Talk:Supercavitation

message: Should not SI units (m/s) be used as primary units and imperial units
(mph) be enclosed in parentheses? Having m/s there is good.
In as international project as this, usage of non standard mile and feet
measures should be avoided. I'd be better to use only SI units or at
least special units such as knots when talking about ships and torpedoes.— Preceding unsigned comment added by Jkj~enwiki (talk • contribs) 14 July 2003
SI units should be used, with mph AND knots attached in paranthesis.  Logic for this follows as, generally it would be nice if [everyone] used SI units, so to accomplish that it should be the primary units.  mph and Knots should be included for those people who have no frame of reference of SI, colleges and most highschools in the United States teach SI units in they're phyiscs, chemisty, (but not in they're engineering classes...) classes.  Even so, I still don't have a proper perspective on how fast 120km/h really is, and less so on m/s.  Thus common alternate measurements should be included to give perspective. --ORBIT 20:42, 6 Feb 2005 (UTC)
thread_title: Units

message: The supercavitation principle has been used for high performance racing boats for a long time. Model racing boats uses supercavitation or alternatively surface piercing exclusively, both for propellers and rudders. The "Squall" is the 1st underwater vessel to use this principle. -- Egil 07:17, 23 January 2006 (UTC)
thread_title: Supercavitation used for racing

message: The line that says the russian underwater firearms do not supercavitate is incorrect- they do in fact supercavitate. It seems that the only information that they don't is that a few websites describe them as "drag stabilized", which doesn't mean they are not supercavitating as well. "drag stabilized" just means that stability is achieved by pulling back on the back, instead of pushing in on the sides. The stability of these is actually a complicated subject, but it will suffice to say that it gets stability from both "lift" and drag (from tail slap mostly, but also from the flat nose)
There is also information on the web saying they do supercavitate.
"Russian rifle ammunition using supercavitation for underwater use 
I have come across some mentions that the Russian APS underwater rifle uses supercavitating ammunition : 
http://world.guns.ru/assault/as69-e.htm. 
The APS is designed for special underwater cartridges, which fire 5.66 mm needle-like projectiles 120 mm long. The projectiles are stabilized using a hydrodynamic cavity, generated by the flat point of the projectile. The cartridges use standard 5.45 x 39 cases, sealed from water."
http://72.14.253.104/search?q=cache:PwwmQ2YapTEJ:www.grosswildjagd.de/fundamen.htm+underwater+rifle+aps+supercavitation&hl=en&gl=us&ct=clnk&cd=7
"Soviet engineers worked on supercavitation in the 60ths. At the end of the decade O.P. Kravchenko and P.F. Sazonov have developed underwater ammunition (4.5X40 mm and 5.66X49 mm) that utilized that principle. For this ammunition the Central Institute for Precision Machine building made a underwater pistol and an assault rifle called SPP-1 and APS. "
http://72.14.253.104/search?q=cache:7YBWh1Vt298J:www.stormfront.org/forum/showthread.php%3Fp%3D2866434+underwater+rifle+aps+supercavitation&hl=en&gl=us&ct=clnk&cd=1
If that is not enough evidence, I can run the numbers for you. Notice the flat tip? That is a cavitator.
The empirical equations (which can be found online in different forms, such as http://cav2003.me.es.osaka-u.ac.jp/Cav2003/Papers/Cav03-GS-6-006.pdf#search=%22supercavitation%22) show that it does infact produce a supercavity.
Cavity radius = Cavitator radius * SQRT(Cd/Cavitation number)
Cavity length = Cavitator radius * SQRT(Cd*ln(1/cavitation number))/cavitation number
Cavitation number = Pressure/(0.5*density*velocity^2)
Cd (drag coefficient) for a flat disk is ~0.82
If you run the numbers (Cd = 0.82, Pressure = 101kpa, Density = 1030kg/m^3, 250m/s, Cavitator radius 2mm), you will find that the initial cavity length is about 0.7 meters near the surface, which is > 0.12meters, which is the projectile length, with a 16mm maximum radius, which is >> 2.83mm, which is the projectile radius. This means the whole projectile is in the cavity.
I got those equation from Professor Emeritus Marshall Tulin (the guy that developed the theory of supercavitation in the 60s), when I met with him this week to discuss supercavitating projectiles such as these. It was clear to him as well that they are supercavitating, although he had not heard of the weapons before.
If you run numbers assuming it is not supercavitating, you will realise the reported ranges are not possible. The drag coefficient would have to be as low as 0.07 to get as far as they claim to at 5m depth and still retain 30% of the speed. 0.07 is not a reasonable number for a dart like this when not supercavitating. This approach does not explain the depth dependence on range, which is more evidence that it is faulty. Here's how I calculated the distance constant (velocity decays exponentially with distance)
http://www.google.com/search?hl=en&lr=&q=1%2F%28%28%285.66mm%2F2%29%5E2*pi*.07*.5*1030kg%2Fm%5E3%29%2F26grams%29&btnG=Search
It's also worth noting that the dart would not be stable if it were not cavitating at all, or only cavitating off the back. The center of mass is roughly 1/2 chord, while the center of pressure is at 1/4 chord, which makes it unstable. If you're claiming the cavity coming off the back "drag stabilizes" it, you would be wrong. The pressure (or lack thereof) pushes normal to the surface, which is through the cg, leaving you with no stabilizing moment"
More on the subject of stability: "The pressure distribution on the disc cavitator is actually slightly stabilizing" - Marshall Tulin. Of course, this only applies to supercavitators.
If there is a way of upoading pictures for the talk page, I can show pictures of simulation, and graphs of closed form equations that predict the supercavitation (including the distance/depth curves, and just about anything else you need to know) of these projectiles.
Change it back.
---Jimmy. — Preceding unsigned comment added by 169.231.23.207 (talk • contribs) 18:06, 13 October 2006‎
:The initial edit was my mistake, I should have been more careful, thanks for the correction, and information.--Sukisuki 22:06, 27 October 2006 (UTC)
thread_title: Russian underwater firearms

message: I have a problem with the evident bias against supercavitators in the discussion. "Time enough to avoid"? I'm far from convinced one minute is enough for a ship to change direction. I can't help recall WW2 boats with much slower, noisy, wake-producing torpedoes successfully sinking even destroyers. I picture spreads of three or four supercavitators, fired close in, possibly in conjunction with noisemakers or autonomous decoys. Additionally, the critic seems to assume supercavitators will never be quieter, or able to be launched silently. Unfortunately, I'm insufficiently up to date on the state of the art today to correct it.  Trekphiler 23:40, 28 February 2007 (UTC)
replies: text: Looks to me as if the writer is in the grip of the guided torpedo lobby. Still.  Trekphiler 00:01, 3 April 2007 (UTC)
thread_title: Tactical theory

message: There might be some merit to the claim at the end ("Supercavitation also produces an incredible amount of noise, which alerts the target to both the torpedo and the location of the launching sub."), but the first bit seems to be trying to argue that taking less time to get to a target is somehow a drawback. Doesn't make much sense...
I'm removing the whole section; if someone can find a source for supercavitation being unstealthy, feel free to add that part back in. 62.30.157.187 04:11, 7 June 2007 (UTC)
thread_title:  "Drawbacks" section 

message: I just removed a number of assertions that were unsourced, although they had been fact-tagged for many months.  I suspect some of the material is at least partially good stuff, but without verifiable, reliable secondary source citations for the claims, they really don't belong in Wikipedia.  Cheers, N2e (talk) 05:49, 29 September 2009 (UTC)
thread_title:  Removed uncited, previously tagged, material 

message: === A) Theory ===
(sorry for the quality of my english)
Cavitation is a known phenomenon. It occurs when a liquid is accelerated at high speed, for example on the blades of a propeller. The fluid pressure drops due to its high speed (Bernoulli's Principle) and when the liquid pressure drops below the vapor pressure, it vaporizes - typically forming small bubbles of water vapor; it is to say water in its gaseous form.
In ordinary hydrodynamics, cavitation is a phenomenon that, mostly, is incidental and undesirable: usually, the bubbles are not sustained but implode because of the sudden deceleration of the fluid and the sudden rise in ambient pressure. These small implosions lead to physical damage. Misconceived propellers are vulnerable to this damages.
An object like a torpedo must at first overcome the friction of the surrounding water. The drag of an object is proportional to the density of the fluid in which it moves. The density of the liquid water being much greater than vapor water, the same pushing force moves the torpedo less rapidly in water than in vapor. So more speed, more drag and certainly not more absence of friction in front of the torpedo.
So, how to create this surrouding film of gaseous fluid in water for a torpedo ?
Bernoulli's principle can be seen, for example in the case of a torpedo, easily like the principle of conservation of energy. The torpedo communicating kinetic energy to the fluid in the form of kinetic and thermal energy. 
Don't forget that the density of water "pumped" more kinetic energy than in gas on the same distance.
When such an object enters a fluid the water is violently deflected (if dropped from helicopter or a bullet ejected from a gun for example). That is more created by the interface air-water than the speed of the torpedo or the bullet and it have anything to do with the creation of the supercavitation phenomenon.
This is obviously not sufficient to reduce friction and pressure of water which is always experienced at the front and which restricts the speed of the torpedo. Moreover the drag will be greater with greater speed. 
Thus, the natural deflection of water alone can not cause a supercavitation by vaporizing the water in front of the torpedo and even before it comes into direct contact with water. There is simply no sense here.
Creating a supercavitation simply by exerting greater force on the water is not realistic since the friction becomes proportionally larger. At some level the water becomes as hard as concrete.
To generate a supercavitation, the torpedo must eject a hot gas who can vaporize water at the front of the object. The torpedo penetrate continuously in this gas and this gas will form a friction-reducing coating of the water. Hence the SUPER cavitation, a SUPER bubble, a neologism by analogy with the phenomenon of cavitation.
Moreover, the dynamics of a propeller or a pump where cavitation is often seen are totally not the same as in the ballistic movement of a torpedo.
This article is highly speculative and needs true experts in the matter who will be able to clear the doubts. Which I am not.— Preceding unsigned comment added by RemyD11 (talk • contribs) 00:57, 15 March 2012‎
-------
:There is a reliable source for the description of the basic phenomenon of supercavitation, which is the 2001 Scientific American article referenced here by Heron since 2003-06-22.  It is true that the basic effect can be enhanced by addition of internally generated gasses, especially near the nose of the vehicle and especially when the speed is not sufficiently high and the bubble needs to be expanded.  Hot temperatures probably help too, but the time available for heat exchange to the water in front of a high speed torpedo would be... very short.  
:Projectiles fired into the water or fired underwater generally don't have a source of hot gas to expel out the nose for supplementing the cavitation bubble.  And yet these devises exist and are an area of active research.  The SciAm2001 article names people as sources and also the organizations that they work for.  It also constitutes a peer-reviewed journal, so on the face of it, the material should probably be considered to be reliable.  
:I'm not an expert on supercavitation, but I am an aerospace engineer with a background in aerodynamics and hydrodynamics.  It seems to me that the sources that are referenced and cited make a pretty good case for what supercavitation is and how it works.  I'm somewhat surprised that the material is available in the open literature, considering the implications of having or not having this type of capability.  It may be that the author of the SciAm2001 article was merely trying to get scientists and engineers in the United States to become familiar with capabilities already developed and deployed by the Soviet Union in the 1970s.  Fielding a weapons system based upon the contents of the article would still be... very expensive and time consuming. PoqVaUSA (talk) 03:21, 11 January 2013 (UTC)
thread_title:  Attention needed from an expert on the subject 

message: (sorry for the quality of my english)
Cavitation is a known phenomenon. It occurs when a liquid is accelerated at high speed, for example on the blades of a propeller. The fluid pressure drops due to its high speed (Bernoulli's Principle) and when the liquid pressure drops below the vapor pressure, it vaporizes - typically forming small bubbles of water vapor; it is to say water in its gaseous form.
In ordinary hydrodynamics, cavitation is a phenomenon that, mostly, is incidental and undesirable: usually, the bubbles are not sustained but implode because of the sudden deceleration of the fluid and the sudden rise in ambient pressure. These small implosions lead to physical damage. Misconceived propellers are vulnerable to this damages.
An object like a torpedo must at first overcome the friction of the surrounding water. The drag of an object is proportional to the density of the fluid in which it moves. The density of the liquid water being much greater than vapor water, the same pushing force moves the torpedo less rapidly in water than in vapor. So more speed, more drag and certainly not more absence of friction in front of the torpedo.
So, how to create this surrouding film of gaseous fluid in water for a torpedo ?
Bernoulli's principle can be seen, for example in the case of a torpedo, easily like the principle of conservation of energy. The torpedo communicating kinetic energy to the fluid in the form of kinetic and thermal energy. 
Don't forget that the density of water "pumped" more kinetic energy than in gas on the same distance.
When such an object enters a fluid the water is violently deflected (if dropped from helicopter or a bullet ejected from a gun for example). That is more created by the interface air-water than the speed of the torpedo or the bullet and it have anything to do with the creation of the supercavitation phenomenon.
This is obviously not sufficient to reduce friction and pressure of water which is always experienced at the front and which restricts the speed of the torpedo. Moreover the drag will be greater with greater speed. 
Thus, the natural deflection of water alone can not cause a supercavitation by vaporizing the water in front of the torpedo and even before it comes into direct contact with water. There is simply no sense here.
Creating a supercavitation simply by exerting greater force on the water is not realistic since the friction becomes proportionally larger. At some level the water becomes as hard as concrete.
To generate a supercavitation, the torpedo must eject a hot gas who can vaporize water at the front of the object. The torpedo penetrate continuously in this gas and this gas will form a friction-reducing coating of the water. Hence the SUPER cavitation, a SUPER bubble, a neologism by analogy with the phenomenon of cavitation.
Moreover, the dynamics of a propeller or a pump where cavitation is often seen are totally not the same as in the ballistic movement of a torpedo.
This article is highly speculative and needs true experts in the matter who will be able to clear the doubts. Which I am not.— Preceding unsigned comment added by RemyD11 (talk • contribs) 00:57, 15 March 2012‎
-------
:There is a reliable source for the description of the basic phenomenon of supercavitation, which is the 2001 Scientific American article referenced here by Heron since 2003-06-22.  It is true that the basic effect can be enhanced by addition of internally generated gasses, especially near the nose of the vehicle and especially when the speed is not sufficiently high and the bubble needs to be expanded.  Hot temperatures probably help too, but the time available for heat exchange to the water in front of a high speed torpedo would be... very short.  
:Projectiles fired into the water or fired underwater generally don't have a source of hot gas to expel out the nose for supplementing the cavitation bubble.  And yet these devises exist and are an area of active research.  The SciAm2001 article names people as sources and also the organizations that they work for.  It also constitutes a peer-reviewed journal, so on the face of it, the material should probably be considered to be reliable.  
:I'm not an expert on supercavitation, but I am an aerospace engineer with a background in aerodynamics and hydrodynamics.  It seems to me that the sources that are referenced and cited make a pretty good case for what supercavitation is and how it works.  I'm somewhat surprised that the material is available in the open literature, considering the implications of having or not having this type of capability.  It may be that the author of the SciAm2001 article was merely trying to get scientists and engineers in the United States to become familiar with capabilities already developed and deployed by the Soviet Union in the 1970s.  Fielding a weapons system based upon the contents of the article would still be... very expensive and time consuming. PoqVaUSA (talk) 03:21, 11 January 2013 (UTC)
thread_title:  A) Theory 

message: A really great photo: looks like a waterborne stealth fighter.
 Headline-1: Maine entrepreneur builds sleek ship, but will military buy it?
* http://www.foxnews.com/us/2014/12/23/maine-entrepreneur-builds-sleek-ship-but-will-military-buy-it/
QUOTE: "The angular vessel looks like a waterborne stealth fighter. It rides atop underwater torpedo-shaped tubes powered by a pair of 2,000-horsepower gas turbine engines. Gyroscopes keep the ride smooth. ... The Ghost rides on struts connected to engine assemblies he says take advantage of "supercavitation," traveling underwater inside a bubble of gas" -- AstroU (talk) 21:46, 23 December 2014 (UTC)
thread_title:  New NEWS (big news today), for future editing 

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thread_title:  External links modified (January 2018)