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I haven't said much recently here, but I may as well mention the newest major change: I've a job!
Well, similar to a job. Work, anyway. I'm going to be starting as a combined Bachelor's/Master's of Science student in the fall, and in the meantime I'm to summarize the present state of knowledge, and order parts for an experiment, in the field of supercavitation.
Supercavitation is something of a questionable name, in my mind. Unlike superconductivity and superfluidity, it isn't actually a new phenomenon – it's just ('just', ha!) an application of cavitation, which we've known about for ages.
Now, why did I scoff at the 'just', up there? The Shkval torpedo.
The Shkval (transliterated from Russian – basically "squall") torpedo couldn't steer. It couldn't detect the target sub (not that it could steer...), it was expensive, but it could do one thing no American torpedo could.
It could travel at over 100 meters per second. It did this with supercavitation.
Now, to explain what supercavitation is properly, I need to say a few words about water – three sentences should do it. Water has three common states*: gas, liquid, and solid. Now, normal temperatures and pressures on earth happen to lie near the triple point of water – that's why the words "ice" and "steam" exist – so it's not hard to change the state of liquid water. In fact, you can do it just by changing the pressure – drop it low enough, and the water will boil.
Sharp edges moving quickly through water make big variations in pressure behind them.
Now, if that sharp edge is the blade of your propellor, that's bad. That's cavitation. It'll make a lot of tiny bubbles, which will sap power, first. Then those bubbles (which were never stable) will implode, making pressure waves that'll damage your mechanism.
Supercavitation, on the other hand, relies on stable, large bubbles. In the case of projectiles like the Shkval, these bubbles are created by little sharp-edged shapes on the nose. (They're called cavitators, for obvious reasons.) By controlling the shape, size, and position of the bubbles, the supercavitating design can achieve something which normal designs do not.
The bubble on the Shkval and the like are designed to be large enough and appropriately shaped to cover the body of the projectile. As a result, projectiles like the Shkval don't move through liquid water – except for the nose, they're flying in gas. And as anyone who's walked around in a pool knows, it's a lot easier to move in gas.
Thus, 100 m/s. Thus, people want to know how to do it, and how to do it right.
* I say 'common' because there are others, like plasma. But those phases are basically irrelevant to this phenomenon (as is the solid phase, actually).
Anyway, researching that makes mostly what I've been up to the last week, and will be up to in the near future.
Well, similar to a job. Work, anyway. I'm going to be starting as a combined Bachelor's/Master's of Science student in the fall, and in the meantime I'm to summarize the present state of knowledge, and order parts for an experiment, in the field of supercavitation.
Supercavitation is something of a questionable name, in my mind. Unlike superconductivity and superfluidity, it isn't actually a new phenomenon – it's just ('just', ha!) an application of cavitation, which we've known about for ages.
Now, why did I scoff at the 'just', up there? The Shkval torpedo.
The Shkval (transliterated from Russian – basically "squall") torpedo couldn't steer. It couldn't detect the target sub (not that it could steer...), it was expensive, but it could do one thing no American torpedo could.
It could travel at over 100 meters per second. It did this with supercavitation.
Now, to explain what supercavitation is properly, I need to say a few words about water – three sentences should do it. Water has three common states*: gas, liquid, and solid. Now, normal temperatures and pressures on earth happen to lie near the triple point of water – that's why the words "ice" and "steam" exist – so it's not hard to change the state of liquid water. In fact, you can do it just by changing the pressure – drop it low enough, and the water will boil.
Sharp edges moving quickly through water make big variations in pressure behind them.
Now, if that sharp edge is the blade of your propellor, that's bad. That's cavitation. It'll make a lot of tiny bubbles, which will sap power, first. Then those bubbles (which were never stable) will implode, making pressure waves that'll damage your mechanism.
Supercavitation, on the other hand, relies on stable, large bubbles. In the case of projectiles like the Shkval, these bubbles are created by little sharp-edged shapes on the nose. (They're called cavitators, for obvious reasons.) By controlling the shape, size, and position of the bubbles, the supercavitating design can achieve something which normal designs do not.
The bubble on the Shkval and the like are designed to be large enough and appropriately shaped to cover the body of the projectile. As a result, projectiles like the Shkval don't move through liquid water – except for the nose, they're flying in gas. And as anyone who's walked around in a pool knows, it's a lot easier to move in gas.
Thus, 100 m/s. Thus, people want to know how to do it, and how to do it right.
* I say 'common' because there are others, like plasma. But those phases are basically irrelevant to this phenomenon (as is the solid phase, actually).
Anyway, researching that makes mostly what I've been up to the last week, and will be up to in the near future.
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