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In this paper a low noise flow duct facility that performs a multimodal characterization of the passive and active acoustic properties of obstacles in the aero-acoustic conditions of an automotive air conditioning system is presented. The experimental procedure is made of two steps. In the first one the passive data, i.e. the multimodal scattering matrix, is measured with a multi-sources method. In the second step the outgoing modal pressure spectra radiated upstream and downstream by the flow obstacle interaction source is achieved. A numerical simulation of the experiment based on a 3D-Finite Element Method is developed. A very good agreement between the theoretical and experimental results of the no flow scattering matrix of a diaphragm is found. The effect of the flow on the scattering matrix is shown before performing the measurement of the aero-acoustic source characteristics of the diaphragm.

The problem of the radiation pattern from sources in the presence of perfectly conducting objects is of great interest in the design of transmitting or receiving antennas on structures. The optimal antenna location is particularly hard to find because of the many costly tests which must be managed. A reliable and fast electromagnetic code, able to model antenna/structure couplings, can allow engineers to reduce this cost considerably. In this article, we present two different numerical approaches to solve this problem, according to the kind of antenna, and its location. In the first case, the antenna is in the vicinity of the structure and is only known by its radiation pattern in free-space. A new far to near field transformation is used to compute the incident field induced by the antenna on the structure. In the second case, the antenna is integrated into the structure. The technique consists in a physical and geometrical modeling of the antenna, using a Finite Element Method. In both cases, a Boundary Element Method coupled with a Fast Multipole Method, is used because of its suitability to cope with propagation outside the obstacle. Some numerical examples are given to illustrate the accuracy and efficiency of these two approaches. To cite this article: N. Zerbib et al., C. R. Physique 6 (2005).