Measurement of the effects of flow velocity and sound pressure on the acoustic impedance of a resonator near an airflow

In a model where a resonator was placed with its neck parallel to an airflow, we measured the effects of varying the distance d between the airflow and the resonator neck, the flow velocity U, and the sound pressure at the resonance frequency and the real part of the dimensionless specific acoustic impedance, the resistance θ. The resonance frequency of the resonator increased with the flow velocity and also increased as d became larger. The acoustic resistance θ increased as the flow velocity U increased when d = 2 mm. At d = 5 and 8 mm, the effect of the airflow was smaller, resulting in less variation in the acoustic resistance θ with changes in flow velocity. Unlike the results from a model where the airflow and resonator neck were perpendicular, we found that the acoustic resistance θ showed a dependence on flow velocity in the low sound pressure region and a dependence on sound pressure in the high sound pressure region.