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Characterization of an acoustic ceramic liner in a subsonic flow by mean of Laser Doppler Velocimetry

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Niveau: Supérieur, Doctorat, Bac+8
Characterization of an acoustic ceramic liner in a subsonic flow by mean of Laser Doppler Velocimetry Romain PETHIEU *, Frank SIMON **, Francis MICHELI *** ONERA Centre de TOULOUSE, DMAE, 2, av. Édouard Belin, BP4025, 31055 TOULOUSE cedex 4, France Abstract As aircraft traffic constantly increases and internationals pollutions norms are even more constraining, serious efforts are made to reduce engine noise. Among them, the design of high performance absorbing materials (liners) placed on the nacelle's internal walls is an exciting challenge. Optimizing these media requires knowing the mechanisms of acoustical propagation near them in the conditions encountered in jet engines: high speed hot shear flows. A particular interest is being granted to the influence of the grazing flow in contact with the liners. This influence is remarkable for those configurations based on perforated plates (modification of resonant frequency, acoustic impedance). However, acoustic wave propagation in the presence of flow is still a difficult problem to study numerically, in particularly due to the complex limit conditions that have to be modelised [1]. That is why in-flow acoustic measurements have to be performed. Therefore, a testing method based on non-intrusive measurements has been developed at Onera [2]. This technique consists in measuring acoustic velocities by Laser Doppler Velocimetry to determine acoustic quantities under grazing turbulent high-speed flow, thanks to an Eulerian-Lagrangian description of the perturbations.

  • aero-thermo-acoustic bench

  • signal auto-power

  • ldv system

  • bi-directional ldv

  • off frequency

  • power spectral

  • perturbation components


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Characterization of an acoustic ceramic liner in a subsonic flow by mean of Laser Doppler Velocimetry
Romain PETHIEU *, Frank SIMON **, Francis MICHELI ***
ONERA Centre de TOULOUSE, DMAE, 2, av. Édouard Belin, BP4025, 31055 TOULOUSE cedex 4, France
Abstract
As aircraft traffic constantly increases and internationals pollutions norms are even more constraining, serious efforts are made to reduce engine noise. Among them, the design of high performance absorbing materials (liners) placed on the nacelle's internal walls is an exciting challenge. Optimizing these media requires knowing the mechanisms of acoustical propagation near them in the conditions encountered in jet engines: high speed hot shear flows. A particular interest is being granted to the influence of the grazing flow in contact with the liners. This influence is remarkable for those configurations based on perforated plates (modification of resonant frequency, acoustic impedance). However, acoustic wave propagation in the presence of flow is still a difficult problem to study numerically, in particularly due to the complex limit conditions that have to be modelised [1]. That is why inflow acoustic measurements have to be performed. Therefore, a testing method based on nonintrusive measurements has been developed at Onera [2]. This technique consists in measuring acoustic velocities by Laser Doppler Velocimetry to determine acoustic quantities under grazing turbulent highspeed flow, thanks to an EulerianLagrangian description of the perturbations.Induct flow 2D LDV measurements are realised on a testbench which consist in a wind tunnel provided by loudspeakers located upstream of a square test cell where a liner is mounted. Acoustic velocities components are extracted from total velocity. The present purpose is to show the study of the interaction between an "honeycomb" material and a grazing flow for several Mach numbers (up to Mach 0.3), in the presence of acoustical excitation. On this configuration, a nonlinear behaviour due to hydrodynamics modes can occurs, increased either by a resonance of the porous material or by the mean flow. This activity takes place as part of national project COMATEC.
Key words:hydrodynamic modes, aeroacoustic, boundary layer, LDV, Galbrun
*Romain.Pethieu@onera.fr  Tel: (33) 5 62 25 25 25 poste 2268  Fax: (33) 5 62 25 25 83 ** Frank.Simon@onecert.fr  Tel: (33) 5 62 25 28 51  Fax: (33) 5 62 25 25 83 *** Francis.Micheli@onera.fr  Tel: (33) 5 62 25 28 48  Fax: (33) 5 62 25 25 83