Some aspects of the sound generation by ventilation outlet systems have been studied. It has been shown that the Nelson-Morfey theory may be used to characterize, to a first approximation, the behaviour of the whole system. In particular, the duct effect seems to be well accounted for by this theory. An attempt to predict the noise generated by the valve alone has been made. However, more investigation would be needed to know how the ratio K(St) varies with the angle of opening alpha. An initial investigation has been made of the grille-valve interaction. Firstly the experiments have shown that the grille reduces sound transmission at the exit with no flow. But this phenomenon is limited in amplitude and there are still questions to be answered about the effect of the grille on sound conversion into vorticity when flow is present. Secondly, we have shown that there is an interaction between the wake shed behind the valve and the deflectors. We have seen that increasing the distance between the valve and the grille is an easy way to reduce the total sound level by several decibels. The investigation of the wake shed behind the butterfly valve and its effect on the noise generation by the grille could be the subject of future research. Analysis in narrow frequency bands has revealed that the configuration for which the deflectors are parallel to mean flow is conducive to the generation of tones at resonance modes. Inclining the deflectors reduces these tones but at the expense of an increase in the broadband noise.
Aeroacoustics of automotive vents
Aeroakustik von Entlüftungen im Automobilbau
Journal of Sound and Vibration ; 285 , 4/5 ; 859-875
2005
17 Seiten, 12 Bilder, 17 Quellen
Article (Journal)
English
Aeroacoustics of automotive vents
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