Wednesday 17 January 2018

fluid dynamics - Why does the gas cloud of an underwater gunshot pulse?


I have been watching some slow motion video and I was intrigued by the slow motion underwater gunshot. The first moments of the video go as expected. The gun fires and a cloud forms in front of the gun. Then the bullet rips through the water, leaving an open space (which I assume is a cavitation vacuum.) Soon after, the rip closes, and the gas bubble shrinks (I'm assuming this is due to the cooling and/or compression of the hot high pressure gasses.) Then something funny happens. The bubble pulses a few times and almost appears to emit light. Each pulse is accompanied by a noise.


The video can be seen here from start, or just showing the bubbles .


What is this pulse effect and/or what causes it?


EDIT: Here is another great video for a possible explanation:




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