Design of an instrumentation system for assessing the acoustic attenuation performance of ducted Helmholtz resonators in the presence of grazing flow

The Helmholtz resonator (HR) has been widely used as a duct silencer to reduce low-frequency noise. However, the presence of grazing flow could influence the noise attenuation performance of the HR in ductwork systems. This study aimed to design an instrumentation system for studying the acoustic attenuation performance of ducted HRs in the presence of grazing flow. The instrumentation system includes a centrifugal fan, diffusion section, anechoic termination, flow development section, test section, and sound source. In this study, a HR as a ducted silencer was installed in the test section of the instrumentation system. Transmission loss (TL) due to the HR insertion was measured in the presence of forward and reverse grazing flows. The results showed that the instrumentation system succeeded in assessing the noise attenuation performance of the HR under a high sound pressure level and different flow rates and directions.