Cavitation on hydrofoil
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- Опубликовано: 11 сен 2024
- See also this video for a ship propeller cavitation experiment: • Propeller cavitation e...
Experiment carried out at the Cavitation Laboratory at Marintek, Trondheim, Norway.
Link to similar experiment done in the same tunnel with a propeller:
• Propeller cavitation e...
A model hydrofoil is submerged into the closed-loop cavitation tunnel, and exposed to moving water to produce cavitation. The water is moved by a ~2m diameter impeller powered by a 1.2 MW electric motor. The cavitation tunnel has a max speed of 18 m/s.
In this experiment, the water is accelerated from 0 m/s to 8 m/s. It is pumped through a flow laminator and a nozzle to produce the top speed of 8 m/s (15.6 knots).
Towards the end of the clip, tunnel pressure is reduced to 23 kPa to produce extreme cavitation. The foil is mounted with 6 degree pitch, and has a projected area of 0.1208 m^2.
The foil produced lift force of 2208 N and drag 147 N with a tunnel pressure of 83 kPa (7.8 m/s) and slight cavitation. Lift was reduced to 2182 N and drag increased to 177 N when the pressure was reduced to 23 kPa. Same fluid speed.
HUGE thanks for telling us those numbers!! 15:1 L/D ratio is fascinating.
@hede88 It is actually true, it is a 1.2 MW electric motor that powers the propeller.
If you google "Marintek cavitation tunnel", you can find all the specs on SINTEF's webpages.
It takes a lot of power to move such great amounts of water. It is only in the working section that the water reaches 18 m/s, and the diameter there is "only" 1.2m. Still, that means that more than 20 m^3 is pumped every second!
just to be more clear the vibration is caused because of the difference in the speed of sound between the liquid/gas/wing as the liquid/gas travels over it.
you are correct !
As far as i know, thats why a wing is flat on the downside and curving on the upperside, letting matter move unhindered under it and pressing it upward at the upperside, the speed increase in the matter on the upperside, will then create a suction on the upperside which makes the wing rise ! If the suction is intense enough it will make the water boil as waters boiling point decrease with lower pressure at total vacum H20 boils near 0 celsius or 32 Fahrenheit, so the...
Congratulations for this impressive and clear testvideo. Good luck guys.
to your question about lift ratings: any time the liquid changes state over the lift surface you can see the cavitation as a "cloud" or "dew point", you lose out on lift and end up with vibration instead.
...so the temperature aint changing much only the pressure.
When the suction gets high enough on the front of the wing the vacum makes the water boil transforming to steam, then when the pressure starting to increase again it condensates momentanuously the steambubbles cant exist and implodes, and the water crashes in on the wing and in some cases it will destroy it with time.
you must not understand cavitation. It's caused when the pressure of the water changes so rapidly that it changes states from a liquid to a gas. So there are two things that cause it in bad designs, stalling (behind the lift), and over-pressure. What you see behind this design's winglet is good cavitation, what you see on the front of the hydrofoil is the water being accelerated faster than it can remain in a liquid state (or "hydro sonic" faster than the speed of sound through a liquid).
rizendell How would one protect with so much cavitation at those higher speeds as to not affect the foil design?
I have understood that some design is searching for cavitation as drag is less with gas to wing compared to fluid to wing? French Hydrophene (?), very fast foiling catamaran is using cavitation at purpose..?
Funny that this video just poped up so many years later. 🤠
Neutral buoyancy plastic balls are commonly used. You can see them in this video if you look closely :)
Would you mind to let me know at WHICH SPEED cavitation starts to develope on your foile?
This experiment took place a few years ago, and I no longer have available the test results, I'm sorry.
Flatlaker Stone He wont have a clue believe me this test failed the moment it went into that tank .....I work for *********** and they would never test in this manner
antipike Of course the speed is known. There are several dataloggers throughout the tank that continuosly record the water velocity.
antipike yeah cause you designed built the foil and you where there when they did the test.... there’s always one dumbass.
have you ever thought of using neutral buoyancy plastic beads to see water flow?
Could you just sweep the foil back like a jet fighter wing to alleviate the cavitation? If it works for turbulence, maybe it will work for cavitation. I am guessing it would be better as a variable-sweep wing, (foil), and may even be required to get up to the cavitation speed in the first place.
So, when designing such a foil, is it best to avoid cavitation? Does it represent a waste of energy that one does not wish to see in the application?
Yeah the “bubble” is actually a vacuum that increases the drag
with the aeration of the water, doesn't the density change, thereby changing the lift ratings? or does the cavitation over the top drop the pressure enough to increase lift? seems you are working with two different fluids. and now I'll have trouble sleeping tonight. am curious though
water is approximately 800 times denser. kind of like hitting concrete when you take the dare and jump off the bridge
natures way of telling you to make the top of the wing fill that cavitation in on your final design.
Because of the drop in pressure, the temperature would be lower than the surrounding water.
This is not true. The water "boils" due to the low pressure, and does not suddenly increase its temperature.
Awesome to see it like that. Stupid question but what profile is that foil?
yeah that sounds about right, water is like seven different kinds more dense than air so of course it'd take exponentially more power to move the same amount of water as we would air. by exponentially i mean the power needed to move the water is not linear.
800 times as dense as air... and 600 times faster at sucking the heat out of you
Dream job! Awesome!
I can't really recall what foil profile was used, sorry.
rarely seen such negative feed back on behalf of someone who puts up a video.
What speed ? = answer beside the question.
What profile ? = Can't remember
Try a naca profile. Speed, well it depends on the set up and angle of attack and thickness of the profile used.
You will do well in the commercial world my friend where secrets are paramount.
amazing to think that inside each one of those bubbles its roughly 5000 degrees kelvin
Next time set ONE camera and afterwards share the video
500 fotos?
Really? I didn't know they were hot.
looks like a 6-Series NACA profil.. 63210 64210 or even slimmer :-)
cool
I dont grt it.
The whole of the test tank had air bubble at higher speeds which in my mind makes the test invalid ....far better to drag the foil at the rear of a fast boat with underwater camera ...that way you going through virgin water making the test true
antipike Are you joking? You want to drag the foil though the water with absolutely NO precise control of the actual water speed (no knowledge about current, irregular motion of the vessel due to ship motions, angle of the foil, etc)I would say that will introducing a lot more variables than having the experiment confined in a cavitation tank, even though there are some leftover cavities that have traveled around the tank. At this velocity the viscous forces are dominating, and you should see little negative effect from the few cavities that are present in the water.
Jan Børge Sætre ...I speak from experience ....We done nearly the same thing with a offshore speed boat as the test rig ....We used gps to verify our SOG and we picked a calm flat day on a lake ....No air bubble were present in the Aqua being presented to our test and we got out of it what we where looking for .......The test on here has way too many cavities to be of any worth ....You need a much larger rig to get what you looking for OR you need to use NATURE ....
+antipike +Jan Børge Sætre Antipike thinks those plastic balls are airbubbles...
just to be more clear the vibration is caused because of the difference in the speed of sound between the liquid/gas/wing as the liquid/gas travels over it.