02-Sept-15
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Laboratoire de Mécanique des Fluides et d'Acoustique Acoustics, Aeroacoustics
Centre Acoustique
   ECL   LMFA 

Dynamique et acoustique des écoulements cisaillés compressibles

Dynamic and acoustic of compressible shear flows

Publications
 
 
 
Investigation of flow features around shallow round cavities
subject to subsonic grazing flow
 
Marsden et al., 2012, Phys. Fluids, vol. 24
shallow round cavity
shallow round cavity
aeroacoustics haut/top
 
Flight effects on screech in underexpanded jets

 

Schlieren picture of an underexpanded jet plume (convergent nozzle, Mj=1.50, Mflight=0.39, exposure time 6.7 µs).

 

The first shock is seen to be twisted within the jet plume, denoting a strong oscillation amplitude, and a large flapping motion of the jet occurs further downstream.

 

Ph.D. Thesis of Benoît André, in collaboration with Snecma and Airbus-France.
supersonic shocked jet - schlieren visualization André et al., 2011, Phys. Fluids
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Large eddy simulation of an overexpanded supersonic jet

 

Snapshot of density gradient norm in gray scale, azimuthal vorticity in color scale in the jet, and fluctuating pressure in color scale outside the jet. Pressure levels from -8000 to 8000 Pa (color bar from -5000 to 5000 Pa).
Reynolds number of 10^5, exit Mach number of 3.30, static pressure and temperature of 0.5x10^5~Pa and of 360~K.

 

Ph.D. Thesis of Nicolas de Cacqueray, in collaboration with the CNES
supersonic shocked jet - schlieren visualization Click on the picture to enlarge !
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Underexpanded supersonic jet & broadband shock noise
Schlieren photography of a round supersonic jet at Mach number 1.5

 

Convergent nozzle - Md=1 - Mj=1.55 - NPR=4. Lower part, mean flow field obtained by averaging 1000 pictures

 

Benoît André & Thomas Castelain
supersonic shocked jet - schlieren visualization
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Shock-vortex interactions
Superposition of density gradient (gray scale), and of pressure (color scale). Shock Mach number of 1.2 and maximum vortex Mach number of 0.25. Bogey, de Cacqueray & Bailly (2009, JCP)

 

shock vortex interaction
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Aeroacoustics phenomena in subsonic and transonic ducted flows
 
aeroacoustics in transonic ducted flow

Strong interactions between shock oscillations, internal aerodynamic noise and acoustic duct modes are often observed in confined flows but are undesirable to prevent vibrations and fatigue of structures. In order to compute this kind of phenomena, a numerical solver called SAFARI (Simulation of Aeroacoustics in Fluids And Resonances and Interactions, EDF) has been developed. Compressible Navier-Stokes equations are solved using high-order finite difference schemes. A non-linear adaptive filter is implemented to capture strong shock waves and a high-order overset grid ability is introduced in order to treat complex geometries. These numerical techniques allow to carry out direct simulation of aeroacoustic couplings in subsonic and transonic flows. A transonic flow passing a sudden expansion in a duct is studied. For certain values of the pressure ratios tau (tau = Poutlet/Pinlet), the supersonic expansion ends up after a normal shock. Strong coupling between the self-sustained oscillations of the normal shock and the longitudinal acoustic modes is captured as in the experiments. An instantaneous snapshot of the density gradient modulus is represented in a plane perpendicular to the spanwise direction. Others flow regimes have been studied. For lower pressure ratios, the flow is entirely supersonic with oblique shocks. For higher pressure ratios, the flow is asymmetric and exhibits shock cells.

 
Emmert et al., Phys. Fluids, 2009
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Noise reduction by impinging microjets
Noise reduction by impinging microjets

The effects of a fluidic control on the aeroacoustic characteristics of a Mach 0.9 high-Reynolds axisymmetric jet are investigated experimentally. The air-microjet system comprised up to 36 impacting microjets directed towards the jet centerline, and was designed to allow the modification of various geometrical and aeraulical microjet parameters. A significant noise reduction was obtained for the entire range of theta, the angle theta designating the direction of noise emission. The dependency of the noise reduction with respect to parameters of the microjets system was studied and three parameters were mainly considered: the outgoing mass flux per microjet, the number of microjets and their layout in the azimuth of the main jet. Depending on the microinjection flow parameters, the global jet-noise reduction varied from 0 to 1.8 dB, showing some non-monotonic behaviors due to the change between subsonic and supersonic regimes of the microjets. For low values of number of microjets, the microjets seem to act independently, which was confirmed by aerodynamic studies by Stereoscopic Particle Image Velocimetry. These studies indicated a strong correlation between the maximum level of turbulence just behind the nozzle exit and the high-frequency noise, previously shown to potentially balance the acoustic benefits obtained for lower frequencies. The maximum level of turbulence measured at the longitudinal position corresponding to half the potential core length was shown to be also highly correlated to the jet noise reduction.

 
Castelain et al., 2008, AIAA Journal, 46(5)
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Generation of screech tones in an underexpanded supersonic jet
screech tone in supersonic noise

 

Snapshot of the density modulus, of the spanwise vorticity and of the near-field pressure, in a plane perpendicular to the spanwise direction. The nozzle lips are represented in black. (fully expanded jet Mach number 1.55, Reynolds number 60,000)

Compression shocks corresponding to high-density gradients are observed inside the jet plume. Upstream-propagating wave-fronts associated with screech tones radiation are also clearly visible on either side of the jet. A further study of the simulation data have permitted to provide evidences of the connection between the shock-leakage process (Suzuki & Lele, JFM, 2003) and the generation of screech tones.

Berland et al., Phys. Fluids, 2007

 

jet noise

The jet operates at off-design conditions with a Mach number M = 1.55. The Reynolds number is Re = 100000. A snapshot of instantaneous spanwise vorticity is shown in purple and green, and corresponding isosurfaces of pressure are in yellow. Upstream-propagating wavefronts, corresponding to screech tones, are visible on both sides of the jet.

DFG - CNRS project with T.U. Munich - Pr. Friedrich.

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Direct Noise Computation of subsonic jet
jet noise Influence of the Reynolds number on the turbulent development of transitional, isothermal subsonic round jets and on their radiated noise. The Mach number of the jets is 0.9, and their Reynolds numbers are: (a) 1,700; (b) 2,500; (c) 5,000 and (d) 400,000. The flow and the acoustic fields are calculated directly using compressible Large Eddy Simulations. The vorticity norm is represented in the jet flow, and the fluctuating pressure is visualized outside.

 

Bogey & Bailly, 2006, Theoret. Comput. Fluid Dyn.
jet noise

Calcul direct du bruit d'un jet rond par simulation compressible des grandes échelles (LES)

 

Nombre de Mach M = 0.9
Nombre de Reynolds ReD = 4 x 105

 

Bogey et al., 2002, Computer & Fluids
noise of subsonic jet Calcul direct du bruit d'un jet subsonique circulaire par simulation compressible des grandes échelles. Représentation d'une composante de la vorticité dans l'écoulement, et du champ acoustique à l'extérieur.

 

Nombre de Mach M = 0.9
Nombre de Reynolds ReD = 6.5 x 104

 

Bogey et al., 2003, Theoret. Comput. Fluid Dyn.

 

aeroacoustics haut/top
 
noise of mixing layer Calcul direct du bruit d'une couche de mélange par simulation compressible des grandes échelles. Représentation d'une composante de la vorticité dans l'écoulement, et du champ acoustique à l'extérieur.

 

Mc = 0.18    Re = 12800

 

Bogey et al., 2000, AIAA Journal

 

aeroacoustics haut/top
 
radiation of instability waves Calcul direct du rayonnement acoustique d'ondes d'instabilité dans un jet plan.
 
M = 2
 
Proceedings of the 3rd CAA workshop, 2000.
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cavity noise cavity noise Calcul direct du bruit d'un écoulement affleurant une cavité. Représentation du gradient transversal de la masse volumique obtenu par DNS à gauche, et expérience de Karamcheti (NACA 3847, 1955) à droite.
 
M = 0.7
 
Gloerfelt et al., 2003, J. Sound Vib.
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Contrôle de jet avec pour objectif la réduction du bruit de jet.

A ce titre, une des voies explorées est le contrôle du développement de la couche de mélange du jet et la taille des structures principales qui y sont générées, sources majeures de bruit. Le système de contrôle utilisé dans la cadre de cette étude est constitué de 18 injecteurs régulièrement espacé dans la direction azimuthale, tel que le représente la figure suivante:

active control in fluid mechanics active control in fluid mechanics
Système d'injection d'air à 18 injecteurs secondaires paramétrable géométriquement Système d'injection d'air à 18 injecteurs secondaires à géométrie fixée (angle d'injection 45°)

Nos études concernent d'une part les grandeurs aérodynamiques de l'écoulement, déterminées par anémométrie à fil chaud et des visualisations par Vélocimétrie à Images de Particules (PIV). Le jet testé est caractérisé par un nombre de Mach M=0.12 et un nombre de Reynolds Re=3.10^5.
Notre objectif est de déterminer les mécanismes d'interaction entre les jets secondaires et la couche de mélange du jet principal et les effets de ces mécanismes sur les grandeurs caractéristiques de la turbulence dans la couche de mélange. Un optimum au sens de la réduction du maximum de ces grandeurs turbulentes a pu être isolé en fonction du débit dans les injecteurs secondaires, et des différents paramètres géométriques d'injection (angle d'injection, distance entre le point d'impact des jets secondaires sur la couche de mélange et la buse du jet principal, distance entre l'origine des jets secondaires et le point d'impact des jets secondaires sur la couche de mélange, etc ...)

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Vorticité dans la couche de mélange entre 0D et 0.5D; jet seul (gauche) et jet contrôlé (droite)
 
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Intensité turbulente longitudinale dans le jet entre 1.5D et 3D;
jet seul (gauche) et jet contrôlé (droite)

D'autre part des essais acoustiques sont menés en chambre anéchoïque, à M=0.28 et Re=3,2.105, afin de comparer l'efficacité en terme de réduction de bruit des différentes configurations testées durant l'étude aérodynamique, par des mesures de pression acoustique en champ proche et en champ lointain.

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Spectre de bruit en champ lointain :
jet seul (rouge) et jet contrôlé (bleu)
Mesure en chambre anéchoïque
 
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Centre Acoustique - Laboratoire de Mécanique des Fluides et d'Acoustique - Lyon - France