Is circulation real?

I agree with you on this point. Quiddams like us have to rely on publications to raise our knowledge, and authors and proofreading commitees shall be vigilant on what is published.

 

The focus on the resulting Force (F) is sharp and simple.

And from there arises the question of

(1) achieving that the resultant Force is better oriented for what we want (for example the centerboard of a sailboat) and

(2) slow down as little as possible the velocity of the fluid so that the resultant Force is greater as the volume of fluid deflected per second is greater.

 

Even this drawing falls into the pedagogical error of focusing the question on Lift, because all the entanglements and misunderstandings arise from there, from believing that Lift exists on its own, and no: we divert fluids, diverting them produces a Force that if we want we can analyze in two components: Lift and Drag

 

What has this to do with the subject of the current thread?

 

I’m looking….

 

this one? (I started re reading this thread… good way to spend some insomniac time!)

I highly recommend googling the author

Deterministic chaos, fractals, and quantumlike mechanics in atmospheric flows https://arxiv.org/html/physics/0010046

 

Yes, indeed, lift and drag are the resolution of the aerodynamic force into two orthogonal components - a straightforward and well-established procedure from structural mechanics. In structures, focusing as it does on structural integrity, the natural coordinate system has the primary axis parallel to the direction of gravity. And that is the principle that is adopted in aeronautics, finding the best designs that will provide a vertical force (lift) sufficient to support the weight of the structure and its cargo (weight), and a horizontal force (thrust) sufficient to overcome the horizontal resistance arising from the passage of the structure through the air (drag).
But where do you go from that?

 

Ah ! Perfect ! This time, I download it. Grazie mille, Paul

 

To get my hands on the subject of clounds and thunderstorms, i have spent some times watching these video series "See the pattern" from youtube. Definitly not the same quality as your reference, but at least, I can see the pattern, now.

 

Happy new year!
The problem with circulation is that aerodynamics has misinterpreted the concept from fluid dynamics.
In fluid dynamics circulation is Kelvin's definition of circulation: the the line integral of velocity around a closed path moving with the fluid.
In aerodynamics, the closed path of circulation is moving with the airfoil.
The two definitions are incompatible.
Despite aerodynamics' claim, the circulation that is used in aerodynamics is not Kelvin's circulation.
No wonder we sailors are confused!

 

"the problem with circulation"

L: Lift
D: Drag

w: downwash velocity

K: Circulation

There is no problem with circulation, which is a mathematical, theoretical construct, to calculate and fit experience and data

The theory of Professor Ludwig Prandtl and his PhD student Max Michael Munk is spectacularly beautiful

The problem is (as we see again and again) in the difficulty of many who get lost in these questions, it is a pedagogical problem, that is why I propose another pedagogical approach since we have been going round in circles for a century (1925-2025) on the same wheel

 

The pedagogical problem in this matter is so gigantic that a respectable magazine, well known for its high level and rigor, published a delirious article saying that nobody understands how Wings work

In reality they meant: nobody knows how to explain these issues to children

That is why I propose another pedagogical approach

 

I shouldn't write this message because it is once again going back to circulation

A wing does four things:

1) it deflects air upwards
2) it accelerates the speed of the air
3) it deflects air downwards
4) it slows down the speed of the air

This four can be put together by replacing the wing with a column of air that rotates interacting with a current of air

and the funny thing about the case is that this mathematical construct has a physical basis in the first vortex created by the viscosity of the fluid at the trailing edge

(Haha, I drew the Circulation exactly the other way around, we have another hundred years of misunderstandings ahead)

 

What has that got to do with the term "circulation" that Kelvin coined around 1850, long before the invention of wings, to name the integral along a closed path through a vector field?
Or in identifying whether it (circulation) is correctly being applied in aerodynamics (that arose half a century later) to a path moving with the air or moving with a lifted body such as a wing or a sail?

 

The key thing about potential theory is that it is linear - you can represent any flow (as long as it is frictionless) as a superposition of a few basic elements.

You want a circulation that moves with the fluid? Define a coordinate system that moves with the fluid - place a vortex at its origin - and draw your path around it. You want an inflow? Define it as a potential. Add the two together - and you have the circulation around an airfoil or a rotating cylinder ... here is no contradiction.