Experimental and numerical investigations on the whistling ability of an orifice in a flow duct

The present study deals with whistling of orifices in pipes and more precisely with characterizing the potential acoustic amplification of such devices using a whistling criterion. This energy criterion defines the frequencies, at which an acoustic amplification may occur and so characterizes the whistling ability of the orifice. First the experimental determination of the scattering matrix and of the whistling criterion is made. Then, a Large Eddy Simulation (LES) is performed for an orifice submitted to a lowMach number turbulent flow. The resulting scattering matrix is also used to compute a whistling criterion. Comparisons between experimental and numerical results, at two different Mach numbers, show a good agreement up to a limit frequency. By applying the whistling criterion, the potential whistling frequency range is well predicted in terms of frequency and amplitude. A second potential whistling frequency range is predicted, for one flow configuration, whereas it is observed in the experiments at higher frequencies.