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Simulação numérica 3D da interação correntes de densidade e de estruturas verticais
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| 11.12 MB | Adobe PDF |
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Resumo(s)
As correntes de densidade são um fenómeno frequente na natureza. Existem diversos
fatores que podem influenciar as condições em que um fluido se encontra, bem como a
forma como este se mistura e interage com outros fluídos. Estes factores estão, muitas
vezes, diretamente relacionados com mudanças de temperatura, deposição de sedimentos
e dissolução dos mesmos, bem como libertação de resíduos provenientes da atividade humana.
Tais fenómenos físicos podem ser prejudiciais ao meio ambiente por funcionarem
como transportadores de poluição, uma vez que a sua mecânica tem como base pequenas
diferenças de massa volúmica de dois ou mais fluídos e estas podem gerar forças de
impulsão, contribuindo desse modo para a movimentação dos mesmos.
Esta dissertação tem como objetivo estudar o comportamento da corrente quando a
diferença de massa volúmica entre os fluídos varia, assim como a influência da vegetação
no escoamento. Tais análises são efectuadas utilizando um conjunto de softwares de
simulação numérica tais como Matlab, Paraview e OpenFOAM. Este estudo está dividido
em tarefas específicas como, análises a) da estrutura da corrente, b) da posição da frente
da corrente, c) da velocidade da frente da corrente, d) do perfil de concentrações, e e) da
altura média da corrente. No âmbito de realizar um estudo o mais competente possível,
foi necessária uma validação rigorosa do modelo numérico.
Inicialmente, procedeu-se ao refinamento adequado da malha da corrente e ao teste
de dois modelos numéricos diferentes: o modelo RANS e o modelo LES. Estes ajudaram
na comparação de parâmetros como a posição da frente, o desenvolvimento da corrente
e a capacidade de cálculo da turbulência para pequenas escalas da malha em cada um
dos modelos. O modelo LES , que mostrou o melhor desempenho foi utilizado para simular
duas condições em 2D com a finalidade de validar os dados experimentais: com e
sem superfície livre. Nestas simulações analisaram-se os parâmetros descritos nas tarefas
específicas, variando a aceleração reduzida da corrente. Por fim, procedeu-se às simulações
em 3-D com a influência de um elemento de vegetação e variando a aceleração
reduzida, comparando assim a estrutura da corrente com os resultados experimentais,
para as condições de com e sem cilindro. Os resultados obtidos nas simulações 3D foram
pós-processados com o âmbito de comparar parâmetros como a velocidade e posição da
frente, os perfís de concentração ao longo da corrente, por variação da altura media da corrente, bem como a influência que o cilindro exerce nesses parâmetros.
Gravity currents are a fairly common phenomenon in nature. There are several factors that can influence the state of a fluid, as well as the way it mixes and interacts with other fluids. Such factors are often related to temperature changes, deposition of sediments and dissolution, as well as to the release of waste from human activity. These physical phenomena may damage the environment by acting as carriers of pollution since their mechanics is based on movement caused by small differences in the density of two or more fluids. Subsequently, these differences can generate driving forces which intensify the fluids flow. The aim of this dissertation is to study the behavior of the current when the density difference between the fluids varies, as well as the influence of vegetation on the flow. This is accomplished by means of numerical simulation using tools such as Matlab, Paraview and OpenFOAM. This study is comprised of specific tasks such as analyses of a) the structure of the current, b) the position of the current front, c) the velocity of the current front, d) the concentration profiles, and e) the height of the current front. A rigorous validation of the numerical model was done with the goal of performing a successful study. Initially, a mesh refinement was performed for the current and two different numerical models were tested, the RANS model and the LES model. These enabled to compare parameters such as the position of the front, the current development and each model’s ability to calculate the turbulence at small mesh scales. The LES model (the best performing one) was used to simulate two different conditions in 2-D, with and without a free surface, in order to compare which condition better represented and validated the experimental data. The parameters described above for the specific tasks were analyzed in these simulations for varying densities of the current. Finally, simulations were performed in 3-D including the effects of a vegetation element and the variation of the reduced acceleration to compare the structure of the current against the experimental results obtained for the conditions with and without a cylinder. These simulation results were post-processed in order to compare parameters such as the speed and position of the front, the concentration profiles along the current, the variation of the average height of the current, as well as the influence that the cylinder have on these parameters
Gravity currents are a fairly common phenomenon in nature. There are several factors that can influence the state of a fluid, as well as the way it mixes and interacts with other fluids. Such factors are often related to temperature changes, deposition of sediments and dissolution, as well as to the release of waste from human activity. These physical phenomena may damage the environment by acting as carriers of pollution since their mechanics is based on movement caused by small differences in the density of two or more fluids. Subsequently, these differences can generate driving forces which intensify the fluids flow. The aim of this dissertation is to study the behavior of the current when the density difference between the fluids varies, as well as the influence of vegetation on the flow. This is accomplished by means of numerical simulation using tools such as Matlab, Paraview and OpenFOAM. This study is comprised of specific tasks such as analyses of a) the structure of the current, b) the position of the current front, c) the velocity of the current front, d) the concentration profiles, and e) the height of the current front. A rigorous validation of the numerical model was done with the goal of performing a successful study. Initially, a mesh refinement was performed for the current and two different numerical models were tested, the RANS model and the LES model. These enabled to compare parameters such as the position of the front, the current development and each model’s ability to calculate the turbulence at small mesh scales. The LES model (the best performing one) was used to simulate two different conditions in 2-D, with and without a free surface, in order to compare which condition better represented and validated the experimental data. The parameters described above for the specific tasks were analyzed in these simulations for varying densities of the current. Finally, simulations were performed in 3-D including the effects of a vegetation element and the variation of the reduced acceleration to compare the structure of the current against the experimental results obtained for the conditions with and without a cylinder. These simulation results were post-processed in order to compare parameters such as the speed and position of the front, the concentration profiles along the current, the variation of the average height of the current, as well as the influence that the cylinder have on these parameters
Descrição
Palavras-chave
modelo LES modelo RANS modelação numérica correntes de densidade vegetação