Vortices occur when gas flow passes through a duct with a tube bank of heat exchangers, such as a gas heater and/or a boiler. Very high level noise called a "self-sustained tone" occurs due to the interference of the vortices 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 are vague. Then, perforated plates are used in both sides of the duct walls to suppress the self-sustained tones. Because we thought that the perforated plate might have acoustic damping and resonance mode of the duct perpendicular direction to the flow may be suppressed by its damping effect, when the self-sustained tone occurred. Some experiments were carried out to examine the suppression effect of the perforated plates installed. As a result, the suppression effect appeared in all cases. The purpose of this study is to clarify the effectiveness of the perforated plates for self-sustained tones.
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