Snow surface energy balance was studied along an elevational gradient and under varying forest cover types during the ablation season of 2007 in the Coldstream Basin, Okanagan, British Columbia, Canada. During the snowmelt period, 1-4% of the peak annual snow-water equivalent (SWE) was lost to sublimation in open sites – averaging 0.4 mm d-1. Melt and sublimation rates increased significantly with elevation, and were higher and more variable in the open sites than under forest canopies. Melt rates were driven almost entirely by sensible heat fluxes and exceeded 30 mm d-1 during large-scale advection events. The melt and sublimation processes observed at the snow surface were significantly linked to conditions in the atmospheric boundary layer. From these linkages, a proxy record of historical ablation season energy fluxes for the period 1972-2007 was created. Significant trends towards earlier dates of snowmelt and freshet onset were detected, as was a trend towards increasing ablation-season temperatures at the 850 mb height. Significant correlations between estimated historical ablation-season melt and sublimation and the regionally dominant teleconnection indices were also found. This study significantly advances the understanding of ablation season snow-surface energy exchanges, and the links to the driving atmospheric conditions in the Okanagan Basin.

[pt] 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. / [en] 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.

Simulações numéricas do escoamento atmosférico em microescala constituem o foco principal deste estudo. Estas simulações são abordadas tendo em vista aplicações para o setor eólico, em especial para avaliações de produção de energia em parques eólicos. Existem diversas categorias de incertezas associadas às estimativas de produção de energia para um projeto eólico, mas na maioria dos casos, a incerteza associada ao modelo de escoamento é a maior e mais relevante de todas. Dentro do setor eólico, o termo “modelo de escoamento” refere-se à ferramenta numérica utilizada para extrapolar o recurso eólico medido na posição das torres anemométricas (e sensores remotos) até as posições projetadas para os aerogeradores. Diversos autores sugerem através de estudos comparativos que os modelos tipo “CFD RANS k-ε” atualmente representam o “estado da arte” para aplicações em parques eólicos e são os mais utilizados comercialmente no setor. Contudo, o escoamento atmosférico livre é intrinsicamente turbulento, e a dinâmica dos escoamentos turbulentos é um campo científico que ainda não foi totalmente dominado pelo conhecimento humano. O presente estudo demonstra que a maioria dos “modelos de escoamento” atualmente disponíveis possuem pontos fracos, em especial quando aplicados em simulações do escoamento atmosférico livre sobre áreas com topografia e rugosidade complexas Uma das fraquezas presentes na maioria dos modelos de microescala para escoamento atmosférico é a “incapacidade” de simular com precisão o escoamento que ocorre durante períodos de “estabilidade atmosférica”. Diversos locais com elevado potencial eólico apresentam ciclos durante os quais as características do escoamento são afetadas pela ocorrência de estratificação térmica dentro da Camada Limite Atmosférica. Tendo como objetivo principal melhorar as simulações do escoamento nestas condições, propõe-se através deste estudo algumas modificações na modelagem “CFD RANS k-ε” tradicionalmente empregada. Dentre estas, destacam-se a inclusão de um perfil estratificado de temperatura potencial como condição de contorno, a inclusão dos efeitos das forças de empuxo no equacionamento “k-ε” e a solução simultânea das equações para balanço de energia e para o fluxo de temperatura potencial. Este modelo foi chamado de “RANS estável”. Para validação deste modelo foram utilizadas cinco torres anemométricas instaladas em um local com topografia complexa. Estas torres foram montadas e instrumentadas conforme as melhores práticas internacionais Os dados anemométricos registrados por essas torres demonstram a presença de ciclos diários de estabilidade atmosférica. Os erros de previsão cruzada foram calculados comparando-se as previsões de cada modelo com as medições reais registradas na posição das torres. O erro global médio de previsão cruzada entre torres anemométricas obtido com a composição dos modelos RANS “estável + neutro” foi de 3,8% enquanto o erro obtido apenas com o modelo RANS k-ε tradicional foi de 5,2%. Para o modelo linear WAsP, amplamente utilizado no setor eólico, o erro foi de 7,1%. Além dos erros de previsão cruzada entre torres, os perfis verticais de velocidade e os fatores de aceleração direcionais obtidos com a composição dos modelos RANS “estável + neutro” também sugerem que esta é uma alternativa versátil e promissora para capturar os ciclos de estabilidade atmosférica utilizando simulações numéricas em regime permanente. / Microscale numerical simulations of the atmospheric wind flow are the central focus of this study. These simulations are analysed from the wind energy perspective. Special attention is given to the usage and application of these simulations in energy production assessments for proposed wind farms. There are multiple uncertainty categories associated with energy production forecasts for future wind farms. However, in most cases the uncertainty factors related with wind flow modelling are the largest and most relevant of them all. The wording “flow model” refers to the numerical simulations (or “models”) that are used to extrapolate the anemometric data recorded at meteorological masts positions to the proposed wind turbine positions. Several authors have demonstrated through comparative studies that the “CFD RANS k-ε” models currently represent the “state of the art” when it comes to microscale wind flow simulations targeted at wind farms. Nonetheless, the atmospheric wind flow is turbulent by nature, and the dynamics of turbulent flows represent one of the scientific fields that have not yet been fully dominated by the human knowledge. The present study demonstrates that the majority of flow models currently available to mankind still lack in precision, even more so when it comes to modelling free atmospheric wind flow over complex terrain. One of the major weak spots of most microscale wind flow models is their inability to precisely simulate the wind flow that occurs during periods of atmospheric stability Numerous locations with large potential for wind energy production present cyclic periods of thermal stratification inside the atmospheric boundary layer. These cycles alter the dynamics and characteristics of the wind stream. With the purpose of improving wind flow simulations under stable atmospheric conditions, some modifications to the standard “RANS k-ε” model implementation are proposed. The most significant of these modifications are the usage of a potential temperature profile among the boundary conditions, the inclusion of the buoyancy forces in the “k-ε” equations and the simultaneous solution of the equations for energy balance and for potential temperature transport. This “modified” model was named “stable RANS”. It was validated using five well mounted meteorological masts installed in a location with complex topography. The anemometric data measured by these site masts suggest the existence of strong daily cycles of atmospheric stability. Cross prediction errors were calculated by comparing the forecasts (outputs) from each flow model against real wind data measured at each mast position The global average cross prediction error yielded by the RANS “stable +neutral” model was around 3,8%, whereas the error yielded by the traditional “RANS k-ε” implementation was near 5,2%. For the linear model WAsP the error was calculated to be 7,1%. In addition to cross prediction errors, the vertical wind speed profiles and speed-up factors calculated with the RANS “stable +neutral” model composition also suggest that it is a promising and versatile alternative for capturing the effects from atmospheric stability on wind flow using steady state numerical simulations.

abstract: Rapid urban expansion and the associated landscape modifications have led to significant changes of surface processes in built environments. These changes further interact with the overlying atmospheric boundary layer and strongly modulate urban microclimate. To capture the impacts of urban land surface processes on urban boundary layer dynamics, a coupled urban land-atmospheric modeling framework has been developed. The urban land surface is parameterized by an advanced single-layer urban canopy model (SLUCM) with realistic representations of urban green infrastructures such as lawn, tree, and green roof, etc. The urban atmospheric boundary layer is simulated by a single column model (SCM) with both convective and stable schemes. This coupled SLUCM-SCM framework can simulate the time evolution and vertical profile of different meteorological variables such as virtual potential temperature, specific humidity and carbon dioxide concentration. The coupled framework has been calibrated and validated in the metropolitan Phoenix area, Arizona. To quantify the model sensitivity, an advanced stochastic approach based on Markov-Chain Monte Carlo procedure has been applied. It is found that the development of urban boundary layer is highly sensitive to surface characteristics of built terrains, including urban land use, geometry, roughness of momentum, and vegetation fraction. In particular, different types of urban vegetation (mesic/xeric) affect the boundary layer dynamics through different mechanisms. Furthermore, this framework can be implanted into large-scale models such as Weather Research and Forecasting model to assess the impact of urbanization on regional climate. / Dissertation/Thesis / Doctoral Dissertation Civil and Environmental Engineering 2016

Simulações numéricas do escoamento atmosférico em microescala constituem o foco principal deste estudo. Estas simulações são abordadas tendo em vista aplicações para o setor eólico, em especial para avaliações de produção de energia em parques eólicos. Existem diversas categorias de incertezas associadas às estimativas de produção de energia para um projeto eólico, mas na maioria dos casos, a incerteza associada ao modelo de escoamento é a maior e mais relevante de todas. Dentro do setor eólico, o termo “modelo de escoamento” refere-se à ferramenta numérica utilizada para extrapolar o recurso eólico medido na posição das torres anemométricas (e sensores remotos) até as posições projetadas para os aerogeradores. Diversos autores sugerem através de estudos comparativos que os modelos tipo “CFD RANS k-ε” atualmente representam o “estado da arte” para aplicações em parques eólicos e são os mais utilizados comercialmente no setor. Contudo, o escoamento atmosférico livre é intrinsicamente turbulento, e a dinâmica dos escoamentos turbulentos é um campo científico que ainda não foi totalmente dominado pelo conhecimento humano. O presente estudo demonstra que a maioria dos “modelos de escoamento” atualmente disponíveis possuem pontos fracos, em especial quando aplicados em simulações do escoamento atmosférico livre sobre áreas com topografia e rugosidade complexas Uma das fraquezas presentes na maioria dos modelos de microescala para escoamento atmosférico é a “incapacidade” de simular com precisão o escoamento que ocorre durante períodos de “estabilidade atmosférica”. Diversos locais com elevado potencial eólico apresentam ciclos durante os quais as características do escoamento são afetadas pela ocorrência de estratificação térmica dentro da Camada Limite Atmosférica. Tendo como objetivo principal melhorar as simulações do escoamento nestas condições, propõe-se através deste estudo algumas modificações na modelagem “CFD RANS k-ε” tradicionalmente empregada. Dentre estas, destacam-se a inclusão de um perfil estratificado de temperatura potencial como condição de contorno, a inclusão dos efeitos das forças de empuxo no equacionamento “k-ε” e a solução simultânea das equações para balanço de energia e para o fluxo de temperatura potencial. Este modelo foi chamado de “RANS estável”. Para validação deste modelo foram utilizadas cinco torres anemométricas instaladas em um local com topografia complexa. Estas torres foram montadas e instrumentadas conforme as melhores práticas internacionais Os dados anemométricos registrados por essas torres demonstram a presença de ciclos diários de estabilidade atmosférica. Os erros de previsão cruzada foram calculados comparando-se as previsões de cada modelo com as medições reais registradas na posição das torres. O erro global médio de previsão cruzada entre torres anemométricas obtido com a composição dos modelos RANS “estável + neutro” foi de 3,8% enquanto o erro obtido apenas com o modelo RANS k-ε tradicional foi de 5,2%. Para o modelo linear WAsP, amplamente utilizado no setor eólico, o erro foi de 7,1%. Além dos erros de previsão cruzada entre torres, os perfis verticais de velocidade e os fatores de aceleração direcionais obtidos com a composição dos modelos RANS “estável + neutro” também sugerem que esta é uma alternativa versátil e promissora para capturar os ciclos de estabilidade atmosférica utilizando simulações numéricas em regime permanente. / Microscale numerical simulations of the atmospheric wind flow are the central focus of this study. These simulations are analysed from the wind energy perspective. Special attention is given to the usage and application of these simulations in energy production assessments for proposed wind farms. There are multiple uncertainty categories associated with energy production forecasts for future wind farms. However, in most cases the uncertainty factors related with wind flow modelling are the largest and most relevant of them all. The wording “flow model” refers to the numerical simulations (or “models”) that are used to extrapolate the anemometric data recorded at meteorological masts positions to the proposed wind turbine positions. Several authors have demonstrated through comparative studies that the “CFD RANS k-ε” models currently represent the “state of the art” when it comes to microscale wind flow simulations targeted at wind farms. Nonetheless, the atmospheric wind flow is turbulent by nature, and the dynamics of turbulent flows represent one of the scientific fields that have not yet been fully dominated by the human knowledge. The present study demonstrates that the majority of flow models currently available to mankind still lack in precision, even more so when it comes to modelling free atmospheric wind flow over complex terrain. One of the major weak spots of most microscale wind flow models is their inability to precisely simulate the wind flow that occurs during periods of atmospheric stability Numerous locations with large potential for wind energy production present cyclic periods of thermal stratification inside the atmospheric boundary layer. These cycles alter the dynamics and characteristics of the wind stream. With the purpose of improving wind flow simulations under stable atmospheric conditions, some modifications to the standard “RANS k-ε” model implementation are proposed. The most significant of these modifications are the usage of a potential temperature profile among the boundary conditions, the inclusion of the buoyancy forces in the “k-ε” equations and the simultaneous solution of the equations for energy balance and for potential temperature transport. This “modified” model was named “stable RANS”. It was validated using five well mounted meteorological masts installed in a location with complex topography. The anemometric data measured by these site masts suggest the existence of strong daily cycles of atmospheric stability. Cross prediction errors were calculated by comparing the forecasts (outputs) from each flow model against real wind data measured at each mast position The global average cross prediction error yielded by the RANS “stable +neutral” model was around 3,8%, whereas the error yielded by the traditional “RANS k-ε” implementation was near 5,2%. For the linear model WAsP the error was calculated to be 7,1%. In addition to cross prediction errors, the vertical wind speed profiles and speed-up factors calculated with the RANS “stable +neutral” model composition also suggest that it is a promising and versatile alternative for capturing the effects from atmospheric stability on wind flow using steady state numerical simulations.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / In this work a parameterization for the transport terms of the turbulent kinetic energy (TKE) budget equation, valid for a convective boundary layer (CBL) is presented. This is a hard task to acomplish from experimental data, especially because of the difficulty associated to the measurements of pressure turbulent fluctuations, which are necessary to determine the pressure correlation TKE transport term. Thus, employing a large eddy symulation (LES), all terms of the TKE budget equation were determined for a CBL. From these data, polynomials that describe the TKE transport terms vertical profiles were adjusted for a CBL. The found polynomial fits are a good description of the LES data, and from them it is shown that a simple formulation that directly relates the transport terms to the TKE magnitude has advantages on other parameterizations commonly used in CBL numerical models. Furthermore, the present study shows that the TKE turbulent transport term dominates over the TKE transport by pressure perturbations and that for most of the CBL these two terms have apposite signs. The simulation consists of a full diurnal PBL cycle utilizing, at the surface, a forcing obtained from experimental data, so that the numerical experiment represents a more realistic case than a idealized CBL. / Neste trabalho, uma parametrização para os termos de transporte da equação de balanço de energia cinética turbulenta (ECT), válida para uma camada limite convectiva (CLC), é apresentada. Esta é uma tarefa complicada de ser realizada a partir de dados experimentais, especialmente devido a dificuldade associada às medidas das flutuações de pressão, que são necessárias para a determinação do termo de correlação de pressão. Desta forma, empregando a simulação dos grandes turbilhões (LES, do inglês Large Eddy Simulation), todos os termos da equação de balanço de ECT foram determinados para a CLC. A partir desses dados, foram ajustados polinômios que descrevem os perfis verticais dos termos de transporte para a CLC. Os polinômios obtidos fornecem uma boa descrição dos dados da simulação LES, e em função deles é mostrado que uma formulação simples, que se relaciona com os termos de transporte a partir da ECT, apresenta vantagens em relação a outras paramametrizações comumente empregadas em modelos numéricos para a CLC. Além disso, o presente estudo mostra que o termo de transporte turbulento domina sobre o transporte devido a flutuações de pressão, e que para a maior parte da extensão vertical CLC estes dois termos tem sinais opostos. A simulação consiste em um ciclo diário da CLP, utilizando como forçante de superfície dados obtidos experimentalmente, assim o experimento numérico representa um caso mais realista que uma simulação de CLC estacionária.

In the wind resource and wind turbine suitability industry Computational Fluid Dynamics has gained widespread use to model the airflow at proposed wind farm locations. These models typically focus on the neutrally stratified surface layer and ignore physical process such as buoyancy and the Coriolis force. These physical processes are integral to the accurate description of the atmospheric boundary layer and reductions in uncertainties of turbine suitability and power production calculations can be achieved if these processes are included. The present work focuses on atmospheric flows in which atmospheric stability and the Coriolis force are included. The study uses Monin-Obukhov Similarity Theory to analyse time series data output from a proposed wind farm location to determine the prevalence and impact of stability at the location. The output provides the necessary site data required for the CFD model as well as stability-dependent wind profiles from measurements. The results show non-neutral stratification to be the dominant condition onsite with impactful windfield changes between stability conditions. The wind flows considered in this work are classified as high Reynolds number flows and are based on numerical solutions of the Reynolds-Averaged Navier-Stokes equations. A two-equation closure method for turbulence based on the k __ turbulence model is utilized. Modifications are introduced to standard CFD model equations to account for the impact of atmospheric stability and ground roughness effects. The modifications are introduced by User Defined Functions that describe the profiles, source terms and wall functions required for the ABL CFD model. Two MOST models and two wall-function methods are investigated. The modifications are successfully validated using the horizontal homogeneity test in which the modifications are proved to be in equilibrium by the model�s ability to maintain inlet profiles of velocity and turbulence in an empty domain. The ABL model is applied to the complex terrain of the proposed wind farm location used in the data analysis study. The inputs required for the stability modifications are generated using the available measured data. Mesoscale data are used to describe the inlet boundary conditions. The model is successfully validated by cross prediction of the stabilitydependent wind velocity profiles between the two onsite masts. The advantage of the developed model is the applicability into standard wind industry loading and power production calculations using outputs from typical onsite measurement campaigns. The model is tuning-free and the site-specific modifications are input directly into the developed User Defined Functions. In summary, the results show that the implemented modifications and developed methods are applicable and reproduce the main wind flow characteristics in neutral and non-neutral flows over complex wind farm terrains. In additions, the developed method reduce modelling uncertainties compared against models and measurements that neglect non-neutral stratification. / Dissertation (MEng)--University of Pretoria, 2018. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

To study especially the influence of a forest canopy on thermodynamic processes in the Atmospheric Boundary Layer (ABL) an one-dimensional model was developed for an ABL including forest as a vertically high resoluted canopy. In contrast to very expensive mesometeorological and LES (Large-Eddy Simulation)-models it is the aim of our study to construct practical simple applicable ABL-model-versions for a rather detailed non steady-state simulation of energy fluxes as well as of windvector, temperature-, humidity- and turbulence-parameter- profiles within and above a forest canopy. The obtained results show clearly that characteristic features of the meteorological fields as temperature are in a general agreement with observations (BEMA). Numerical experiments also describe the considerable influence of the closure approach used and the values for vegetation parameters on the simulation results. / Um den Einfluß eines Waldbestandes auf die thermodynamischen Prozesse in der Atmosphärischen Grenzschicht (AGS) zu untersuchen, wurde ein eindimensionales Modell für eine AGS mit einem Waldbestand als vertikal hoch aufgelöster Vegetationsschicht entwickelt. Im Gegensatz zu den sehr aufwendigen mesoskaligen und LES (Large-Eddy Simulation)-Modellen ist es Ziel dieser Untersuchung, praktisch leicht anwendbare Modellversionen der AGS für die detaillierte instationäre Simulation von Energieflüssen sowie des Windvektors, von Temperatur-, Feuchte- und Turbulenzparameterprofilen inner- und oberhalb des Waldbestandes zu konstruieren. Die erhaltenen Resultate zeigen deutlich, daß die charakteristischen Eigenschaften der meteorologischen Felder, z.B. Temperatur, in genereller Übereinstimmung mit Messungen (BEMA) sind. Die numerischen Experimente geben außerdem den bedeutenden Einfluß der verwendeten Schließungsannahme und der Werte für die Vegetationsparameter auf die Ergebnisse der Simulationen wieder.

Neben der Abnahme des Schalldruckes bzw. der Schallintensität mit zunehmender Entfernung von einer Schallquelle (Kugelwellendivergenz) spielt bei der Schallausbreitung in der atmosphärischen Grenzschicht der Einfluss der höhenveränderlichen meteorologischen Größen, speziell der Temperatur und des Windvektors, auf die Geschwindigkeit und Richtung der Schallwellen eine entscheidende Rolle. Da in den bisherigen Richtlinien zur Erstellung von Lärmkatastern (über einen bestimmten Zeitraum gemittelte Schalldruckpegelverteilung in einem Gebiet) oder zur Messung der Schallimmission in der Umgebung von Schallquellen aktuelle meteorologische Informationen nicht einfließen, wird in dieser Studie untersucht, inwieweit ein entsprechend erweitertes Konzept bzw. Modell zu modifizierten Ergebnissen führt. Die Untersuchungen münden in ein Verfahren, das die Schallausbreitungsbedingungen an einem Ort für einen einzelnen Zeitpunkt bzw. während eines bestimmten Zeitraumes entsprechend der aktuellen thermischen Atmosphärenschichtung und den Vertikalprofilen von Windgeschwindigkeit und –richtung bestimmt. Die dafür benötigten Eingangsinformationen können durch Atmosphärenmodelle jederzeit und für beliebige Gitterpunkte bereitgestellt werden. / Except for the decrease of the acoustic pressure and the acoustic intensity with increasing distance between sound source and receiver (spherical divergence) the sound propagation and thereby the velocity and direction of sound waves inside the atmospheric boundary layer will be mainly influenced by the height-variable meteorological quantities, especially temperature and wind vector. Because actual meteorological information are ignored by the existing rules to create a noise register (averaged sound-pressure level distribution during a definite time interval and over a fixed region) or for the measurement of noise in the environment of sound sources, it will be investigated in this study whether an extended concept and model for the sound propagation will lead to modified results or not. The investigations lead to a technique which quantify the local conditions of sound propagation for one time or for a definite period corresponding to the vertical profiles of the air temperature as well as of wind speed and wind direction. The needed input data can be provided anytime and for any grid point by an atmospheric model.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19986号 / 工博第4230号 / 新制||工||1654(附属図書館) / 33082 / 京都大学大学院工学研究科都市環境工学専攻 / (主査)教授 酒井 伸一, 教授 米田 稔, 准教授 平井 康宏 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM