No description available.

No description available.

No description available.

Le travail réalisé au cours de cette thèse, suite à l’initiative de Turbomeca, est une contribution à l’étude du bruit à large bande à l’échappement d’un turbomoteur d’hélicoptère, portant plus précisément sur la gamme de fréquences qui s’étend sur la gamme de fréquences qui s’étend de 100 à 5000 Hz. Contrairement au bruit à l’échappement des turboréacteurs d’avion sur lesquels le bruit de jet prédomine, ici ce dernier est négligeable en raison de la faible vitesse d’échappement des gaz. L’analyse des données disponibles à Turbomeca et une étude bibliographique approfondie ont permis de préciser la signature fréquentielle du bruit à large bande à l’échappement avec notamment trois contributions distinctes :- Le bruit de combustion direct généré au niveau de la chambre par la flamme (100-400 Hz)- Le bruit de la combustion indirect généré par la turbine haute-pression (500-800 Hz)- Le bruit de combustion indirect généré par la turbine libre (1-3 Hz)Le bruit de combustion indirect est issu de la déformation des perturbations tourbillonnaires et entropiques issues de la combustion lors de leur passage dans les turbines. Ce travail de thèse porte plus précisément sur ce mécanisme. Notamment, des essais sur une turbine industrielle ont été réalisés afin de mettre sa présence en évidence. En parallèle, un modèle analytique de type « disque d’action » (c’est-à-dire dans lequel la turbine est assimilée à une surface de discontinuité) a été développé. Ceci est justifié par le fait que les longueurs d’ondes (acoustique et aérodynamique) sont grandes devant les dimensions des aubes, notamment la corde axiale. On néglige ainsi la géométrie fine des aubes. Seule est prise en compte leur influence sur l’écoulement qui se traduit uniquement par l’accélération et/ou la déviation de ce dernier, et le changement des propriétés thermodynamiques correspondant. La difficulté de la modélisation réside dans l’écriture des relations de saut entre les grandeurs de l’écoulement en amont et en aval de la grille d’aubes. / This thesis work, carried out at the initiative of Turbomeca, focuses on the study of the turboshaft broadband exhaust noise. It aimed more specifically at the frequency range between 100 and 5000 Hz. Unlike turbojet exhaust noise, on which jet noise is the main contribution, jet noise is the main contribution, jet noise is negligible in our case due to low speed of gas ejection. Turbomeca database analysis and extensive literature review helped to clarify the broadband exhaust noise signature, including three distinct contributions :- Direct combustion noise generated by the flame (100-400 Hz)- Indirect combustion noise generated by the high pressure turbine (500-800 Hz)- Indirect combustion noise generated the power turbine (1-3kHz)The indirect combustion noise generation mechanism is the deformation of vorticity and entropy combustion perturbations in turbine stages. This work aimed specifically at the understanding and modelling of this mechanism. In particular, tests were performed on an industrial turbine in order to demonstrate its presence. In parallel, we developed an “action disc” analytical model (in which the turbine is considered as a discontinuity surface). Indeed, acoustic and aerodynamic wavelengths are large compared to the blades dimensions and the axial cord, so the fine geometry of blades is negligible. The blade influence of the flow leads exclusively to flow acceleration or deviation, along with its thermodynamic property changes. The main difficulty of this modelling is the writing of jump relations between upstream and downstream flow parameters.

A maior parte do ruído de aeronaves é advinda dos motores. Como houve grande avanço no controle do ruído tonal, atualmente grande parte do esforço se dá para redução do ruído de banda larga, que é menos compreendido. O ruído de banda larga é gerado pela interação entre um escoamento turbulento e uma superfície, como por exemplo, a turbulência ingerida interagindo com o rotor, o escoamento na ponta das pás, entre outros. Apesar das diversas fontes citadas, sabe-se que a principal fonte de ruído de banda larga em tal tipo de motor é a interação da esteira turbulenta do rotor com as aletas da estatora. Assim, o presente estudo manterá seu enfoque apenas em tal causa. O objetivo deste então é o desenvolvimento de um modelo capaz de previsão do ruído de banda larga pela interação da esteira turbulenta causada pelo rotor, interagindo com as aletas da estatora, bem como o entendimento da propagação do ruído em duto. A primeira abordagem em relação a tal tipo de ruído é através da previsão do ruído gerado. Para previsão de ruído podem ser utilizados métodos analíticos, numéricos, ou empíricos, cada qual com suas vantagens e penalizações. Para tal, foi utilizado um método semi-analítico, em tais métodos utiliza-se simulação numérica para previsão da característica da turbulência e uma teoria analítica para a geração e propagação do ruído no duto. A principal motivação para o método semi-analítico é sua vantagem em relação aos métodos numéricos que demandam custo computacional extremamente alto e vantagem em relação a métodos analíticos que necessitariam uma demasiada simplificação geométrica. Dessa maneira, utilizou-se a geometria do ANCF, uma plataforma de ensaios desenvolvida pela NASA, onde havia geometria e resultados divulgados, tornando possível a verificação dos resultados obtidos. Os resultados mostram que as tendências capturadas são condizentes com o esperado, e então com um tempo relativamente baixo, de maneira prática, é possível a previsão do ruído de interação e sua propagação em dutos nos motores turbofans. / The major noise source in aircraft is the engine. Since tonal noise control is well developed, the current effort concentrates on broadband noise reduction, which is less understood. The broadband noise is generated when a turbulent flow interacts with a surface as, for example, rotor blade tip flow, boundary layer and the rotor interaction. Although there are different sources of broadband noise it is known that the major broadband source in turbofan engine is the rotor turbulent wake interacting with the stator vanes. This study is focused in that source of noise and the goal is to develop a model capable of predicting the rotor/stator interaction noise as well as in duct noise propagation. Noise prediction can be carried out by analytical, numerical or empirical methods, each one with advantages and disadvantages. In the present work the semi-analytical method was used. Turbulence characteristics were estimated by a numerical method and the noise generation and duct propagation was estimated by an analytical method. The biggest advantage comparing with the numerical methods is that this method is less time consuming. A purely analytical method would require excessive geometric simplification. The ANCF, a rig developed by NASA was used as basis for the simulations, since its geometry and noise data are available. The results show that the correct trends are consistently captured. So it is concluded that it is possible to predict the broadband noise and its propagation in turbofans engines with a practical and low cost method.

A maior parte do ruído de aeronaves é advinda dos motores. Como houve grande avanço no controle do ruído tonal, atualmente grande parte do esforço se dá para redução do ruído de banda larga, que é menos compreendido. O ruído de banda larga é gerado pela interação entre um escoamento turbulento e uma superfície, como por exemplo, a turbulência ingerida interagindo com o rotor, o escoamento na ponta das pás, entre outros. Apesar das diversas fontes citadas, sabe-se que a principal fonte de ruído de banda larga em tal tipo de motor é a interação da esteira turbulenta do rotor com as aletas da estatora. Assim, o presente estudo manterá seu enfoque apenas em tal causa. O objetivo deste então é o desenvolvimento de um modelo capaz de previsão do ruído de banda larga pela interação da esteira turbulenta causada pelo rotor, interagindo com as aletas da estatora, bem como o entendimento da propagação do ruído em duto. A primeira abordagem em relação a tal tipo de ruído é através da previsão do ruído gerado. Para previsão de ruído podem ser utilizados métodos analíticos, numéricos, ou empíricos, cada qual com suas vantagens e penalizações. Para tal, foi utilizado um método semi-analítico, em tais métodos utiliza-se simulação numérica para previsão da característica da turbulência e uma teoria analítica para a geração e propagação do ruído no duto. A principal motivação para o método semi-analítico é sua vantagem em relação aos métodos numéricos que demandam custo computacional extremamente alto e vantagem em relação a métodos analíticos que necessitariam uma demasiada simplificação geométrica. Dessa maneira, utilizou-se a geometria do ANCF, uma plataforma de ensaios desenvolvida pela NASA, onde havia geometria e resultados divulgados, tornando possível a verificação dos resultados obtidos. Os resultados mostram que as tendências capturadas são condizentes com o esperado, e então com um tempo relativamente baixo, de maneira prática, é possível a previsão do ruído de interação e sua propagação em dutos nos motores turbofans. / The major noise source in aircraft is the engine. Since tonal noise control is well developed, the current effort concentrates on broadband noise reduction, which is less understood. The broadband noise is generated when a turbulent flow interacts with a surface as, for example, rotor blade tip flow, boundary layer and the rotor interaction. Although there are different sources of broadband noise it is known that the major broadband source in turbofan engine is the rotor turbulent wake interacting with the stator vanes. This study is focused in that source of noise and the goal is to develop a model capable of predicting the rotor/stator interaction noise as well as in duct noise propagation. Noise prediction can be carried out by analytical, numerical or empirical methods, each one with advantages and disadvantages. In the present work the semi-analytical method was used. Turbulence characteristics were estimated by a numerical method and the noise generation and duct propagation was estimated by an analytical method. The biggest advantage comparing with the numerical methods is that this method is less time consuming. A purely analytical method would require excessive geometric simplification. The ANCF, a rig developed by NASA was used as basis for the simulations, since its geometry and noise data are available. The results show that the correct trends are consistently captured. So it is concluded that it is possible to predict the broadband noise and its propagation in turbofans engines with a practical and low cost method.

No description available.

This thesis presents the development and testing of distributed vibration absorber designs with specific application to heavy plates for the reduction of vibration and sound radiation. Two particular designs, already under investigation for use on thin panels or composite materials, were adapted to passively reduce broadband vibration and noise from large and heavy plates. These absorbers are referred to as Distributed Vibration Absorbers [DVAs] and Heterogeneous [HG] Blankets. Numerical models were developed, based on the theory of sound propagation through layered media and the vibration of plates, to simulate the performance of such absorbers for a variety of applications and media characteristics. The new absorber designs were then tested on a large, marine-type plate (4 feet by 2 feet by 1/4 inch) and showed both broadband noise and vibration control from 60 Hz to 5 kHz. DVAs could reduce the vibrating plate resonance magnitudes on the order of 15 dB at their tuning frequencies while providing overall vibration reduction of 5 dB or greater at higher frequencies. HG blankets were also capable of reducing plate resonance vibration up to 15 dB at their tuning frequencies and produced overall vibration reduction of 5 dB at higher frequencies. These absorbers are entirely passive, i.e. requiring no controller or prior modal testing of the structure, were placed randomly during testing, and are designed to contribute less than 10% additional mass to the structure, making them a robust vibration and noise control solution. / Master of Science

L’atténuation des bruits gênants dans une automobile est classiquement réalisée par ajustement des caractéristiques mécaniques du véhicule : masse, raideur et amortissement. C’est une approche dite passive. Malheureusement, elle induit un ajout de masse important pour traiter les basses fréquences. Le contrôle actif de bruit (atténuation d’un bruit par superposition d’un contrebruit) est actuellement envisagé comme une solution possible à ce problème. L’objectif de cette thèse est d’évaluer les performances atteignables par cette solution. Un système acoustique étant par essence fortement résonant, sa modélisation sur une large plage de fréquence conduit à des modèles d’ordre élevé, pour l’obtention desquels une méthode d’identification appropriée doit être utilisée. C’est la méthode dessous espaces par approche fréquentielle dans le domaine continu qui a été retenue.La traduction du cahier des charges conduit à un problème de régulation multivariable H1 multi-objectif et multi-modèle avec contrainte de stabilité forte. Par ailleurs, actionneurs et capteurs ne sont pas colocalisés et on ne mesure pas la perturbation à rejeter. La volonté d’évaluer au plus près les performances atteignables justifie la résolution du problème par optimisation non lisse. Cette approche évite tout pessimisme, mais nécessite de par son caractère local une bonne initialisation et une structuration du régulateur parcimonieuse.La méthodologie proposée a été validée en simulation et expérimentalement. Elle permet une évaluation et une comparaison précises des performances atteignables en fonction des contraintes sur les mesures et les moyens d’action disponibles. / Classical methods used for noise reduction in cars are based on adjusting the mechanical properties: mass, stiffness and damping. They are qualified as passive and induce significative addition of weight for reducing low frequency noises. Active noise control is seen as a possible solution to achieve low frequency noise attenuation and weight reduction.The goal of this work is to evaluate achievable performances with such solution.Acoustic enclosures are known to be resonant systems of highorder. Obtaining a model of it, therefore requires a suitable identification method. The approach chosen is based on subspace methods. It processes data in the frequency domain for obtaining a continuous time model.The control problem derived from the specifications is a MIMO H1, multi-objective and multi-model problem with a strong stability constraint. Futhermore, actuators and sensors are not-colocated, and no measure of the disturbance is available. In order to precisely evaluate the achievable performances, this problem is solved using non smooth optimization.Such approach ensures the absence of pessimism, but requires an appropriate initialization and a parsimonious controller structure, because it does not ensure convergence toward the global optimum. The proposed methodology was validated in simulation and experimentally. It allows a precise evaluation and comparison of achievable performances according to the constraints on available measures and means of action.

Owing to the ever-changing developments of battery and electric powertrain, vehicle electrification is the trend in the future. Without the presence of a combustion engine, masking effect from it reduces and noises from other components become perceivable. Among all, the cooling fan is one of the major noise sources. The design of cooling fan modules is usually carried out in the early stage before building prototype vehicles. Therefore, it is essential to come up with a method for selecting optimal fan design without performing complete vehicle testing. This is a Master's degree project in collaboration with Volvo Cars, with a focus on cooling fan noise at the charging state of electric vehicles. The main objective of this thesis is to understand the effects of fan installation. Three different setups of acoustic measurement are carried out, namely free-space, wall-mounted, and in-vehicle measurement. Correlations of these measurements are investigated through comparisons of the measurement results and the installation effects are identified through spectrum difference between free-space and in-vehicle measurement. Moreover, the implementation of spectral decomposition method enables the separation of source strength and propagation effect. Analyses of sound pressure levels are studied by looking into tonal and broadband components. In addition, sound power levels are determined by following ISO standards. Finally, a subjective rating session is held to understand the human perception of cooling fan noise. / Med anledning av den pågående utvecklingen mot elektrifiering där bilarna går mot batterier och elmotorer för framdrivning så ändras ljudbilden. Utan förbränningsmotorer som tidigare maskerade mycket av ljudet från bilarna så framträder nya ljudkällor. En sådan är kylfläkten som allt mer blir en störningskälla. Vanligtvis sker designen av kylfläktsmodulen i en tidig fas innan det finns någon prototypbil att tillgå. Detta gör att det är viktigt att utveckla metoder för att i tidig fas kunna optimera designen av kylfläkten.  Detta är ett examensarbete i samarbete med Volvo Cars med fokus på det ljud som uppstår vid laddning av eldrivna bilar. Uppsatsens huvudsakliga mål är att förstå fläktinstallationens påverkan på ljud genom att korrelera olika typer av mätningar. Detta genomfördes m.h.a tre separata konfigurationer, fritt-upphängd mätning, väggmonterad och installerad i bil. Korrelation undersöktes genom att jämföra mätresultat och analys av spektrumet. Analysen av ljudtrycksnivåerna genom att titta på dels de tonala komponenterna men också på bredbandsnivåerna. Utöver detta fastställs även ljudeffekten genom att följa gängse ISO standard. Slutligen så gjordes en subjektiv utvärdering för att få en förståelse av upplevelsen av ljudet från en kylfläkt.