Communication Dans Un Congrès Année : 2020

The radiated field of circular arrays of sources near a scattering cylinder

Résumé

The present study addresses analytically the diffractionof circular arrays of phased sources by a cylindrical obs-tacle at very low frequencies. The interest is the tonal ma-rine propeller noise at the first harmonics of the blade-passing frequency. At the very low Mach numbers of in-terest, the expectedly dominant sources of propeller noiseare the lift fluctuations on the blades, radiating as rotatingdipoles. At a given frequency the field is a superpositionof spinning modes. Each mode is exactly reproduced bya set of fixed dipoles of similar amplitude but radiating atdifferent emission times, called source-mode. The modesare used to model the near-field scattering by a cylindri-cal body at short distance, with the exact tailored Green’sfunction in two dimensions. The configuration is acous-tically compact, i.e the sizes of the cylinder and of thesource circle, as well as the distance, are small compa-red to the wavelength. The diffraction is found to induce astrong amplification with respect to what the source moderadiation would be in free field. This regime is explainedby an asymptotic analysis. The study stresses that marinepropeller noise cannot be predicted in free-field and thatinstallation on a ship is the most crucial aspect.

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Dates et versions

hal-03229462 , version 1 (21-05-2021)

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Elina Cros, Michel Roger, Gilles Serre. The radiated field of circular arrays of sources near a scattering cylinder. e Forum Acusticum 2020, Dec 2020, Lyon, France. pp.2951-2958, ⟨10.48465/fa.2020.0426⟩. ⟨hal-03229462⟩
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