Propeller Cavitation

[R00RAL]

12alien12, Hi, the composition of what is in the bubbles depends on what water you are testing or running the prop in. The bubbles are essentionally the water boiling. It does this when you drop the water pressure, as kona181 said, cavitation happens on the Low side. The best way to film it is to put your prop into a flow tank, pressurize the water if your working with a smaller prop and film the prop then later slow the film footage down.

[12alien12]

I would like to know the composition of that gas that cavitates on the blades.

[707RipOtee]

Would divots and smooth sufaces also cause cavitation?

[theglib]

very good video.

[kona181]

I guess i didn't quite think of that, good work on the video though.

[karuspery]

Design a prop that fixes that and sell it to the chinese military.

[pudd750]

its running backwards to the props design- spin it the other way and itd not cavitate as much

[kona181]

It might be spinning the right way, if the flash is off sync it can make it look like it is going another direction.

[rickypigazzini]

@kona181 You're right, the flash may be off sync, but, unfortunately it's spinning "backwards". Because Cavitation occours on the low-pressure face of the propeller's bades, if? u watch around 00:50 you see that it is spinning in the right direction to cause cavitation on the upper face. In terms of Visualization of the phenomena i think it counts marginally , the bubble formation is well visible.

[manbinichalt]

my name ist cavit hahahahaha

[guesswhotoo6]

Look at this in the dark, you might see pico-second light pulses!

[kroneage]

Swedes have come up w/ a composite material prop blade that shows far less wear effects from cavitation.

Also the better tuned a blade is, the closer you get, to a silent running blade (no sick singing). It also shows far less wear!

For positive effects of cavitation, you only need look at experimental submarines. Where they basically run fast inside of a cavatation bubble (less drag).

But newest US Military subs aren't using a prop. But pump jet, in shrouded propellar configuration!

[timbr33]

yeah thats because cavitation is noisy and by using a housing they can REDUCE cavitation to reduce the noise,

[BUDO15]

Why the pressure of the liquid falls below its vapour pressure? (local)? Has it something to do with the law of Bernoulli? Or is it because of the turbulence?

[iridethewave]

I do believe cavitation occurs when the vapor pressure of the bubbles falls below the pressure of the liquid. The drop in vapor pressure is only local, and usually only drops in the areas within a small distance of the propellor blades.

[pilko2500]

It is due to Bernoulli balance. Increasing the velocity of the fluid is balanced by a decrease in local pressure. Reducing pressure reduces the temperature needed for water to vapourise (like water boiling at around 70C on Everest). That's why the vapour bubbles can form. They almost immediately colapse and can cause quite a bit of damage from the energy released.

[mooseling1]

because one side of the propeller produces a low pressure that allows the water to boil below 100 degrees, so it can boil at 15 or 20 or so.

[youarelackluster]

Viktor Schauberger and John Keely utilized cavitation on purpose, and used the constructive/positive aspect of the full effect, not just the wearing down/destructive aspect. this hasn't ever really been researched that well, due to the tendency to view cavitation as a harmful effect, one to be minimized rather than caused and studied.

however, biomimicry will be one that provides capabilities of utilizing cavitation for good.

[Paxmax]

Cool vid! Cavitation is not something we covet! Nice and simple demo!

[DanielKTW]

I might be wrong but it looks like you had the propeller installed upside down (or speed reversed) purposely to create caviation.

[ingareinar007]

Well, cavitation eats up the propellerblades like moths on wood. You can actually cook an egg there.. That is why some make an "antisinging edge". (on the opposite side of the propellers turn, a knifelike edge.) To make cavitation on purpose is new for me.

Well submarines is different though. Normally 6-7 blades or moore. Less sufficiant, but silent.. And normally a "monoblock", and the cost of a small city.

[Fidelio0690]

And to mention for all high speed boats like cigarettes you have a surface piercing props that are working half in air and half submerged ( while submerged they are causing ventilated cavitation ) and it's high efficiency is caused by reduction of appendage drag and they have bigger diameters then convectional props.

[Fidelio0690]

cause of the high speeds of water that is going around the surface of propeller ( ship's screw ) pressure drops to a boiling point of water and it vaporise, so the only thing you can do is to design a propeller that will make a cavitation that imploads away from the surface of prop.

[Fidelio0690]

Cause you have paramters that states :

high efficient prop is one that has a big diameter and it's rpm is very low, so if you shrink a prop and want to have a good efficiency you gotta feed it with higher rpm, so most of low props are going in high rpm in range of 4500-5500 rpm, so with those speeds you can't avoid cavitation,

[thevigiles]

In most situation cavitation is bad. When the bubbles collapse, they cause what are essentially impact loads on the propeller. This causes pitting and ultimately premature failure of the propeller. You may be able to come up with a few situations in which cavitation may be beneficial, but for most applications, it's a thing you want to avoid.

[SlavaVB]

they should make the prop change its geometry so that the low pressure section expands to avoid cavitation.

[jazzGT]

cavitation does cause problems in pumps and turbines if im not mistaken

[opchidexio]

I beg to differ with those who assume that cavitation is due to poor design. It's just the OPPOSITE! A GOOD design produces cavitation (because it is working as it should.) However. Submarine propellers need low cavitation IN ORDER TO ESCAPE DETECTION in war time! Duh.

[Twinkier1]

Thank you. Those of us Submariners out here know that cavitation is a bda thing. Unless, say, a torpedo is coming after you at a high rate of speed.

[ingareinar007]

You are right. And stealth is crutial for you guys in "the deep". Submarines uses more blades on it`s propeller-system, bechause of stealth. A system of that size with more than four propellers is less efficiant, but it is more silent. And they are expensive as h... :)

Norway

[opchidexio]

Neat! 5 stars. What you're doing is creating a vacuum. Water placed in a vacuum will instantly "boil" -- without using or producing any heat. Hmmm... I think... maybe that's why ASTRONAUTS must WEAR pressurized "SPACE SUITS" and live in a pressurized "capsule"!

[igoriliev16]

Excellent job dude, very nice point of view, the bubbles are to visible. It's a kind of a shame for the company that produced this low efficient propeller. A typical effect of a very bad calculations and production. :)

[Fidelio0690]

Well most of small props are working in cavitation field , it's not like they are bad design, bad design is a prop that crates cavitation bubbles that collapse before they leave surface of the blade, so they impload creating a big pressure on surface that causes pitting, vibration, bending moment to increase , "theviglies" explaind it good.

[suckerpinch]

very cool!

[whiternoise2]

Roughly what frequency is that?

[oid123]

Nice, i think i'll see if my stroboscope is fast enough.

[nahuelito2007]

I forgot, it is not the same a static experiment and one tath the propeller are designed for... when the boat goes forward the cavitation disaper ones the waterflow copy the shape.

[nahuelito2007]

It is the result of a an inefficient shape of the blade.

[ingareinar007]

Correct, and often you can hear "sick singing" from the propeller, when you put a microphone close to it underwather. We make "antisinging edge" on each blade to eliminate that. (I used to make propellers for Rolls Royce Marine)

[Blastogy]

yea,,,, very neat, up until now Ive only seen it in textbooks.

[Flyberius]

pretty nicely done. I really wanted to see this happening so its kinda made my day.