Abstract
In order to investigate the acoustic radiation characteristics of underwater, a pipe casing was introduced and the effects of its main structural characteristics on underwater combustion acoustic radiation were studied by acoustic testing. The results show that the addition of the pipe casing significantly increased the sound pressure level of underwater pyrotechnic combustion, especially the peak of sound pressure level that was increased by 15.9 dB from 155.5 to 171.4 dB at the frequency of 125 and 100 Hz. But the addition of the pipe casing had little effect on the frequency. These results indicated that adding a pipe casing is effective for improving sound pressure level in underwater pyrotechnic combustion. An increase in nozzle diameter from 10 to 12.5 mm resulted in an increase of gas volume, so the peak of sound pressure level and broadband sound pressure level is higher. Changing the pipe casing direction to vertical downward will make the bubble formation period shorter, which will generate more bubbles and strong wake; the interaction between bubbles and wake results in a higher intensity of turbulence, which accounts for the coalescence and breakup of bubbles in the fluid. Besides, changing the diameter of pipe casing can be used to lower the frequency of underwater noise.
Highlights
Pyrotechnics composed of oxidant, combustible agent, and adhesive are self-contained oxygen systems as the oxidant provides oxygen for the combustion,[1] and through continuous and steady underwater combustion, it can produce a large amount of high temperature gases and solid residues which produce certain sound effects and could be used for interfering sonar or against mines, and so on
The spectra of acoustic radiation characteristics show that the noise of underwater pyrotechnic combustion is mainly at low frequency, reflecting the characteristics of exhaust during underwater combustion
An increase in nozzle diameter from 10 to 12.5 mm resulted in an increase of gas volume, so the peak of sound pressure level (SPL) and broadband SPL is higher
Summary
Pyrotechnics composed of oxidant, combustible agent, and adhesive are self-contained oxygen systems as the oxidant provides oxygen for the combustion,[1] and through continuous and steady underwater combustion, it can produce a large amount of high temperature gases and solid residues which produce certain sound effects and could be used for interfering sonar or against mines, and so on.
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