On the monopolar and dipolar acoustic responses of a passive single point scatterer subjected to low-Mach-number grazing air flow

Abstract

The acoustic response of a passive single point scatterer under grazing flow is shown theoretically and experimentally to have both monopolar and dipolar contributions. The monopolar response is dominated by the pressure-induced flux Qp, which is related to the specific acoustic impedance of the point scatterer as ζ=−1/Qp. By contrast, the main dipolar response is the pressure-induced force Fp, which is experimentally proven to be modelled by introducing a complex-valued factor η. In fact, η is related to the ratio between Qp and Fp. By employing these two complex-valued parameters ζ and η in the proposed theoretical transfer matrix model, the scattering properties of a single point scatterer (e.g., a Helmholtz resonator) subjected to grazing flow can be well predicted. This model can be readily used in practical applications such as the design of passive absorbers and silencers in ventilation systems.