On Relation between Similarity Ratio and Acoustic Damping Ratio in One Dimensional Sound Field Partitioned by Perforated Plate with Geometric Similarity

Kunihiko ISHIHARA, Akari GOTO

Noise control, Sound and acoustics, Acoustic damping ratio, Perforated plate, Transfer matrix method, Similarity ratio

In heat exchangers like a boiler, as a tube bank is set in a duct the alternative vortices occur behind a tube bank and the vortex shedding frequency increases with the flow velocity when the boiler is operated. High level sound is suddenly generated when the vortex frequency comes close to the acoustic natural frequency of the duct. The high level sound keeps the frequency and the amplitude constant even if the flow velocity increases in the case of small acoustic damping due to the self-excited mechanism. This is generally called the self-sustained tone and the factory is forced to stop the operation due to the complaints of the neighborhood. The effective countermeasure is required in the design stage. One of the authors has many studies concerned to the clarification of the generation mechanism and the counter- measures and their effects. In recently, it was clarified that the perforated plate suppressed the high level sound. The author has a question what is the relation between the suppression effect of the perforated plate and the dimension ratio. Then in this paper, after confirming the validity of the analysis we tried to obtain the relation between the acoustic damping ratio and dimension ratio theoretically for several geometrically similar ducts. As a result, it was clarified that the acoustic damping ratio became smaller with larger of dimension ratio.

https://dx.doi.org/10.31873/IJEAS.8.2.08