ボイラ管群ダクト内で発生する大音響騒音の穴あき板を利用した ボイラ管群ダクト内で発生する大音響騒音の穴あき板を利用した対策法に関する研究

(限界開口率の把握と空洞部体積の抑制効果に及ぼす影響)

抄録

Karman vortex shedding occurs when the gas passes through the duct with 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. Then, perforated plates are installed in both sides of the duct to suppress the self-sustained tones. As a result, it was clarified that the perforated plate could suppress the self-sustained tone as expected. However this experiment was conducted using perforated plates with aperture ratio over 1% and the suppression effect appears in all of these aperture ratios. Wherefore the critical aperture ratio at which the suppression effect begin to appear could not be grasped in that experiment. This paper aims to clarify the critical aperture ratio and the effect of a cavity volume which is used with perforated plate on the SPL. Experiments were carried out to clarify these items. As a result, it could be obtained that the critical aperture ratio is about 0.25% and the influence of the cavity volume on SPL is a little. The optimum aperture ratio is concluded to be 4%.