In recent years, jet noise has been an active area of research due to an increase in the use of aircraft in both commercial and military applications. To meet the noise standards laid out by government agencies, novel nozzle design concepts are being developed with an aim to attenuate the noise levels. To reduce the high costs incurred by experiments, simulation techniques such as large eddy simulation (LES) in combination with a surface integral acoustic method have received much attention for investigating various nozzle concepts. LES is utilized to predict the unsteady flow in the nearfield, whereas the surface integral acoustic method is used for the computation of noise in the farfield. However, Reynolds numbers at which nozzles operate in the real world are very high making wall-resolved LES simulations prohibitively expensive. To make LES simulations affordable, wall-models are being used to model the flow in the near wall region. Using a highly scalable, sixth-order finite-difference-based, in-house LES code, both wall-resolved and wall-modeled simulations of jets through the baseline short metal chevron (SMC000) nozzle were carried out earlier using an implicit LES (ILES) approach. However, differences exist in noise levels between the two simulations. Understanding the cause and reducing the differences between the two methodologies, while at the same time improving the fidelity of the wall-modeled LES is the main aim of the present work. Three new wall-models are implemented in the in-house LES code. A generalized equilibrium wall-model (GEWM) is implemented along with two wall-models that can account for non-equilibrium effects. First, a series of preliminary SMC000 wall-modeled LES simulations were performed and analyzed using the GEWM. The effect of turbulent length scales and velocity fluctuations specified at the inflow, wall-model formulation, and wall-normal grid refinement are analyzed. The adjustment of the fluctuations levels at the inflow proves to be useful in producing flowfields similar to that of the wall-resolved simulation. The newly implemented wall-models are validated for non-canonical problems such as an accelerating boundary layer developing over a flat plate and flow through a converging-diverging channel. It is noticed that the Reynolds number should be high enough for the non-equilibrium wall-models to be effective. At low Reynolds numbers, both equilibrium and non-equilibrium models produce similar wall shear-stresses. However, the wall shear stress boundary conditions supplied by the wall-models do not affect the mean velocity, turbulent kinetic energy, and Reynolds shear stress. Since all the wall-models produce similar results, and the GEWM is the most economical among the implemented wall-models, it is used in performing two wall-modeled LES SMC000 nozzle simulations for noise predictions. The inflow velocity and density fluctuations are varied between the simulations. The first SMC000 simulation uses similar inflow conditions as the previous wall-resolved SMC000 simulation. The second wall-modeled simulation was carried out by reducing the density and velocity fluctuations added to the mean flow at the inlet by 65%. The flowfield and acoustics agree reasonably well in comparison with the wall-resolved LES and similar experiments. Lowering of the velocity and density fluctuations in the wall-model LES improves the agreement of the far-field noise predictions with the wall-resolved LES at most observer locations. However, the preliminary SMC000 simulations performed using a higher Reynolds number and Mach number than that of the previous case show that the approach of adjusting the velocity and density fluctuations added to the mean flow have minimal impact on the developing flowfield which in turn affects the farfield noise. Thus, unless a more effective wall-modeling method is developed, possibly employing an explicit SGS model, the postdictive process of using a wall-model while adjusting the velocity and density fluctuations, seems to be an affordable tool for testing various nozzle designs, subject to the Reynolds number and Mach number being used.

Esta dissertação aborda um estudo sobre algoritmos matemáticos (Método da Variância, Método das Imagens, Método do Gradiente (MG), WCT - Wavelet Covariance Transform), os quais possibilitam a obtenção da altura máxima da Camada Limite Planetária (CLP) a partir de dados fornecidos por um sistema lidar. Em um primeiro momento será descrita a CLP e as suas principais variáveis, assim como também os métodos juntamente com os seus pontos positivos e negativos. Em seguida serão abordadas duas situações de medida: a primeira consiste em um estudo de casos realizado na cidade de Vitória-ES, para o qual foram escolhidas três situações típicas (calmaria, presença de subcamadas de aerossóis e/ou camadas de nuvens e turbulência) em que os métodos foram: testados, comparados entre si, com a análise visual do perfil e o BRN (Bulk Richardsons Number); a segunda situação aborda uma medida feita na cidade de São Paulo-SP durante um período de 12 horas contínuas, sendo o grande diferencial deste experimento, o lançamento de radiossondas dentro de intervalos de 3 horas, isso aliado a utilização de modelagem WRF (Weather Research Forecasting) permitiu uma maior comparação e validação dos dados. A partir dos estudos de casos foi possível observar que com o aumento da complexidade do perfil apresentado pela atmosfera, há um decréscimo na qualidade dos resultados apresentados pelos métodos e um aumento no tempo de processamento, já que há necessidade de um maior refinamento nos parâmetros que serão utilizados. Nas situações de \"calmaria\"o perfil da atmosfera se mostra mais simplificado, o que facilita a escolha de qual método utilizar, sendo que com exceção da Variância, todos os outros métodos forneceram resultados satisfatórios. Para o caso de \"presença de subcamadas de aerossóis e/ou nuvens\"a qualidade dos resultados apresentados pelos métodos decai sendo exceção da Variânci, uma vez que esta passa a apresentar resultados mais próximos do esperado devido ao aumento na complexidade do sinal lidar. Na situação caracterizada como \"turbulência\", todos os métodos passam a apresentar maiores dificuldades para detectar corretamente a CLP, sendo que o WCT se mostra o mais robusto, porém exige uma complexa escolha de parâmetros, demandando um alto tempo de processamento. Na medida de 12 horas contínuas todos os métodos conseguem representar satisfatoriamente a ascensão e o decaimento da CLP, ficando as maiores divergências para o meio do dia, principalmente quando há dispersão dos aerossóis gerando atenuação no sinal, com isso os métodos mais sensíveis (MG e Método das Imagens) passam a apresentar várias oscilações, dificultando a detecção do topo da CLP. As análises realizadas permitiram observar as vantagens e desvantagens de cada método, assim como descobrir qual possui o uso mais indicado para cada cenário meteorológico, sendo o algoritmo WCT o mais robusto em todas as situações apresentadas. / This dissertation discusses a study about mathematical algorithms (Variance Method, Method of Images, Gradient Method, WCT - Wavelet Covariance Transform) that allow obtaining the maximum height of the Planetary Boundary Layer (PBL) from data provided by the lidar system. Initially it will be described the PBL and their main variables, as well as methods along with their strengths and weaknesses. After, two situations of measurements will be discussed: the first one consists of a case study conducted in the city of Vitória-ES, where were chosen three typical situations (\"calm\", \"sublayers of aerosols and/or layers of cloud cover\"and \"turbulence\") and the methods were compared among themselves and here after validated qualitatively by a visual verify and quantitatively by obtain of the Bulk Richardson Number (BRN) extracted from radiosounding data; the second situation deals with a measurement made in the city of São Paulo - SP for a period of 12 continuous hours, and the great advantage of this experimen, launching radiosondes within 3 hour intervals, the use of this combined with WRF ( Weather Research Forecasting) model allowed a most accurate comparison and validation. Based on case studies it was observed with the increased of complexity of the profile presented by the atmosphere, there is a decrease in the quality of the results provided by the methods and an increase in processing time being necessary greater refinement of the parameters that are used. In situations of \"calm\"the profile of the atmosphere appears more simplified, which facilitates the choice of which method to use, and with exception of Variance, all other methods provided satisfactory results. For the situation of \"presence of sublayers of aerosols and/or clouds\"the quality of the results presented by the methods decays, with the exception of Variance, once this begins to show results closer than expected due to the increase in the complexity of the signal handling. In situations characterized as \"turbulence\", all methods have more difficulties to correctly detect the PBL, and the WCT shown the most robust than others, but requires a complex choice of parameters and a high processing time. The measurement of 12 hours continuous all methods can satisfactorily represent the rise and decay of PBL, the largest differences being for the middle of the day, especially when there is dispersion of aerosol generating attenuation in the signal, thus the most sensitive methods (Gradient Method and Method of Images) present several variations, making it difficult to detect the top of the PBL. The analyzes allowed to observe the advantages and disadvantages of each method, as well as find out which has the most appropriate use for each meteorological scenario, being the WCT the most robust algorithm in all situations presented.

No description available.

In this thesis, we investigate flow past an array of micro-electro-mechanical-type (MEMS-type) heating elements placed on a flat surface, where MEMS devices have hump-shaped surfaces, using the triple deck theory. In this work we start by investigating the problem with a single heating element. MEMS devices can be used to control the fluid dynamics over the surface. Hence, we present a review of the boundary layer and the triple deck theories, followed by a literature review of the problem of flow past an array of MEMS devices. Next, we formulate our problem with the aid of the method of matched expansions for supersonic and subsonic flows. Thirdly, we solve analytically the linear version of the problem for supersonic flows. Thereafter, the non-linear problem is solved numerically where a detailed description of a hybrid method to solve the formulated non-linear problem for supersonic flow is exhibited. Fourthly, for subsonic flows we continue investigating flow past a heating element placed on a flat surface. Linear analysis of this problem is conducted. A novel numerical method to solve the non-linear problem for subsonic flows is described. The results are then discussed. In a similar context, we formulate a problem which can be considered as an the extension of previous subsonic flow problem to the three dimensional case. Analytical results are obtained using the Fourier transform where the linear approximation of the problem is considered and numerical results are then obtained using the Fast Fourier Transform. Finally, we consider a case of transonic flow past a heating element placed on a flat surface, where MEMS device has a hump-shaped surface. This transonic flow problem is non-linear in the upper deck and the lower deck equations where they should be solved simultaneously. Hence, a numerical method is required where we will use a finite difference method in stream-wise direction and Chebyshev collocation method in the wall normal direction. The results are then analysed. In conclusion, the use of localised heating elements in boundary layers for flow types considered in the thesis can contribute to the possibility of favourably controlling the fluid flow perturbations.

Le modèle RANS à une équation de fermeture est utilisée avec une nouvelle longueur de mélange. par interpolation, notre loi est universelle. Nous avons étendue ce résultat pour considérer les fonds rugueux. L'existence d'une solution au système d'équation associée est montrée, c'est un problème elliptique avec un terme source dans L¹. Nous utilisons le modèle "under location uncertainty" pour obtenir un profil de vitesse cohérent dans toute la couche limite turbulente. Le raisonnement que nous apportons ici lie un terme sous-grille à ce profile. Nous apportons également une estimation des variances à temps courts dans la zone visqueuse. / The RANS one-closure equation is tested with a new formulation of the turbulent mixing length. By interpolation, the law is universal. It also take account of any roughness of the ground. The existence of solution of the RANS model is also proven and bring a new proof of elliptic problem with source term in L¹. We use the model under location uncertainty to derive a velocity profile in the whole boundary layer. An expression of the small-scale velocity component is also provided in the viscous zone.

Ye Mao. / "May 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 116-123). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Temperature inversions in the boundary layer over Prague Abstract The main objective of this study is to analyze temperature inversions in the atmospheric boundary layer (ABL) over Prague. In the first part, the concept of the ABL is defined and main theoretical aspects of air stratification are explored. The main part of the background research summarizes current knowledge of temperature inversions, especially how the landscape pattern influences their development and parameters under different synoptic situations, and methods used for their detection, measurement and evaluation. Considering the theme of the thesis, main geographic factors influencing temperature inversions in the area of Prague are also defined. The focus of actions is placed on inversions analysis based upon time series of Praha-Libuš rawinsonde station. Homogeneity of used data is tested and all inversions within the 2000- meters-thick-layer close to the ground are derived. Diurnal, annual and interannual frequency variations are described. Significance of long-term trends is tested and trends are compared to data from Prostějov and Kümmersbruck stations. Keywords: temperature inversions, boundary layer, climate, Prague

The Planetary Boundary Layer (PBL) is a relevant part of the atmosphere with a variable extension that clearly plays an important role in fields like air quality or weather forecasting. Passive and active remote sensing systems have been widely applied to analyze PBL characteristics. The combination of different remote sensing techniques allows obtaining a complete picture on the PBL dynamic. In this study, we analyze the PBL behavior using four types of remote sensing systems: Microwave Radiometer (MWR), Elastic Lidar (EL), Doppler Lidar (DL) and Ceilometer data. The measurements were performed in two cities Granada (Spain) and São Paulo (Brazil). Firstly, at Granada, the PBL height (PBLH) obtained from MWR data is validated against PBLH provided by analyzing co-located radiosondes, showing a good agreement. In a second stage, active remote sensing systems were used for deriving the PBLH. Thus, Extended Kalman filter is applied to EL data while the vertical wind speed variance method was applied to the DL. The derived PBLH\'s by these approaches are compared to PBLH retrieved by the MWR. The results show a good agreement among the retrievals based on active remote sensing in most of the cases, although some discrepancies appear in instances of intense PBL changes (either growth and/or decrease). Then it is performed the analysis of four and five-year dataset of measurements gathered with a ceilometer and a microwave radiometer, respectively, at Granada. The methodologies applied for the PBLH detection (gradient method for ceilometer and the combination of parcel method and temperature gradient method for microwave radiometer) provided a satisfactory description of the PBL structure in simple cases. In addition, the PBL behavior is characterized by a statistical study of the convective and stable PBLH obtained from microwave radiometer measurements. The analysis of the PBLH statistical study shows some coincidence with other PBLH studies such as daily pattern, and year cycles but also some differences caused by distinct latitudes, topography and climate were found. It was performed as well a combined long-term analysis of Ceilometer retrieved Residual Layer and the Stable and Convective Layer heights determined by microwave radiometer, thus offering a complete picture of the PBL evolution by synergetic combination of remote sensing techniques. This is the reason why systems with high temporal and spatial resolution, like lidars, have been increasingly applied in studies about this atmospheric region. In this work, also was performed, at São Paulo, an analysis on lidar backscattered signal at three wavelengths (355, 532 and 1064 nm) retrieving the turbulence by the analyses of the high-order moments (variance, skewness and kurtosis) in the backscattered signal. The wavelength of 355 nm has low applicability in the proposed methodology, due to its low intensity (due to predominance of molecular backscattering) and large presence of noise, while the 532 nm wavelength showed results similar to those provided by the wavelength of 1064 nm, which was used as reference. Then, it was analyzed two case studies using the wavelengths of 532 and 1064 nm (in separately). This approach provided information about PBL height, (derived by the variance method (Menut et al., 1999), displacement of aerosol layers (skewness) and level of mixing at several heights (kurtosis). These results show the viability of the proposed methodology when the wavelengths of 532 and 1064 nm are used for the PBL description by high-order moments of the backscattered distribution. Furthermore, it is demonstrated how some variables (air temperature, aerosol concentration, vertical wind, relative humidity and net radiation) can influence the PBL dynamic with data from DL, EL and MWR at Granada. The high-order moments of the vertical velocity high frequency distributions derived from DL, and EL range corrected signal, were corrected by two methodologies (first lag and -2/3 correction). The corrected profiles present small differences when compare against the uncorrected profiles, showing low influence of noise and the viability of the proposed methodology. A detailed 2-case studies analysis was carried on, the first case corresponding to a well-defined PBL while the second one corresponds to a situation with presence of an aloft Saharan dust layer and clouds. In both cases the results provided by the different instruments ended up complementing one another, so that the synergistic use of the different systems allowed us a detailed monitoring of the PBL. / A Camada Limite Planetária (PBL - Planetary Boundary Layer) é uma parte relevante da atmosfera com uma extensão variável e que claramente desempenha um papel importante em áreas de estudo, como: a qualidade do ar ou a previsão do tempo. Sistemas de sensoriamento remoto passivo e ativo têm sido amplamente utilizado para analisar as características da PBL. A combinação de diferentes técnicas de sensoriamento remoto permite obter uma imagem completa da dinâmica desta camada. Neste estudo, analisamos o comportamento da PBL utilizando quatro tipos de sistemas de sensoriamento remoto: Radiômetro de Micro-ondas (MWR), Lidar Elástico (EL), Lidar Doppler (DL) e Ceilômetro. As medições foram realizadas em duas cidades, Granada (Espanha) e São Paulo (Brasil). Primeiramente, em Granada, a altura da PBL (PBLH) obtida a partir dos dados do MWR foi validada pela PBLH gerada pela análise dos dados de radiossondas, mostrando uma boa concordância. Em um segundo estágio, sistemas ativos de sensoriamento remoto foram usados para a obtenção da PBLH. Assim, o método do filtro de Kalman foi aplicado aos dados do EL enquanto o método da variância da velocidade vertical do vento foi aplicado aos dados do DL. As PBLH derivadas dessas abordagens foram comparadas com o PBLH fornecida pelo MWR, sendo que os resultados mostram uma boa concordância na maioria dos casos, embora algumas discrepâncias apareçam nas situações de mudanças intensas da PBL (crescimento e/ou diminuição). Em seguida, é realizada a análise dos dados das medidas coletadas com um ceilômetro e um radiômetro de micro-ondas durante quatro e cinco anos, respectivamente, em Granada. As metodologias aplicadas para a detecção da PBLH (método de gradiente para o ceilômetro e a combinação do método de parcela e do método de gradiente de temperatura para o radiômetro de micro-ondas) forneceram uma descrição satisfatória da estrutura da PBL em casos simples. Além disso, o comportamento da PBL foi caracterizado por um estudo estatístico das PBLH convectiva e estável, as quais foram obtidas a partir das medidas do radiômetro de micro-ondas. A análise do estudo estatístico realizado para a PBLH mostra algumas coincidências com outros estudos já realizados para a mesma variável, como o padrão diário e os ciclos anuais. Mas também há algumas diferenças, as quais são causadas por latitudes, topografia e clima distintos. Foi realizada também uma análise combinada de longo prazo da Camada Residual (gerada pelos dados do Ceilômetro) e da Camada Estável e Convectiva (obtida pelos dados do radiômetro de micro-ondas), oferecendo assim um quadro completo da evolução da PBL por combinação sinérgica de técnicas de sensoriamento remoto. Essa é a razão pela qual sistemas com alta resolução temporal e espacial, como os lidars, têm sido cada vez mais aplicados em estudos sobre essa região atmosférica. Neste trabalho, também foi realizada, em São Paulo, uma análise do sinal retroespalhado em três comprimentos de onda (355, 532 e 1064 nm), o qual provê informações da turbulência através da análise dos momentos de alta ordem (variância, assimetria e curtose). O comprimento de onda de 355 nm apresenta pouca aplicabilidade na metodologia proposta, devido à sua baixa intensidade (por conta da predominância do retroespalhamento molecular) e grande presença de ruído, enquanto o comprimento de onda de 532 nm apresentou resultados semelhantes aos fornecidos pelo comprimento de onda de 1064 nm, o qual foi usado como referência. Em seguida, foram analisados dois estudos de caso utilizando os comprimentos de onda de 532 e 1064 nm (em separado). Essa abordagem forneceu informações sobre a altura da PBL (derivada pelo método de variância (Menut et al., 1999), deslocamento de camadas de aerossol (assimetria) e nível de mistura em várias alturas (curtose), mostrando a viabilidade da metodologia proposta, quando os comprimentos de onda de 532 e 1064 nm são usados para a descrição da PBL a partir dos momentos de alta ordem. Além disso, demonstrou-se, com dados de DL, EL e MWR obtidos em Granada, como algumas variáveis (temperatura do ar, concentração de aerossóis, vento vertical, umidade relativa e radiação líquida) podem influenciar a dinâmica da PBL. Os momentos de alta ordem das distribuições de velocidade vertical derivadas dos dados do DL e o sinal retroespalhado obtido a partir do EL foram corrigidos por duas metodologias (first lag e correção de -2/3). Os perfis corrigidos apresentam pequenas diferenças quando comparados com os perfis não corrigidos, mostrando baixa influência do ruído e a viabilidade da metodologia proposta. Foi realizada uma análise detalhada de dois estudos de casos, o primeiro correspondendo a uma PBL bem definida, enquanto o segundo corresponde a uma situação com a presença de uma camada de nuvens e poeira saariana. Em ambos os casos, os resultados fornecidos pelos diferentes instrumentos acabaram se complementando, de modo que o uso sinérgico dos diferentes sistemas nos permitiu um monitoramento detalhado da PBL.

Submitted by Cátia Araújo (catia.araujo@unipampa.edu.br) on 2017-01-25T12:23:34Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Influência do aquecimento global antropogênico sobre a temperatura noturna uma abordagem teórica.pdf: 6400608 bytes, checksum: 28665efa34a8803c77a056a46625bec3 (MD5) / Approved for entry into archive by Cátia Araújo (catia.araujo@unipampa.edu.br) on 2017-01-25T12:24:05Z (GMT) No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Influência do aquecimento global antropogênico sobre a temperatura noturna uma abordagem teórica.pdf: 6400608 bytes, checksum: 28665efa34a8803c77a056a46625bec3 (MD5) / Made available in DSpace on 2017-01-25T12:24:06Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Influência do aquecimento global antropogênico sobre a temperatura noturna uma abordagem teórica.pdf: 6400608 bytes, checksum: 28665efa34a8803c77a056a46625bec3 (MD5) Previous issue date: 2013-12-05 / Neste trabalho é analisada a variação da temperatura atmosférica próximo à superfície associada a efeitos antropogênicos, utilizando um modelo atmosférico simplificado. São utilizadas nas análises, alterações locais na cobertura de nuvens e quatro diferentes cenários de concentração atmosférica de dióxido de carbono. Os resultados mostram que as maiores variabilidades de temperatura ocorrem no estado desconectado e na região de transição entre os regimes de escoamento. Em concordância com esforços anteriores, os resultados indicam que grande parte da redução da variação diurna de temperatura (VDT) está relacionada com a bi-estabilidade atmosférica, característica da camada limite estável. Todavia, no regime desconectado, a presença de eventos intermitentes de turbulência pode tornar as variações de temperatura entre os diferentes cenários imprevisíveis. O que pode implicar que seja pouco provável que se consiga prever o comportamento da VDT em regiões caracterizadas pela presença de ventos fracos. / In this work it is analyzed the variation of the atmospheric temperature near the surface associated with anthropogenic effects, by using a simplified atmospheric model. In the analyzes are used local changes in cloud cover and four different scenarios of atmospheric concentration of carbon dioxide. The results show that the highest variability in temperature occur in the disconnected state and in the transition region between the flow regimes. In agreement with previous efforts, the results indicate that the reduction of diurnal temperature range (DTR) is related to the atmospheric bi-stability, which is a characteristic of the stable boundary layer. However, in the disconnected state, the presence of intermittent burts of turbulence may make temperature variations between the different scenarios unpredictable. Which may imply that it should be hard to predict the behavior of the VDT in regions characterized by the presence of weak winds.

An instrumented unmanned aerial vehicle (UAV) was developed and employed to observe the full range of turbulent motions that exist within the inertial subrange of atmospheric surface layer turbulence. The UAV was host to a suite of pressure, temperature, humidity, and wind sensors which provide the necessary data to calculate the variety of turbulent statistics that characterize the flow. Flight experiments were performed with this aircraft, consisting of a large square pattern at an altitude of 100 m above ground level. In order to capture the largest turbulent scales it was necessary to maximize the size of the square pattern. The smallest turbulent scales, on the other hand, were measured through the use of a fast response constant temperature hot wire anemometer. The results demonstrates that the UAV system is capable of directly measuring the full inertial subrange of the atmospheric surface layer with high resolution and allowing for the turbulence dissipation rate to be calculated directly.