Abstract：The noise characteristics of the jets exhausted from nozzles with diameters of 10 mm and 20 mm are experimentally studied at the gas flow rate of 30-150 m3/h. The effects of nozzle size on the underwater exhaust noise in different frequency bands are analyzed. Moreover, the noise reduction effect of a multi-nozzle exhaust scheme is investigated. The results show that the noise with frequencies of 10-100 Hz would decrease with nozzle size decreasing. The noise with frequencies of 100-1 000 Hz are very sensitive to gas velocity, and would increase with gas velocity increasing. Hence under certain gas flow rate conditions, reducing the nozzle size would increase the noise with frequencies of 100-1 000 Hz. For the reason, replacing a single large-size nozzle with several small-size nozzles would reduce the exhaust noise in the case of the total cross-sectional area unchanged.
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