# Is circulation real?

Discussion in 'Hydrodynamics and Aerodynamics' started by Mikko Brummer, Jan 25, 2013.

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### Sailor AlSenior Member

Not "zero normal velocity". "Velocity is zero".
I repeat my request above: "Please provide a references to one or two"

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### Sailor AlSenior Member

@Doug Halsey assured me the foundations of aerodynamics were to be found in Drela's book, and @Alan Cattelliot confirmed the "boundary layer" referenced in that book is indeed Prandtl's boundary layer (which is "no-slip").
You are now directly contradicting one or both of those positions.
To whose version of aerodynamic theory are you referring?

Last edited: Nov 27, 2022
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### Sailor AlSenior Member

You bet there's confusion.
The confusion is how a condition can occur in a physical material (air) "at a surface" (the airfoil) if that condition doesn't permeate into either of the two mediums meeting at the boundary?
This isn't theoretical maths, where an asymptotic function can approach its asymptote indefinitely without ever reaching it.
It's physics, with real stuff: the air and the solid airfoil.
You wisely won't allow this stationary layer to be analysed at a molecular scale, but still you require it to be bounded " at a surface, not at any small distances from the surface"
It's physics. It can't be infinitely thin like "the bungee cord being stretched indefinitely".
So just how thick is this stationary layer?

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### DCockeySenior Member

Sailor Al, do you understand that the entire boundary layer has zero velocity relative to the adjacent surface? If so then your understanding of the boundary layer concept is very fundamentally flawed.

Sailor Al apparently has missed one of the most important part of Prandtl's contributions - the idea of dividing of the flow field around an airfoil into the outer, inviscid flow and then inner boundary layer. The zero normal velocity boundary condition is used for the outer, inviscid flow. The no-slip condition is applicable to the boundary layer. It is impossible to understand aerodynamic theory without understanding this basic idea.

Further discussion at this time is pointless.

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### Sailor AlSenior Member

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### Sailor AlSenior Member

1. How thick is the stationary part of the boundary layer?
2. To whose version of aerodynamic theory do you subscribe?
3. Please provide a reference to one or two experiments validating no-slip boundary.
4. Where's a) the theory or b) evidence that the air comes to rest at the interface?

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Indeed.
On all his threads, it is the same.
I do not understand, please dumb it down to my high school level so I can understand. If you do not you are rubbish..

This is the problem when people do not understand things beyond their grasp...they berate, moan, criticise and become become extremely irate in their replies, all because the world around them is beyond their understanding.
Wanting to learn, is great and highly commended, yet criticising the messenger for their own failings in comprehension, ..most people grow out of this by the end of their teenage years when they start to grasp they have reached their limits and the world does not bend to their whim....sadly, some don't.

I gave up when he couldn't provide any evidence to his claims, he just keet repeating the same mantra - everyone is wrong...because he doesn't understand the concept of peer reviewed critiquing starts with the person making the claims.

It was initially amusing to read these threads, but i gave up a long time ago...it is just a waste of bandwidth.
These threads should be closed, as they are not assisting anyone, nor do they address the MO of the website - BOATS!

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### Sailor AlSenior Member

So you are in agreement with Drela and Babinsky, that an undergraduate course in aerodynamics is required before the mystery of the aerodynamic force from a sail can be revealed in a post-grad course of study. I politely beg to differ. If you can't explain it to a high-school student, either you are a poor educator or you're talking gibberish.
I call "foul" on that "Straw Man" argument.
Ah, following @DCockey back to the monastery. You had better knock loudly, he has his hands over his ears.
When I last looked, the title of this thread included "aerodynamics". My detour into galactic vortices was a little flight of fancy, but it sure brought out some interesting viewpoints

Instead of trolling me, why don't you try answering the questions I posed at #531?

Last edited: Nov 28, 2022
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### gonzoSenior Member

Do not include me. I may discuss science and technology, but won't join you on personal attacks to make up for inadequacies in education and understanding.

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### TANSLSenior Member

Instead of the personal disqualifications to Sailor Al, why not present arguments that show that he is wrong (if he is)?.
Is this the tone that a civilized discussion should take on?.

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### gonzoSenior Member

There is a minimum level of fluid dynamics and calculus needed to follow the math in the theories.

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### TANSLSenior Member

Of course, but if someone does not have that level, it is enough to politely point it out. No need to despise anyone. Once again, when Ad Hoc intervenes, the thread gets out of hand or drifts towards personal disqualification.

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### Sailor AlSenior Member

I posed these questions to @DCockey in order to determine the existence of Prandtl's no-slip boundary layer.
1. How thick is the stationary part of the boundary layer?
2. To whose version of aerodynamic theory do you subscribe?
3. Please provide a reference to one or two experiments validating no-slip boundary.
4. Where's a) the theory or b) evidence that the air comes to rest at the interface?

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### Sailor AlSenior Member

My questions do not relate to the maths of theoretical fluid dynamics. They relate to the physics of aerodynamics.

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### gonzoSenior Member

They are both the same. What is the difference you see?

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