Estimation of whistling of an orifice in a reverberating duct at low Mach number

International audienceSingle hole circular orifices can generate pure tone noise in industrial pipes. This phenomenon results from vortex shedding with lock-in, as a consequence of an acoustic amplification of incipient pressure waves inside the orifice and of an acoustic resonator outside. Key features of this phenomenon are the ability of an orifice to amplify acoustic waves in a range of frequencies and the acoustic feedback mechanism. First, the study deals with the estimation of the whistling ability of an orifice from an incompressible flow simulation. As the studied flow is limited to low Mach number, this kind of simulation fairly describes the hydrodynamic instability. Superimposed harmonic velocity perturbations allow then to identify the impedance of an orifice and so to define the frequency at which amplification occur. The next step of the study deals with whistling features of orifices in a reverberating duct. The extracted impedance is used in a network model, taking into account acoustic propagation and acoustic reflections. A linear stability analysis is then performed and the whistling frequency is predicted. The parameters controlling the whistling amplitude are finally identified. All the results of the study are compared to experiments, showing well agreements for the whole procedure