Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The purpose of this work is to study and characterize aerodynamically a free jet operating at subsonic regime and identify its acoustic signature. This study aims to analyze fundamentally the turbulent structures and the total noise produced at different Mach numbers. This kind of research is crucial to the understanding of these mechanisms of noise generation and propagation, and it is extremely important for aeronautical applications, for instance, the jet engine exhaust. The research is done by analysing the data obtained in experiments using pitot tube, hot-wire anemometer and acoustic measurements. This work also describes the experimental procedures for each step of analysis, as well as the characteristics of jet noise facilities. The data from measurements with a pitot tube was used to study the mean velocity profiles. The average properties are also analyzed with an anemometry system, likewise used to study the turbulent intensity at eleven axial lines, ranging from the centerline to the edge of the nozzle (lipline). These results are compared with literature and has verified the accuracy of hot-wire anemometers for turbulent intensities lower than 15%. The aerodynamic data are obtained for Mach numbers 0.25, 0.50 and 0.75, from the nozzle exit to thirteen diameters in the direction of the jet. The acoustic study is carried out by analyzing the sound pressure level obtained at six positions in the far field, with observer angles ranging from 40 to 110º. In this campaign more velocities are studied with Mach numbers from 0.18 to 1.00 with step of 0.05 are described. A database with the sound pressure level as a function of frequency is constructed from this information. / O objetivo deste trabalho é estudar e caracterizar aerodinamicamente um jato livre operando em regime subsônico e identificar a assinatura acústica do mesmo. Esse estudo busca analisar fundamentalmente as estruturas turbulentas e o ruído total produzido em diferentes números de Mach. Tal estudo é crucial para o entendimento desses mecanismos de geração e propagação, e encontra extrema importância para aplicações aeronáuticas, como, por exemplo, a exaustão de motores a reação (jato). A investigação é feita através da análise dos dados obtidos em experimentos utilizando tubo de pitot, anemômetro de fio-quente e ensaios acústicos. Neste trabalho também são descritos os procedimentos experimentais de cada etapa de análise, bem como as características dos laboratórios utilizados para o estudo do ruído de jato. Com os dados provenientes das medições com tubo de pitot são estudados os perfis de velocidade média. As propriedades médias também são analisadas com o sistema de anemometria, que ainda é utilizado para estudo da intensidade turbulenta em onze linhas axiais, variando da linha de centro até a borda do bocal (lipline). Estes resultados são comparados com a literatura e é constatada a acurácia dos anemômetros de fio-quente para intensidades turbulentas menores que 15%. Os dados aerodinâmicos mencionados são obtidos para números de Mach 0,25, 0,50 e 0,75, a partir da saída do bocal até treze diâmetros na direção do jato. O estudo acústico é feito através da análise do nível de pressão sonora obtido em seis posições no campo distante, com ângulos de observação variando de 40 a 110º. Diferentes velocidades também foram analisadas, desta vez, com números de Mach de 0.18 a 1.00 com passo de 0.05. Um banco de dados com o nível de pressão sonora em função da frequência é construído a partir destas informações. / Mestre em Engenharia Mecânica

Foram feitas simulações de um jato plano livre e incompressível usando o modelo de uma equação Spalart-Allmaras padrão e um modelo Spalart-Allmaras modificado através da alteração da escala de comprimento turbulenta. Sabe-se da literatura que no caso de jatos livres o modelo Spalart-Allmaras não consegue predizer adequadamente os resultados observados experimentalmente. Os resultados das simulações foram comparados com experimentos da literatura através de perfis de velocidade e da taxa de expansão do jato. Como esperado, os resultados obtidos das simulações utilizando o modelo Spalart-Allmaras padrão foram considerados insatisfatórios, porém o modelo Spalart-Allmaras modificado teve uma melhor concordância com os resultados experimentais. Além disso, o modelo Spalart-Allmaras modificado foi usado para simular os casos do escoamento sobre uma placa plana sem gradiente de pressão e o escoamento em um degrau com separação e gradiente adverso de pressão. Quando comparados com resultados experimentais da literatura e com resultados obtidos usando o modelo padrão, os resultados do modelo modificado obtidos para ambos os casos foram muito satisfatórios, concluindo-se que a modificação da escala de comprimento permite obter uma maior generalidade para o modelo Spalart-Allmaras. / Simulations of a plane and incompressible free jet using the standard Spalart-Allmaras model and a Spalart-Allmaras model modified by changing the turbulent length scale were carried out. It is known from literature that, in the case of the free jet, the Spalart-Allmaras model fails to adequately predict the experimentally observed results. The results of our simulations were compared with published experiments using the velocity profiles and the jet spreading rate. As expected, the results of simulations using the standard Spalart-Allmaras model were considered unsatisfactory while the modified Spalart-Allmaras model had a better agreement with the experimental results. Furthermore, the modified Spalart-Allmaras model was used to simulate the cases of flow over a flat plate with no pressure gradient and flow through a backward facing step with separation and adverse pressure gradient. When compared with experimental results from the literature and with results obtained using the standard model, the results of the modified model for both cases were very satisfactory, allowing the conclusion that the change in the length scale provided a greater generality for the Spalart-Allmaras model.

Tato diplomová práce je zaměřena na porovnání různých turbulentních a chemických modelů na příkladu volné metanové trysky ústící do vzduchu. Nejprve je uveden teoretický úvod k modelům, následován CFD (Ansys Fluent) simulacemi plamene pomocí vybraných modelů. Jako součást práce je provedeno a vyhodnoceno experimentální měření. V závěru jsou experimentální výsledky porovnány s nasimulovanými daty.

This diploma thesis is focused on determination of plan situating influence of weir discharging capacity. The part of this work is a summary of the information about weirs, principally about determination of discharging capacity on normal weirs, plan deflected and plan radius weirs. Executed model research, which deals with determination of plan situating influence on discharging capacity plan deflected and plan radius weirs in comparison to normal weir, is evaluated in another part of this work. The research is also dealing with influence of aeration of the space under down surface of free jet and influence of downstream water level on discharging capacity. This work compares the results of executed research with available knowledge of other authors, who have dealt with determination of discharging capacity on weirs with different plan situating.

Ce travail traite de l’atomisation des structures ligamentaires. Cette étude est focalisée sur les ligaments produits par des jets libres de solutions viscoélastiques diluées. La description multi-échelles est utilisée pour étudier les dynamiques d’amincissement de ces ligaments. La description multi-échelles d’un système liquide est initialement présentée : elle décrit le système à travers sa distribution d’échelles. Cette description est appliquée à des ensembles théoriques ainsi qu’à des systèmes modélisant les ligaments étudiés, améliorant la compréhension de cet outil de description. De nouvelles méthodes sont utilisées pour mesurer les distributions d’échelles : méthode de segmentation d’images sub-pixels et méthode de Monte-Carlo. Leur combinaison apporte une amélioration notable aux petites échelles et permettent une mesure des distributions d’échelles 3D. Ce résultat incite à revisiter les études antérieures où la description multi-échelles a été utilisée. A notre connaissance, c’est la première fois qu’une étude sur les jets libres de solutions viscoélastiques diluées est réalisée de manière statistique. L’influence de trois paramètres est étudiée : la concentration en polymère de la solution, les dimensions de la buse d’injection et le débit d’injection. Basé sur les résultats donnés par la description multi-échelles, un protocole d’identification des régimes d’amincissement des ligaments est présenté. Les caractéristiques de ces régimes sont mesurées, en particulier le temps de relaxation de la solution. Les temps mesurés sont compris entre 24 μs et 6,3 ms, ce qui est en accord avec les temps de relaxation mesurés dans la littérature pour les jets. L’approche multi-échelles confirme ici sa pertinence pour l’étude des processus d’atomisation. Les temps de relaxation mesurés présentent une forte corrélation vis-à-vis du taux de déformation subit par la solution durant l’injection. Ce résultat indique que la solution a subi une dégradation mécanique. Il convient de tenir compte de l’étape d’injection lorsque l’on souhaite atomiser de telles solutions viscoélastiques diluées. / This work concern the atomization of ligament structures. This study focuses on ligaments produced by free jets of dilute viscoelastic solutions. The multi-scale description is used to study the thinning dynamics of these ligaments. The multi-scale description of a liquid system is initially presented: it describes the system through its scale distribution. This description is applied to theoretical systems as well as to systems modelling the ligaments studied, improving the understanding of this description tool. New methods are used to measure the scale distributions: sub-pixel image segmentation method and Monte-Carlo method. Their combination provides a significant improvement at small scales and allows a measurement of 3D scale distributions. This result prompts us to revisit previous studies where the multi-scale description was used. To our knowledge, this is the first time that a study on free jets of dilute viscoelastic solutions has been carried out statistically. The influence of three parameters is studied: the polymer concentration of the solution, the dimensions of the injection nozzle and the injection flow rate. Based on the results of the multi-scale description, a protocol for identifying ligament thinning regimes is presented. The characteristics of these regimes are measured, in particular the relaxation time of the solution. The measured times are between 24 μs and 6.3 ms, which is in accordance with the relaxation times measured in the literature for jets. The multi-scale approach here confirms its relevance for the study of atomization processes. The measured relaxation times show a strong correlation with the deformation rate of the solution during injection. This result indicates that the solution has undergone mechanical degradation. The injection step should be taken into account when atomizing such dilute viscoelastic solutions.