Supercavitation

From Wikipedia, the free encyclopedia.

Supercavitation is the use of cavitation effects to create a large bubble of gas inside a liquid, allowing an object to travel at great speed through the liquid by being wholly enveloped by the bubble. The cavity (i.e., the bubble) reduces the drag on the object and precisely this makes supercavitation an attractive technology: drag is normally about 1,000 times greater in water than in air.

In 1977, Russian engineers developed the first projectile to use supercavitation: the VA-111 Shkval ("Squall") torpedo. This can travel at 230 mph (100 m/s) underwater, compared to the top speed of about 80 mph (35 m/s) for conventional aquatic craft, but it is reportedly not steerable. Even faster speeds of about 310 mph (ca. 140 m/s) and higher have also been rumored. News of the device reached the West in the 1990s. A malfunctioning Shkval torpedo has been officially alleged to have been the cause of the destruction of the K-141 Kursk submarine.

The Naval Undersea Warfare Center in Newport, Rhode Island, USA is now also working on the phenomenon.

From cavitation to supercavitation

To hydroengineers, cavitation is a known phenomenon. Cavitation happens when water is forced to move at extremely high speed, e.g. inside of a pump or around an obstacle, such as a rapidly spinning propeller. The pressure of the fluid drops due to its high speed (Bernoulli's principle) and when the pressure drops below the vapor pressure of the water, it vaporizes — typically forming small bubbles of water vapour, i.e. of water in its gas phase. In ordinary hydrodynamics, cavitation is a mostly unintended and undesirable phenomenon: the bubbles are typically not sustained but implode as they and the water around them suddenly slows down again, with a resulting sudden rise in ambient pressure. These small implosions can even lead to physical damage, e.g., to badly designed fast-rotating propellers.

A supercavitating object uses this phenomenon in a much larger (and sustained) manner, hence the name. A supercavitating object's main features are a specially shaped nose, typically flat with sharp edges, and a streamlined, aquadynamical and aerodynamical shape. When the object is traveling through water at speeds of above roughly one-hundred miles per hour, the water — which needs to avoid the object it is being displaced by — is forced to move around the flat, sharp nose so fast that it vaporizes. In other words, cavitation occurs. However, given sufficient speed and a suitable shape of the object, the (intended) cavitation can extend as a single large bubble of water vapour, enveloping the entire object. This generation and utilization of this very large gas bubble is what is called supercavitation. A supercavitating object quite literally 'flies' through the gas it is enveloped by. New gas is constantly being generated at its nose, while the water vapor condenses again to water behind the tail of the object. Various underwater methods of propulsion have been proposed to reach the necessary speed, with a possible concept being a rocket engine burning aluminium with water. The use of conventional propellers or turbines is not an option because the very hydrodynamic effects that make them work are disrupted by cavitation.

Current applications

As of 2004, Russian Shkval torpedoes are the only publicly known existing application of supercavitation technology. It has also been claimed that Russia (formerly the Soviet Union) also possessed underwater firearms discharging supercavitating projectiles, which are said to have been developed prior to the Shkval torpedoes.

In 1999 the supercavitation technology was adopted to hunting projectiles. These "SuperPenetrator" bullets feature a very stable straight line penetration in aqueous media. (http://www.grosswildjagd.de/penetrat.htm)

To date, the main emphasis of research into supercavitation has been into the development of torpedoes, due to the fact that supercavitating torpedoes can give an overwhelming advantage to a navy possessing them in quantity (assuming that the opposing navy doesn't possess them).

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Alf,

All you would have to do to prove/disprove it is the experiment, using the appropriate imaging technology, and have the money to spend on the experiments. The faster the bullet speed the greater the likelihood of cavitation, whether it is pure water or a mixture.

Keep me updated on the data.

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Alf,
You are right. Shoulder stabilization. Whatever. Flat nose solids penetrate reliably in a straight line long after the round nose solids have tumbled. No doubt. Any tendency to supercavitation in liguids does not hurt anything.

quote:

By Alf,
Can you evoke Newtonian flow in living tissue as this is the prerequisite for supercavitation to happen?

Wrong, also turbulent flow can cause a low pressure regime which is filled with water vapor, not vacuum.

quote:

If your cavitating projectile passes through varying media such as bone, air, fascia, tendon, muscle, stomach contents etc and it does so over a very short fraction of time, how can the bubble be evoked and maintained?

If it passes bone etc., the bubble is destroyed and after in aqueous tissue formed again. I tested it up to 12 times changing the media on the bullets path.

quote:

Looking at the macro anatomy of the elephant skull I find it near impossible to speak of supercavitation as being the mode of penetration.
So the only tissue that potentially can maintain a supercavitation bubble would be the brain ? ....... you do not need a large bore cavitating projectile to penetrate brain matter, a simple 22 cal bullet from a 22 long rifle would suffice. ( the object of the excercise is to get to the brain, one there and beyond little is needed to disrupt CNS function).
The optimum projectile shapes used in the RAMICS systems are all slim with smallest possible cavitators. ( they all look like slim very sharp darts)

A non-issue. The bullets we are discussing here are hunting bullets. They are optimized for bone and aqueous tissue, not for ele heads. But they penetrate ele heads more than RN. Ele cow heads honeybomb structure are reportedly filled with liquid. And they are not for marine warfare as the Ramics are.

quote:

Simply implying that a living body is bag of water or a bag of blood is not true and thus my reluctance to accept that supercvitation can or is evoked when a projecile is fired through it.

The 60 to 80 % of water in living tissue is not chemical bonded. So it is very easily released by the mechanical stresses and heat induced. There may be only a slight increase in vapor pressure, that doesn´t matter too much.

quote:

As I have stated I believe that the wadcutter penetrates better due to shoulder stabilization and not supercavitation.

Shoulder stabilisation is not possible with our long hunting bullets. In contrary, if the bullet starts tumbling, the "stagnation" pressure would act in the wrong direction and support tumbling.
Shoulder stabilization is only possible with short or flat bodies like falling leaf. It depends strongly on the COG.
I did some experiments which showed there is no SS with bullets. I asked those persons, who are claiming SS for hunting bullets, to show me one experiment, which would support this idea. I never got one.

All this to shoot a nasty old buffalo or elephant...???????

Bottom line is flat nose solids do work better and the only plus you get from a round nose is they feed better and thats a mighty big plus, but I tweek my rifles to use the flat nose...

I used flat nose bullet before they were ever accepted around here or anyplace else..I had ITTD makes some for me and all they did was grind off the front, Barnes showed not interrest at all, and told me it wouldn't make any difference and on and on for years, and early on I got a lot of flack for using them, and was told on this and HA that a cutting shoulder didn't serve any real purpose, I pushed for them for years without success until GS Customs came along..I knew it worked in pistols, so it must in rifles was my only therory...

I still get some disagreement on the cutting shoulder, but I have used them with and without and I know I get a better entrance hole and exit hole with a pronounced cutting shoulder if its hard and sharp, and it shaves hair that allows better bleeding on longer haired animals particularly...

I had read little about why they worked, and it made since, and experience in using them seemed to bolster what this thread says..

Bottom line with me is only one thing, what works in the field, all else is twaddle, simi interresting conversation that sometime goes out of the sphere of reality and becomes a converstation close to what one would expect from a couple of old time hippies trying to test who's vocabulary was the grandest.!

As a result of my efforts, as meager of actual proof as they were, I enjoy these type threads and others like it, but again only if they don't go too far abroad.

If someone doesn´t like the expression Supercavitation for the stabilizing effect of hunting bullets featuring a special meplat or frontal disk, he may use another expression.

Supercavitation is used for the phenomenon when bodies moving in a fluid are surrounded by a gaseous structure, which reduces the interaction with the fluid. It may form a single bubble or an object of myriads of smaller bubbles.

Since the effect of reduced interaction and friction is evident and only possible with less contact to the fluid, it may be called bullet induced cavitation, BIC, or bullet induced bubble, BIB.

Fast torpedoes that can't be controlled is nothing new. When I was in submarine school we looked at the history of torpedoes, and also their capabilities. The USN submarine Mk 16 torpedo would go about half the speed of the Squall, but they were all ove the ocean. Reduction gearing reduces the speed by about half, and they can be controlled there.

Of course in those days we used mechanical control systems. No high-speed digital control systems as you could use today.

The Soviet underwater guns I have heard of were for Speznatz (special forces) use, essentially a kind of spear gun.

Back to my underwater cave...

jim

quote:

As I have stated I believe that the wadcutter penetrates better due to shoulder stabilization and not supercavitation.

Alf, do you have any data that will substantiate that theory?

A superpenetrator will lightly bump to a stop nose first after 3 meters of water, say in the lid of plastic bucket in a train of 5 gallon water buckets lain end to end. Right?

And a round nosed Kynoch will tumble and come to rest within 2 meters of those buckets. I have seen it.

Is the supercavitation bubble being disrupted by the baffles every 14" in the form of bucket bottoms and lids?

Would the superpenetrator in an Olympic sized swimming pool punch a hole in the far end wall? I think not.

If the round nosed solid would just keep going nose first instead of tumbling, it would come awfully close to the SuperPenetrator.

I think Alf is right in that supercavitation is not important in game shooting. I don't know what it is if it is not "shoulder stabilization," but it is certainly something about the geometry of the nose of the bullet.

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Supercavitation is what we called farting in the bath tub when we were young, and it did propellus at great speed, or was it dad with his belt that did the deed?? Charlie

Alf,
3 meters or about 10 feet of water is what Norbert mentioned as approximate capability of his .458 SuperPenetrator. I'll bet the same weight and caliber bullet by GSC (FN) or North Fork (FP) will do the same.

Your military 20mm super penetrators must be like a spear or dart with a small disk at the tip. And that is an entirely different league than a sporting rifle.

Could the 20mm (not rocket propelled, but fired from a gun) punch a hole in the far wall of an Olympic swimming pool? I doubt it.

I hear Charlie used to bite the bubbles.

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Alf,
The Steel Maiden will have no walls and will vent the water hammer in the full circle, 360 degrees perpendicular to bullet path.

The supercavitation bubble will be disrupted every 6 inches along the way by about 1" thickness of plywood between the water bags.

It will allow meaningful comparisons of Mo/XSA numbers to REALITY. Not live game, but REAL.

Alf,
your response on my statements is neglecting what I really said. As you did in previous threads.
I never said, that newtonian flow is evoked in tissue. But cavitation from turbulent flow with hunting bullets doesn´t cause instability.
You are mixing up effects and objects, which are not under discussion here.
WW2 torpedos and as I know, also the ramics and other marine warheads are fin stabilized, like an arrow. The supercavitation effect is only used for reducing the friction and viscous drag in water. I am not willing to repeat all my saying.

quote: "The Japanese WW2 torpedoes used this theory in practce for the first time. They did not supercavitate but had stable passage due to the shape of the nose. Exactly as how it is described in the modern shooting literature."
Pls. give me more info on that, esp. modern shooting literature. Not the myth on shoulder stabilisation, which is published with a crude sketch and no experimental or basic scientific evidence.

Pls. shoot a hunting bullet from a smooth bore into water or game and report your findings. Remember: not the cavitation bubble is the stabilizing element, but the spin rotation, which is not stopped by the drag in water. It is still rotating in the bubble.

quote:"If a bullet fired from a 458 win is truelly supercavitating it should by all accounts penetrate way beyond the limits you have set cause that bullet is actually encountering little or no resitance in it's passage in water."
What is your intention, to state such a BS? Or do you really not understand what we are dealing with and only generating academic questions from very different matter? The SP bullet has about 10 % less potential of penetrating targets compared to the Kynoch nose shape if only the drag is working. That would hold also in water, but the RN will tumble and so show less penetration.
All very simple, but you have the talent to make things complicated.

As the SP and FN bullets are optimized for any material in game, the ele head anatomy is not an issue here. Important is only, that you can shoot ele´s very effectively.

BTW, the bubble needs a very low amount of water, which is easily released from the tiny encapsulation or what so ever.

Physics Daily, the physics encyclopedia, says the same thing about supercavitation as Wikipedia.

http://www.physicsdaily.com/physics/Supercavitation

The GS Custom website has an explanation of both supercavitation and shoulder stabilization.

http://www.gsgroup.co.za/articlepvdw.html

The Discovery Channel says this about supercavitation:

quote:

Supercavitation occurs when an object moving though water reaches speeds in excess of 100 knots (110mph). If the object has a correctly shaped ‘cavitator’ on its nose, a bubble of air starts to form around the object... This extends to cover the entire object, and hence the object is no longer moving through water, but through air, which creates but a fraction of the friction! Hence craft will be capable of racing at high speed on or below the surface of the ocean.

Traveling in a bubble kills off all traditional marine propulsion techniques. Propellers spinning in air won't be much good after all… The only engines that will work are the same ones which power our ships to the stars… Rocket engines. Supercavitational craft will be high speed, highly maneuverable rocket powered fighters.

http://www.deepangel.com/html/what_is_it_.html

Supercavitation rather than fighting the process of cavitation exploits it to create a near frictionless environment for a craft to travel in. Instead of trying to avoid or minimize cavitation, it attempts to create a renewable large bubble, a ‘supercavitational bubble’ which is designed to totally envelope the craft and thus make it travel within the bubble of air.

The breakthrough speed at which this occurs is 180 km/h, or some 110 mph or 100 knots. At this speed, with a correctly crafted nose the pressure of the water at the tip of the vessel would drop sharply, and start to change the water coming into contact with it from its liquid form to its gaseous one. As this happens a bubble would begin to form, extending back along the craft.

A supercavitational craft would have to have a nose with a specially designed ‘cavitator’ which extends the bubble and makes it stable. The size and length of the bubble is dependant on speed, although it size can be increased by ‘ventilated supercavitation’. In ventilated supercavitation, air is pumped into the bubble to increase its size and ensure that it covers the entire supercavitating projectile. The Shkval for example, uses ventilated supercavitation by redirecting part of the exhaust gases from its rocket engines through outlets near the nose of the torpedo.

http://www.deepangel.com/html/the_science.html

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Alf,

How do you know that animal tissue behaves as a solid when struck by a bullet?

Perhaps it behaves as a liquid in which some solids are suspended.

What percentage of a cape buffalo's body mass is H2O?

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Alf,

orthopaedic science has other matter in mind than terminal ballistics.
If you have an elastic body, (it doesn´t matter wether you call it solid, semisolid, heterogeneous mixture or liquid,) which can release a relative small amount of vapour or gas for a surrounding bubble, we call it supercavitation. Formerly the expression supercavitation in basic science was more strongly related to the water vapour homogeneous bubble. But nowadays any effect, which separates the viscous boundary layer from the moving object, is subsummerized (spelling?) under this term. For instance the method of gas injection or the creation of myriads of bubbles like a foam. May be a purist doesn´t like to call it SP. Than pls. create a new term for the phenomenon of separating the boundary layer.

So your question, solid or liquid is again a non-issue.

But I really miss your answer with respect to an experimental and scientific verification of shoulder stabilisation.

Just some info on the torpedo...



Found here...

At my other favorite weapons site.

It LOOKS like the boundry layer is created from rocket eflux and not from true cavitation (impact)

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quote:

Originally posted by ALF:
500 gr:

How do I know, cause it does!

I will copy and paste the tables and graphs of the physical properties of human connective tissues for you if you wish. Or I can refer you to a good book to read on biomechanics of living tissue !

I can add to that if I operate on people the tiussue does not simply flow out of them when we cut them The steak you eat on your plate at dinner is solid, you need to cut it with a knife and then chew it not so ? Some steak is so tough you need to beat it with a hammer to get it so you can actually get to it with your teeth

So how do you propose you are going to get that steak to flow around the projectile and what is more undergo phase change due a drop in the pressure in the boundry layer ?

Alf, what a steak does on my plate or what a patient does under your knife is a completely different from what happens when a bullet hist an animal at 2400 fps with 60kpsi stagnation pressure in front of the bullet nose. A watermelon shot with a .270 behaves differently than one which I cut open with a paring knife.

Alf,
That watermelon has a lot of free water in it, more than a game animal.

I believe in shoulder stabilization. I take it on faith.

I studied fluid mechanics, etc., as a chemical engineering student long ago. It helped me get a 99th percentile science score on the old MCAT. I have instrumented live, anesthetized dogs with strain guages in physiology labs, etc.

I am impressed with your thoroughness of presentation here. I am with you.

Some contribution of supercavitation may be involved in a minor way, but mostly, it ain't important in game animals. It is not even very important in my water buckets. It may help stabilize the FN solid there, but so does shoulder stabilization.

This is no detraction from the greater effectiveness of the FN solid.
Anyone using round nose solids is whistling in the dark, or has a rifle that needs a feed job.

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I have two questions and one reply. Who cares? and how did we get on this subject? Book a hunt on the South East Nort Western East African Watermellon Buff , shoot him and post the report. Charlie

Charlie,

you are absolutely right.

RIP:

If shoulder stabilisation is working on long FN hunting bullets, any excess force which is not acting at the center of the nose is thought to move the center of the bullet´s nose in the direction to this force and makes an angeling bullet to go straight again.

A RN bullet with no shoulder than should show no stable path, but it does sufficient for normal hunting purposes.

When the FN bullets starts to veer, the center of gravitation is at the wrong side and the tumbling is amplified. see sketch:

A bullet hitting the target at an angle should tilt to become perpendicular to the target surface. We never observe such a behaviour. Some shape charged devices (bazooka) are constructed to do this. They are short projectiles with an appropiate COG.

Any inhomogeneity in the target, e.g. tissue and even wood, should tilt the bullet and cause a very erratic path.

If not the keeping of the spin stabilisation is causing the straight path, but shoulder stabilisation, firing a bullet from a smooth bore should go straight. But this bullet is tumbling immediatly.

So I would like to shoot only bullets without shoulder stabilisation.

Alf,

Norbert's point that water is easily liberated from muscle/liver/etc. as the bullet enters an animal certainly seems valid. Of course the supercavitation bubble has been shown to exist in fluids, such as seawater. So it would be logical to deduce that water can be vaporized in an animal and that supercavitation can occur. Certainly the greater depth of penetration that many people are observing with FN solids tends to support the supercavitation side.

As for shoulder stabilization, it is another theory to explain the data. But in the articles I have read, there does not appear to be any more irrefutable actual proof of shoulder stabilization than there is of supercavitation if we are to be strict about it.

With regard to the steak on my plate, when I cut it there is not enough heat or pressure to liberate any substantial of water from the tissue. So supercavitation will not occur in that instance. (Especially since I do not use a flat nosed knife. )

quote:

Originally posted by ALF:

I can add to that if I operate on people the tiussue does not simply flow out of them when we cut them The steak you eat on your plate at dinner is solid, you need to cut it with a knife

So how do you propose you are going to get that steak to flow around the projectile?

Or I can refer you to a good book to read

How do I know, cause it does!

So ALF, after reams of "doctorate dogma" here, it all boils down to whether the tissue "flows" out of the body on its own or not to constitute the definition of liquid/solid?

I would ask if the said steak were to be put under the ram of a fifty ton press and "squeezed" what you might call the "fluid" that runs out?

Is ballistic gelatin a liquid or a solid?

What about animal fat? What if we heat it up?

What about oil vs. grease?

As sure as stepping on the brake pedal of your car transfers hydraulic pressure to each wheel cylinder to apply your brakes; there is a hydraulic "force" ahead of our bullet, induced by our bullet, for the couple of milliseconds its traverses our animal. While this "force" may vary it is not as simple as water vs. wood!

If one shoots a can of broth, a can of green beans, a can of canned meat, with a high velocity bullet a dramatic hydraulic "explosion" takes place! If a can of dry chow mein noodles are shot the violence diminishes...... Why??
It doesn't seem to relate to whether the substance will pour from the can.....

I believe whatever is in front of our penetrating bullet is in a compressed or pressurized state. This applies to gas, liquid, semi-liquid or solid. Extremely short duration may prevent anything other than this such as bubbles, etc.? I am not sure how much super-cavitation takes place at elevated speeds; but plenty of what that 50 ton press gave us above does! It will squeeze out plenty of the "juices" that you want for hydrodynamics to do its thing!

A good book on the subject? If you want one you will have to write it yourself ALF! Write it after much hands on experimentation!..... I am sure the scribes scratched out the "proof" on the world being flat if we "dated" our reams of data enough.....

How do I know, cause it does!

Does it?

BigRx

quote:

Originally posted by 500grains:
As for shoulder stabilization, it is another theory to explain the data. But in the articles I have read, there does not appear to be any more irrefutable actual proof of shoulder stabilization than there is of supercavitation if we are to be strict about it.

500grains,

When 6 years ago I was looking after an explanation for the straight line penetration of FN bullets, there was only evidence in parallels to a boundary separating effect by cavitation. There was no real contradiction.

But with shoulder stabilisation I found many non effective things and contradictions.

A third explanation I couldn´t find.

Damnnnnnn, you guys is plumb et up with therory!!

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All I know is if I place the bullet in the right place.............the animal dies.

the chef

ALL theories aside, I know that a 480 Woodleigh Solid out of my 450 No2 WILL penetrate an elephant bull skull from the front.
I know Norbert has taken several elephants with his bullets, perhaps he should relate some of his actual kills. I have seen some of them on video. They seem to work pretty good.

O.K. guys. The three factors in Flat Nose Solid Superiority:

1) Supercavitation
2) Shoulder stabilization
3) Cookie Cutter Effect

Believe in this trinity and never use a round nose solid again.

Now if you will excuse me I will go shootin' ...

Alf,

Norbert has applied the scientific method in finding the only viable theory which explains the data collected. And the theory is proven fact in other fields (subs and underwater guns).

It does seem that the shoulder stabilization theory is weak. Has shoulder stabilization been proven in any other field?

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