally unchanged mean velocity values but modified turbulence intensity and turbulent kinetic energy (TKE). A TKE budget analysis reveals that the turbulent production and dissipation are increased with the introduction of idealised surge motion. The energy spectra of the flow are affected by the introduction of motion. Idealised single frequency motion leaves a clear signature in the wake spectra. A shift to higher frequencies can be observed for several motion regimes. Realistic 3 Dof motion affects the wake differently compared to idealised 3 Dof motion

O formato do perfil de velocidades do vento varia de acordo com as características locais da superfície terrestre e de rugosidade do terreno, parâmetros que definem o perfil da Camada-Limite Atmosférica (CLA). As características do escoamento do ar atmosférico sobre e ao redor de acidentes geográficos, tais como morros e colinas, são de grande interesse para aplicações relacionadas à Engenharia de Turbinas e Parques Eólicos. No topo de morros, ocorre a aceleração do vento, fenômeno que pode representar um fator decisivo para a instalação de aerogeradores. Este trabalho dedica-se ao estudo do comportamento da CLA como função da inclinação e rugosidade superficial da elevação, fazendo uso da Dinâmica de Fluidos Computacional (CFD) para construir perfis de velocidade do vento e de intensidade de turbulência. O problema de fechamento das Equações Médias de Reynolds (RANS) é contornado com o uso do modelo de turbulência k-ω SST; os resultados numéricos obtidos são comparados com dados experimentais medidos em túnel de vento sobre modelos em escala dos morros. São testados oito modelos de morros com declives que variam de 25° a 64° para dois tipos de categorias de terreno, em 2D e 3D, e são aplicados dois códigos analíticos para representar o perfil de velocidades de entrada. Resultados numéricos para os perfis de velocidade apresentam diferença inferior a 4% em relação aos respectivos dados obtidos experimentalmente. Os perfis de intensidade de turbulência apresentam diferença máxima na casa dos 7% em comparação aos dados experimentais, o que é explicado pelo fato de que não é possível inserir o perfil de entrada de intensidade de turbulência nas simulações numéricas. Em alternativa, foi usado um valor constante resultado da média dos valores dos perfis usados no túnel de vento. Os modelos de morro em 3D apresentam maior concordância nos resultados de velocidade que os modelos em 2D e que ademais quanto maior é a inclinação do morro maior é a concordância com as medições experimentais.
The shape of the wind velocity profile changes according to local features of terrain shape and roughness, which are parameters responsible for defining the Atmospheric Boundary Layer (ABL) profile. Air flow characteristics over and around landforms, such as hills, are of considerable importance for applications related to Wind Farm and Turbine Engineering. The air flow is accelerated on top of hills, which can represent a decisive factor for Wind Turbine placement choices. The present work focuses on the study of ABL behavior as a function of slope and surface roughness of hill-shaped landforms, using the Computational Fluid Dynamics (CFD) to build wind velocity and turbulent intensity profiles. Reynolds-Averaged Navier-Stokes (RANS) equations are closed using the SST k-ω turbulence model; numerical results are compared to experimental data measured in wind tunnel over scale models of the hills under consideration. Eight hill models with slopes varying from 25° to 64° were tested for two types of terrain categories in 2D and 3D, and two analytical codes are used to represent the inlet velocity profiles. Numerical results for the velocity profiles show differences under 4% when compared to their respective experimental data. Turbulent intensity profiles show maximum differences around 7% when compared to experimental data, this can be explained by not being possible to insert inlet turbulent intensity profiles in the simulations. Alternatively, constant values based on the averages of the turbulent intensity at the wind tunnel inlet were used. The 3D models present greater concordance in the speed results than the 2D models and that in addition the greater the slope of the hill, the greater the agreement with the experimental measurements.

Ce travail traite de l'utilisation des outils de modelisations physique et numerique dans le domaine du transport eolien de differentes particules. La modelisation physique en soufflerie diphasique et la theorie de la couche limite turbulente ont permis de reproduire les conditions de transport in situ. Dans le cadre de cette approche, nous avons concu et mis en place un dispositif optique de visualisation laser, et une chaine de prise et de traitement d'images pour la determination des profils de concentration massique de l'ecoulement charge. La phase transitoire qui mene vers la saturation est etudiee. L'influence des caracteristiques des particules sur les profils de concentration est aussi analysee. Cette technique de mesure non intrusive donne des resultats tres encourageants par rapport aux profils prevus par la theorie, et permet d'obtenir un nombre de points de mesure tres important. Une simulation numerique basee sur les lois de conservation de la mecanique des fluides est presentee. L'interaction entre l'ecoulement et le lit de particules est prise en compte par l'intermediaire d'un flux massique determine experimentalement, grace a un dispositif optique (diode laser) qui permet de mesurer l'evolution de l'epaisseur du lit de particules. Ces observations experimentales donnent lieu a une analyse du phenomene de ripples observe lors de l'evolution temporelle de l'epaisseur du lit. Une premiere simulation par le code flow3d (cfds-aea technology, angleterre) indique une bonne reproduction des champs de vitesses. Cependant, meme si les ordres de grandeur pour les profils de concentration sont corrects dans les premiers millimetres, ce code numerique ne permet pas d'obtenir une diffusion verticale suffisante des particules. Une seconde approche numerique permet de resoudre l'equation de conservation de la masse solide dans la zone de suspension, et donne une distribution spatiale de la concentration tres proche de la distribution experimentale

La modélisation inverse de la dispersion atmosphérique consiste à reconstruire les caractéristiques d’une source (quantité de polluants rejetée, position) à partir de mesures de concentration dans l’air, en utilisant un modèle direct de dispersion et un algorithme d’inversion. Nous avons utilisé dans cette étude deux modèles directs de dispersion atmosphérique SIRANE (Soulhac, 2000; Soulhac et al., 2011) et SIRANERISK (Cierco et Soulhac, 2009a; Lamaison et al., 2011a, 2011b). Il s’agit de deux modèles opérationnels de « réseau des rues », basés sur le calcul du bilan de masse à différents niveaux du réseau. Leur concept permet de décrire correctement les différents phénomènes physiques de dispersion et de transport de la pollution atmosphérique dans des réseaux urbains complexes. L’étude de validation de ces deux modèles directs de dispersion a été effectuée après avoir évalué la fiabilité des paramétrages adoptés pour simuler les échanges verticaux entre la canopée et l'atmosphère, les transferts aux intersections de rues et la canalisation de l’écoulement à l’intérieur du réseau de rues. Pour cela, nous avons utilisé des mesures en soufflerie effectuées dans plusieurs configurations académiques. Nous avons développé au cours de cette thèse un système de modélisation inverse de dispersion atmosphérique (nommé ReWind) qui consiste à déterminer les caractéristiques d’une source de polluant (débit, position) à partir des concentrations mesurées, en résolvant numériquement le système matriciel linéaire qui relie le vecteur des débits au vecteur des concentrations. La fiabilité des résultats et l’optimisation des temps de calcul d’inversion sont assurées par le couplage de plusieurs méthodes mathématiques de résolution et d’optimisation, bien adaptées pour traiter le cas des problèmes mal posés. L’étude de sensibilité de cet algorithme d’inversion à certains paramètres d’entrée (comme les conditions météorologiques, les positions des récepteurs,…) a été effectuée en utilisant des observations synthétiques (fictives) fournies par le modèle direct de dispersion atmosphérique. La spécificité des travaux entrepris dans le cadre de ce travail a consisté à appliquer ReWind dans des configurations complexes de quartier urbain, et à utiliser toute la variabilité turbulente des mesures expérimentales obtenues en soufflerie pour qualifier ses performances à reconstruire les paramètres sources dans des conditions représentatives de situations de crise en milieu urbain ou industriel. L’application de l’approche inverse en utilisant des signaux instantanés de concentration mesurés en soufflerie plutôt que des valeurs moyennes, a montré que le modèle ReWind fournit des résultats d’inversion qui sont globalement satisfaisants et particulièrement encourageants en termes de reproduction de la quantité de masse totale de polluant rejetée dans l’atmosphère. Cependant, l’algorithme présente quelques difficultés pour estimer à la fois le débit et la position de la source dans certains cas. En effet, les résultats de l’inversion sont assez influencés par le critère de recherche (d’optimisation), le nombre de récepteurs impactés par le panache, la qualité des observations et la fiabilité du modèle direct de dispersion atmosphérique
The aim of this study is to develop an inverse atmospheric dispersion model for crisis management in urban areas and industrial sites. The inverse modes allows for the reconstruction of the characteristics of a pollutant source (emission rate, position) from concentration measurements, by combining a direct dispersion model and an inversion algorithm, and assuming as known both site topography and meteorological conditions. The direct models used in these study, named SIRANE and SIRANERISK, are both operational "street network" models. These are based on the decomposition of the urban atmosphere into two sub-domains: the urban boundary layer and the urban canopy, represented as a series of interconnected boxes. Parametric laws govern the mass exchanges between the boxes under the assumption that the pollutant dispersion within the canopy can be fully simulated by modelling three main bulk transfer phenomena: channelling along street axes, transfers at street intersections and vertical exchange between a street canyon and the overlying atmosphere. The first part of this study is devoted to a detailed validation of these direct models in order to test the parameterisations implemented in them. This is achieved by comparing their outputs with wind tunnel experiments of the dispersion of steady and unsteady pollutant releases in idealised urban geometries. In the second part we use these models and experiments to test the performances of an inversion algorithm, named REWind. The specificity of this work is twofold. The first concerns the application of the inversion algorithm - using as input data instantaneous concentration signals registered at fixed receptors and not only time-averaged or ensemble averaged concentrations. - in urban like geometries, using an operational urban dispersion model as direct model. The application of the inverse approach by using instantaneous concentration signals rather than the averaged concentrations showed that the ReWind model generally provides reliable estimates of the total pollutant mass discharged at the source. However, the algorithm has some difficulties in estimating both emission rate and position of the source. We also show that the performances of the inversion algorithm are significantly influenced by the cost function used to the optimization, the number of receptors and the parameterizations adopted in the direct atmospheric dispersion model

La pénétration d'eau de pluie à travers une toiture à pentes constituée de petits éléments est principalement liée à la différence de pression externe et interne, générée par le vent sur le toit. Le champ de pression externe est accessible aux mesures, sur maquette en soufflerie atmosphérique. En revanche, le champ de pression interne ne peut pas être obtenue qu'en vraie grandeur. Une modélisation numérique de ce dernier a donc fait l'objet de cette thèse. Il s'agit plus précisement de calculer la pression instantanée en sous-face de la couverture, dotée ou non d'un écran qu'il soit souple ou rigide. L'estimation de la pression interne est délicate faute d'une bonne connaissance des caractéristiques de l'écoulement à travers des parois perméables. Une campagne de mesures en vraie grandeur a donc été menée pour caractériser la perméabilité à l'air de la toiture pour un revêtement donné (banc de mesures), ensuite pour étudier les effects de la vitesse et de la turbulence du vent et de l'intensité de la pluie sur cette perméabilité (soufflerie climatique). La pression interne issue du modèle sans écran reproduit bien celle mesurée. L'étude paramétrique du cas avec écran à montré la possibilité de réduire considérablement la pression différentielle. Une bonne connaissance des paramètres qui influencent le différentiel de pression permet de concevoir des toits à pentes, pour lesquels les problèmes de pénétration d'eau de pluie sont considérablement réduits
Generally, the rain penetration through pitched lapped roofs is created by the difference of external and internal pressure, generated by the wind. In this thesis, a numerical model has been developped for prediction of internal pressure under the elements (the external pressure can be measured on a model in a boundary layer wind-tunnel). Two cases have been studied : roof without underlay, roof with flexible or stiff underlay. The dynamics of internal pressure is, in general, a complex problem. This is due to the poor knowledge on the leakage paths characteristics. Therefore, full-scale experimental studies have been carried out to characterize the roof wind permeability (test appartus) and to investigate the effects of windspeed, atmospheric turbulence and rain intensity on this permeability (climatic wind-tunnel). The analytical results were compared with full-scale results (roof without underlay case), and they matched closely. Parametric studies (underlay case) have shown that it is possible to reduce considerably the wind loads. Through a complete knowledge of the controlling parameters it will be possible to design and construct pitched lapped roofs, from which the problems of rain penetration is strongly reduced

Des bâtiments de grande hauteur sont construits avec un poids et un amortissement structurel de plus en plus faibles en lien avec l'évolution des techniques de construction et des matériaux. La connaissance des charges de vent dynamiques est un enjeu important pour la conception des grands bâtiments afin de garantir leur sécurité structurelle. L'objectif de cette thèse est d’évaluer la capacité de la simulation numérique des grandes échelles (LES) à prédire les charges de vent sur les structures et d’étudier l'influence des conditions d’entrée d’une simulation LES sur ces charges. Des expériences ont été menées à échelle réduite dans la soufflerie atmosphérique NSA du CSTB afin de documenter l’écoulement atmosphérique modélisé, de caractériser son interaction avec un bâtiment et les charges de vent statiques et dynamiques résultantes. Le sillage du bâtiment a été caractérisé grâce à des mesures PIV. Les efforts globaux et les pressions locales ont été mesurés par une balance et des prises de pression à haute fréquence. Ces expériences en soufflerie ont permis de développer un générateur de conditions amont (GCA) pour la simulation LES, visant à reproduire les principales caractéristiques de la turbulence dans la couche limite. La base de données constituée a également permis de qualifier les résultats des simulations LES réalisées avec le code OpenFOAM dans la configuration de l’expérience. L’utilisation du nouveau GCA et d’un générateur dégradé qui ne respecte pas toutes les caractéristiques de l'écoulement a permis de montrer la nécessité de bien reproduire les caractéristiques du vent incident pour accéder aux charges dynamiques sur le bâtiment
High-rise buildings are built with increasingly low weight and structural damping in relation to the evolution of construction techniques and materials. The understanding of dynamic wind loads is an important issue for the design of high-rise buildings in order to guarantee their structural safety. The objective of the present work is to assess the ability of large eddy simulation (LES) to predict wind loads on structures and to investigate the influence of the inflow boundary conditions of a LES simulation on these loads. Experiments were carried out at a small scale in the NSA atmospheric wind tunnel of CSTB to document the modeled atmospheric boundary layer, to characterize its interaction with a building and the resulting static and dynamic wind loads. The wake flow around the building has been characterized by PIV measurements. Global and local wind loads were measured by a high frequency force balance and high frequency pressure taps. These wind tunnel experiments allowed for the development of an inflow turbulence generator for the LES simulation,which was aimed at reproducing the main characteristics of turbulence in the boundary layer. The database also made it possible to assess the quality of the results of the LES simulations carried out with the OpenFOAM code in the same configuration as the experiment. The use of both the new turbulence generator and a degraded one that does not account for all the characteristics of the flow has made it possible to show the necessity to reproduce the characteristics of the upstream wind flow in order to access the dynamic wind loads on the building

A numerical model for inductive plasma wind tunnels is developed. This model provides the flow conditions at the edge of a boundary layer in front of a thermal protection material placed in the plasma jet stream at the outlet of an inductive torch. The governing equations for the hydrodynamic field are derided from the kinetic theory. The electromagnetic field is deduced from the Maxwell equations. The transport properties of partially ionized and unmagnetized plasma in weak thermal nonequilibrium are derived from the Boltzmann equation. A kinetic data base of transport collision integrals is given for the Martian atmosphere. Multicomponent transport algorithms based upon Krylov subspaces are compared to mixture rules in terms of accuracy and computational cost. The composition and thermodynamic properties in local thermodynamic

equilibrium are computed from the semi-classical statistical mechanics.

The electromagnetic and hydrodynamic fields of an inductive wind tunnel is presented. A total pressure measurement technique is thoroughly investigated by means of numerical simulations.

Doctorat en sciences appliquées
info:eu-repo/semantics/nonPublished

La couche limite urbaine est caractérisée par la présence de structures cohérentes complexes, telles que des structures de grande échelle à basse vitesse, et par des processus turbulents intermittents de balayage et d’éjection, responsables du transport de masse, de chaleur et de quantité de mouvement. Ces structures sont bien identifiées qualitativement mais leurs interactions avec les petites structures induites par la présence de la canopée urbaine sont encore mal connues. Afin d'étudier ces interactions, des écoulements de couche limite se développant sur des parois rugueuses sont étudiés en soufflerie. Le signal à petite échelle n'étant pas résolu temporellement, l'estimation stochastique linéaire est utilisée pour décomposer le champ de vitesse en grandes et petites échelles. On confirme que les structures à grande échelle dans la couche limite influencent les petites échelles proches de la rugosité à travers un mécanisme non linéaire similaire à une modulation d'amplitude. On montre également que la modification de la géométrie des éléments de rugosité entraîne une modification de cette interaction non linéaire dans la couche cisaillée. Le bilan complet de l'énergie cinétique turbulente (TKE), incluant la dissipation, est calculé à l'aide d'un modèle LE-PIV et démontre que les structures à petite échelle dans la couche de cisaillement sont importantes pour la production, le transport et la dissipation de l'énergie. Enfin, la décomposition triple du bilan de TKE confirme que la relation non linéaire qui existe entre les structures à grande échelle et les petites échelles proches de la rugosité est liée au transfert d'énergie entre ces structures
The urban boundary layer consists of complex coherent structures, such as large-scale low momentum regions and intermittent turbulent sweeps and ejections, which are responsible for the transport of heat, momentum and pollution. Although these structures have been well identified, their quantitative relationship with the flow inside the canopy is still unknown. Wind tunnel modelling of flow over simplified rough terrain consisting of either three-dimensional or twodimensional roughness elements are able to reproduce these structures and are used to investigate the nonlinear relationship between large-scale momentum regions and small-scales induced by the presence of the roughness. As the temporally resolved small-scale signalis not available Linear Stochastic Estimation is used to decompose the flow into large and small-scales and confirm that the large-scale structures within the overlying boundary layer influence the small-scales close to the roughness through a non-linear mechanism similar to amplitude modulation. Changing terrain configuration from 3D to 2D roughness results in a modification of the non-linear relationship closer to the shear layer that develops near the top of the obstacles. The full turbulent kinetic energy (TKE) budget including dissipation is calculated using an LE-PIV model and demonstrates that small-scale structures within the shear layer are important to the production, transport and dissipation of energy. Finally, triple decomposition of theTKE budget confirms that the non-linear relationship that exists between large-scale momentum regions and small-scales close to the roughness is related to energy transfer between these structures

碩士
朝陽科技大學
建築及都市設計研究所
99
Wind tunnel laboratory in Architecture Department of CYUT is arranged for simulating the wind field in urban environment and building surroundings for research and experiments. It is planned to offer reference for site and buildings location arrangement when under design and planning. To do the urban design, architectural design, green design, structure, disaster prevention, building physical condition and equipment design, wind tunnel experiment practice is important for students to understand the wind field changing in the environment by using model simulation. It is helpful to realize the actual situation in the environment to do the urban planning and building design. Main in research is to establish the simulating atmospheric boundary layer in wind tunnel according to the different site conditions. The wind field will be affected by various site localities like seashore, plain, suburb, and urban type of terrain to form different shape of atmospheric boundary layer. Passive devices such as spires, barriers, and roughness elements were implemented in the tunnel for the simulations. We try to use different size of passive devices and spacing to generate our exclusive atmospheric boundary layer in our low speed, small size wind tunnel. These results will be judged to correct the drift or partly drift from the theory profile line of the atmospheric boundary layer by changing the size and spacing of passive devices. Finally, we will have a suitable atmospheric boundary layer which fit the theory profile line as the achievement. These wind profile will be suitable for the experiment and relevant researches. The purposes of this research are trying to can build up our wind tunnel experiment simulation abilities effectiveness and efficiency in order to help students to understand the wind effects in the environment and promote cooperation of academic circle and the field. Also these will help us to construct the data base for offering references to other researches.

碩士
淡江大學
土木工程學系碩士班
99
The population is growing rapidly in Taiwan, and as a result the geographical area encapsulating the population is decreasing dramatically. This is forcing people to use space more efficiently, and this was reflected by constructing tall, multi-storey buildings. Therefore, it is often common to see a lot of tall buildings in modern and congested cities. However, according to reinforcing of wind, tall buildings are of exceptional height and relatively low mass. These two characteristics have their advantages and disadvantages. Since Taiwan is located in the subtropical zone, it has northeast monsoon in the winter and typhoons in the summer, so people have to be extremely considerate when it comes to designing tall buildings in such conditions. It is critically important that they understand the causes and effects of wind power on the buildings’ physical structures. For example, tall constructions are stiffer than low ones; however they suffer more pressure from wind. The main objective of this research is to discuss the different characteristics of atmospheric boundary layer between Taipei city and Danshui. It also focuses on the comparison between the wind tunnel experiments and field measurement. It includes characteristics of atmospheric boundary layer, wind profile, turbulence intensity, turbulence length scale, turbulence spectrum, gust factor, and coherence function. According to the experiment result, it shows that the average intensity of wind velocity have some effects on the wind profile figure under a strong wind circumstance; the turbulence intensity decrease steadily when there is an increase on the average intensity of wind velocity. On the other hand, the turbulence length scale expands while the average intensity of wind velocity increases. The Von-Karman spectrum density function represent the recommended figure of local’s normal wind characteristics. Different level of height of Coherence Function satisfied Davenport’s recommended figure. Under the accurate reduced scale conditions, both the Practical situation model and wind tunnel investigation have similar outcome after comparing the result of the Characteristics of wind field and Field measurement.

碩士
淡江大學
土木工程學系碩士班
99
Before, we only have three typical terrain’s roughness blocks. If we want to know a real topography’s wind feature, we have to make a reduced scale’s model to simulate it. But it will be waste human resources and spend a lot of time and money. So if we can find some way to use roughness blocks to simulate the real topography, it will be more efficiently. On the other hand, in the field measurement we can’t got the information of the turbulence. If we successfully use the way to simulate terrain, we can got more information of terrain. The results show that we can use the mean height of the build and density of the terrain to simulate the real topography. In roughness block’s experiment, we successfully simulate the wind profile, turbulence intensity and turbulence length scale.

碩士
國立中興大學
土木工程學系
93
A part-depth simulation of atmospheric boundary layer which is based on full-depth simulation techniques developed by Counihan and Standen is conducted in this study. The vortex-generator and roughness elements are used in this study to simulate atmospheric boundary layer in wind tunnel. The mean velocity profile, turbulence intensity, power spectra, and integral length scale of flow field are checked. The results shown that the properties of the simulated flow field are accepted and suitable to be used in the aerodynamic tests. Also we found that the scale factor of flow field could be another important reference in wind tunnel tests besides boundary layer thickness. The part-depth simulated flow field was used to check the pressure distribution on the roof of scaled down low-rise building model used by TTU real field test. The measured pressure distribution are compared to the TTU results and shown they were similar. In this study we found that the size of vortex-generator is related to the integral length scale and effect height of the boundary flow field. The probability distribution function of the roof corner, front face, side face and rear face of the model are also investigated with different angles of approaching flow. The probability distribution of peak pressures on roof are almost identical to the Type I extreme value distribution. This study shown that the aerodynamic experiments results got in part-depth simulated atmospheric boundary layer is similar to the results in the full-depth simulated atmospheric boundary layer in larger wind tunnel for the tests of low-rise buildings, but the technique developed in this study will be much more economical.

Title: Urban Ventilation Dependence on Geometric Configuration Author: RNDr. Ing. Libor Kukačka Department: Department of Atmospheric Physics Supervisor: prof. RNDr. Zbyněk Jaňour, DrSc., Academy of Sciences of the Czech Republic, Institute of Thermomechanics, v. v. i. Abstract: The main goal of the thesis is to investigate the impact of urban geometry on the urban ventilation using wind-tunnel modelling. To measure the pollutant transport, both advective and turbulent, within complex urban geometries with a high temporal resolution a special measurement method was developed. At first, the pollution of a simplified urban area was simulated by a ground-level point source and the ventilation of the intersection with respect to four wind directions was studied. Later, the pollution of other simplified and complex urban areas was simulated by a ground-level line source and the ventilation of three different street canyons with respect to wind direction perpendicular and oblique to their along-canyon axis was investigated. The clear impact of urban complexity and wind direction on street canyon ventilation is demonstrated at lateral and top openings of all investigated canyons and the intersection. Whilst the dominance of the pollutant advection is demonstrated at the eaves of pitched roofs, at the roof ridges...

碩士
國立中央大學
土木工程研究所
92
The turbulence transport of momentum, heat and mass (water vapor, CO2, O2, seed and pollen) between the plant canopies and atmosphere not only affect the growth of plants, but also influence the evaporation, transpiration and micro-meteorology of forest area. This study used wind tunnel experiment to investigate the mixing layer flow above the plant canopy and wake flow in the canopy. Mean velocity profiles and turbulence parameters were measured at several down-wind distances. Based on the velocity measurements, the shear velocity, roughness length, displacement height, momentum thickness and cross-correlation function all were calculated and analyzed. The results showed that: Mean velocity profiles were related to canopy spacing and could be non-dimensionalized. The momentum transport was dominated by the sweep and ejection events above the tree top.

Thesis (Ph. D.)--Florida State University, 2006.
Advisors: Kevin Speer, Martin Wegkamp, Florida State University, College of Arts and Sciences, Dept. of Statistics. Title and description from dissertation home page (viewed Sept. 20, 2006). Document formatted into pages; contains x, 48 pages. Includes bibliographical references.

The aerodynamic applications of plasma science is a field of growing interest. Investigations using various approaches have been initiated by several research groups that are designed to manipulate the aerodynamic boundary layer and to re-attach the flow to airfoils. EHD (ElectroHydroDynamic) flow control has proven at least as effective as other methods of boundary layer flow control. In the EHD approach, glow discharge plasma actuators are placed on the wings and fuselage of the aircraft, or on the turbine blades in the engine, to influence the boundary layer flow. This thesis is concerned with plasma actuators based on the OAUGDP ® (One Atmosphere Uniform Glow Discharge Plasma). An actuator consists of two conducting electrodes separated by a dielectric plate. When a sufficiently high RF voltage is supplied to the electrodes, the surrounding air ionizes and forms plasma in regions in which the electric field is above approximately 10 kV/cm. The ionized air, in the presence of an electric field gradient, produces a body force on the neutral gas flow.This work is concerned with two EHD effects: paraelectric flow acceleration and peristaltic flow acceleration. In the paraelectric mode, electric field gradients act on the net charge density of plasma, and the plasma drags the neutral gas along with it due to ion-neutral and electron-neutral Lorentzian collisions. In the peristaltic mode, successive actuators are energized with the same voltage, but increasing phase angles. The first part of this thesis describes experiments at the NASA Langley Research Center, Hampton, VA in the 7 x 11 Inch Low Speed Wind Tunnel in which Pitot tube velocity profile measurements and smoke flow visualization tests were conducted.The second part of this thesis describes the development of a low cost power supply to energize OAUGDP ® plasma actuators. The power supply consists of automotive ignition coil transformers, audio amplifiers, and a DC battery. Using this power supply, plasma actuators were energized at voltages up to 8 kV, and at frequencies between 0.5 and 8 kHz. This thesis also presents illustrative paraelectric flow acceleration data obtained using the low-cost power supply.