Esta dissertação apresenta o desenvolvimento e otimização de uma metodologia baseada em código comercial para previsão de ruído em um eslate, além do estudo da dependência do ruído ao variar a camada limite do aerofólio. Com a contínua redução do ruído produzido por motores em aeronaves e as sucessivas restrições nos níveis de certificação, o ruído produzido por dispositivos aerodinâmicos tem ganhado importância no projeto de uma aeronave. Durante o pouso, o ruído gerado pelos dispositivos hiper-sustentadores é classificado dentre os mais relevantes, sendo o eslate um de seus componentes. Este trabalho busca criar e otimizar uma metodologia baseada no código PowerFLOW, assim como estudar a influência das camadas limite do aerofólio na geração de ruído. Tal código é baseado na formulação de Lattice- Boltzmann. As fontes acústicas simuladas são propagadas utilizando uma analogia acústica de Ffowcs-Williams e Hawkings e, então, analisadas utilizando métodos estatísticos de análise de sinais. Estudos de validação e verificação do código baseados em soluções analíticas são apresentados, tais como uma camada de mistura periódica no espaço e a solução dos vórtices de Taylor-Green. A seguir, o aerofólio 30P30N é utilizado em todo o estudo relacionado a eslates, analisando primeiramente a independência da solução em relação ao nível de refinamento da malha e do tamanho do domínio empregados. Baseado nas recomendações de tal estudo, o resultado é comparado com simulações disponíveis na literatura. Com uma maior confiança na metodologia, o trabalho então apresenta estudos variando a camada limite em regiões do eslate, assim como removendo-a completamente em certas regiões do aerofólio ao empregar condições de contorno de livre-escorregamento. O trabalho mostra que a influência das camadas limite do aerofólio é desprezível em relação ao erro do método. Isso é causado pela aparente independência do ruído do eslate em relação ao escoamento perto de sua cúspide. Tal independência permite que a malha computacional seja otimizada, reduzindo o custo da simulação em até 60%. / This dissertation presents the development and optimization of a methodology based on a commercial software to predict slat noise, also studying noise dependency when varying airfoil boundary layers. Due to continuous reduction on aircraft engine noise and successive restrictions on noise certification levels, airframe noise has been gaining importance on aircraft design. During landing, high-lift noise is ranked as one of the most relevant ones, being slat noise one of its components. This work focuses on creating and optimizing a noise prediction methodology based on the software PowerFLOW, and also on studying the influence of airfoil boundary layers on noise generation. Such software is based on Lattice-Boltzmann formulation. The simulated sound sources are propagated using Ffowcs-Williams and Hawkings acoustic analogy and then analyzed by signal analysis methods. Code validation and verification studies based on analytical solutions are presented, such as the spacially-periodic mixing layer and the Taylor-Green vortices solutions. Following, the 30P30N airfoil is employed through the rest of this work, firstly studying the solution independency related to mesh refinement level and computational domain size. Based on recommendations from this study, the results are compared to simulations from the literature. With higher confidence levels on this methodology, the work then presents studies varying the slat boundary layer and also removing it completely by employing free-slip boundary conditions on certain airfoil regions. This work presents that the airfoil boundary layer influence is neglectable when compared to the method error. This is caused by the apparent slat noise independency related to the flowfield near the slat cusp. Such independency allows the computational mesh to be optimized, reducing the simulation cost by up to 60%.

Com o desenvolvimento para aeronaves de propulsores turbo-fan com elevada razão de derivação, componentes da estrutura do avião passaram a ter relevância na geração de ruído aerodinâmico, principalmente durante a aproximação e o pouso. Dentre esses componentes, o eslate se destaca por ser uma fonte que se estende ao longo de praticamente toda a envergadura da asa. Neste trabalho, simulações numéricas foram feitas no intuito de considerar configurações práticas nas análises do ruído aeroacústico gerado pelo eslate. Um código comercial baseado no Método Lattice-Boltzmann foi usado no cálculo do escoamento transiente em torno do aerofólio MD30P30N. O domínio computacional simulado imitou a configuração geométrica de um túnel de vento. Foi levado em consideração o efeito da presença de duas formas de excrescência que são comuns na cova do eslate de aeronaves comerciais. Uma delas foi um selo que fica posicionado na parede da cova e a outra, um tubo do sistema anti-gelo. Tanto o escoamento transiente na região da cova quanto as características do ruído aeroacústico propagado para o campo distante foram analisados. Uma metodologia que impõe condição de parede com escorregamento livre no es- late e elemento principal, permitindo assim uma redução do custo computacional, foi usada. A abordagem foi ainda testada para a condição de um aerofólio submetido a escoamento cruzado, simulando uma asa infinita com enflechamento. Também uma modificação na metodologia, para que ela possa ser empregada em aerofólios com elevados ângulos de ataque, foi proposta e testada. O código híbrido MSES foi usado para o cálculo da espessura de deslocamento na camada limite do aerofólio. A modificação na geometria baseada em \'delta\'* causou uma melhora da solução aeroacústica de uma simulação empregando paredes com escorregamento livre, tomando como base de comparação a solução com paredes sem escorregamento. Simulações com selo dentro da cova, perto do recolamento, mostraram que, em certas circunstâncias, há um bloqueio dos vórtices da camada de mistura, intensificando picos tonais no espectro do ruído. A variação da posição do selo mostrou um efeito significativo no ruído do eslate, de forma que um selo suficientemente afastado do recolamento modificou o espectro do ruído do eslate. Os resultados com o aerofólio enflechado indicam que, também neste caso, o ruído do eslate não depende diretamente da camada limite na cúspide, mas da circulação do aerofólio. Por sua vez, a presença do tubo na cova aumenta significativamente a intensidade do ruído de banda larga produzido pelo eslate. Em uma asa sem enflechamento, o tubo causa também um aumento substancial na intensidade de picos tonais de baixa frequência. / The development of high by-pass ratio turbo-fan engine turned the airframe noise into an important component in a commercial airplanes\' noise characteristics. Between the airframe noise sources the slat can be highlighted as it extends almost along the whole wing span. Numerical simulation was carried out in order to consider practical configuration in the aeroacoutic noise generated by the slat. The effects of two different excrescences, which are normally present in commercial airplanes\' slat cove, were taken into account. One of them was a seal attached to the cove wall and the outher one was a tube that compose the anti-icing system. Both unsteady flow in cove region and far-field noise characteristics were analysed. A methodology that impose free-slip wall boundary condition on slat and main element surfaces was employed, which allowed the reduction of computational requirements. This approach was also tested for airfoil with crossflow, which simulates an infinite swept wing. Also a modification of the methodology was proposed and tested to extend its application in high-lift airfoils under higher angle of attack. A commercial code based on the Lattice-Boltzmann Method was used to compute the unsteady flow over the MD30P30N airfoil. The simulated computational domain imitates the geometry of a wind tunnel. The hybrid Euler/IBL code MSES was employed to calculate the displacement thickness of the airfoil\'s boundary layers. The geometry modification based on \'delta\'* caused a improvement on the aeroacoustic solution of a free-slip simulation, the no-slip simulation results being taken as reference. Simulations of geometries with relatively small seal close to the reattachment point showed that a blockage of the mixing layer vortices hapens and tonal peaks are intensified in the far-field noise spectrum. The variation of the seal position showed a significant effect on the slat noise, so that a seal farther from the reattachment modified affected both the shape and intensity of the noise spectrum. Results with the swept airfoil indicates that, even in the presence of crossflow, the slat noise does not depend on the cusp boundary layer, namely it is more sensitive to the airfoil circulation. The tube crossing the slat cove augmented significantly the broadband noise generated by the slat. In an unswept wing it also caused a substantial increase in the low-frequency tonal peaks.

Com o desenvolvimento para aeronaves de propulsores turbo-fan com elevada razão de derivação, componentes da estrutura do avião passaram a ter relevância na geração de ruído aerodinâmico, principalmente durante a aproximação e o pouso. Dentre esses componentes, o eslate se destaca por ser uma fonte que se estende ao longo de praticamente toda a envergadura da asa. Neste trabalho, simulações numéricas foram feitas no intuito de considerar configurações práticas nas análises do ruído aeroacústico gerado pelo eslate. Um código comercial baseado no Método Lattice-Boltzmann foi usado no cálculo do escoamento transiente em torno do aerofólio MD30P30N. O domínio computacional simulado imitou a configuração geométrica de um túnel de vento. Foi levado em consideração o efeito da presença de duas formas de excrescência que são comuns na cova do eslate de aeronaves comerciais. Uma delas foi um selo que fica posicionado na parede da cova e a outra, um tubo do sistema anti-gelo. Tanto o escoamento transiente na região da cova quanto as características do ruído aeroacústico propagado para o campo distante foram analisados. Uma metodologia que impõe condição de parede com escorregamento livre no es- late e elemento principal, permitindo assim uma redução do custo computacional, foi usada. A abordagem foi ainda testada para a condição de um aerofólio submetido a escoamento cruzado, simulando uma asa infinita com enflechamento. Também uma modificação na metodologia, para que ela possa ser empregada em aerofólios com elevados ângulos de ataque, foi proposta e testada. O código híbrido MSES foi usado para o cálculo da espessura de deslocamento na camada limite do aerofólio. A modificação na geometria baseada em \'delta\'* causou uma melhora da solução aeroacústica de uma simulação empregando paredes com escorregamento livre, tomando como base de comparação a solução com paredes sem escorregamento. Simulações com selo dentro da cova, perto do recolamento, mostraram que, em certas circunstâncias, há um bloqueio dos vórtices da camada de mistura, intensificando picos tonais no espectro do ruído. A variação da posição do selo mostrou um efeito significativo no ruído do eslate, de forma que um selo suficientemente afastado do recolamento modificou o espectro do ruído do eslate. Os resultados com o aerofólio enflechado indicam que, também neste caso, o ruído do eslate não depende diretamente da camada limite na cúspide, mas da circulação do aerofólio. Por sua vez, a presença do tubo na cova aumenta significativamente a intensidade do ruído de banda larga produzido pelo eslate. Em uma asa sem enflechamento, o tubo causa também um aumento substancial na intensidade de picos tonais de baixa frequência. / The development of high by-pass ratio turbo-fan engine turned the airframe noise into an important component in a commercial airplanes\' noise characteristics. Between the airframe noise sources the slat can be highlighted as it extends almost along the whole wing span. Numerical simulation was carried out in order to consider practical configuration in the aeroacoutic noise generated by the slat. The effects of two different excrescences, which are normally present in commercial airplanes\' slat cove, were taken into account. One of them was a seal attached to the cove wall and the outher one was a tube that compose the anti-icing system. Both unsteady flow in cove region and far-field noise characteristics were analysed. A methodology that impose free-slip wall boundary condition on slat and main element surfaces was employed, which allowed the reduction of computational requirements. This approach was also tested for airfoil with crossflow, which simulates an infinite swept wing. Also a modification of the methodology was proposed and tested to extend its application in high-lift airfoils under higher angle of attack. A commercial code based on the Lattice-Boltzmann Method was used to compute the unsteady flow over the MD30P30N airfoil. The simulated computational domain imitates the geometry of a wind tunnel. The hybrid Euler/IBL code MSES was employed to calculate the displacement thickness of the airfoil\'s boundary layers. The geometry modification based on \'delta\'* caused a improvement on the aeroacoustic solution of a free-slip simulation, the no-slip simulation results being taken as reference. Simulations of geometries with relatively small seal close to the reattachment point showed that a blockage of the mixing layer vortices hapens and tonal peaks are intensified in the far-field noise spectrum. The variation of the seal position showed a significant effect on the slat noise, so that a seal farther from the reattachment modified affected both the shape and intensity of the noise spectrum. Results with the swept airfoil indicates that, even in the presence of crossflow, the slat noise does not depend on the cusp boundary layer, namely it is more sensitive to the airfoil circulation. The tube crossing the slat cove augmented significantly the broadband noise generated by the slat. In an unswept wing it also caused a substantial increase in the low-frequency tonal peaks.

Esta dissertação apresenta o desenvolvimento e otimização de uma metodologia baseada em código comercial para previsão de ruído em um eslate, além do estudo da dependência do ruído ao variar a camada limite do aerofólio. Com a contínua redução do ruído produzido por motores em aeronaves e as sucessivas restrições nos níveis de certificação, o ruído produzido por dispositivos aerodinâmicos tem ganhado importância no projeto de uma aeronave. Durante o pouso, o ruído gerado pelos dispositivos hiper-sustentadores é classificado dentre os mais relevantes, sendo o eslate um de seus componentes. Este trabalho busca criar e otimizar uma metodologia baseada no código PowerFLOW, assim como estudar a influência das camadas limite do aerofólio na geração de ruído. Tal código é baseado na formulação de Lattice- Boltzmann. As fontes acústicas simuladas são propagadas utilizando uma analogia acústica de Ffowcs-Williams e Hawkings e, então, analisadas utilizando métodos estatísticos de análise de sinais. Estudos de validação e verificação do código baseados em soluções analíticas são apresentados, tais como uma camada de mistura periódica no espaço e a solução dos vórtices de Taylor-Green. A seguir, o aerofólio 30P30N é utilizado em todo o estudo relacionado a eslates, analisando primeiramente a independência da solução em relação ao nível de refinamento da malha e do tamanho do domínio empregados. Baseado nas recomendações de tal estudo, o resultado é comparado com simulações disponíveis na literatura. Com uma maior confiança na metodologia, o trabalho então apresenta estudos variando a camada limite em regiões do eslate, assim como removendo-a completamente em certas regiões do aerofólio ao empregar condições de contorno de livre-escorregamento. O trabalho mostra que a influência das camadas limite do aerofólio é desprezível em relação ao erro do método. Isso é causado pela aparente independência do ruído do eslate em relação ao escoamento perto de sua cúspide. Tal independência permite que a malha computacional seja otimizada, reduzindo o custo da simulação em até 60%. / This dissertation presents the development and optimization of a methodology based on a commercial software to predict slat noise, also studying noise dependency when varying airfoil boundary layers. Due to continuous reduction on aircraft engine noise and successive restrictions on noise certification levels, airframe noise has been gaining importance on aircraft design. During landing, high-lift noise is ranked as one of the most relevant ones, being slat noise one of its components. This work focuses on creating and optimizing a noise prediction methodology based on the software PowerFLOW, and also on studying the influence of airfoil boundary layers on noise generation. Such software is based on Lattice-Boltzmann formulation. The simulated sound sources are propagated using Ffowcs-Williams and Hawkings acoustic analogy and then analyzed by signal analysis methods. Code validation and verification studies based on analytical solutions are presented, such as the spacially-periodic mixing layer and the Taylor-Green vortices solutions. Following, the 30P30N airfoil is employed through the rest of this work, firstly studying the solution independency related to mesh refinement level and computational domain size. Based on recommendations from this study, the results are compared to simulations from the literature. With higher confidence levels on this methodology, the work then presents studies varying the slat boundary layer and also removing it completely by employing free-slip boundary conditions on certain airfoil regions. This work presents that the airfoil boundary layer influence is neglectable when compared to the method error. This is caused by the apparent slat noise independency related to the flowfield near the slat cusp. Such independency allows the computational mesh to be optimized, reducing the simulation cost by up to 60%.

Transportation is the main source of environmental noise in Europe, with an estimated 125 million people affected by excessive noise levels from road traffic, causing a burden of noise related diseases and having a substantial economic impact on society. In order to reduce exposure to high levels of traffic noise, two approaches are the topic of extensive research: preventing sound from propagating from roads and railways using for example noise barriers, and reducing the sources of noise themselves. The second solution, which addresses directly the cause of the problem, requires improved design methods, with a more systematic resort to multi-functional design. Addressing cross-functions simultaneously reduces the number of design iterations and the high cost of prototyping. The work presented in this thesis aims at developing methods that can be used to design quieter vehicle concepts within a multi-functional approach, and is articulated around two main axis of research, aerodynamic sound generation and sound propagation. The first axis aims at performing an aeroacoustic analysis to predict aerodynamic sound sources. A hybrid method is used on the example of a type of submerged air inlet called a NACA duct, where the near-field flow is solved through detached eddy simulation (DES) and where the far-field acoustics is computed using the Ffowcs Williams and Hawkings integral. Results for the flow for various operating conditions are presented and validated against experimental data from the literature, with very good agreement. Far-field acoustic results are shown, exhibiting levels and components that are strongly dependent on the operating conditions. This analysis gives a framework for future aeroacoustic analysis in the project, and sets the path for the development of air inlets with improved aerodynamic and aeroacoustic characteristics. The second axis focuses on the propagation of sound from a given source, moving in an urban environment. An approximate boundary method is presented, which relies on the Kirchhoff approximation applied to the Kirchhoff-Helmholtz integral equation. Using this approximation speeds up the computational time compared to using a regular boundary element method. The resulting expression is extended to account for multiple scattering through consecutive updates of the surface pressures, and for moving sources through the introduction of a retarded time and of a Doppler shift. Validation tests for this method are presented, from simple scatterers to a more realistic configuration, showing good agreement with analytical, experimental and simulated work. / Fordon är den främsta källan till bullerexponering i Europa med uppskattningsvis 125 miljoner människor som är utsatta för höga ljudnivåer från vägtrafik, vilket kan orsaka bullerrelaterade häsloproblem samt har en betydande ekonomisk effekt på samhället. För att minska exponeringen för höga ljudnivåer från fordon, finns det två angreppssätt som båda idag är ämne för omfattande forskning: att förhindra ljudutbredning från vägar och järnvägar (till exempel med hjälp av bullerskydd), samt att minska ljudnivån från olika bullerkällor. Den sistnämnda, som direkt riktar sig till problemets orsak, kräver förbättrade designmetoder med mer systematisk användning av multifunktionell design. Att hantera flera funktioner hos fordonet samtidigt minskar antalet designiterationer och den höga kostnaden för prototyper. Arbetet som presenteras i denna avhandling syftar till att utveckla metoder som kan användas för att utforma tystare fordonskoncept inom ramen för en multifunktionell strategi och fokuserar på två spår i forskningen: aerodynamisk ljudalstring och ljudutbredning från rörliga källor. Det första spåret i forskningen syftar till att utföra en aeroakustisk undersökning för att modellera aerodynamiska ljudkällor. En hybridmetod tillämpas på ett typ av nedsänkt luftintag, kallat NACA-intag, där källområdet i strömningen löses genom detached eddy simulation (DES) och akustiken i fjärrfältet beräknas enligt Ffowcs Williams och Hawkings integral. Resultat för strömningen för olika driftförhållanden presenteras och valideras mot experimentella data från litteraturen, med mycket god överensstämmelse. Resultat för det akustika fjärrfältet visas, vilket uppvisar nivåer och komponenter som är starkt beroende av driftförhållandena. Denna analys ger en ram för kommande analyser av aeroakustik inom projektet och visar vägen för utvecklingen av luftintag med förbättrade aerodynamiska och aeroakustika egenskaper. Det andra spåret i forskningsprojektet är inriktat på ljudets utbredning från en given källa som rör sig i en urban miljö. En approximativ randvärdesmetod presenteras som bygger på Kirchhoff approximation tillämpad på Kirchhoff-Helmholtz integralekvation. Med hjälp av denna approximation minskas beräkningstiden jämfort med vanlig boundary element method (BEM). Modellen utvecklas sedan för att kunna hantera flera reflektioner genom att det akustiska trycket på ytorna uppdateras för varje reflektion samt för att kunna hantera rörliga källor genom att introducera tidsfördröjningar och Dopplerförskjutning. Validering för denna modell presenteras, från enkla spridare till en mer realistisk urban konfiguration, som visar god överensstämmelse med analytiskt, experimentellt och simulerat data. / <p>QC 20151002</p>

As improving the performance of turbofan designs becomes increasingly difficult, manufacturers are looking to new technologies for the next generation of jet engines. An 'open rotor' replaces the fan of the turbofan with a set of external rotors. This has the potential to offer a significant improvement in propulsive efficiency, but the design for low noise is a key challenge. Hence, high fidelity noise prediction methods are needed to accurately predict and compare the noise of different designs. This thesis focuses on one set of methods based on the Ffowcs Williams-Hawkings (\fwh) equation. This equation is considered to be the most realistic description of aeroacoustic noise generation, as it is a direct rearrangement of the Navier-Stokes equations. The \fwh\ equation is difficult to solve for realistic test cases such as an open rotor, and is susceptible to several types of error. This thesis categorises these errors as ``input'', ``neglection'' and ``discretisation'' errors. Discretisation errors arise from the need to integrate a discretised source field for the total noise, neglection errors result from needing to ignore part of the source field for practical reasons, and input errors relate to any errors caused by inaccurate input to the solver. The fundamental motivation of this thesis is to advance the understanding of neglection and discretisation errors and how they can be mitigated, in order to develop best practice solvers and methodologies for application to open rotors. Dimensional analysis is combined with analytical flow solutions to develop a process for isolating and quantifying discretisation errors. This process is used to study a wide range of solver methodologies and select a best practice solver methodology for open rotor noise prediction. This first-of-a-kind study produces a solver methodology that reduces discretisation errors by an order of magnitude compared to an industry standard solver. Previous research into neglection errors has shown that avoiding density perturbations in acoustic source terms can be beneficial. This thesis uses a generic aeroacoustic analogy to provide a new, physically intuitive method of incorporating a surface discontinuity that enables density perturbations to be avoided in a far more elegant manner than previous research. The above method improvements are investigated using a modern open rotor rig test case. The results demonstrate that discretisation and neglection errors can be severe in realistic cases and the potential of the method improvements to significantly mitigate them.

Les nuisances sonores sont devenues une importante préoccupation environnementale. L'accroissement des exigences de confort et le durcissement des réglementations européennes et mondiales ont rendu la réduction du bruit aérodynamique des turbomachines un enjeu primordial pour plusieurs industries. Ce travail a pour objectif principal le développement d'outils de modélisation de la composante à large bande du bruit des ventilateurs de façon à l'intégrer comme critère d'optimisation dès leur phase de conception. L'étude est concentrée sur les deux sources reconnues pour leurs contributions significatives dans le bruit rayonné : l'interaction des pales avec l'écoulement turbulent amont et la diffraction de la couche limite turbulente au niveau du bord de fuite. Dans un premier temps, une approche reposant sur la formulation analytique d'Amiet pour la prédiction du bruit d'un profil isolé disposé dans un écoulement turbulent est mise en oeuvre. L'effet de l'épaisseur n'est pas pris en compte dans la formulation initiale d'Amiet. Une correction gaussienne a été proposée sur la base des travaux de Gershfeld améliorant ainsi considérablement les résultats de calculs. Une extension vers la turbomachine est ensuite proposée et validée expérimentalement. Un ventilateur axial est disposé à l'amont de différents écoulements incidents turbulents générés par cinq dispositifs de contrôle de turbulence. La turbulence incidente est caractérisée par le modèle spectral de von Kármán à partir des mesures à fils chauds. La confrontation des spectres de puissance acoustique calculés à ceux mesurés donne un accord satisfaisant sur une large bande fréquentielle audible. Dans la deuxième partie, une modélisation hybride combinant des Simulations des Grandes Echelles avec une solution intégrale dans le domaine temporel de l'analogie de Ffowcs Willimas & Hawkings est développée. Une validation complétée par une étude des erreurs numériques du code acoustique développé sur la base de la formulation intégrale 1A de Farassat avec une surface perméable de Di Francescontonio a été réalisée. Les simulations LES bidimensionnelles de l'écoulement turbulent autour d'un profil ont reproduit la transition de la couche limite turbulente et le détachement tourbillonnaire au bord de fuite. L'analyse des spectres de pression pariétale a révélé que l écoulement amont a un important effet sur les fluctuations de pression pariétale et leurs localisations.

The use of steady-state aerodynamic optimization methods in the computational fluid dynamic (CFD) community is fairly well established. In particular, the use of adjoint methods has proven to be very beneficial because their cost is independent of the number of design variables. The application of numerical optimization to airframe-generated noise, however, has not received as much attention, but with the significant quieting of modern engines, airframe noise now competes with engine noise. Optimal control techniques for unsteady flows are needed in order to be able to reduce airframe-generated noise. In this thesis, a general framework is formulated to calculate the gradient of a cost function in a nonlinear unsteady flow environment via the discrete adjoint method. The unsteady optimization algorithm developed in this work utilizes a Newton-Krylov approach since the gradient-based optimizer uses the quasi-Newton method BFGS, Newton's method is applied to the nonlinear flow problem, GMRES is used to solve the resulting linear problem inexactly, and last but not least the linear adjoint problem is solved using Bi-CGSTAB. The flow is governed by the unsteady two-dimensional compressible Navier-Stokes equations in conjunction with a one-equation turbulence model, which are discretized using structured grids and a finite difference approach. The effectiveness of the unsteady optimization algorithm is demonstrated by applying it to several problems of interest including shocktubes, pulses in converging-diverging nozzles, rotating cylinders, transonic buffeting, and an unsteady trailing-edge flow. In order to address radiated far-field noise, an acoustic wave propagation program based on the Ffowcs Williams and Hawkings (FW-H) formulation is implemented and validated. The general framework is then used to derive the adjoint equations for a novel hybrid URANS/FW-H optimization algorithm in order to be able to optimize the shape of airfoils based on their calculated far-field pressure fluctuations. Validation and application results for this novel hybrid URANS/FW-H optimization algorithm show that it is possible to optimize the shape of an airfoil in an unsteady flow environment to minimize its radiated far-field noise while maintaining good aerodynamic performance.

The use of steady-state aerodynamic optimization methods in the computational fluid dynamic (CFD) community is fairly well established. In particular, the use of adjoint methods has proven to be very beneficial because their cost is independent of the number of design variables. The application of numerical optimization to airframe-generated noise, however, has not received as much attention, but with the significant quieting of modern engines, airframe noise now competes with engine noise. Optimal control techniques for unsteady flows are needed in order to be able to reduce airframe-generated noise. In this thesis, a general framework is formulated to calculate the gradient of a cost function in a nonlinear unsteady flow environment via the discrete adjoint method. The unsteady optimization algorithm developed in this work utilizes a Newton-Krylov approach since the gradient-based optimizer uses the quasi-Newton method BFGS, Newton's method is applied to the nonlinear flow problem, GMRES is used to solve the resulting linear problem inexactly, and last but not least the linear adjoint problem is solved using Bi-CGSTAB. The flow is governed by the unsteady two-dimensional compressible Navier-Stokes equations in conjunction with a one-equation turbulence model, which are discretized using structured grids and a finite difference approach. The effectiveness of the unsteady optimization algorithm is demonstrated by applying it to several problems of interest including shocktubes, pulses in converging-diverging nozzles, rotating cylinders, transonic buffeting, and an unsteady trailing-edge flow. In order to address radiated far-field noise, an acoustic wave propagation program based on the Ffowcs Williams and Hawkings (FW-H) formulation is implemented and validated. The general framework is then used to derive the adjoint equations for a novel hybrid URANS/FW-H optimization algorithm in order to be able to optimize the shape of airfoils based on their calculated far-field pressure fluctuations. Validation and application results for this novel hybrid URANS/FW-H optimization algorithm show that it is possible to optimize the shape of an airfoil in an unsteady flow environment to minimize its radiated far-field noise while maintaining good aerodynamic performance.

In a society where environmental noise is becoming a major health and economical concern, sound emissions are an increasingly critical design factor for vehicle manufacturers. With about a quarter of the European population living close to roads with heavy traffic, traffic noise in urban landscapes has to be addressed first. The current introduction of electric vehicles on the market and the need for sound systems to alert their presence is causing a shift in mentalities requiring engineering methods that will have to treat noise management problems from a broader perspective. That in which noise emissions need not only be considered as a by-product of the design but as an integrated part of it. Developing more sustainable ground transportation will require a better understanding of the sound field emitted in various realistic operating conditions, beyond the current requirements set by the standard pass-by test, which is performed in a free-field. A key aspect to improve this understanding is the development of efficient numerical tools to predict the generation and propagation of sound from moving vehicles. In the present thesis, a methodology is proposed aimed at evaluating the pass-by sound field generated by vehicle acoustic sources in a simplified urban environment, with a focus on flow sound sources. Although it can be argued that the aerodynamic noise is still a minor component of the total emitted noise in urban driving conditions, this share will certainly increase in the near future with the introduction of quiet electric engines and more noise-efficient tyres on the market. This work presents a complete modelling of the problem from sound generation to sound propagation and pass-by analysis in three steps. Firstly, computation of the flow around the geometry of interest; secondly, extraction of the sound sources generated by the flow, and thirdly, propagation of the sound generated by the moving sources to observers including reflections and scattering by nearby surfaces. In the first step, the flow is solved using compressible detached-eddy simulations. The identification of the sound sources in the second step is performed using direct numerical beamforming with linear programming deconvolution, with the phased array pressure data being extracted from the flow simulations. The outcome of this step is a set of uncorrelated monopole sources. Step three uses this set as input to a propagation method based on a point-to-point moving source Green's function and a modified Kirchhoff integral under the Kirchhoff approximation to compute reflections on built surfaces. The methodology is demonstrated on the example of the aeroacoustic noise generated by a NACA air inlet moving in a simplified urban setting. Using this methodology gives insights on the sound generating mechanisms, on the source characteristics and on the sound field generated by the sources when moving in a simplified urban environment. / I ett samhälle där buller håller på att bli ett stort hälsoproblem och en ekonomisk belastning, är ljudutsläpp en allt viktigare aspekt för fordonstillverkare. Då ungefär en fjärdedel av den europeiska befolkningen bor nära vägar med tung trafik, är åtgärder för minskat trafikbuller i stadsmiljö en hög prioritet. Introduktionen av elfordon på marknaden och behovet av ljudsystem för att varna omgivningen kräver också ett nytt synsätt och tekniska angreppssätt som behandlar bullerproblemen ur ett bredare perspektiv. Buller bör inte längre betraktas som en biprodukt av konstruktionen, utan som en integrerad del av den. Att utveckla mer hållbara marktransporter kommer att kräva en bättre förståelse av det utstrålade ljudfältet vid olika realistiska driftsförhållanden, utöver de nuvarande standardiserade kraven för förbifartstest som utförs i ett fritt fält. En viktig aspekt för att förbättra denna förståelse är utvecklingen av effektiva numeriska verktyg för att beräkna ljudalstring och ljudutbredning från fordon i rörelse. I denna avhandling föreslås en metodik som syftar till att utvärdera förbifartsljud som alstras av fordons akustiska källor i en förenklad stadsmiljö, här med fokus på strömningsgenererat ljud. Även om det aerodynamiska bullret är fortfarande en liten del av de totala bullret från vägfordon i urbana miljöer, kommer denna andel säkerligen att öka inom en snar framtid med införandet av tysta elektriska motorer och de bullerreducerande däck som introduceras på marknaden. I detta arbete presenteras en komplett modellering av problemet från ljudalstring till ljudutbredning och förbifartsanalys i tre steg. Utgångspunkten är beräkningar av strömningen kring geometrin av intresse; det andra steget är identifiering av ljudkällorna som genereras av strömningen, och det tredje steget rör ljudutbredning från rörliga källor till observatörer, inklusive effekten av reflektioner och spridning från närliggande ytor. I det första steget löses flödet genom detached-eddy simulation (DES) för kompressibel strömning. Identifiering av ljudkällor i det andra steget görs med direkt numerisk lobformning med avfaltning med hjälp av linjärprogrammering, där källdata extraheras från flödessimuleringarna. Resultatet av detta steg är en uppsättning av okorrelerade akustiska monopolkällor. Steg tre utnyttjar dessa källor som indata till en ljudutbredningsmodel baserad på beräkningar punkt-till-punkt med Greensfunktioner för rörliga källor, och med en modifierad Kirchhoff-integral under Kirchhoffapproximationen för att beräkna reflektioner mot byggda ytor. Metodiken demonstreras med exemplet med det aeroakustiska ljud som genereras av ett NACA-luftintag som rör sig i en förenklad urban miljö. Med hjälp av denna metod kan man få insikter om ljudalstringsmekanismer, om källegenskaper och om ljudfältet som genereras av källor när de rör sig i en förenklad stadsmiljö. / <p>QC 20170425</p>