Study on a countermeasure for high level sound generated from boiler tube bank duct using walls made of perforated plate (In case of aperture ratio being more than 1%)

Abstract

Karman vortex shedding occurs when the gas passes through a duct with a tube bank of the heat exchangers, such as gas heaters and boilers. Very high level sound in called “self-sustained tones” occurs due to the interference of the vortex and the sound field in the duct. In general, baffle plates are used to suppress the self-sustained tone. However, it is difficult to use them effectively, because insertion conditions have not been established yet. The purpose of this study is to clarify the effectiveness of the perforated plates for self-sustained tones. Then, perforated plates were installed in both sides of the duct to suppress the self-sustained tones. Because we thought that the perforated plate might have acoustic damping and resonance mode of the duct transverse direction to the flow might be suppressed by its damping effect, when the self-sustained tone occurred. Experiments were carried out to examine the suppression effect of the perforated plates installed. As a result, the suppression effect appeared in almost aperture ratio φ of perforated plate in case of φ > 0.01 (1%).