An array of small, lightweight acoustic sources was investigated to determine how such an arrangement of sources would acoustically interact with a duct similar to that of a turbofan engine inlet. The sources were cylindrically curved aluminum panels excited in vibration by the application of a sinusoidally varying voltage to a piezoceramic actuator bonded to them. The finite element method was used as a design tool to size the panel based on desired vibration characteristics. A boundary element acoustic analysis was used to predict the acoustic output from various arrangements of sources. The central portion of the research was a series of experiments using an array of twelve sources arranged circumferentially in a duct. Measurements of the performance of each source revealed that the performance of the acoustic sources varied from source to source. This variation was assumed to have been caused by differences in the quality of the bond of each of the piezoceramic actuators to the panels. Directivity measurements were made in the far field. Measurements were also taken of the pressure field established in the duct cross-section. Modal decomposition was applied to the data. It was found that the dominant acoustic modes in the duct are those whose cut-on frequencies were near the frequency of excitation. / Master of Science

A series of experiments was conducted to evaluate the aerodynamic and acoustic performance of a supersonic inlet with a modified auxiliary door geometry. A 1/14 scale model of an axisymmetric, mixed-compression, supersonic inlet designed for civil transportation was used in conjunction with a 10.4cm (4.1 in.) turbofan engine simulator to test a new inlet door geometry designed to reduce flow distortion and noise radiation. The new door geometry uses door passages with increased circumferential span to improve the distribution of the flow entering through the doors. In addition, the new design employs sonic flow velocity at the inlet throat and a converging flow passage in the auxiliary doors to attenuate propagating fan noise through the choking effect. To provide a basis for comparison, a baseline door geometry representative of current designs was also tested. The experiments were conducted at simulated aircraft takeoff engine speeds under static conditions. Steady-state measurements of the inlet flow field were made along with far field acoustic measurements of the fan noise. The results show the new door geometry is successful in reducing circumferential flow distortion at the fan entrance by a factor of 2.3 compared to the baseline configuration. In addition, far field radiation of the blade passing frequency tone and overall noise is reduced by an average of 4dB(SPL) in the forward and aft sectors (0° to 110° from the inlet axis). As a compromise for the distortion and acoustic improvements, the overall inlet total pressure recovery is reduced by approximately 2% with the new auxiliary doors. / Master of Science

Attenuation of low frequency turbofan engine noise has been a challenging task in an industry that requires low weight and tightly-packed solutions. Without innovative advancements, the technology currently used will not be able to keep up with the increasingly stringent requirements on aircraft noise reduction. A need exists for novel technologies that will pave the way for the future of quiet aircraft. This thesis investigates acoustic metamaterials and their ability to achieve superior transmission loss characteristics not found in traditional honeycomb liners. The acoustic metamaterials investigated are an array of Helmholtz resonators with and without coupled cavities periodically-spaced along a duct wall. Analytical, numerical, and experimental developments of these acoustic metamaterial systems are used herein to study the effects of this technology on the transmission loss. Particularly focusing on analytical modeling will aid in understanding the underlying physics that governs their interesting transmission loss behavior. A deeper understanding of the physics will be used to aid in future acoustic metamaterial liner design. A parameter study is performed to understand the effects of the geometry, spacing, and number of resonators, as well as resonator cavity coupling on performance. Increased broadband transmission loss, particularly in low frequencies, is achieved through intelligent manipulation of these parameters. Acoustic metamaterials are shown to have appealing noise cancellation characteristics that prove to be effective for aircraft engine liner applications. / Master of Science / Aircraft noise reduction is an ongoing challenge for the aerospace industry. Without innovative advancements, the next generation of aircraft will not be able to keep up with increasingly stringent noise regulations; novel acoustic technology is needed to pave the way for a future of quieter aircraft. This thesis investigates acoustic metamaterials and their ability to achieve superior noise reduction over traditional methods. Modeling techniques were developed, and experimental tests were conducted to quantitatively evaluate the effectiveness of a new acoustic metamaterial system. The acoustic metamaterial design explored herein was proven to reduce noise effectively and shows promise for a world of quieter aircraft.

The influences of bypass ratio variation of turbofan engines in airplane runway performance are investigated more deeply in this work utilising a take-off analysis software developed by Ishizuka (2003). An initial study was carried out by Mourão, Negrão and Barbosa (2003). The results are analysed and discussed according to the operational feasibility of operators and technical feasibility of engine manufacturers. The analysis is based on comparisons of gains/losses in take-off distance, accelerate-stop distance and take-off weight for a range of bypass ratio values. Also, suggestions for future studies and researches are given his document is intended also to provide satisfactory background information of the take-off process and its mandatory regulations (FAR Part25, 1998) as much for commercial airplanes as for military airplanes. The aim is to contribute to readers' knowledge interested instudying more deeply the particularities of this specific flight phase and improving its operational safety.

A Computational Aeroacoustics (CAA) and a novel semi-empirical model is developed for predicting the noise generated by the jet flow through dual stream (coaxial) nozzles, as found in modern turbofan engines. The acoustic source model was developed in a 2D and 3D framework, based on the Lilley's Equations, following the traditional MGBK method from NASA Langley Research Center. The semi-empirical model was based on the Four-Source model from the Institute of Sound and Vibration (ISVR). This suite of methodologies provided a mean of investigating the mechanisms of noise generation and propagation of subsonic coaxial jet flows, as well as the noise prediction at different operating conditions. The work done contributed to the development and improvement of a numerical tool for jet noise prediction of dual-stream exhaust systems, commonly employed in turbofan engines. Such research also subsidies the improvement of semi-empirical methods used in the Center of Reference in Gas Turbine (ITA) for the noise prediction of turbofans in all operating conditions.

abstract: The objective of this study is to understand how to integrate conical spike external compression inlets with high bypass turbofan engines for application on future supersonic airliners. Many performance problems arise when inlets are matched with engines as inlets come with a plethora of limitations and losses that greatly affect an engine’s ability to operate. These limitations and losses include drag due to inlet spillage, bleed ducts, and bypass doors, as well as the maximum and minimum values of mass flow ratio at each Mach number that define when an engine can no longer function. A collection of tools was developed that allow one to calculate the raw propulsion data of an engine, match the propulsion data with an inlet, calculate the aerodynamic data of an aircraft, and combine the propulsion and aerodynamic data to calculate the installed performance of the entire propulsion system. Several trade studies were performed that tested how changing specific design parameters of the engine affected propulsion performance. These engine trade studies proved that high bypass turbofan engines could be developed with external compression inlets and retain effective supersonic performance. Several engines of efficient fuel consumption and differing bypass ratios were developed through the engine trade studies and used with the aerodynamic data of the Concorde to test the aircraft performance of a supersonic airliner using these engines. It was found that none of the engines that were tested came close to matching the supersonic performance that the Concorde could achieve with its own turbojet engines. It is possible to speculate from the results several different reasons why these turbofan engines were unable to function effectively with the Concorde. These speculations show that more tests and trade studies need to be performed in order to determine if high bypass turbofan engines can be developed for effective usage with supersonic airliners in any possible way. / Dissertation/Thesis / Run file and text files from the propulsion simulations performed in NPSS. / Input and output file used in EDET to generate aerodynamic data of Concorde. / Five column propulsion data of tested engines after inlet matching. / Masters Thesis Aerospace Engineering 2018

Pour les constructeurs de moteurs d'avions comme Snecma, la disponibilité est un des enjeux clés de l'avenir. En effet, la limitation des retards et annulations de vols ainsi que la réduction de la fréquence et de la durée des opérations de maintenance pourraient entraîner des économies importantes. Pour accroître la disponibilité, l'outil le plus utilisé actuellement est le "prognostics and health management" (PHM). La première contribution de la thèse est de proposer des cadres terminologique et fonctionnel pour le développement du PHM adapté aux spécificités des moteurs d'avions. Par la suite, une approche intégrée basée sur le nouveau modèle en V3 est formalisée. La seconde contribution est un processus basé sur les modèles pour le développement de la partie embarquée chargée de l'extraction des indicateurs de santé. Elle est basée sur l'analyse de sensibilité, la régression par vecteurs supports et des nouveaux indicateurs de performances. Puisque ce processus est réalisé avant l'entrée en service, les données stochastiques sont obtenues par propagation d'incertitudes. Pour surmonter les temps de calcul liés aux évaluations du modèle, des métamodèles sont utilisés. Plus particulièrement, la troisième contribution de la thèse est une technique originale combinant régression par vecteurs supports et Krigeage. L'approche globale est finalement testée sur le système carburant d'un moteur d'avion. Les résultats sont prometteurs, tant au niveau industriel pour les précieuses informations qu'elle fournit sur la qualité du jeu d'indicateurs de santé qu'au niveau académique pour la précision apportée par la nouvelle approche du Krigeage-SVR. / For manufacturers of aircraft engines such as Snecma, the increase of systems availability is one of the key challenges of the future. Indeed, the limitation of delays and cancellations and the reduction of maintenance operations frequency and duration could lead to important costs savings. To improve availability, the most proven tool is currently prognostics and health management (PHM). The first contribution of this thesis work is to propose complete terminological and functional frameworks for the development of PHM adapted to the specific application on aircraft engines. Subsequently, an integrated development approach based on the original V3-model is formalized. The second contribution is an original model-based process for the development of the embedded extraction of health indicators, based on sensitivity analysis, support vector regression and original performance indicators for the validation. Since it is aimed at being performed before the entry into service, the stochastic data are issued from Monte-Carlo based uncertainties propagation. In order to overcome the prohibitive computation time of the model evaluations, surrogate models are used. More particularly, the third contribution of this thesis work is an original technique combining support vector regression with Kriging. The whole approach is finally tested on an aircraft engine fuel system. The results are promising, both at the industrial level with the release of valuable information about the quality of the health indicators set and at the academic level with the proven accuracy of the novel SVR-Kriging approach.

No description available.

Résumé:<p><p>Cette dissertation s’intéresse aux méthodes numériques dans le domaine de l’acoustique. Les propriétés acoustiques d’un produit sont devenues une part intégrante de la conception. En effet, de nos jours le bruit est perçu comme une nuisance par le consommateur et constitue un critère de vente. Il y a de plus des normes à respecter. Les méthodes numériques permettent de prédire la propagation sonore et constitue dès lors un outil de conception incontournable pour réduire le temps et les coûts de développement d’un produit.<p><p>Cette dissertation considère la propagation d’ondes acoustiques dans le domaine fréquentiel en tenant compte de la présence d’un écoulement. Nous pouvons citer comme application industrielle, le rayonnement d’une nacelle de réacteur d’avion. Le but de la thèse est de proposer une nouvelle méthode et démontrer ses performances par rapport aux méthodes actuellement utilisées (i.e. la méthode des éléments finis).<p><p>L’originalité du travail consiste à étendre la méthode de partition de l’unité polynomiale dans le cadre de la propagation acoustique convectée, pour des domaines extérieurs. La simulation acoustique dans des domaines de dimensions infinies est réalisée dans ce travail à l’aide d’un couplage entre éléments finis et éléments infinis.<p><p>La dissertation présente la formulation de la méthode pour des applications axisymétriques et tridimensionnelles et vérifie la méthode en comparant les résultats numériques obtenus avec des solutions analytiques pour des applications académiques (i.e. propagation dans un conduit, rayonnement d’un multipole, bruit émis par la vibration d’un piston rigide, etc.). Les performances de la méthode sont ensuite analysées. Des courbes de convergences illustrent à une fréquence donnée, la précision de la méthode en fonction du nombre d’inconnues. Tandis que des courbes de performances présentent le temps de calcul nécessaire pour obtenir une solution d’une précision donnée en fonction de la fréquence d’excitation. Ces études de performances montrent l’intérêt de la méthode présentée.<p><p>Le rayonnement d’un réacteur d’avion a été abordé dans le but de vérifier la méthode sur une application de type industriel. Les résultats illustrent la propagation pour une nacelle axisymétrique en tenant compte de l’écoulement et la présence de matériau absorbant dans la nacelle et compare les résultats obtenus avec la méthode proposée et ceux obtenus avec la méthode des éléments finis.<p><p>Les performances de la méthode de la partition de l’unité dans le cadre de la propagation convectée en domaines infinis sont présentées pour des applications académiques et de type industriel. Le travail effectué illustre l’intérêt d’utiliser des fonctions polynomiales d’ordre élevé ainsi que les avantages à enrichir l’approximation localement afin d’améliorer la solution sans devoir créer un maillage plus fin.<p><p><p>Summary:<p><p>Environmental considerations are important in the design of many engineering systems and components. In particular, the environmental impact of noise is important over a very broad range of engineering applications and is increasingly perceived and regulated as an issue of occupational safety or health, or more simply as a public nuisance. The acoustic quality is then considered as a criterion in the product design process. Numerical prediction techniques allow to simulate vibro-acoustic responses. The use of such techniques reduces the development time and cost.<p><p>This dissertation focuses on acoustic convected radiation in outer domains such as it is the case for turbofan radiation. In the current thesis the mapped infinite partition of unity method is implemented within a coupled finite and infinite element model. This method allows to enrich the approximation with polynomial functions. <p><p>We present axisymmetric and three-dimensional formulations, verify and analyse the performance of the method. The verification compares computed results with the proposed method and analytical solutions for academic applications (i.e. duct propagation, multipole radiation, noise radiated by a vibrating rigid piston, etc.) .Performance analyses are performed with convergence curves plotting, for a given frequency, the accuracy of the computed solution with respect to the number of degrees of freedom or with performance curves, plotting the CPU time required to solve the application within a given accuracy, with respect to the excitation frequency. These performance analyses illustrate the interest of the mapped infinite partition of unity method.<p><p>We compute the radiation of an axisymmetric turbofan (convected radiation and acoustic treatments). The aim is to verify the method on an industrial application. We illustrate the radiation and compare the mapped infinite partition of unity results with finite element computations.<p><p>The dissertation presents the mapped partition of unity method as a computationally efficient method and illustrates its performances for academic as well as industrial applications. We suggest to use the method with high order polynomials and take the advantage of the method which allows to locally enrich the approximation. This last point improves the accuracy of the solution and prevent from creating a finer mesh.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Uma metodologia para Determinação de Tração em Vôo é apresentada. Trata-se de uma variação do Método do Erro Residual, um dos métodos de Análise do Escoamento/Bocal apresentados no documento SAE AIR 1703A. Na medida em que o valor de tração não é uma medida direta, o método procura minimizar os desvios do resultado dos cálculos, que levam em considerações medições nos bocais do motor, em relação ao valor real. Para isso, são utilizados ensaios em solo, em que se comparam resultados calculados e medidos em bancada. O resultado dessa comparação é um escalar, o FPC, aplicado à razão de pressão no Fan de modo a minimizar os erros de vazão mássica e de tração líquida em relação aos valores calculados. Para cada razão de pressão no Fan (FPR) é obtido um FPC a partir da minimização de uma função que considera o erro residual de tração e vazão em solo. A metodologia apresentada propõe o uso de diferentes pesos para os desvios de tração e vazão. O procedimento é implementado através de rotinas em VISUAL BASIC, no ambiente do MICROSOFT EXCEL. Tais rotinas são usadas com dados de ensaios em vôo e em solo para dois motores de mesmo modelo usados na aviação comercial. Inicialmente, os dados de ensaios são utilizados para a determinação de dados de FPC e tração e vazão em vôo. É possível verificar a repetibilidade do método e a variação da tração líquida com parâmetros como rotação do Fan, altitude e Mach. Em seguida, analisa-se a variação dos pesos da tração e da vazão na determinação de FPC e nos valores finais de tração líquida e vazão mássica. Com esses dados, verifica-se a sensibilidade dos erros residuais para o ensaio em solo e a variação dos valores finais de tração e vazão em relação aos valores de pesos. Finalmente, são feitas considerações sobre o uso da metodologia proposta em uma campanha de ensaios em vôo.