# Is circulation real?

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

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### Paul ScottSenior Member

I’m still obsessing about the marble rolling down an incline analogy. It’s gnarly! What if someone sneezed?

Last edited: Dec 3, 2022
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### Sailor AlSenior Member

I don't understand why you require "AND when the number of these molecule is very low". I don't see any such requirement in the quoted reference.
The interpretation of "number... very low" is entirely subjective in kinetic theory. How many is very low?

You have nailed it with "when you look at phenomenon at molecular scale ... , then this non-slip (sic) condition do not apply." (I think you meant "no-slip", not non-slip).

And that is exactly my point. When this core concept of theoretical aerodynamics is examined from from the perspective of Kinetic Theory, the no-slip boundary layer cannot exist.

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### Sailor AlSenior Member

Convincing this forum that the no-slip boundary is a myth is more akin to the analogy of pushing a boulder up a slope than rolling marbles down an incline!
I wonder how I'll get on busting the myth of the immortal starting vortex?

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### Sailor AlSenior Member

I wonder if there is any point in pointing out that the axis of the vorticity, Γ, of Kelvin's Circulation Theory is perpendicular to the plane of the circulation which, on a wing would be in the direction of the span, not in the vertical direction of the Lift of aerodynamics.

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### DCockeySenior Member

Γ is the circulation, not the vorticity, and is a scalar, not a vector. A scalar does not have a direction.
There is no requirement that the closed curve used for the integral defining circulation be planar.
Circulation (physics) - Wikipedia https://en.wikipedia.org/wiki/Circulation_(physics)
Kelvin's circulation theorem - Wikipedia https://en.wikipedia.org/wiki/Kelvin%27s_circulation_theorem#Poincar%C3%A9%E2%80%93Bjerknes_circulation_theorem
Stokes' theorem - Wikipedia https://en.wikipedia.org/wiki/Stokes%27_theorem
Perhaps additional study is in order. Anyone wishing to get into the subtleties of potential flow aerodynamics should be familiar with vector calculus.

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### Sailor AlSenior Member

OK, I used the wrong symbol. Γ is indeed the circulation, but vorticity is the curl of the flow velocity

This is a vector not a scalar.
Anderson :

Also I believe that the plane of the Circulation that is widely adopted in aerodynamic theory (and as described by Anderson) is indeed planar:

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### Stephen DitmoreSenior Member

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### Boat Design Net ModeratorModerator

Very sorry to hear this news. Tom was a wealth of information and so generous with his knowledge and time. He will be missed.

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### Paul ScottSenior Member

Alan Cattelliot likes this.
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### tlouth7Senior Member

I don't know when I was last moved by news of the death of someone who I only knew as a handle on a forum, but tspeer was that rarest of things: a true expert who was capable and willing to explain the intricacies of his field beautifully.

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### Paul ScottSenior Member

He also designed this bi directional ogival foil that I had Phil’s Foils shape. He thought it might need a trip on the low pressure side. It didn’t. Mk 3, IIRR.

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### Sailor AlSenior Member

What I find fascinating is that so many folks, like many of the contributors to this forum, feel it is necessary to attempt their own interpretation of the published works.
Everywhere I turn, people are falling over themselves to come up with their own interpretation, their own explanation, their own attempt to clarify the issue.
There are scores, no hundreds of books on the subject.
It may not be too much of an overstatement to point out that not since the Bible has so much effort gone into interpreting the words of a prophet!
Surely, if the published stuff was any good, there would be no reason for so many to provide an interpretation.
Does this mean the authors are poor writers? They can’t all be crap communicators. There must be at least one who can explain the stuff clearly.
No, it means they are all fumbling with the same problem.
They don’t know!
The scientific American article nailed it: No one can Explain Why Planes Stay in the Air.
And nobody wants to shout “the emperor is naked!”
At the moment, I am struggling to sell my version, primarily because my audience is convinced that the truth is already out there (even they themselves don’t quite get it).
And because my version is not based on current theoretical aerodynamics, it has to be wrong.
So my task at the moment is to demonstrate that the current version of theoretical aerodynamics (the truth) is based on about five palpable fallacies. Until I can make some progress, and not get stoned to death as a heretic, no-one will consider an alternative.
One of these fallacies is this no-slip boundary.

And that, I am discovering is a tough nut to crack. It is so deeply ingrained. Today I downloaded a physics textbook by a recent Nobel laureate, who, whilst, interestingly not explaining it, blithely babbles on about the no-slip boundary.

At least, for now, the stones are only digital.

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### Alan CattelliotSenior Member

Interpretations are maybe necessary because the acquisition of knowledge, or appropriation of a subject by any individuals, is made out of re-phrasing any proposition into one's understanding, with the use of his own words, based on his own experience. If propositions, theories, concepts are to stand some more general cultural evolution, it is also necessary to revise the lexical field in order to avoid contradictions.

Still, the airplanes and the sailplanes are designed and flown. The last question about any subject is always either "we don't know", or "just because it is". Journalist and media, in general, are real hardcore users of these kind of questions. First, because you can make a buzz in the instant. Second, when you're lacking some inspirations, you can always put a coin in the machine and replay the song, another time.

I don't know if that will help you, but here is some grist for you to grind in the attached link (perhaps). Happy new year to all.

"Einstein assured him that he had not misunderstood the
original question, and went on to elaborate that the only
mechanism by which one could truly and deeply understand
the fundamental meaning of a physical entity appearing in
the guise of a mathematical symbol in a theoretical
equation was by going through the mental exercise of
systematically and methodically identifying the
sequence of steps prerequisite to an unambiguous
experimental determination of that entity.
"

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### Sailor AlSenior Member

@Alan Cattelliot Do you have any more info on the Brenner paper? Any paper that contains thoughts like this:
"This experimental fact negates Euler's 250- year old generic, mass-based definition of the velocity field in fluid continua, undermining thereby the heretofore seemingly rational foundations of fluid mechanics and derivative subjects. This, in turn, requires a fundamental re- formulation of the basic equations of fluid mechanics as well as of molecular theories of transport processes in fluid continua." has certainly got my attention!
It's going to take me a little while to digest the article.
There's no publication date.
Has it been peer reviewed, where?
It's tantalising.
[EDIT] Unfortunately Howard Brenner (16 March 1929 – 17 February 2014) is no longer with us. I wonder where this ideas went? [/EDIT]

Last edited: Jan 2, 2023

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### gonzoSenior Member

You need to provide evidence to back your claims. Up to now, you have only posted opinions and claims that you are being personally attacked for them. The boundary layer is a statistic artifact. That is what the theory states. It is one molecule thick. The air molecules bounce off the surface of a body. At one instant, they are immobile and attached to the surface until they change direction. Statistically, they form an attached layer. Using statics will not give you an answer, because it is a dynamic problem. Nobody called you a heretic, simply misguided and lacking in understanding of basic principles.

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