Cool demo. This force is apparently used in silicon fabs to pick up and handle wafers. Since it is contactless, no worries about contamination. Called Bernoulli grip.
Kohler toilets have a bell-shaped entry to the inlet at the bottom of the tank. Coupled with a valve design that lifts away from that inlet completely, the water from the tank goes down the pipe leading to the bowl much more quickly than that of a conventional flapper valve design using a conventional angular connection between tank and pipe. It really does work well.
2:33 The shape in the drawing is often called a velocity stack or venturi tube in hot rod car circles. I don't think they're going for levitation but the shape is the same.. It's also used on intakes to maximize lift on some kinds of flying vehicles, hovercraft and increase thrust on jet intakes.
If you look at the air intakes on carburetors or some fuel injection systems you'll notice the intake stacks are generally bell-mouthed as you showed in cross section. Without the bell mouth the intake of air is much less efficient.
In the RC plane world, electric ducted fans usually come with a curved inlet called a 'thrust ring' that really helps the static thrust. If it's not a tight fit, it sometimes gets sucked off the front of the duct!
@Matthias random stuff I think the tube is creating a restricted path so the vacuum pulls the volume through the gap at the base - this flow forces the tube to either rise or deflect until sufficient volume can enter the inlet - the hot glue around the mouth of the tube just served to stiffen the sides which stopped the wall deflection at the bottom of the tube allowing the air to flow freely past thus it resumed lifting (bouncing!) A great way to further the experiment would be to add smoke so we can visualize the flow Really fun experiment, very interested to know if you're sure you're correct or if my theory has merit. Tried to search through the comments a bit to see if a physics person knocked it out
I don't know if the centrifugal force is entirely necessary to explain it. That would contribute as well, but the reason you have flow in the first place is that the suction itself creates a partial vacuum and the fluid flows across the gradient. In the cone example, this should be pretty pronounced (on the vertical axis) as long as the cone is seated. I think maybe the cylinder oscillates so wildly because it's a finer balance (vertically) and the "leaked" pressure and flow would fall off rapidly over a very small distance as it reseats.
Nicely done! In fluid mechanics terms, what we are seeing is the transition from laminar to turbulent flow at the inlet. Laminar flow is a smooth predictable flow stream, with the force vectors mostly aligned in the direction of flow. Turbulent flow is chaotic and multidirectional, with the force vectors pointing in many different directions. With the bell mouth, air enters the tube smoothly and the flow is mostly laminar and the force vectors are pointing in the flow direction, causing the tube to suck down. Without the bell mouth the transition is abrupt and there is turbulent flow in the tube. Vectors in every direction. A portion of those vectors are pointing upward, resulting in an upward movement of the tube.
I've always thought of bell mouths (or "horns") as the fluid version of impedance matching in electronics, but now I'm having trouble making sense of that. That's probably because I don't understand impedance matching *or* fluid dynamics very well. :)
Sometimes velocity stacks can pop out of the holder if the screws are loose. I'd always assumed it was rattling (even tho the engine was relatively well balanced - just idling static) maybe this is why.
Brilliant problem solving and demonstration. And how funny that such a simple comment held the answer. Cheers Matthias from the Southern US! You are an iconic role model for your creativity, rationality, and ingenuity.
2:13 I wonder if this can be used to multiply the pressure difference of a high-flow pump and generate a strong vacuum. Make a pair of concentric pipes, with less than a millimeter of gap at the top. Pull air through the inner pipe. The space in between the pipes should want to drop to a pressure that's lower than the pressure you use to suck the air down the central pipe.
2:19 "And just the Centrifugal force ..." Nothing to do with centrifugal - its just lift over a curved surface, like any wing. Its true that lift is caused by air trying to change direction relatively suddenly, creating a partial vacuum in the process, but it doesn't have to be rotating around a sharp enough turn to invoke centrifugal effects.
Those bell shapes are implemented since long time in "itb" type of air supply to sports car motors, and in subwoofers vents. They make a noticeable difference in air flow.
Reminds me of the Turbotube, a toy from Whammo when I was a kid, A short tube of plastic with a thickened leading edge that would fly if thrown properly.
The same thing happens with the inlet of aircraft engines. The front of the inlet basically acts as a wing and creates lift in the direction the air is coming from
If you look at your 2d drawing, what you have is a shape similar to an air foil. It would be interesting to see a smoke test so you can visualize the currents. I bet you have some swirling low pressure vortices around the outside of the bellmouth.
For the first part, it is easily explained by the conservation of momentum. Since the inlet and the outlet are at atmopheric pressure, the force (assumed in the same direction of the air flow) to keep the cone in place is given by F = m_dot*(V_out - V_in). Since V_out > V_in, F is positive therefore the direction of the force is correct. The same principle explains why a firefighter will “push forward” to hold a hose nozzle in place.
That momentum/turbulence at the top is what lowers the pressure from above/inside. But, I wouldn't think in terms of the pipe being lifted from the top. I'd think in terms of the air outside the bottom of the pipe being able to over-power that lower pressure from above and push it's way under the pipe.
This is my explanation for the chain/rope fountain, the chain is getting accelerated so fast it generates a centrifugal force, raising the chain off the lip of the bucket.
im sure your channel is in the eye of the algorithm because one month before your videos didnt get auto generated captions. even when they were several days olds. NOW they has it instantly.
this channel has alwasy been ok with auto captions. Its my main channel that they are broken for. What I started doing is uploading main channel videos to this channel unlisted, wait for the auto captions, then download them and upload them for the main channel
Saw the other video a day or two ago, but the answer I've known for ages didn't hit me. Seeing this one brought it up. A 'straight' tube isn't straight aerodynamically, it acts as a restriction, due to the viscosity of the air hitting the sides and opposing free flow. IIRC the answer was the walls of the tube have to move out at 7 degrees in order for the air flow to be free. Believe that was both sides so 14 degrees spreading cone, and been ages, it could have been 7% instead of degrees. And suction is basically just reverse flow. So almost guaranteed this effect is why the straight tube still works and generates forces. Make a reverse cone from what is in the video, with a larger say 4" suction hole and narrowing to a smaller hole, with approximately 7 degree slope on the sides, and that should be the neutral point where it doesn't generate lift, so it should just sit there. No doubt ties in with several of the other answers here in the comments that roughly work out to similar ideas. But that's an isolated value I've known since the early 2000's mailing lists, it came up in a discussion and a side wall has to go out at 7 degrees for airflow to act as a smooth airflow and wall to not restrict the flow. And of course that's a rough approximation, no doubt the horn or bell type curve is actually a more correct fit.
Airliner jet engines make use of that. By having a rounded over edges at the front and increasing the front area more than necessary for the air inlet they not only make the air inlet more efficient they also produce additional thrust from the low pressure at those curved edges. I find this surprising as it means the air is really sucked in even at the pretty high speeds.
Once you understand the pressure differential thing, I don't get what's the mystery, a cone has a 45 degree angle to be pushed up on, a straight walled tube does not. Boom.
The rounded top makes the tube essentially an upright cylindrical airfoil, which makes me wonder: Does the shape of a plane's wing also slightly suck the plane forward?
On a plane, you use a propeller or jet to force the wing forward through the air. The wings are shaped so that some of the 'drag' ends up pointing upwards. We call the upwards drag 'lift'.
I would still like to see a small scale experiment on the water columns example that you explained in the last video. Is there any chance that you could do a video about that, with two columns of water with one jet holding a plate onto the jet of the other column please?
I wonder how much this would affect the efficiency of a ducted fan type arrangement. Similar to the "jet" pack in spy kids and as replicated on the MythBusters.
So back to the hanging J pipe in the earlier video.. there must be two forces that more or less cancel out 1) the air going around the J bend pulling it to the left and 2) the air going around the edge of the opening into the pipe pulling it to the right.
My motorcycle has the carburetors facing backwards with velocity stacks. It would be better if the carbs were facing forwards so it would help pull the motorcycle faster forwards. How could the engineers do this?
You're drawing the streamlines as if the flow is laminar. I don't believe it is. The o-ring could be tripping the turbulent boundary layer. Can you estimate the Reynolds number?
Awesome! This is fascinating. Makes me wonder what direction your handing J bend would move if it had an inverted cone on the end, with the smaller side at the intake?
But wait, if it is about air inertia, the thinner rim must create bigger vacuum and higher lift. So it's rather due to viscousity then? Also, what proportion to the lift contributed from the lower rim? You only made changes to the hole diameter, but not the gap
A common misconception about roofs. While shingles get blown off, flat roofs get sucked off by a vacuum effect of the air passing over the vertical parapet walls.
Is the explanation that the top of the cylinder is acting as a round airfoil that pulls the cylinder up or did I misunderstand completely? Does the same thing happen when air is being pushed in? What happens if the cylinder starts inside the suction tube? Does it get lifted out? I have so many questions now.
Not convinced by this explanation. Your radius does provide more surface area to act on but simultaneously eliminated the vena contracta so that there is much less pressure differential between the entry and the exit, you changed the flow coef from ~.5 to ~1. That means there is less overall suction pulling down on the tube, allowing it to rise higher. If it were only the rounded lip causing all the lift then the same lip could be added to your pendulum elbow test and it should also swing further than with a plain lip. There is more than 1 thing going on at the same time here.
yes, chances are, if I put a fatter lip on the pice of pipe and held it in front of the pendulum, it would deflect it more, as you say. But if the fat lip wee part of the pendulum, it would make as much difference as the cone being part of the pendulum, which is hardly observable, as shown in my previous video
@@matthiasrandomstuff2221 If it does not deflect it more then it means it is not operative in lifting the tube either and the explanation is wrong. I'd guess it will increase it somewhat but there is another force at work here. Need more data, more testing, more measurement. This is very interesting.
i have always thought that the bell shaped mouth of a blunderbuss is purely decorative.. but now i wonder if there is some of this effect happening in reverse.
Yeah, you'd want parabolic rather than ~logarithmic (you'd want the rate of widening to decrease as you got further from the center of the explosion or again, you'd want the asymptote parallel to the direction of fire).
There is also another thing for this sucking-blowing movement "mistery". The same thing applies to the drive of pop-pop boats, and it was described by Steve Mould in his clip on that topic (around 8 minutes) th-cam.com/video/3AXupc7oE-g/w-d-xo.html I hope it helps in further solving your problem 🙂
only if the sailboat has a huge blower to suck air from all the bellmouths. But if you have a blower, you'd be better off using its motor to turn a propeller
@@matthiasrandomstuff2221 I don't mean about sucking in this case, I mean about blowing. If the wind is blowing into the many bellmouths and the boat hull and aerodynamics were efficient enough, could the boat move into the wind?
What Matthias' demonstration shows is that you could create a force lateral to the wind. In his demonstration, air moving parallel to the X-Z plane reduces pressure and allows movement along the Y axis. Orthogonal motion is already used in sailing to 'tack' into the wind. Who knows, though, with enough thought maybe you can come up with a relatively inefficient (at least at first) auto-tacking system based on the Coanda effect 😉.
I’m not sure you have your full answer bc it doesn’t explain the oscillation.., I just posted a comment on the previous video which may explain the oscillation effect
The oscillation is due to that fact that the lifting force gets weaker as the tube lifts higher until gravity takes over and brings it down, to be lifted again.
Is this the same thing as when you use a stick blender in a liquid and it pulls itself to the bottom of the pan? Vacuum effect but a lot more moving flows
@@matthiasrandomstuff2221true, there is no reduction in the tube diameter to cause the velocity and pressure differences associated with the Venturi effect.
@@chiphill4856 Yes there is . Venturi effect happens to be a bell shape, a change in diameter over length. The typical square or slightly rounded edge of a pipe/tube is 'too fast' a change in diameter.
I don't think your explanation is correct. Maybe I can make some CFD models to show it since I don't have a workshop. The action is happening at the interface between the short tube and the fixed tube/table. The added ring at the top increases the pressure drop across the short tube (makes the pressure loss at inlet higher). The surrounding air is flowing into the small gap at the bottom of the short tube. With a higher pressure loss, the air rushes in more strongly and pushes the tube higher. Your thinner white tube didn't show the effect because rather than getting pushed up to allow the air to rush in, it collapsed (went oval in shape) and allowed the air to flow beside the tube into the low pressure area. You could better demonstrate this by adding a second, slightly larger tube mounted to the table and put the small short tube inside of it. That would ensure air cannot rush into that gap. If the short tube still gets lifted with that setup, you have disproved my explanation. Something to think about: where does the energy come to make the air flow around the inlet around the ring? It comes from the force exerted on the bottom of the short tube, pulling the inner air column down. If you integrate that pressure on that surface, you get a force downward and that more than counter-acts the upward force generated by the flow curving around the top of the tube. It has to, otherwise conservation laws are violated.
Great bit of unplanned collaborative science. Reasonable hypothesis proposed and tested. Love these kinds of experimental/explanatory videos.
You and your channel are everything that is good about TH-cam. We need more curiosity, discovery and explanation in everyday life.
The clip with the O-ring is awesome 👍
"It's all about the rim" you say? The RESEARCH IN MOTION? Fancy that!
Awesome!
The force is strong with this one 😆💕👏👍 thanks for sharing Matthias
Cool demo. This force is apparently used in silicon fabs to pick up and handle wafers. Since it is contactless, no worries about contamination. Called Bernoulli grip.
bernoulli grip involves air being blown, not sucking
Kohler toilets have a bell-shaped entry to the inlet at the bottom of the tank. Coupled with a valve design that lifts away from that inlet completely, the water from the tank goes down the pipe leading to the bowl much more quickly than that of a conventional flapper valve design using a conventional angular connection between tank and pipe. It really does work well.
I like these videos.
Break out some smoke... Show it, don't tell it...!
Cheers from Denmark 🇩🇰🇩🇰🇩🇰
2:33 The shape in the drawing is often called a velocity stack or venturi tube in hot rod car circles. I don't think they're going for levitation but the shape is the same.. It's also used on intakes to maximize lift on some kinds of flying vehicles, hovercraft and increase thrust on jet intakes.
I love that the comment that finally solved it was written nonchalantly, like it was a wild guess.
If you look at the air intakes on carburetors or some fuel injection systems you'll notice the intake stacks are generally bell-mouthed as you showed in cross section. Without the bell mouth the intake of air is much less efficient.
Without the bell mouth the flow becomes turbulent and chaotic, definitely less efficient. The bell mouth creates a laminar smooth flow.
The O-ring is a great demonstration!!
In the RC plane world, electric ducted fans usually come with a curved inlet called a 'thrust ring' that really helps the static thrust. If it's not a tight fit, it sometimes gets sucked off the front of the duct!
Very interesting! Amazing how much you can learn from a simple test. Thanks for the updated video.
@Matthias random stuff I think the tube is creating a restricted path so the vacuum pulls the volume through the gap at the base - this flow forces the tube to either rise or deflect until sufficient volume can enter the inlet - the hot glue around the mouth of the tube just served to stiffen the sides which stopped the wall deflection at the bottom of the tube allowing the air to flow freely past thus it resumed lifting (bouncing!)
A great way to further the experiment would be to add smoke so we can visualize the flow
Really fun experiment, very interested to know if you're sure you're correct or if my theory has merit. Tried to search through the comments a bit to see if a physics person knocked it out
I don't know if the centrifugal force is entirely necessary to explain it. That would contribute as well, but the reason you have flow in the first place is that the suction itself creates a partial vacuum and the fluid flows across the gradient. In the cone example, this should be pretty pronounced (on the vertical axis) as long as the cone is seated. I think maybe the cylinder oscillates so wildly because it's a finer balance (vertically) and the "leaked" pressure and flow would fall off rapidly over a very small distance as it reseats.
Nicely done! In fluid mechanics terms, what we are seeing is the transition from laminar to turbulent flow at the inlet. Laminar flow is a smooth predictable flow stream, with the force vectors mostly aligned in the direction of flow. Turbulent flow is chaotic and multidirectional, with the force vectors pointing in many different directions.
With the bell mouth, air enters the tube smoothly and the flow is mostly laminar and the force vectors are pointing in the flow direction, causing the tube to suck down. Without the bell mouth the transition is abrupt and there is turbulent flow in the tube. Vectors in every direction. A portion of those vectors are pointing upward, resulting in an upward movement of the tube.
I've always thought of bell mouths (or "horns") as the fluid version of impedance matching in electronics, but now I'm having trouble making sense of that. That's probably because I don't understand impedance matching *or* fluid dynamics very well. :)
its vaugely like impedance matching
Coanda effect that generates a negative vacuum on the outside to move in the opposite direction of the air flow.
Sometimes velocity stacks can pop out of the holder if the screws are loose. I'd always assumed it was rattling (even tho the engine was relatively well balanced - just idling static) maybe this is why.
I drone company I worked for designed ducted lifting rotors and they said the a well optimized inlet can provide something like 30% of the lift.
That was freaking cool! An answer that made sense for a change!
Brilliant problem solving and demonstration. And how funny that such a simple comment held the answer. Cheers Matthias from the Southern US! You are an iconic role model for your creativity, rationality, and ingenuity.
2:13 I wonder if this can be used to multiply the pressure difference of a high-flow pump and generate a strong vacuum. Make a pair of concentric pipes, with less than a millimeter of gap at the top. Pull air through the inner pipe. The space in between the pipes should want to drop to a pressure that's lower than the pressure you use to suck the air down the central pipe.
2:19 "And just the Centrifugal force ..." Nothing to do with centrifugal - its just lift over a curved surface, like any wing. Its true that lift is caused by air trying to change direction relatively suddenly, creating a partial vacuum in the process, but it doesn't have to be rotating around a sharp enough turn to invoke centrifugal effects.
Thanks for the follow up, this makes a ton of sense!
Good morning, thank you for the follow up.
Those bell shapes are implemented since long time in "itb" type of air supply to sports car motors, and in subwoofers vents. They make a noticeable difference in air flow.
Reminds me of the Turbotube, a toy from Whammo when I was a kid, A short tube of plastic with a thickened leading edge that would fly if thrown properly.
Glad you figured it out partially. I will watch to see if you figure out the rest or not.
This was delightful. Thank you for sharing the update.
The same thing happens with the inlet of aircraft engines. The front of the inlet basically acts as a wing and creates lift in the direction the air is coming from
If you look at your 2d drawing, what you have is a shape similar to an air foil. It would be interesting to see a smoke test so you can visualize the currents. I bet you have some swirling low pressure vortices around the outside of the bellmouth.
For the first part, it is easily explained by the conservation of momentum. Since the inlet and the outlet are at atmopheric pressure, the force (assumed in the same direction of the air flow) to keep the cone in place is given by F = m_dot*(V_out - V_in). Since V_out > V_in, F is positive therefore the direction of the force is correct. The same principle explains why a firefighter will “push forward” to hold a hose nozzle in place.
That momentum/turbulence at the top is what lowers the pressure from above/inside. But, I wouldn't think in terms of the pipe being lifted from the top. I'd think in terms of the air outside the bottom of the pipe being able to over-power that lower pressure from above and push it's way under the pipe.
This is my explanation for the chain/rope fountain, the chain is getting accelerated so fast it generates a centrifugal force, raising the chain off the lip of the bucket.
That is so cool, really makes me think differently about bernoulli's principle!
except this wasn't about bernoulli's principle
Fascinating indeed! Thanks, Matthias! 😃
Stay safe there with your family! 🖖😊
And happy holidays!
Navier-Stokes gets you every time :-)
Brilliant!
im sure your channel is in the eye of the algorithm because one month before your videos didnt get auto generated captions. even when they were several days olds. NOW they has it instantly.
this channel has alwasy been ok with auto captions. Its my main channel that they are broken for. What I started doing is uploading main channel videos to this channel unlisted, wait for the auto captions, then download them and upload them for the main channel
@@matthiasrandomstuff2221Great. I didn't notice it wasn't your primary channel. Nice to know you are doing that workaround.
Saw the other video a day or two ago, but the answer I've known for ages didn't hit me. Seeing this one brought it up.
A 'straight' tube isn't straight aerodynamically, it acts as a restriction, due to the viscosity of the air hitting the sides and opposing free flow. IIRC the answer was the walls of the tube have to move out at 7 degrees in order for the air flow to be free. Believe that was both sides so 14 degrees spreading cone, and been ages, it could have been 7% instead of degrees. And suction is basically just reverse flow. So almost guaranteed this effect is why the straight tube still works and generates forces.
Make a reverse cone from what is in the video, with a larger say 4" suction hole and narrowing to a smaller hole, with approximately 7 degree slope on the sides, and that should be the neutral point where it doesn't generate lift, so it should just sit there.
No doubt ties in with several of the other answers here in the comments that roughly work out to similar ideas. But that's an isolated value I've known since the early 2000's mailing lists, it came up in a discussion and a side wall has to go out at 7 degrees for airflow to act as a smooth airflow and wall to not restrict the flow. And of course that's a rough approximation, no doubt the horn or bell type curve is actually a more correct fit.
Next install a manometer tube or pressure gauge.
Welp... Guess I have to add fluid dynamics to my list of "things I'm fascinated by and barely understand" now...
Airliner jet engines make use of that. By having a rounded over edges at the front and increasing the front area more than necessary for the air inlet they not only make the air inlet more efficient they also produce additional thrust from the low pressure at those curved edges. I find this surprising as it means the air is really sucked in even at the pretty high speeds.
It depends on inlet speed an air speed. If the plane's air speed matches the inlet speed, a bellmouth would only add drag to the plane.
Good explanation, I hearted this video
what if the bead or lip is on the inside upper lip
Perhaps why commercial aircraft jet engines seem to have the same intake shape? Perhaps it helps complement the propulsion.
Very cool! Thanks for sharing
I thought it was friction but yeah this makes more sense.
Once you understand the pressure differential thing, I don't get what's the mystery, a cone has a 45 degree angle to be pushed up on, a straight walled tube does not. Boom.
Fantastic! Keep going. Don't stop here!
Cool. Can you show it with smoke.
Flow over a rounded object -> Coanda effect
The rounded top makes the tube essentially an upright cylindrical airfoil, which makes me wonder: Does the shape of a plane's wing also slightly suck the plane forward?
it doesn't suck the plane forward, but it makes much less drag than a square front on the wing would.
On a plane, you use a propeller or jet to force the wing forward through the air. The wings are shaped so that some of the 'drag' ends up pointing upwards. We call the upwards drag 'lift'.
It would IF the airflow was steaming vertically up the curve of the wing. Flettner Rotors work on that principle.
@@dnomyarnostaw
In the case of a very wide ~500 MPH updraft, yeah. The flaps would control forward vs. backwards 😁.
Awesome
I shall sleep well tonight now that I know the answer!
I would still like to see a small scale experiment on the water columns example that you explained in the last video. Is there any chance that you could do a video about that, with two columns of water with one jet holding a plate onto the jet of the other column please?
I tried to replicate part of it, but I think I would need much bigger tanks to make it work
I wonder how much this would affect the efficiency of a ducted fan type arrangement. Similar to the "jet" pack in spy kids and as replicated on the MythBusters.
I was thinking the same. It's probably not insignificant.
Also I wonder how this would interact with >0 inbound stream velocity.
Would make a great classroom experiment :) gotta love physics.
Potential take away? More efficent sucking means more lift.
Carpet cleaners might benifit from redesigning where it comes to lifting dirt off carpets.
Is the bell mouth an example of impedance matching by exponential tapering?
it is impedance matching in a way, but you don't need exponential tapering. The bellmouth dosn't need to be bigger than 3x the pipe diameter, tops
So back to the hanging J pipe in the earlier video.. there must be two forces that more or less cancel out 1) the air going around the J bend pulling it to the left and 2) the air going around the edge of the opening into the pipe pulling it to the right.
My motorcycle has the carburetors facing backwards with velocity stacks. It would be better if the carbs were facing forwards so it would help pull the motorcycle faster forwards. How could the engineers do this?
If you optimised it, how much lift could you achieve I wonder?
Matthias: Now apply this principle to a ducted fan. Particularly to that of one used on aircraft.
Could you get better results if you suspend a marble maybe an inch marble right in the mouth of the opening
You're drawing the streamlines as if the flow is laminar. I don't believe it is. The o-ring could be tripping the turbulent boundary layer. Can you estimate the Reynolds number?
intake from still air are surprisingly non-turbulent.
Whao, an armchair internet warrior that bested Mathias Wandel. Once in a life time.
There were actually several that guessed this, just skimming thru, that one was the first I noticed -- partly cause the answer was so short!
I guess you never heard of Bernoulli's principle!
Awesome!
This is fascinating. Makes me wonder what direction your handing J bend would move if it had an inverted cone on the end, with the smaller side at the intake?
same way
But wait, if it is about air inertia, the thinner rim must create bigger vacuum and higher lift. So it's rather due to viscousity then?
Also, what proportion to the lift contributed from the lower rim? You only made changes to the hole diameter, but not the gap
A common misconception about roofs. While shingles get blown off, flat roofs get sucked off by a vacuum effect of the air passing over the vertical parapet walls.
I'm sure shingled roofs experience similar lift if the wind is coming from the gable end
use smoke to "see" the airflow.
Is the explanation that the top of the cylinder is acting as a round airfoil that pulls the cylinder up or did I misunderstand completely?
Does the same thing happen when air is being pushed in? What happens if the cylinder starts inside the suction tube? Does it get lifted out?
I have so many questions now.
Yes, that is correct. Exactly the same effect as an airfoil
Can you measure how efficient a bellmouth is by the amount of force it produces upward from the suction?
I thought this was called a lifting edge?
👍👍
Not convinced by this explanation. Your radius does provide more surface area to act on but simultaneously eliminated the vena contracta so that there is much less pressure differential between the entry and the exit, you changed the flow coef from ~.5 to ~1. That means there is less overall suction pulling down on the tube, allowing it to rise higher. If it were only the rounded lip causing all the lift then the same lip could be added to your pendulum elbow test and it should also swing further than with a plain lip. There is more than 1 thing going on at the same time here.
yes, chances are, if I put a fatter lip on the pice of pipe and held it in front of the pendulum, it would deflect it more, as you say. But if the fat lip wee part of the pendulum, it would make as much difference as the cone being part of the pendulum, which is hardly observable, as shown in my previous video
@@matthiasrandomstuff2221 If it does not deflect it more then it means it is not operative in lifting the tube either and the explanation is wrong. I'd guess it will increase it somewhat but there is another force at work here. Need more data, more testing, more measurement. This is very interesting.
thats the coanda effect for you :-)
i have always thought that the bell shaped mouth of a blunderbuss is purely decorative.. but now i wonder if there is some of this effect happening in reverse.
its for dumping crap in there. The bell is a poor shape for an ejection nozzle if you want things to be directional
Yeah, you'd want parabolic rather than ~logarithmic (you'd want the rate of widening to decrease as you got further from the center of the explosion or again, you'd want the asymptote parallel to the direction of fire).
Science
There is also another thing for this sucking-blowing movement "mistery". The same thing applies to the drive of pop-pop boats, and it was described by Steve Mould in his clip on that topic (around 8 minutes)
th-cam.com/video/3AXupc7oE-g/w-d-xo.html
I hope it helps in further solving your problem 🙂
What happens if you flip the cone around so it tapers up?
It's like crossing the streams, you risk destroying the universe.
@@pvanukoff Well… we can’t have none of that.
Is this an example of the coanda effect?
no
So, if sailboats were installed with hundreds of bell mouth tubes on a swivel, sailing directly into the wind should be possible? Please test this!
only if the sailboat has a huge blower to suck air from all the bellmouths. But if you have a blower, you'd be better off using its motor to turn a propeller
@@matthiasrandomstuff2221 I don't mean about sucking in this case, I mean about blowing. If the wind is blowing into the many bellmouths and the boat hull and aerodynamics were efficient enough, could the boat move into the wind?
Put differently, does the same thing happen when blowing air into the tube instead of sucking it out of the tube?
What Matthias' demonstration shows is that you could create a force lateral to the wind. In his demonstration, air moving parallel to the X-Z plane reduces pressure and allows movement along the Y axis. Orthogonal motion is already used in sailing to 'tack' into the wind. Who knows, though, with enough thought maybe you can come up with a relatively inefficient (at least at first) auto-tacking system based on the Coanda effect 😉.
I’m not sure you have your full answer bc it doesn’t explain the oscillation..,
I just posted a comment on the previous video which may explain the oscillation effect
The oscillation is due to that fact that the lifting force gets weaker as the tube lifts higher until gravity takes over and brings it down, to be lifted again.
so a band will work just as well as a bellmouth?
no, a bellmounth would work better. But maybe I should have demonstrated it with a rubber band, cause that adds even less thickness
Is this the same thing as when you use a stick blender in a liquid and it pulls itself to the bottom of the pan? Vacuum effect but a lot more moving flows
A stick blender has the blades at an angle, so they act as an airfoil. They suck on the bottom and blow the blended stuff out of the holes in the top.
@@grieske I guess then a bit of ground effect as you get close to the bottom.. Cheers!
@@jeffers727 That does sound plausible. Have a nice day!
Why has no one mentioned 'this is venturi effect.' The word bell has 150 mentions, and venturi 0.
For the same reason no one has mentioned pocket holes either. Its just not about that.
@@matthiasrandomstuff2221true, there is no reduction in the tube diameter to cause the velocity and pressure differences associated with the Venturi effect.
@@chiphill4856 Yes there is . Venturi effect happens to be a bell shape, a change in diameter over length. The typical square or slightly rounded edge of a pipe/tube is 'too fast' a change in diameter.
@@jimbarchuk a change in diameter over length. Yes. I'm not sure what else you are referring to.
Venturi Effect is the Name. Yet for the 150x the word bell is used the Name itself is never said.
Is this the coanda effect?
no
Nice one @eVITORIOe one comment mystery solver 😄
I think this is very much related to this 'chain fountain' controversy we had on TH-cam some time ago...
yes, it is in a way. Now I just need the electroboom guy to tell me I'm wrong!
He'll be able to add some sparks to it!
What does your ex employer to do with it?!
Sorry, I had to do it 🙄😂
:)
I don't think your explanation is correct. Maybe I can make some CFD models to show it since I don't have a workshop. The action is happening at the interface between the short tube and the fixed tube/table. The added ring at the top increases the pressure drop across the short tube (makes the pressure loss at inlet higher). The surrounding air is flowing into the small gap at the bottom of the short tube. With a higher pressure loss, the air rushes in more strongly and pushes the tube higher.
Your thinner white tube didn't show the effect because rather than getting pushed up to allow the air to rush in, it collapsed (went oval in shape) and allowed the air to flow beside the tube into the low pressure area. You could better demonstrate this by adding a second, slightly larger tube mounted to the table and put the small short tube inside of it. That would ensure air cannot rush into that gap. If the short tube still gets lifted with that setup, you have disproved my explanation.
Something to think about: where does the energy come to make the air flow around the inlet around the ring? It comes from the force exerted on the bottom of the short tube, pulling the inner air column down. If you integrate that pressure on that surface, you get a force downward and that more than counter-acts the upward force generated by the flow curving around the top of the tube. It has to, otherwise conservation laws are violated.
just make a CFD and show it
Coandă effect
Boring wood working channel ? Let's deep dive in Bernoulli details !!!