Effect of flow on various Helmholtz resonators

The acoustic performance of Helmholtz resonators with different configurations in the presence of mean flow is experimentally investigated. The transmission loss of Helmholtz resonators is measured using a flow-impedance tube setup to identify mean flow effects. First, Helmholtz resonators under two different flow conditions, grazing and direct flow, are considered at Ma = 0.05 and 0.1. Then the impact of mean flow on the transmission loss of Helmholtz resonators with leakage holes is also demonstrated. For Helmholtz resonators with leakage holes, single peak of transmission loss is identified at Ma = 0.0 and 0.1. However, two peaks appear at Ma = 0.05 as the number of opening holes increases. The experimental results show that the effect of mean flow strongly depends on the configurations of Helmholtz resonators and the conditions of mean flow. Thus the variation of acoustic performance due to mean flow should be considered in the design of Helmholtz resonators.