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, rubber sheets as flexible walls are installed in both sides of the duct to suppress the self-sustained tone. The reasoning being that the resonant mode of the duct perpendicular to the flow may be suppressed by rubber sheet vibrations when the self-sustained tone occurred. Some experiments were carried out to examine the suppression effect of the installed rubber sheets. As a result, the suppression effect appeared at a certain condition. The purpose of this study is to clarify the effectiveness of the rubber sheet for self-sustained tones.

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