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1nutworld -> RE: Cavitation noise (6/14/2015 5:03:41 PM)
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quote:
ORIGINAL: p1t1o
Cavitation is caused by the pressure behind a propelling blade, that is, at the retreating face, dropping past the point where cavities in the water open up.
The cavities are not vacuum, but filled with water vapour. Essentially, the water is "boiling" as the temperature at which water can exist as a vapour drops as the pressure goes down. Think of it as the propeller "sucking" the water into steam, as you pull, little areas of water flash to gas, and as the conditions are far from steady the bubbles almost immediately re-condense and snap back to liquid. When the bubble collapses it concentrates a lot (relatively) of energy into a very small area (the bubbles can collapse at speeds approaching the local speed of sound), this is where the noise comes from.
The threshold at which cavitation occurs is dependant on water pressure, the higher the pressure, the harder you have to try to get the pressure behind your propelling blade to drop to a level where cavities can form.
The water pressure around a surface vessel's propellers is always going to be somewhere between 1-2 or maybe 3 (if the propeller is as far as 20m deep) atmospheres, so cavitation almost always occurs at a relatively low speed. The depth of water under your boat, or around it, will not have an impact, only the pressure of the water around the propeller, which for surface ships is pretty much the same from boat to boat.
Submarines can descend to where the pressure is many, many times that and as you go deeper and the pressure increases, the faster you can go before cavitation.
CMANO seems fairly consistant with the science, you would expect surface vessels to suffer from cavitation quite commonly. Its possible that is less of a pronounced effect in other sims as ships are generally fairly noisy, perhaps they just figure the cavitation in with that, as surface vessels will almost always be cavitating whilst travelling at any significant speed.
Thank you, that explains it very well!!!
I hope that none of the developers took offense to my comment, because it was never meant as a criticism, just my own curiosity.
I knew submarines would have less cavitation noise, because of the depth factor, in other simulations that I've played, surface vessel cavitation mostly occured when running at Full or Flank settings, and Kudos to the CMANO team for giving us a far more accurate portrayal of this.
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