Effect of small cavity in in-line tube banks on acoustic resonance

In the present paper the attention is focused on the effect of small cavities inside in-line tube banks on acoustic resonance which occurred in the two-dimensional model of boiler. We measured sound pressure level (SPL), amplitude and phase delay of acoustic pressures and gap velocity. As a result, we found many peak frequencies of sound pressure level with different Strouhal numbers, mainly about St=0.15, 0.26 and 0.52. The variation of SPL for St=0.26, 0.52 components in tube banks with cavities were the same as the result of no cavities. The existence of cavities inside inline tube banks caused the resonance of St=0.15. And the acoustic resonance of first mode in the transverse direction was generated if the small cavities existed inside tube banks. This resonance was not generated from tube banks of no cavities. The resonance onset velocity in the transverse mode was fairly slower than that of no cavities. It was easy to generate acoustic resonance when there were small cavities inside in-line tube banks. And we have examined the effect of baffle plates for controlling acoustic resonance generated from tube banks with cavities.