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Old 08-10-2009, 02:08 AM   #1 (permalink)
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Interesting read: Supercavitation

SpringerLink - Book Chapter

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Old 08-10-2009, 03:56 AM   #2 (permalink)
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That's for James Bond, in the underwater car chase scene

I heard about supercavitation a few years ago. After the Kursk accident, with Russia cutting off the front of the boat and being all secretive about it, it was speculated that the cause of the explosion was a supercavitating test torpedo.

I've tried supercavitating in the swimming pool, but I can't seem to make enough bubbles
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Old 08-10-2009, 04:05 AM   #3 (permalink)
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Yes, I've achieved super cavitation on my Tempo. A simple flap ahead of and behind each wheel keeps me safely on the road at most sub-sonic speeds. To take it to the next level I will mount a 6-foot pole to the front of the car, "jousting style", with a cone on the front of it. Think of it as "drafting myself".

There was a semi-recent piece re: I think that same phenomenon in Pop Sci; they were talking about underwater weapons and such?

Ah yes, here it is: Supercavitating Torpedo | Popular Science

Ooh! Lookit what else was on Pop Sci:

A Cocktail of Diesel and Gasoline Runs 20 Percent More Efficiently Than Either One Alone | Popular Science

Could be kinda neat.
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Old 08-10-2009, 05:14 AM   #4 (permalink)
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Quote:
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IIRC 2-cycle engines run on a cocktail of gasoline and diesel. Around here, if you go to a small rural gas station you get a cocktail of fuel and water. The further from a large city, the more water. How's that for saving fuel?
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Old 08-10-2009, 09:12 AM   #5 (permalink)
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Built in water injection? Neato.
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Old 08-10-2009, 11:33 AM   #6 (permalink)
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Well, I wasn't too awful worried about actually bringing the concept to the real world, but it's still interesting.

Supercavitation makes it seem like that at some currently undetermined inexact speed, fluid dynamics no longer apply, since no matter what shape you're starting with, a super bubble forms, creating the most dynamic shape available in front of the object.

This has been evidenced in cartoons far and wide - Most notably: Speed Racer, DragonBall Z, and several other Japanese Animations.
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Old 08-10-2009, 03:47 PM   #7 (permalink)
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The Russians probably got the idea from SpeedRacer LOL

It is a neat idea; too bad I can't figure out how to use it on something of mine.
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Old 08-11-2009, 07:58 PM   #8 (permalink)
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It's been used for torpedoes for quite a while... I thought the main point was to cut down on surface drag by making sure that most of the length of the torpedo is not in contact with the water?

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Old 08-11-2009, 08:27 PM   #9 (permalink)
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Quote:
Originally Posted by some_other_dave View Post
It's been used for torpedoes for quite a while... I thought the main point was to cut down on surface drag by making sure that most of the length of the torpedo is not in contact with the water?

-soD
At a somewhat higher speed, the same thing occurs in air. I can't find the formula to confirm speed, but it's based on the density of the fluid medium through which one is traveling.

Water is one of the easiest mediums to test it in, due to it's extreme density compared to other fluids, and the fact that it's clear as well.

IIRC, the speed at which cavitation is achieved is inversely proportionate to the density of the fluid (which seems obvious), i.e. the fluid is less dense, the speed is higher. I believe I recall reading something at one point which mentioned that necessary speed is related to the square of the density of the fluid medium, but that may be a cross-memory from another technical paper.
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Old 08-11-2009, 11:55 PM   #10 (permalink)
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I've heard it referred to as "aero-spike" although all my research ended up being about a centralized cone linear arranged rocket engine. I was wondering the other day, seeing all the boat tail stuff, if anyone had tried some kind of retractable pre-wake generator, punching a hole for the car to run in. The ones used on hypersonic missiles are generally just a simple flat disc of a calculated size on a pole at a calculated distance ahead of the main body. Calculations based on effective speed and size of the vehicle. Can't punch a hole for the whole thing or you loose aerodynamic effective steering.

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