The present paper focuses on the effect of air jets through a perforated thin plate on the characteristics of an acoustic absorption coefficient. We measured the flow rate, internal pressure, acoustic pressure, and tr...The present paper focuses on the effect of air jets through a perforated thin plate on the characteristics of an acoustic absorption coefficient. We measured the flow rate, internal pressure, acoustic pressure, and transfer function by using an improved acoustic impedance tube. The normal incidence absorption coefficient was calculated from the measured transfer function using transfer function methods. As a result, the frequency characteristics of the acoustic absorption coefficient against the frequency showed a maximum value at the local frequency. The peak frequency of the acoustic absorption coefficient depended on the thickness of the background air space and the thickness of the perforated plate. As the flow rate increased through the micropores, the peak level of the acoustic absorption coefficient also increased until a flow rate of 80?l /min. As the flow rate further increased, the peak level of the acoustic absorption coefficient decreased and that of the high frequency band increased.展开更多
In the present paper the attention is focused on effect of arrangement of tube banks on acoustic resonance which occurred in the two-dimensional model of boiler. We have examined the characteristics of vortex shedding...In the present paper the attention is focused on effect of arrangement of tube banks on acoustic resonance which occurred in the two-dimensional model of boiler. We have examined the characteristics of vortex shedding and acoustic resonance generated from in-line and staggered tube banks. At the small tube pitch ratio in in-line tube banks, acoustic resonance of third and fourth mode in the transverse direction occurred. As the tube pitch ratio in the flow direction decreased, the vortex shedding frequency became broad-band. The alternative vortex shed from in-line tube banks. The multiple resonance modes were generated within the broad-band vortex shedding frequency. And the acoustic resonances of lower-order modes occurred at the higher gap velocity. On the other hand, at the small tube pitch ratio in staggered tube banks, acoustic resonance did not occurred, although the vortex shed at the resonance frequency in tube banks. The pressure drop at staggered tube banks was larger than that of in-line tube banks. The symmetric vortices were observed inside staggered tube banks at the small tube pitch ratio.展开更多
文摘The present paper focuses on the effect of air jets through a perforated thin plate on the characteristics of an acoustic absorption coefficient. We measured the flow rate, internal pressure, acoustic pressure, and transfer function by using an improved acoustic impedance tube. The normal incidence absorption coefficient was calculated from the measured transfer function using transfer function methods. As a result, the frequency characteristics of the acoustic absorption coefficient against the frequency showed a maximum value at the local frequency. The peak frequency of the acoustic absorption coefficient depended on the thickness of the background air space and the thickness of the perforated plate. As the flow rate increased through the micropores, the peak level of the acoustic absorption coefficient also increased until a flow rate of 80?l /min. As the flow rate further increased, the peak level of the acoustic absorption coefficient decreased and that of the high frequency band increased.
文摘In the present paper the attention is focused on effect of arrangement of tube banks on acoustic resonance which occurred in the two-dimensional model of boiler. We have examined the characteristics of vortex shedding and acoustic resonance generated from in-line and staggered tube banks. At the small tube pitch ratio in in-line tube banks, acoustic resonance of third and fourth mode in the transverse direction occurred. As the tube pitch ratio in the flow direction decreased, the vortex shedding frequency became broad-band. The alternative vortex shed from in-line tube banks. The multiple resonance modes were generated within the broad-band vortex shedding frequency. And the acoustic resonances of lower-order modes occurred at the higher gap velocity. On the other hand, at the small tube pitch ratio in staggered tube banks, acoustic resonance did not occurred, although the vortex shed at the resonance frequency in tube banks. The pressure drop at staggered tube banks was larger than that of in-line tube banks. The symmetric vortices were observed inside staggered tube banks at the small tube pitch ratio.
