Comparison of sound radiated by shallow cavities and backward facing steps
Résumé
Sound radiation of very shallow cavities under a fully developed low Mach number plane wall jet is investigated. A comparison with equivalent backward facing steps shows that for a cavity with a length-todepth ratio exceeding 7, the cavity behaves acoustically as a pair of acoustically independent steps, a backward facing one and an upward facing one. These two sources are due to the diffraction of turbulent sources by the two edges of the cavity. In particular, feedback mechanisms as those observed for shorter shallow cavities, do not seem to govern the flow field. The investigation is based both on a numerical and an experimental approach: it includes aerodynamic mean flow and turbulence parameters as well as acoustic far field measurements and source localizations.