Seminar by Joannès Chambon

Dipolar based equivalent sources method for three-dimensional aeroacoustic source identification

In accordance with aeroacoustic analogies, the noise arising from the interaction of an object and a low Mach number flow is likely to be accurately described by the radiation of elementary monopoles, dipoles and quadrupoles. Combined with the diffracting behaviour of the car as a rigid body, three-dimensional source identification in wind tunnel is thus prone to sketchy or misleading interpretations when only free field monopolar steering vectors are used.
With a view to provide relevant beamforming maps for 3D automotive acoustic imaging, this paper investigates model refinements inspired from aeroacoustic analogies.
In this framework, it is assumed that loading noise dipoles prevail over cavities and vortices produced acoustic sources. A variation of the Equivalent Source Method is proposed to account for the scattered part of the acoustic transfer toward the microphone array. This approach is derived to deal with dipolar source identification and assessed analytically on an academical test case.
Finally, since the additional noise and practical issues encountered with wind tunnel experimental data are not tackled in this paper, the choice is made to present industrial results from Computational Fluid Dynamic based simulated acoustic fields.
The latter are becoming widespread to design car pieces upstream to actual wind tunnel measurements since they enable to put source models to the test without struggling with installation effects. The identification of sound sources produced by a flow impacting an Idealized Side Mirror mesh is discussed, in light of the proposed Equivalent Source Method presented in the first sections.