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The present work is dedicated to turbulence synthesis tailored to lateral periodic boundary conditions for direct noise computations through compressible large eddy simulations. Synthetic turbulence can be essential for aeroacoustic applications when computing airfoil turbulent inflow noise or for accurately capturing the behavior of boundary layers. This behavior determines both trailing edge noise and complex flow structures such as laminar separation bubbles. For airfoil simulation purposes, spanwise periodic boundary conditions are usually considered. If synthetic perturbations are injected without observing the periodicity rule, strong spurious pressure waves are emitted and pollute the entire computational domain. In this work, the random Fourier modes method for turbulence generation is adapted in order to respect the spanwise periodicity constraint right at the computational domain inlet. This approach does not affect the turbulence properties such as the spectral shape and the turbulent kinetic energy decay. Since the emphasis is put on the generation and convection of the turbulence, only the turbulence convection region between the inlet and the airfoil is considered in this paper, without the airfoil. Two geometrical configurations are tested: the first one is a simple box with a constant mesh size, and the second one concentrates the fine cells on the area in front of the airfoil. In the second configuration, the computational cost is reduced by up to 25%, but more spurious noise is present because of interpolation areas between different grids using the Chimera method. Finally, the results’ reproducibility is assessed using different turbulence realizations.

This work presents an efficient and accurate method for the calculation of the properties of carbon dioxide. This is motivated by the massive employment of this fluid in the industrial domain, especially in the refrigeration industry through supersonic ejector cycles, and in the CO2 capture and storage (CCS) industry. A tabulated equation of state (EoS) is developed in the density-internal energy space, based on the Span-Wagner EoS formulation which is the current international reference for computing CO2 properties. The tabulated EoS is coupled to the Homogeneous Equilibrium Model to calculate properties of the liquid−vapor mixture. To assess the performance of the developed EoS, three configurations are simulated, namely a shock tube, a tube depressurization, and a converging−diverging nozzle. Throughout the comparisons to other EoSs, such as the Peng−Robinson, the Stiffened Gas and the original Span-Wagner EoSs, the high efficiency of the tabulated equation of state is revealed.

The excitation of trapped diametral acoustic modes within a rectangular cavity attached to a cylindrical duct is investigated numerically and experimentally. Because the excited acoustic modes are ...

International audience; The interaction of inflow turbulence with an airfoil is significant for low Reynolds number applications, as it generates leading edge noise, but also strongly modifies the airfoil boundary layer properties and thus the produced noise. Inflow turbulence impact still demands to be better understood and is also a numerical challenge. Large Eddy Simulations are here carried out with both incompressible and compressible solvers. The Synthetic Eddy Method and the Random Fourier Modes method, used to generate synthetic turbulence, are studied in this work. In order to eventually perform airfoil simulations, the second method is modified to take into account spanwise periodic boundary conditions, to reduce spurious noise level in compressible simulations. First, properties of the methods are studied with a spatially decaying turbulence academic case. Even if the decay is not well represented, the methods show satisfactory properties in terms of isotropy, homogeneity and one-dimensional spectra. Furthermore, spurious noise levels are reduced thanks to the modified method. Preliminary airfoil simulations are then carried out with inflow turbulence for flow validation in presence of a laminar separation bubble. The drag coefficient is in very good agreement with experimental results. However, there are some discrepancies between simulations and experiments on the lift coefficient, which is extremely sensitive to perturbations. These discrepancies are attributed to a lack of experimental turbulence characteristic information, such as isotropy or integral length scale and to too short simulations at high angles of attack.

International audience; Natural grounds can exhibit small scale geometric irregularities, compared to the acoustic wavelength, known as ground roughness. This roughness has a noticeable effect on sound pressure levels and produces a surface wave. In the context of prediction methods improvement for outdoor sound propagation, using an effective impedance appears to be an useful approach to model the effects of surface roughness. Two time-domain numerical methods are considered: finite difference schemes (FDTD), and the transmission line modeling (TLM) method. An effective impedance model for random ground roughness defined by a roughness spectrum, called the SPM model, is exposed. The efficiency of this model for taking into account the mean effects of random roughness on sound pressure levels and for modeling the roughness-induced surface wave is shown, by comparing with results of TLM simulations of propagation above random rough grounds. The direct implementation of the SPM model as a boundary condition in both TLM and FDTD methods is then studied. This approach allows the modeling of ground roughness effects in numerical methods without having to mesh finely the ground roughness profile, allowing easier and faster computations, and more accurate predictions for future impact studies in environmental acoustics.

Electricité de France (EDF), with the scientific cooperation of Université Catholique de Louvain (UCL), is starting new investigations about the blowdown phenomena. For these purposes, EDF is considering to build a new experimental installation called BRECHE. In this article, the main features of the design of the test rig are presented together with the numerical simulation carried out with EUROPLEXUS code for the hydraulic and mechanical design of BRECHE.

Flow over ducted cavities can lead to strong resonances of the trapped acoustic modes due to the presence of the cavity within the duct. Aly and Ziada (2010, “Flow-Excited Resonance of Trapped Modes of Ducted Shallow Cavities,” J. Fluids Struct., 26(1), pp. 92–120; 2011, “Azimuthal Behaviour of Flow-Excited Diametral Modes of Internal Shallow Cavities,” J. Sound Vib., 330(15), pp. 3666–3683; and 2012, “Effect of Mean Flow on the Trapped Modes of Internal Cavities,” J. Fluids Struct., 33, pp. 70–84) investigated the excitation mechanism of acoustic trapped modes in axisymmetric cavities. These trapped modes in axisymmetric cavities tend to spin because they do not have preferred orientation. The present paper investigates rectangular cross-sectional cavities as this cavity geometry introduces an orientation preference to the excited acoustic mode. Three cavities are investigated, one of which is square while the other two are rectangular. In each case, numerical simulations are performed to characterize the acoustic mode shapes and the associated acoustic particle velocity fields. The test results show the existence of stationary modes, being excited either consecutively or simultaneously, and a particular spinning mode for the cavity with square cross section. The computed acoustic pressure and particle velocity fields of the excited modes suggest complex oscillation patterns of the cavity shear layer because it is excited, at the upstream corner, by periodic distributions of the particle velocity along the shear layer circumference.

A high-order finite-difference algorithm is proposed in the aim of performing LES calculations for CAA applications. The subgrid scale dissipation is performed by the explicit high-order numerical filter used for numerical stability purpose. A shock-capturing non-linear filter is also used to deal with compressible discontinuous flows. In order to tackle complex geometries, an overset-grid approach is used. High-order interpolations make possible the communication between overlapping domains. The whole algorithm is first validated on canonical flow problems to illustrate both its properties for shock-capturing as well as for accurate wave propagation. Then, the influence of the multi-domain approach on the high-order spatial accuracy is assessed. Finally, a rod-airfoil configuration is studied to highlight the potential of the proposed algorithm to deal with multi-scale aeroacoustic applications.

Flow over ducted cavities can lead to strong resonances of the trapped acoustic modes due to the presence of the cavity within the duct. Aly & Ziada [1–3] investigated the excitation mechanism of acoustic trapped modes in axisymmetric cavities. These trapped modes in axisymmetric cavities tend to spin because they do not have preferred orientation. The present paper investigates rectangular cross-sectional cavities as this cavity geometry introduces an orientation preference to the excited acoustic mode. Three cavities are investigated, one of which is square while the other two are rectangular. In each case, numerical simulations are performed to characterize the acoustic mode shapes and the associated acoustic particle velocity fields. The test results show the existence of stationary modes, being excited either consecutively or simultaneously, and a particular spinning mode for the cavity with square cross-section. The computed acoustic pressure and particle velocity fields of the excited modes suggest complex oscillation patterns of the cavity shear layer because it is excited, at the upstream corner, by periodic distributions of the particle velocity along the shear layer circumference.Copyright © 2015 by ASME

The discharge of a subcooled liquid or a liquid-vapor mixture at high temperature and pressure can occur in many industrial situations. This paper is focused on the analysis of critical flow models that are already available in the fast transient dynamics software EUROPLEXUS, or that are being implemented as new break boundary conditions. The results of the Moody, Fauske, Flinta, Henry-Fauske and DEM models are presented and compared with the Super Moby Dick experimental results. The best results are obtained for the DEM. Then preliminary results concerning the implementation of the DEM model as a break boundary condition in EUROPLEXUS are given.Copyright © 2015 by ASME

Most aeroacoustic noise-prediction methods rely on an acoustic analogy featuring a propagation equation associated with source terms. These models were mainly applied to computation of acoustic far fields radiated by simple free flows like jets. The assumption is made in many formulations that the radiated acoustic field is not perturbed by the shear flow giving rise to the noise sources. These acoustic analogies thus do not provide a full description of acoustic/flow interactions. The Lilley equation was introduced to account, to a certain extent, for mean shear effects on propagation. More recently, this problem has been treated by making use of the linearized Euler equations, which are more flexible and more adequate for numerical simulations. As several types of modes are supported by the Euler equations, problems linked to their coupling have to be considered. It is then necessary to investigate acoustic field computations in complex flows. Our aim in the present article is to validate the wave operator associated with linearized Euler equations. Numerical tests deal with propagation in two-dimensional sheared ducted flows. Results are compared with other solutions deduced from analytical developments and direct numerical simulations. This study shows that the linearized Euler operator may be used to account for mean effects on wave propagation in the presence of sheared ducted flows. Processes that are specifically considered are 1) convection effects on axial disturbances, 2) refraction effects on oblique wave generation, and 3) source radiation effects on propagation in sheared flows.

Subsonicandsupersonicjetnoiseisdeterminednumerically from statisticalsourcemodels.Thegoalistodevelop prediction methods for high-speed jet noise for application to aeronautical and space transportation systems. In this framework, a combination of a k-≤ turbulence closure with an acoustic analogy provides an interesting way to compute such radiated acoustic e elds. Three acoustic analogies are investigated. First, the classical Lighthill theory in combination with Ribner' s results is applied to calculate jet mixing noise. The second method relies on the Goldstein -Howes convected wave equation, which is used to improve the predicted supersonic jet mixing noise in the upstream direction. It is necessary to properly account for acoustic wave convection, and then, one e nds that the Doppler factor features an exponent of i 3 in the associated power law. A model based on the Ffowcs Williams-MaidanikanalysisthenisdevelopedtoestimatetheMach-wavenoisecomponentthatdominatesforward arc radiation when theconvection Mach number is supersonic. Comparisons between aerodynamicand calculated acoustic results on the one hand, and available measurements on the other hand, are carried out. It is shown that the last two models yield improved supersonic jet mixing noise predictions.

The excitation mechanism of acoustic resonances has long been recognized, but the industry continues to be plagued by its undesirable consequences, manifested in severe vibration and noise problems in a wide range of industrial applications. This paper focuses on the nature of the excitation mechanism of acoustic resonances in piping systems containing impinging shear flows, such as flow over shallow and deep cavities. Since this feedback mechanism is caused by the coupling between acoustic resonators and shear flow instabilities, attention is focused first on the nature of various types of acoustic resonance modes and then on the aeroacoustic sound sources, which result from the interaction of the inherently unstable shear flow with the sound field generated by the resonant acoustic modes. Various flow-sound interaction patterns are discussed, in which the resonant sound field can be predominantly parallel or normal to the mean flow direction and the acoustic wavelength can be an order of magnitude longer than the length scale of the separated shear flow or as short as the cavity length scale. Since the state of knowledge in this field has been recently reviewed by Tonon et al. (2011, “Aeroacoustics of Pipe Systems With Closed Branches”, Int. J. Aeroacoust., 10(2), pp. 201–276), this article focuses on the more practical aspects of the phenomenon, including various flow-sound interaction patterns and the resulting aeroacoustic sources, which are relevant to industrial applications. A general design guide proposal and practical means to alleviate the excitation mechanism are also presented. These are demonstrated by two examples of recent industrial case histories dealing with acoustic fatigue failure of the steam dryer in a boiling water reactor (BWR) due to acoustic resonance in the main steam piping and acoustic resonances in the roll posts of the Short Take-Off and Vertical Lift Joint Strike Fighter (JSF).

A pure tone phenomenon has been observed at 460 Hz on a piping steam line of a power plant. The source has been identified to be generated in a gate valve and to be of cavity noise type. This paper presents the investigations carried out on experimental models in order to analyze the problem. 2D and 3D axisymmetric models are used and lock-in situations between shear layer modes and acoustic duct modes are proven to give rise to powerful tones. Some counter measures are also tested with the objective of lowering the amplitude of pressure oscillations.Copyright © 2013 by ASME

Piping systems conveying gases at high pressure often generate high level of vibration and noise. These phenomena, in many cases, are initiated by the coupling between an unstable separated flow and an acoustic mode of the piping system. Various types of cavities in pipe flow are among the flow geometries which are known to be liable to the generation of tonal noise. Flow over cavities in ducts and piping systems has been investigated extensively for two and three dimensional situations. In this case, the feedback loop which generates the tonal noise is caused by the coupling between the instability of the shear layer forming at the cavity opening and an acoustic mode. This paper presents a study of tonal noise generation by subsonic pipe flows over a cavity formed inside a fully open gate valve. Previous 2D and 3D studies, presented in a companion paper, have shown that the presence of the valve-seat cavity is responsible for the generation of acoustic tonal noise. In this paper, the full 3D geometry of the valve, on a small scale model, is studied with experiments and using an unsteady compressible flow solver developed at EDF. Experimentally, the evolution of the fluid acoustic coupling in term of frequency and amplitude with the flow velocity is studied. Also, a modal analysis have been done to identify the frequency of acoustic mode of the valve. Numerically, the complex 3D geometry is meshed and computation is performed. The results show an acoustic tonal noise in a frequency range compatible with that experimentally. The study is underway, future analysis of the velocity and acoustic fields in the simulation may help to identify the shear layer and acoustic modes and to identify how they couple together.Copyright © 2013 by ASME

A statistical energy analysis approach was developed in this paper for the prediction of the sound transmitted through a flexible plate loaded by the turbulent wake of a car rear view mirror. The fluid loading is simulated using a direct noise computation code. This code solves the full compressible three dimensional Navier-Stokes equations with highly accurate space and time algorithms and is able to capture the low amplitude acoustic part of the wall pressure fluctuations. The computed wall pressure field is used as power input in a statistical energy analysis model coupling the flexible plate to an acoustic cavity. Although the acoustic component is of small magnitude compared to the convected component of the fluid loading, it is shown that the non-resonating plate modes provide an efficient transmission path to the acoustic excitation which cannot be neglected below the coincidence frequency of the plate. Above this critical frequency, the sound pressure inside the cavity is driven by the resonant modes and the acoustic component of the wall pressure fluctuation.

We develop in this paper an analytical solution for the sound transmitted into a rigid rectangular cavity by a flexible plate loaded by the turbulent boundary layer of a grazing external flow. This simplified geometry aims to represent the vibro-acoustic response of a car front door window excited by the turbulent air flow that forms along the exterior surface of the vehicle. The modal expansion method is used to describe the plate displacement as well as the acoustic pressure in the cavity. The fluid loading is simulated using a direct noise computation code in the wake of a car rear view mirror. This code solves the full compressible three dimensional Navier-Stokes equations with highly accurate space and time algorithms and is able to capture the low amplitude acoustic part of the wall pressure fluctuations. The advantage of the modal approach is that the structural modes of the plate are represented in the wavenumbers’ space as an array of dots. It is thus possible using a wavenumber diagram to separate the plate modes which are spatially coupled to the propagative acoustic component from the modes which are spatially coupled to the aerodynamic convected component of the wall pressure fluctuations. Although the acoustic component is of small magnitude compared to the convected component of the fluid loading, it is shown that its contribution to the interior sound pressure level is crucial above the acoustic critical frequency of the plate.

Development of optimal reduced-order models for linearized Euler equations is investigated. Recent methods based on proper orthogonal decomposition (POD), applicable for high-order systems, are presented and compared. Particular attention is paid to the link between the choice of the projection and the efficiency of the reduced model. A stabilizing projection is introduced to induce a stable reduced-order model at finite time even if the energy of the physical model is growing. The proposed method is particularly well adapted for time-dependent hyperbolic systems and intrinsically skew-symmetric models. This paper also provides a common methodology to reliably reduce very large nonsymmetric physical problems.

The numerical prediction of the wind noise in a car cabin requires distinguishing between the aerodynamic and the acoustic components of the wall pressure fluctuations loading the car side windows. It is theoretically possible to separate them using a time and space Fourier transform. Nevertheless the acoustic component is much smaller in amplitude than the aerodynamic one, and may be obscured by the numerical noise. We use in this work a direct noise computation code which can solve the full compressible three dimensional NavierStokes equations with highly accurate space and time algorithm. This code is able to capture the acoustic wall pressure fluctuations and to deal with complex geometry. We focus in this paper on the case of a car side mirror over a flat plate that has also been experimentally studied in a wind tunnel. The good agreement between the computed and the measured wall pressure fluctuations in the wake of the mirror validates the numerical predictions and allows the post processing of the simulated data: The wavenumber frequency diagram of the power spectral density shows clearly two distinct cones corresponding to the acoustic and the aerodynamic components of the wall pressure fluctuations.

The influence of the filter shape on the effective scale separation and the numerical accuracy of large-eddy simulations based on relaxation filtering (LES-RF) is investigated. The simulation of the turbulent flow development of a high-Reynolds number low-subsonic compressible mixing layer is performed using the LES-RF procedure, for discrete filters of order 2–10. A reference solution is first obtained using high-order numerical algorithms and shows a good agreement with experimental data found in the literature. Discrete filters of order 2, 4, 6, 8 and 10 are then considered to study the influence of the filter shape on numerical results. The 2nd-order scheme turns out to be too dissipative and prevents the emergence of unsteady motions within the mixing layer. For higher order schemes, from 4th- to 10th-order, the flow solutions are turbulent but exhibit mean flows and turbulent intensities depending on the filter. The investigation of the one-dimensional kinetic energy spectra then shows that the 4th-order filter may still be too dissipative whereas large scales remain unaffected using the 6th-, 8th- and 10th-order filters. A further study of the kinetic energy spectra nonetheless demonstrates that the effective spatial bandwidth of the LES increases with the order of the filtering scheme. Simulations using the 6th-, 8th- and 10th-order filters, with mesh sizes chosen to provide the same effective LES cut-off wavenumber, are performed and yield similar results. It is hence found that the value of the effective LES cut-off wavenumber, rather than to the filter shape itself, is mainly responsible for the discrepancies between the flow statistics obtained using different filters. One may conclude that filter shape independence is consequently achieved in the present LES of a mixing layer.

A partir du modele theorique propose initialement par Goldstein pour un jet libre turbulent circulaire, on etablit des expressions analytiques (modele Ga) permettant le calcul du bruit emis a partir des grandeurs statistiques locales du jet turbulent. Ces grandeurs sont estimees par resolution des equations de Navier-Stokes moyennees a l'aide d'un code numerique de turbulence utilisant un modele de fermeture de type K - e. La comparaison entre les resultats numeriques obtenus et les donnees experimentales, pour un jet simple et deux jets coaxiaux, montre que ce modele estime correctement l'evolution des grandeurs acoustiques etudiees. Les calculs indiquent que le modele Ga developpe pour une turbulence axisymetrique convectee par un ecoulement moyen est mieux adapte que celui de Ribner associe a une turbulence isotrope. De plus, une comparaison entre differents modeles bases sur la theorie de Lighthill indique que le modele Ga donne la meilleure directivite de l'intensite acoustique aux vitesses d'ejection elevees.

International audience; A sonic flow in a plane duct passing an abrupt increase in cross section is studied using compressible large-eddy simulations. Different flow patterns are likely to appear in this configuration according to the ratio between the downstream ambient pressure and the upstream reservoir pressure. For low pressure ratios, the flow is entirely supersonic in the channel and a steady symmetrical shock pattern is observed. For higher pressure ratios, the flow can be attached to one side of the channel with a jet-like shock cell structure, or can be characterized by strong oscillations of a single normal shock located near the sudden expansion, known as base-pressure oscillations in literature. A hysteresis phenomenon is found experimentally and the state reached by the transonic flow depends on the path followed by the pressure ratio. Moreover, a coupling of these base-pressure oscillations with the quarter-wavelength resonance of the duct can occur. All these regimes are numerically investigated and the results are favorably compared to available experimental data. A case of frequency locking of this self-excited mechanism is also reproduced, in agreement with a modeling of the resonator. The governing equations are solved using high-order central finite differences combined with an overset grid approach. The large-eddy simulations are based on a relaxation filtering and a nonlinear shock-capturing scheme is also implemented for shock waves.

Lafon Philippe. Le syndicalisme des sportifs professionnels : quel soutien et quels services ? Le cas de l’Union nationale des footballeurs professionnels. In: Les Cahiers de l'INSEP, n°42, 2008. Le sport professionnel : état des lieux et perspectives. pp. 102-104.

A sonic flow in a plane duct passing an abrupt increase in cross-section is numerically studied by solving the 3-D compressible Navier-Stokes equations. Different flow patterns are likely to appear in such configuration. For a very low downstream pressure, the flow is entirely supersonic. For higher pressures, unstable flow patterns emerge. One of these patterns features a normal shock, that oscillates due to a self-exciting mechanism. As the duct is open at the outflow, aeroacoustic coupling occurs when the shock oscillations get in resonance with the longitudinal acoustic modes of the duct. The main flow features are well captured by the present numerical simulations but no coupling with longitudinal duct modes is found. The governing equations are solved using high-order methods based on central finite differences. To damp out spurious oscillations supported by central differences selective filtering and a well established non-linear shock-capturing term are used. A highorder overset grid approach is implemented in order to tackle with complex geometries.

A direct computation of the noise radiated by a turbulent flow in a duct obstructed by a diaphragm is performed by compressible large-eddy simulation. For the low Mach number configuration considered, a two-step hybrid method could be less expensive, but would fail at characterizing sound-flow interactions. The application of direct calculation is thus challenging but gives both the acoustic and aerodynamic fields in the same computation in order to shed light on the noise generation mechanisms. Acoustic energy is produced and dissipated in the asymmetric jet-type flow issuing from the diaphragm. A low-frequency radiation is correlated with the breakdown of the coherent jet-column structures as the plane jet reattaches the upper wall. The Kelvin–Helmholtz vortices in the shear layers of the jet constitute the primary instabilities but do not radiate sound. On the contrary, this vorticity shedding seems to dissipate waves propagating upstream by enforcing the unsteady Kutta condition.

High levels of vibrations have been observed on the last row blades of a low pressure steam turbine for nominal operating conditions. A self-excited phenomenon known as flutter is suspected to be the cause of the vibrations for non-stall transonic conditions. The non-homogeneous distribution of vibratory levels on the row is attributed to mistuning effects. They are beyond the scope of our study. A time-dependent ALE formulation of Euler equations is derived on a quasi-3D domain and coupled with a one-degree-of-freedom structural model. The work-by-cycle (WBC) method is performed in order to analyse the stability of the vibrating blades in the surrounding flowfield, for a perfectly tuned assembly. On the top part of the blades, the flow is transonic and fully attached. It is shown that, for these operating conditions, the cascade aeroelastic behaviour is linear. By using the influence coefficient method, an instability region is exhibited. The effects of the flowfield on the vibrating blades are discussed. They are expressed in terms of added damping and stiffness in order to be used as the input data of a structural mistuning analysis.Copyright © 2005 by ASME

A pure tone phenomenon has been observed in a PWR line. The source has been identified to be generated in a valve and to be of cavity noise type. In this paper, two 2D Euler computations are presented : the first one concerns the configuration that was used for experiments on a scale model (air flow) in order to compare with the on site observations (steam flow) and the second one concerns a modified geometry that was also used experimentally in order to search for a solution. Both experimental and numerical results show that the tested solution (a 15° chamfer at the upstream corner of the cavity) gives a decrease of the oscillation amplitude.

A pure tone phenomenon has been observed at 460 Hz in a PWR steam line. The acoustical energy has been identified to be generated in an open gate valve and to be of cavity noise type. The objective here is to understand the flow acoustic coupling in the cavity and in the duct. Both experimental and numerical investigation ways are used. The flow acoustic phenomena are modeled by computing the Euler equations. Two different computations are carried out: in the first one, a pure Euler modeling is used, in the second one, a boundary layer obtained from experimental data is introduced in the computation in order to have a realistic flow profile upstream the cavity. In the first computation, the acoustic excitation due to the cavity is qualitatively retrieved but the frequency is too high compared to the experimental one and no cavity duct coupling is detected. In the second computation, the frequency of the cavity oscillation is very close both the theoretical one and the experimental one. As it is also very close the frequency of the first transverse mode of the duct, the two modes of oscillation (the cavity one and the duct one) are coupled.Copyright © 2002 by ASME

A pure tone phenomenon has been observed at 460 Hz in a PWR steam line. The acoustical energy has been identified to be generated in an open gate valve. The objective here is to understand the way of energy transfer from the fluid to the main pipe using two fully coupled methods. The first method consists in a modal analysis of the line using a fluid-structure finite elements model. The second one is based on the analysis of dispersion diagrams derived from the local equations of cylindrical shells filled with fluid. The way of energy transfer in transverse acoustical waves induced combined flexion-ovalisation deformations of the pipe is highlighted using both methods. The dispersion diagrams allow a fast and accurate analysis. The modal analysis using a finite elements model may complete the first one with quantitative data.

New aeroacoustic noise prediction methods rely on the computation of linearized Euler equations (LEE) associated with source terms. The process may be described as follows : aerodynamic mean fields are deduced from the time-averaged Navier-Stokes equations associated with a closure scheme ensured for example by a k-6 turbulence modelling ; the source terms resulting from turbulent fluctuation effects are calculated separately ; these terms are finally incorporated into the linearized propagation equations providing the acoustic field. While the LEE are known to bear convective modes, the difficulty associated with the growth of this mode in an inflexional shear flow profile has not been adressed explicitely. This issue is considered in this article. It is first shown that a small flow perturbation, solution of the Rayleigh equation, when used as input to the LEE, will grow exponentially. In order to avoid this unwanted behaviour, a new semilinearized wave operator including non linear terms is built. This ensures stability and in this way acoustic flow interactions may be correctly described. The SLEE set features finite amplitude perturbations.

L’aviculture n’est plus le metier d’aventurier du debut du XX e siecle et la production de l’œuf, qui demande des investissements considerables, tant intellectuels que financiers, est devenue une industrie tres importante. C’est sur cette industrie moderne que la production des ovoproduits a pu se developper, souvent initiee par des aviculteurs soucieux de rechercher des produits a valeur ajoutee plus forte que celle du banal œuf en coquille. A l’industrie deja ancienne de la casserie d’œufs succede aujourd’hui une activite industrielle qui emploie les technologies les plus evoluees du domaine de la biochimie, du froid, de la physique et de la mecanique pour inventer, mettre au point, fabriquer, conserver et distribuer de nouvelles presentations de l’œuf et de nouveaux produits derives d’une innovation fertile et prometteuse. Dans le monde entier, une industrie puissante produit des œufs et transforme une part croissante de ces œufs en ovoproduits . La France, leader europeen dans le domaine de la selection avicole, utilise les techniques et les materiels les plus evolues et a mis au point les machines et les procedes les plus performants du monde pour augmenter la productivite, abaisser les prix de revient et ameliorer la qualite des ovoproduits. Or cette tendance au developpement de l’aviculture et de l’utilisation des ovoproduits va s’accelerer en Europe de l’Est, sur tout le continent asiatique, en Amerique du Sud et en Afrique, car il faut mieux nourrir les peuples, et l’œuf presente d’indeniables avantages tant sur le plan nutritionnel qu’economique. Ces pays peuvent avoir interet a s’inspirer des realisations decrites dans cet article et de l’experience acquise pour eviter les echecs et aussi ne pas tout reinventer.

Stochastic modelling techniques are currently used to deal with various problems in turbulence. These methods are explored in this article with as objective the computation of the solution of aeroacoustic noise problems. The principle may be described as follows. The mean flow field is first deduced from a RANS calculation associated with a turbulence closure scheme like the k — e model. Next, a space-time turbulent field is synthetized stochastically, providing the local turbulent fluctuations and the associated noise sources. The radiated sound field is then calculated numerically. The present article is structured around the three following points. The aeroacoustic calculation is presented in the first part. The stochastic model of turbulence is described in the second part. The last section is devoted to computational methods and to numerical results related to noise generation by diaphragms placed in ducted flows. Three-dimensional numerical results are compared with experimental data in terms of acoustic levels. Results of calculations are in good agreement with predictions.

International audience; Acoustic radiation of shock free supersonic jets is modified in comparison with subsonic jet noise because of Mach wave emission. Intense noise is radiated when turbulent structures are convected supersonically relative to the ambient sound speed. Using the framework of Lighthill's equation, Ffowcs Williams and Maidanik developed an approximation of Lighthill's term for a supersonically convected acoustic source in a turbulent shear layer. From this result, a model can be deduced for axisymmetric jets. One then shows that the local knowledge of the mean flow and a characteristic time of turbulence in the source volume may be used to calculate the spectral directivity of Mach wave noise. As a consequence of this local formulation of the acoustic source term, the noise model contains a single unknown multiplicative constant. It also requires a calculation of the mean flow which may be carried out with a k − e compressible turbulence model. Two cold jet cases at M = 1·7 and M = 2·0 and a hot jet at M = 2·0 and Tj /T0 = 2·5 are analyzed. Comparisons with available experimental data and Tam's calculations based on an alternative description in terms of instability waves travelling at the convection speed show a good agreement between calculations and measurements.

This paper deals with, the application of the SNGR ( Stochastic Noise Generation and Radiation) model to compute turbulent mixing noise generated in a duct obstructed by a diaphragm. Two problems must be solved in the framework of an acoustic analogy. First, a wave operator must be derived for sound waves travelling in any mean flow. In the SNGR model, the system of linearized Euler equations is used. An expression of the source term is then deduced from the conservation laws of motion, and can be simplified with classical assumptions of aeroacoustics in the case of subsonic mixing noise. Secondly, the knowledge of the turbulence velocity field is required to compute this source term. In the SNGR model, the spacetime turbulence velocity field is generated by a sum of random Fourier modes. Finally, the radiated acoustic field is calculated numerically by solving the inhomogeneous propagation system. The method is applied in this paper to the case of a two-dimensional duct obstructed by a diaphragm. Numerical results are compared with available experimental ones. Computed noise levels closely match experimental ones and follow the expected U* law.

A numerical solution of a κ‐e turbulence model is used to provide local and statistical properties throughout simple and coaxial round jets. These are inserted into predictive formulas for jet noise based on Lighthill’s theory: Ribner’s formalism postulates locally isotropic turbulence superposed on mean flow; Goldstein and Rosenbaum’s formalism generalizes this to accommodate the more realistic assumption of axisymmetry. Numerical jet noise predictions via the Ribner/κ‐e model (designated Ra) and the Goldstein/κ‐e model (designated Ga), and some variants, are compared with experiment. Only a single empirical factor is used. The Ga model, with its threefold longer axial scale, shows closer agreement with experiment than the Ra model. The predictive capacity of the Ga model is demonstrated by further calculations for coaxial jets. The results confirm the experimental observation of a minimum of acoustic radiation when the outer flow has 0.4 the velocity of the inner flow. An advantage of the κ‐e method is ...

A new approach to noise modeling for free turbulent flows is presented. The equations governing the sound field are obtained in two steps. The first step consists of treating the mean and turbulent components of the flow while the acoustic perturbations are neglected. In the second step, a set of equations is derived for the acoustic variables. On the left-hand side of this system, one finds the linearized Euler equations, whereas the right-hand side exhibits source terms related to the turbulent fluctuations and their interactions with the mean flow. These terms are modeled using a stochastic description of the three-dimensional turbulent motion. This is achieved by synthesizing the velocity field at each point in space and for all times with a collection of discrete Fourier modes. The synthesized field posesses the suitable one- and two-point statistical moments and a reasonable temporal power spectral density. The linearized Euler equations including a stochastic description of noise sources are solved numerically with a scheme based on a fractional step treatment. Each one-dimensional problem is solved with a weak formulation. A set of calculations are carried out for a simple freejet. Comparisons between calculations and experiments indicate that a spatial filtering of the source terms is required to obtain the expected level in the far field. Realistic pressure signals, power spectral densities, and sound field patterns are obtained. It is indicated that the stochastic noise generation and radiation (SNGR) approach may be applied to more complex flows because the numerical codes used to calculate the mean flowfield and the wave propagation are not specific of jet configurations. The limitations of the present model lie in the statistical properties of the synthetic turbulent field and in the use of an axisymmetric modeling of the acoustic propagation.

Solving the Linear Euler Equations (LEE) is the reference method that allows to take into account all the phenomena involved in Outdoor Sound Propagation. However, the huge size of the problems to be treated is still a great limitation to the practical application of this method. The concept of multi domain computations associated with the use of massively parallel computers now pushes the limits away. The code SAFARI, recently developed by EDF, solves LEE with high order numerical schemes on structured grids. To deal with complex and large geometries, a multi domain approach is used. The computational domain is composed of several partially overlapping grids (overset grids). Computations are parallelized by domain decomposition to be runned on cluster facilities. The presentation means to show the capability of SAFARI to deal with propagation over realistic 3D domains. The strategy used to carry out the calculations is detailed. The new perspectives of this kind of method are finally given.

In order to model flow phenomena involving interactions between aerodynamics and acoustics, it is necessary to use Direct Noise Computation (DNC) instead of hybrid methods that are not suitable to take into account the feedback of acoustics on the flow. The methods that are now available in the field of Computational AeroAcoustics (CAA) allows us to deal with DNC in realistic configurations. The numerical code SAFARI (Simulation of Aeroacoustics in Fluids And with Resonance and Interactions) has been developed for this goal. The set of equations are the compressible 3‐D Navier‐Stokes equations. High order finite difference schemes are used. Multidomain capabilities are implemented in order to deal with complex geometries. Block decomposition is used in order to take advantage of parallel processing on large clusters Validation cases are presented: diffraction by a cylinder, shock tube. Results on realistic configurations are also shown: ducted cavity, transonic sudden enlargment, airfoil interactions.

The introduction of efficient numerical techniques like Tam’s DRP scheme allows one to develop aeroacoustic modeling based on Euler equation solvers and applied on realistic configurations. It is already clear that the system of Euler equations is the most complete one in order to compute acoustic propagation in fluids, but the way to calculate noise generation with the same equations needs to be established. So, it is necessary to introduce in the propagation calculation some information coming from a previous or a simultaneous flow calculation. One approach is to try to define source terms for the Euler equations as it was set up for Lighthill’s or Lilley’s equation. Others approaches can rely on the coupling of the two equation systems by domain decomposition or by introducing disturbances linked to flow calculation. The SNGR model belongs to the first category. A source term is defined by analogy with Lilley’s equation. A stochastic space time turbulent field is used in order to avoid expensive LES or DNS flow computations. This approach is mainly applied to the calculation of noise radiated by internal flows where the methods based on the classical acoustic analogy do not work easily.

A high-order finite-difference algorithm is proposed in the aim of LES and CAA applications. The subgrid scale dissipation is performed by the explicit high-order numerical filter used for numerical stability purpose. A shock-capturing non-linear filter is also implemented to deal with compressible discontinuous flows. In order to tackle complex geometries, an overset-grid approach is used. High-order interpolations make it possible to ensure the communication between overlapping domains. The whole algorithm is first validated on canonical flow problems to illustrate both its properties for shock-capturing as well as for accurate wave propagation. Then, the influence of the multi-domain approach on the high-order spatial accuracy is assessed. Afterwards, the algorithm is extended to dynamic mesh applications with overlapping grids. Finally, two industrial cases are presented to highlight the potential of the proposed algorithm.

The sound radiated by an airfoil in the wake of a rod is predicted by means of compress- ible large-eddy (LES) simulation. The LES strategy is based on high-order spectral-like numerical methods to allow the direct noise calculation of the sound sources. Owing to the complexity of the geometry, an overset grid approach is implemented in order to tackle with turbulent flows around multiple solid bodies. The aerodynamic data as well as the acoustic far-field are thoroughly compared to the experimental data of Jacob et al. (J. Theoret. Comput. Fluid Dyn., 19(3), 2005) in order to demonstrate the accuracy of the present simulation.