Design of silencer using resonator arrays with high sound pressure and grazing flow

Resonator arrays have been used to obtain broad band transmission loss in the relatively low frequency range of exhaust systems. This transmission loss characteristics is determined by the acoustic impedance characteristics of the resonators. However, the acoustic impedance of the resonators is not constant under conditions of high sound pressure and grazing mean flow. High sound pressure and grazing mean flow generate the nonlinear behaviors near the orifice, such as vortex shedding and circulation, As a result, the noise reduction performance is degraded, because the impedance matching is not fulfilled anymore. In order to obtain the desired transmission loss, these nonlinear impedance characteristics of the resonators need to be carefully considered. For resonator arrays in particular, changing impedance is an essential design parameter to decide the arrangement of the resonators. This is because various combinations of multiple resonators can produce different acoustic characteristics. The effects of high sound pressure and grazing mean flow are primarily represented by empirical formulas based on experimental results, however, most previous studies have independently considered the effects of high sound pressure and grazing mean flow. In this study, a combined acoustic impedance model was proposed and verified by experiments, using the existing empirical formulas, which considers high sound pressure and grazing mean flow at the same time. The predicted and measured results of transmission loss for resonator arrays were compared to verify this proposed impedance model. From the results, an effective design method for determining the arrangement of resonator arrays using an optimization process under given constraints was proposed. Finally, this study demonstrated that it is possible to design an effective silencer using resonator arrays with high sound pressure and grazing mean flow.