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%.

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>

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.

Although it is possible to directly solve an entire flow-acoustics problem in one computation, this approach remains prohibitively large in terms of the computational resource required for most practical applications. Aeroacoustic problems are therefore usually split into two parts; one consisting of the source computation and one of the source propagation. Although both these parts entail great challenges on the computational method, in terms of accuracy and efficiency, it is still better than the direct solution alternative. The source usually consists of highly turbulent flows, which for most cases will need to be, at least partly, resolved. Then, acoustic waves generated by these sources often have to be propagated for long distances compared to the wavelength and might be subjected to scattering by solid objects or convective effects by the flow. Numerical methods used solve these problems therefore have to possess low dispersion and dissipation error qualities for the solution to be accurate and resource efficient. The wave expansion method (WEM) is an efficient discretization technique, which is used for wave propagation problems. The method uses fundamental solutions to the wave operator in the discretization procedure and will thus produce accurate results at two to three points per wavelength. This thesis presents a method that uses the WEM in an aeroacoustic context. Addressing the propagation of acoustic waves and transfer of sources from flow to acoustic simulations. The proposed computational procedure is applied to a co-rotating vortex pair and a cylinder in cross-flow. Overall, the computed results agree well with analytical solutions. Although the WEM is efficient in terms of the spatial discretization, the procedure requires that a Moore-Penrose pseudo-inverse is evaluated at each unique node-neighbour stencil in the grid. This evaluation significantly slows the procedure. In this thesis, a method with a regular grid is explored to speed-up this process. / <p>QC 20161121</p>

À l'allumage d'un lanceur spatial équipé de moteurs à propergol solide (MPS), une onde de souffle (ODS), caractérisée par un pic de grande amplitude et une large dépression, est générée pendant le transitoire de montée en pression. Puis le jet supersonique chaud rayonne un bruit de jet (BDJ) intense riche en composantes hautes fréquences. Cette thèse a été consacrée à la mise au point de méthodologies de simulation de ces phénomènes à l'aide de la plateforme de calcul CEDRE, en se comparant à des mesures expérimentales réalisées sur un petit MPS. Les phénomènes sont reproduits à l'aide de simulations aux grandes échelles (SGE). Les choix numériques (maillages, schémas) sont effectués à partir de cas-tests de validation. La méthodologie retenue pour l'ODS repose sur une approche directe simulant la génération et le transport de l'onde jusqu'aux capteurs expérimentaux. Ce calcul, qui estime aussi le transfert radiatif du jet, permet l'interprétation physique des phénomènes générateurs de l'ODS (effet piston du jet se développant). La prise en compte de la post combustion dans les premiers instants se révèle être un facteur de premier ordre concernant l'amplitude de l'ODS et son interaction avec le jet. Une approche hybride est adoptée pour le BDJ, chaînant une SGE du champ proche à la résolution des équations de Ffowcs Williams & Hawkings (FWH). Le bon accord du champ aérodynamique avec les mesures de la littérature incite à appliquer cette méthode au calcul de l'ODS. Finalement, celle-ci met en évidence le caractère fortement non-linéaire de l'ODS qui ne peut donc être rayonnée par FWH, et une interaction modèrée avec le jet, plus conforme aux observations expérimentales.