Experimental aeroacoustic research was conducted on a wind turbine specific airfoil at low Reynolds numbers. The goal of this thesis was to study trailing edge noise generation from the airfoil and investigate correlations between the noise and the flow field. Before experiments were performed the current wind tunnel had to be modified in order to make it more suitable for aeroacoustic tests. Sound absorbing foam was added to the inside of the tunnel to lower the background noise levels and turbulence reduction screens were added which lowered the turbulence. An S822 airfoil was chosen because it is designed for low Reynolds flows attainable in the wind tunnel which are on the order of 104. Smoke wire flow visualization was used to gain insight into the airfoil wake development and oil film flow visualization was used to qualitatively assess the boundary layer development. Laser Doppler anemometry (LDA) was used to measure two components of velocity at high data rates in the airfoil wake. Wake profiles were measured in addition to single point measurements to determine the velocity spectrum. A microphone was mounted inside the test section in order to measure the trailing edge noise. Initial plans included measuring the trailing edge noise with a microphone array capable of quantifying and locating noise sources. Although an array was built and beamforming code was written it was only used in preliminary monopole source tests. Oil film results showed the behaviour of the boundary layer to be consistent with previous low Reynolds number experiments. LDA results revealed sharp peaks in the velocity spectra at 1100 Hz from U0 = 15–24 m/s, and 3100 and 3800 Hz, from U0 = 25–35 m/s, which were inconsistent with vortex shedding results of previous researchers. Also present were a series of broad peaks in the spectra that increase from 1200–1700 Hz in the U0 = 25–35 m/s range. The shedding frequency from the smoke wire flow visualization was calculated to be 1250 Hz at U0 = 26 m/s. These sharp peaks were also present in the acoustic spectrum. It was reasoned that these peaks are due to wind tunnel resonance which is a common occurrence in hard wall wind tunnels. In particular the tone at 1100 Hz is due to a standing wave with a wavelength equal to half the tunnel width. The shedding frequency from the smoke wire flow visualization was calculated to be 1100 Hz at U0 = 20 m/s. These tones exhibited a “ladder-like” relationship with freestream velocity, another aspect indicative of wind tunnel resonance. It was reasoned that the wind tunnel resonance was forcing the shedding frequency of the airfoil in the U0 = 15–24 m/s range, and in the U0 = 25–35 m/s range, the shedding frequency corresponded to the broad peaks in the LDA spectra.

La problématique des résonances acoustiques dans un tube corrugué sous écoulement a été étudiée conjointement sur le plan expérimental et numérique. Des analyses portant sur la structure de l’écoulement lors de l’apparition du sifflement sont réalisées. Elles visent à mieux comprendre la nature du phénomène et le couplage aéroacoustique en jeu.Des expériences en laboratoire sur trois géométries de veines corruguées de petites longueurs(1 à 2 m) ont été réalisées. Un écoulement d’air était appliqué pour des vitesses comprises entre10 et 25 m/s et une pression voisine de la pression atmosphérique faisant apparaître les résonancesacoustiques longitudinales. Des mesures par fil chaud, microphone et par technique laser (Particle ImageVelocimetry) ont permis de caractériser l’écoulement dans des conditions favorisant le sifflement. Sur ces différentes mesures, nous avons appliqué une technique de reconstitution spatio-temporelle, laLinear Staochastic Estimation (LSE). Des simulations numériques de type Lattice Boltzmann (2D, codePOWERFLOW, EXA) ont permis de prédire ce phénomène aéroacoustique avec une bonne détermination des modes préférentiels selon les conditions d’écoulement dans un tuyau corrugué court(1 à 2 m).Finalement, des essais à haute pression (P < 40 bars) conduits sur un riser industriel de 18 m ontcomplété cette étude. Dans ce cas, la résonance produite devenait transverse. Des traitements dessignaux tels que la transformation de Hilbert Huang ou par ondelettes de Gabor ont été appliqués mettant en évidence l’influence de la géométrie des corrugations sur le sifflement en temps, en fréquence et enamplitude.Dans les deux configurations, que ce soit en laboratoire ou en installation industrielle, les structures au sein de l’écoulement, dont la fréquence caractéristique était celle du sifflement, se déplaçaient à la vitesse de l’écoulement. Dans les deux cas, lorsque le tuyau corrugué se met à chanter, les mesures de vitesse et de pression dans l’écoulement montre une prédominance du pseudo-bruit sur le signal sonore. L’excitation observée sur les risers en condition de sifflement est celle d’un pseudo-bruit de niveau defluctuations très important sans distorsion non linéaire, et ce malgré un niveau de 170 dB. / The problem of acoustic resonances in a corrugated pipe under flow has been studied both experimentally and numerically. Analyzes concerning the flow structure during the whistling phenomenon are performed. They aim to better understand the nature of the phenomenon and the aeroacoustic coupling involved.Laboratory experiments were carried out on three geometries of corrugated veins of short lengths(1 to 2 m). An air flow was applied for speeds between 10 and 25 m/s and a pressure close toatmospheric pressure showing the longitudinal acoustic resonances. Measurements by hotwires,microphone and laser technique (Particle Image Velocimetry) allowed to characterize the flow under conditions favoring whistling. On these different measures, we applied a spatio-temporal reconstructiontechnique, the Linear Staochastic Estimation (LSE). Numerical simulations of Lattice Boltzmann method (2D, POWERFLOW code, EXA) have made possible the prediction of this aeroacousticphenomenon with a good determination of the preferential modes according to the flow conditions in ashort corrugated pipe (1 to 2 m).Finally, high pressure tests (P < 40 bars) conducted on an industrial riser of 18 m completed thisstudy. In this case, the resonance produced became transverse. Signal processing such as the HilbertHuang transformation or Gabor wavelet has been applied, highlighting the influence of the corrugation geometry on whistling in time, frequency and amplitude.In both configurations, whether in the laboratory or in an industrial facility, the structures within the flow, whose characteristic frequency was whistling, moved at the rate of flow. In both cases, when the corrugated pipe sings, velocity and pressure measurements in the flow show a predominance of the pseudo-noise on the sound signal. The excitation observed on the risers in the whistling condition is that of a pseudo-noise of very high level of fluctuations without non-linear distortion, and this despite a level of 170 dB.

Le présent travail a consisté à évaluer, améliorer et valider plus avant une méthode de couplage faible CFD/CAA, notamment relativement à son application à des problèmes réalistes de bruit avion. Entre autres choses, il a été ici montré dans quelle mesure une telle méthode hybride peut effectivement (i) s’accommoder des contraintes inhérentes aux applications réalistes, (ii) sans être menacée par certains de ses inévitables effets de bord (tels que la dégradation du signal auxquelles sont soumises les données CFD, lorsqu’elles sont traitées ou exploitées acoustiquement). / The present work consisted in improving, assessing and validating further the CFD/CAA surface weak coupling methodology, with respect to its application to realistic problems of aircraft noise. In particular, it was here shown how far such hybrid methodology could (i) cope with all stringent constraints that are dictated by real-life applications, (ii) without being jeopardized by some of the unavoidable side-effects (such as the signal degradation to which CFD data are subjected, when processed or being then acoustically exploited).

La contribution relative du bruit de combustion au bruit global des moteurs aéronautiques augmente progressivement dû d'un coté à la réduction des autres sources et d'un autre à l'implémentation des nouvelles technologies de chambre de combustion pour la réduction des émissions de NOx. Deux mécanismes sont responsables de cette source de bruit : d'abord le bruit direct, dû aux ondes acoustiques générées par la flamme qui se propagent à la sortie du moteur d'avion, et ensuite le bruit indirect, généré par les ondes d'entropie quand elles sont accélérées et ralenties dans les étages de turbine. Dans ce travail, les modèles analytiques utilisés pour la propagation des ondes à travers les flux non-homogènes, y compris la génération de bruit indirect, sont révisés et étendus. Tout d'abord, le cas quasi-1D est étudié: la méthode analytique est étendue pour les fréquences non nulles et validée avec des méthodes numériques et des données expérimentales. Dans la seconde partie, la méthode analytique 2D dans le cas d'aubes de turbines compactes est étudiée et validée à l'aide de simulations numériques d'un rotor et d'un étage de turbine complète. Enfin, ces modèles sont combinés avec des simulations aux grandes échelles réactives et compressibles de chambres de combustion pour construire une approche hybride appelée CHORUS capable de prédire le bruit de combustion. / Combustion noise is increasing its relative contribution to aircraft noise, while other sources are being reduced and new low-NOx emission combustion chambers being built. Two mechanisms are responsible for this noise source: direct noise in which acoustic waves are generated by the flame and propagate to the outlet of the aero-engine, and indirect noise, where entropy waves generate noise as they are accelerated and decelerated in the turbine stages. In this work the analytical models used for the propagation of waves through non-homogeneous flows, including the generation of indirect noise, are revised and extended. In the first part, the quasi-1D case is studied, extending the analytical method to non-zero frequencies and validating the results with numerical methods and experimental data. In the second part, the 2D method for the case of compact turbine blades is studied and validated using numerical simulations of a rotating blade and of a complete turbine stage. Finally, in the third part of this thesis, these models are combined with reactive and compressible Large Eddy Simulations (LES) of combustion chambers to build a hybrid approach, named CHORUS, able to predict combustion noise.

Avant leur lancement dans l'espace, les satellites font l'objet de tests afin d'éprouver leurs comportements à diverses sollicitations (thermiques, acoustiques, etc.). Pour les essais acoustiques, la société Intespace soumet les satellites à de forts niveaux sonores (de l'ordre de 145 dB SPL dans la chambre réverbérante) comparables à ceux existant lors du décollage du lanceur. Elle utilise pour cela des sources électropneumatiques couplées à des pavillons débouchant dans une chambre réverbérante. Ce système acoustique assure sa mission avec succès mais la société Intespace s'interroge sur ses possibilités d'amélioration. Deux prototypes de sources pneumatiques (à disque oscillant ou rotatif, à l'échelle 1 sur 5) sont développés et construits. Les prédictions théoriques avec vena contracta sont comparées aux données expérimentales issues d'un banc de mesure. Leurs différences concernant les niveaux sonores à la sortie de la source n'excèdent pas 1 dB pour des pressions d'alimentation de 1 à 3,5 bars absolus. Un prototype de pavillon de géométrie optimisée a été construit à l'échelle 1 sur 5. Les mesures montrent des performances intéressantes. Compte tenu des niveaux sonores générés par la source, une étude de la propagation dans le pavillon met en évidence des phénomènes non linéaires, qui s'avèrent peu influencés par la présence d'un écoulement moyen pour les vitesses envisagées dans l'étude. Finalement, des mesures sont réalisées sur l'ensemble du système à l'échelle 1 sur 5, afin d'en évaluer les performances. Les niveaux sonores mesurés sont comparés aux prédictions d'un modèle issu de la théorie de Sabine. Les différences n'excèdent pas plus ou moins 3 dB. / Before their launch in space, satellites are the object of tests in order to test their behaviors with diverse constraints (thermal, acoustic, etc.). In terms of acoustic qualification, the Intespace company submits the satellites to high sound levels (of the order of 145 dB SPL in the reverberating room) comparable to those existing during the take-off phase of the launcher. For this purpose, it uses electropneumatic sources coupled to horns opening into a reverberating room. This acoustic system ensures its mission successfully but Intespace is wondering about the possibilities of improving the system. Two prototypes of pneumatic sources (oscillating or rotating disk, 1 on 5 scale) are developed and constructed. Theoretical predictions taking into account the vena contracta are compared with the experimental data from an instrumented measuring bench. Their differences in the sound levels at the source outlet do not exceed 1 dB at supply pressures of 1 to 3.5 bars absolute. A horn prototype whose shapes have been optimized was built on a 1 on 5 scale. The measurements show interesting performances. Considering the sound levels generated by the source, a study of the propagation in the horn highlights nonlinear phenomena. The latter are not influenced by the presence of an average flow for the velocities envisaged in the study. Finally, measurements are realized on the whole system at 1 on 5 scale, in order to evaluate their performance. The measured sound levels are compared to the predictions of a model derived from the Sabine theory. The differences do not exceed 3 dB or less.

Desde a última década, as autoridades aeronáuticas dos países membros da ICAO vem, gradativamente, aumentando as restrições nos níveis de ruído externo de aeronaves, principalmente nas proximidades dos aeroportos. Por isso os novos motores aeronáuticos precisam ter projetos mais silenciosos, tornando as técnicas de predição de ruído de motores cada vez mais importantes. Diferente das técnicas semi-analíticas, que vêm evoluindo nas últimas décadas, as técnicas semiempíricas possuem suas bases lastreadas em técnicas e dados que remontam à década de 70, como as desenvolvidas no projeto ANOPP. Uma bancada de estudos aeroacústicos para um conjunto rotor/estator foi construída no departamento de Engenharia Aeronáutica da Escola de Engenharia de São Carlos, permitindo desenvolver uma metodologia capaz de gerar uma técnica semi-empírica utilizando métodos e dados novos. Tal bancada é capaz de variar a rotação, o espaçamento rotor/estator e controlar a vazão mássica, resultando em 71 configurações avaliadas. Para isso, uma antena de parede com 14 microfones foi usada. O espectro do ruído de banda larga é modelado como um ruído rosa e o ruído tonal é modelado por um comportamento exponencial, resultando em 5 parâmetros: nível do ruído, decaimento linear e fator de forma da banda larga, nível do primeiro tonal e o decaimento exponencial de seus harmônicos. Uma regressão superficial Kriging é utilizada para aproximar os 5 parâmetros utilizando as variáveis do experimento e o estudo mostrou que Mach Tip e RSS são as principais variáveis que definem o ruído, assim como utilizado pelo projeto ANOPP. Assim, um modelo de previsão é definido para o conjunto rotor/estator estudado na bancada, o que permite prever o espectro em condições não ensaiadas. A análise do modelo resultou em uma ferramenta de interpretação dos resultados. Ao modelo são aplicadas 3 técnicas de validação cruzada: leave one out, monte carlo e repeated k-folds e mostrou que o modelo desenvolvido possui um erro médio, do nível do ruído total do espectro, de 2.35 dBs e desvio padrão de 0.91. / Since the last decade, the countries members of ICAO, via its aeronautical authorities, has been gradually increasing the restrictions on external aircraft noise levels, especially in the vicinity of airports. Because that, the new aero-engines need quieter designs, so noise prediction techniques for aero-engines are getting even more important. Semi-analytical techniques have undergone a major evolution since the 70th until nowadays, but semi-empirical techniques still have their bases pegged in techniques and data defined on the 70th, developed in the ANOPP project. An Aeroacoustics Fan Rig to investigate a Rotor/Stator assembly was developed at Aeronautical Engineering Department of São Carlos School of Engineering, allowing the development of a methodology capable of defining a semi-empirical technique based on new data and methods. Such rig is able to vary the rotation, the rotor/stator spacing and mass flow rate, resulting in a set of 71 configurations tested. To measure the noise, a microphone wall antenna with 14 sensors were used. The broadband noise was modeled by a pink noise and the tonal with exponential behavior, resulting in 5 parameters: broadband noise level, decay and form factor and the level and decay of tonal noise. A superficial kriging regression were used to approach the parameters using the experimental variables and the investigation has shown that Mach Tip and RSS are the most important variables that defines the noise, as well on ANOPP. A prediction model for the rotor/stator noise are defined with the 5 approximation of the parameters, that allow to predict the spectra at operations points not measured. The model analyses of the model resulted on a tool for results interpretation. Tree different cross validation techniques are applied to model: leave ou out, Monte Carlo and repeated k-folds. That analysis shows that the model developed has average error of 2.35 dBs and standard deviation of 0.91 for the spectrum level predicted.

O desenvolvimento de uma ferramenta de Dinâmica de Fluidos Computacional que utiliza Método de Elementos Finitos baseada na discretização de Galerkin descontínuo é apresentado neste trabalho com objetivo de resolver a equação de Euler linearizada para escoamento compressível em duas dimensões usando malhas estruturadas e não estruturadas. Procuramos utilizar esta ferramenta como um propagador de ondas sonoras para estudar fenômenos aeroacústicos. O problema de Riemann presente no fluxo convectivo da equação de Euler é tratado com um método upwind HLL e para o avanço da solução no tempo é usado o método de Runge-Kutta explícito de 4 estágios com segunda ordem de precisão. A eficiência computacional, a convergência do método e a precisão são testadas através de simulações de escoamentos já apresentadas na literatura. A taxa de convergência para altas ordens de aproximação é assintótica que é um resultado compatível com a formulação Galerkin descontínuo. / The development of a Computation Fluid Dynamic Tool based on the Finite Element Method with discontinuous Galerkin discretization is presented in this work. The aim of this study is to solve the compressible linearized Euler\'s equation in two dimensions on structured and non structured meshes. This tool has been used as a means to study aeroacoustics phenomena. The Riemann\'s problem presented on a convective flow in Euler\'s equation is tackled by a HLL\'s method and the time integration being used is the four-stage Runge-Kutta explicit method with second order of accuracy. The computational efficiency, the convergence of the method and the accuracy are tested by comparing our results for flow simulations with those that are available in the literature. The convergence rate to high approximation order is asymptotic and it shows a result which is compatible with a discontinuous Galerkin formulation.

O presente trabalho refere-se a um estudo aeroacústico experimental visando caracterizar o ruído de eslate sob a presença de excrescências instaladas no interior de sua cova, e em ângulos de ataque extremos (entre -4 e 18 [º]). O eslate é um dispositivo hipersustentador posicionado no bordo de ataque do perfil aerodinâmico que objetiva a operação da aeronave em voo com uma menor velocidade. Desta maneira, é proporcionado um maior ângulo de estol e consequente maior sustentação, permitindo que os procedimentos de pouso e decolagem sejam mais seguros e que uma pista menor para ambas as operações possa ser utilizada, por exemplo. Este estudo contempla um modelo de perfil MDA 30P30N, com as excrescências no formato de selos de seção transversal bidimensional, circular e quadrada, presentes em diferentes posições na cova do eslate e ao longo de toda a sua envergadura. Foram compreendidos diferentes ângulos de ataque do modelo e velocidades de escoamento livre. O trabalho experimental utilizou-se de um túnel de vento de seção de testes e circuito fechados da USP-EESC, o modelo MDA 30P30N pré-existente na universidade e equipamentos de medições acústicas (microfones, sistemas de aquisição de dados e etc.), e de pressão (escâneres, manômetros, etc.). O pós-processamento dos dados aeroacústicos adquiridos nos ensaios realizados é uma etapa que objetiva a caracterização do ruído a partir de espectros de frequência e mapas acústicos, para localização e determinação da intensidade das fontes sonoras. Este processo é efetivado com códigos de beamforming implementados pelo grupo de pesquisa contendo o método de deconvolução DAMAS. A técnica de beamforming é um método para localização e estimativa da amplitude de fontes de ruído utilizando medidas realizadas a partir de uma antena de microfones, baseando-se em um modelo matemático que descreve a propagação de ondas acústicas em um meio com propriedades físicas bem definidas. Estes modelos são simplificados em relação à complexidade dos fenômenos de geração e propagação do som. O cálculo basicamente resolve a contribuição relativa das fontes provindas de diferentes direções no campo sonoro de interesse. O método DAMAS almeja compensar a influência das características da antena de microfones empregada para aquisição dos dados do resultado proveniente do cálculo efetuado com a técnica de beamforming convencional, resolvendo um problema de deconvolução. Os espectros de ruído obtidos neste trabalho apresentam o ruído de eslate bem definido em três componentes principais, que são os múltiplos picos tonais de baixa frequência, banda larga e pico tonal de alta frequência. Para a configuração de referência, sem a presença de selos na cova do eslate, verifica-se que ângulos de ataque extremos, muito baixos ou muito altos, apresentam o espectro de frequências quase que inteiramente como de banda larga e de intensidade muito próxima ao ruído de fundo do túnel. Também há um ângulo de ataque em que a emissão sonora é máxima. Quando há a presença de um selo na cova do eslate, existe um grande impacto em seu espectro acústico. Dependo da posição em que o selo se encontra, este pode atenuar ou intensificar os múltiplos picos tonais de baixa frequência, trocar o pico dominante, suprimir a componente de múltiplos picos, modificar o comportamento da componente da banda larga e ainda amplificar ou reduzir o ruído global do eslate. / The present work refers to an experimental aeroacoustic study aiming to characterize slat noise over the presence of excrescences installed at the interior of its cove, and at very high and very low angles of attack (between -4 e 18 [º]). A slat is a high-lift device located at the leading edge of an airfoil which target to maintain the aircraft in flight at a lower speed by providing a greater stall angle and consequently greater lift coefficient, allowing safer landing and take-off procedures. Therefore, a smaller airport runaway for both operations may be used. This study includes a model of a MDA 30P30N airfoil, with a seal excrescence of two-dimensional cross-section shape, circular or square, positioned at different locations at slat cove throughout the extent of its span. Different models angles of attack and some free-stream velocities were tested. The experimental work employed a closed-section wind tunnel situated at USP-EESC, a preexisting MDA 30P30N model, and acoustic measurement equipments (microphones, data acquisition systems, etc.), and pressure measurement equipments (scanners, pressure gauges, etc.). The data post-processing of aeroacoustics experiments intend to characterize the slat noise due to frequency spectrums and acoustic maps to locate and evaluate the intensity of the noise sources. This process is made with beamforming in-house codes, implemented by the research group, containing a deconvolution method named DAMAS. Beamforming technique is a method to localize and assess noise sources amplitude using measurements from an antenna of microphones, based on a mathematical model that describes the propagation of acoustic waves in a medium with well defined physical properties. Such models are simplified compared to the complexity of the phenomena of generation and propagation of sound. The calculation basically resolves the relative contribution of sources emanating from different directions at the sound field of interest. DAMAS method aim to extract the characteristics of the microphones antenna employed to acquire data, from the result of the calculation performed with conventional beamforming algorithm, solving a deconvolution problem. The noise spectrum obtained at this work shows that the slat noise can be well defined in three main components, which are the multiple tonal peaks of low frequency, broadband and high-frequency tonal peak. For the baseline configuration, without seals at slat cove, it is possible to notice that for extreme angles of attack, very low or very high, the noise spectrum is almost entire of broadband type. Its noise intensity is very near to the background wind tunnel noise. There is an angle of attack which has a maximum sound emission. A seal at MDA 30P30N slat cove has a huge impact on slat noise spectrum. Depending on the seal position, it can mitigate or enhance the multiple low-frequency tonal peaks, change the dominant peak, suppress multiple tonal peaks, modify the behavior of the broadband component and reduce or amplify the overall slat noise.

Une couche de mélange est généralement considérée comme un prototyped'écoulements libres cisaillés trouve sa présence au sein des nombreuses phénomènesnaturelles et applications industrielles. Le fort développement de l'aéroacoustique, notammentgrâce aux progrès des simulations numériques, a permis d'identifier les structures cohérentesqui se développent dans l'écoulement comme les principales sources de bruit. En outre,l'analyse de stabilité permet de caractériser l'émergence des ondes d'instabilités sous forme deces structures. Dans ce cadre, nous proposons de réaliser à travers ce mémoire une analysede stabilité globale, afin de comprendre l'émergence de fréquences fondamentales, ainsi qu'unedécomposition modale linéaire et non-linéaire, afin de caractériser les structures cohérentesessentiellement responsables du rayonnement acoustique. En particulier, nous proposons dedévelopper les méthodes de stabilité globale en régime compressible ainsi qu'une technique decalcul de structures cohérentes appliquée en régime non-linéaire basée sur la méthode« DMD ». De tels outils d'analyse sont validés et illustrés sur une configuration académiqued'une couche de mélange à co-courant, de type d'amplificateur de bruit, d'un simple cas où uneseule source est impliquée dans le rayonnement acoustique à un cas plus complexe où deuxsources sont présentes. Aussi bien la DMD temporelle que la DMD spatiale sont montréscapables de décrire le comportement des structures cohérentes en champ proche et lescaractéristiques des ondes acoustiques en champ lointain. Enfin, les méthodes dedécomposition modale s'avèrent une base de réduction de modèle pertinente, dans l'objectifd'un contrôle efficace. / A mixing layer is generally considered as a prototype of free shear flows whichoccur in a very broad spectrum of applications from natural phenomena to the engineeringscience. The increasing development of the aeroacoustics, more particularly thanks to theprogress in numerical simulations, has allowed to identify the coherent structures which evolvein the flow as the main sound sources. Furthermore, the emergence of the instability wavestaking the form of the coherent structures can be characterized by the stability analysis. In thiscontext, we propose through this work to perform a global stability analysis, in order tounderstand the emergence of fundamental frequencies, as well as a modal decompositionwithin both a linear and nonlinear framework, to characterize the coherent structures primarilyresponsible for the sound generation. In particular, we propose to develop the methods of theglobal stability with respect to the compressible flows as well as a technique of calculation ofcoherent structures applied to the nonlinear regimes based on the DMD method. Such analysistools are validated and illustrated on an academic configuration of a co-flowing mixing layer, atypical noise amplifier, from a simple case where a single source is implicated in the acousticradiation to a more complex case where two sources are present. Both the temporal and spatialDMD are shown capable of describing the characteristics of the coherent structures in the nearfield and the behaviour of the acoustic waves in the far field. Finally, the methods of the modaldecomposition have proven themselves as a relevant model reduction aiming at designing anefficient control strategy.

Au sein d’un échangeur à air, les trompes à air permettent de créer l’écoulement d’air froid nécessaireà son bon fonctionnement. Ces dispositifs, qui peuvent ^etre assimilés à des jets subsoniques confinésen conduit, peuvent contribuer au bruit rayonné par les avions lors des phases au sol. Nous proposonsdans cette thèse de développer un outil numérique prédictif de l’acoustique rayonnée par ces dispositifsafin de pouvoir proposer des solutions de réduction de bruit appropriées. Cet outil est adapté au contexteindustriel de Liebherr Aerospace. Une méthode stochastique permet, à partir d’un calcul stationnaireRANS, de générer un champ de vitesse turbulente qui autorise la formation d’un terme de forçage dansles équations d’Euler linéarisées qui sont alors utilisées comme un opérateur de propagation. Un nouveaumodèle stochastique basé sur l’hypothèse de sweeping est développé. Ce dernier permet de produiredes champs instationnaires respectant certaines propriétés aérodynamiques statistiques dans le cadre dejets libres subsoniques. Cette méthode est couplée avec le solveur Euler de l’Onera sAbrinA_v0 et l’outilrésultant est appliqué sur le cas d’un jet libre subsonique à M=0.72. Moyennant une calibration duterme source, la méthodologie permet de reproduire les spectres acoustiques en champ lointain, exceptépour les angles faibles. L’outil numérique est ensuite couplé avec un solveur FW-H pour étudier le casconcret de la trompe à air. Les résultats aérodynamiques et acoustiques sont validés par comparaison àune base de données aérodynamique et acoustique constituée au préalable à partir d’une campagne d’essaiscomprenant des mesures par anémométrie laser Doppler à l’intérieur du conduit et des microphonesacoustiques en champ lointain. / In air exchangers, the cool air flow can be produced by jet pumps. These devices, which can be consideredas subsonic jets confined in ducts, could contribute directly to ramp noise. A predictive numerical toolof the acoustic radiated by jet pumps is therefore developped in order to be able to propose appropriatenoise reduction solutions. This tool is adapted to Liebherr Aerospace’s industrial context. A stochasticmethod allows, starting from a steady RANS computation, to synthetise a turbulent velocity fields andto enforce source terms in the linearized Euler equations therefore used as a wave propagator. A newstochastic model relying on the sweeping hypothesis is developped. Unsteady fields reproducing someaerodynamics features of a free subsonic jet flow can be generated. This method is then coupled withOnera’s Euler solver sAbrinA_v0 and the resulting tool is applied on a free subsonic jet configuration atMach 0.72. Assuming a cabration of the source terms, this methodology models properly the far fieldacoustic spectra except for small angles. The numerical tool is then coupled with a FW-H solver to studya realistic jet pump. Aerodynamic and acoustic results are validated by comparison with a data baseobtained from an experimental campaign including laser Doppler anemometry measures inside the ductand pressure recording in the far-field.