Contribution au développement d'une analogie vibroacoustique pour la modélisation du bruit d'origine aérodynamique

Abstract : This study proposes a model for the noise generated aerodynamically, while focusing on energy transfer mechanisms between the main flow and the propagating medium. Energy harvest in aerodynamic condition is therefore the subject of a first part. Three general trends may be identified ; the eulerian approach uses linearized Euler's equations for inviscid flows in a form of a conservation law ; the dissipating approach expands Navier-Stokes equations in series, relies on vorticity fluctuations to excite the medium or splits velocity or momentum vectors in a general potential theory ; the lagrangian approach describes the lagrangian displacement of the perturbation inherent to an acoustic wave. The first approach is the most commonly adopted. The second one is the most complete and provides aerodynamical mechanisms for energy generation. A general fashion follows where acoustics is a generalized field, trapped by a hydrodynamic impedance. The last one may be subject of close attention for future considerations. In a second part, computational models are presented with their ability to predict acoustic radiation from a surface excitation. These are the Kirchhoff formalism based on the pressure, the Ffowcs Williams & Hawkings formalism based on the mass flow rate and the Rayleigh integral based on the vibration velocity. These are applied in a third part of the study to investigate the response of the acoustic medium to a generique excitation in the form of a wavepacket, representative of unsteady aerodynamics. Such acoustic response is caracterised by its direction of maximum radiation and its efficiency, defined as the rate of energy transfer between the excitation and its surrounding medium. Introducing an upstream-downstream asymmetry in the excitation is showed to significantly enhance its efficiency, as well as a convection velocity in the propagating medium. Within these general considerations, the last part of this study models acoustic excitation in a mixing layer flow based on Liepmann's analogy. This relatively unexplored theory consists in a Rayleigh integral excited by the temporal derivative of the displacement thickness. Results are compared with direct noise computation database and two other methods of surface excitation. Directivity is likely to be found while pressure amplitude is correctly predicted by using a model for radiation impedance.
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Ronan Serre. Contribution au développement d'une analogie vibroacoustique pour la modélisation du bruit d'origine aérodynamique. Acoustique [physics.class-ph]. Ecole nationale supérieure d'arts et métiers - ENSAM, 2014. Français. ⟨NNT : 2014ENAM0052⟩. ⟨tel-01132929⟩

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