Is circulation real?

[Alan Cattelliot]

There is also this article that poses the issue in readable terms, with figures :
No One Can Explain Why Planes Stay in the Air https://www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/

 

[jehardiman]

There is also this article that poses the issue in readable terms, with figures :
No One Can Explain Why Planes Stay in the Air https://www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/

Funny that the article mentions Dr. McLean.
Vortices as source of aerodynamic force? https://www.boatdesign.net/threads/vortices-as-source-of-aerodynamic-force.65315/#post-903976

 

[Doug Halsey]

There is also this article that poses the issue in readable terms, with figures :
No One Can Explain Why Planes Stay in the Air https://www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/

This is the article that prompted me to cancel my subscription.

 

[Alan Cattelliot]

Oups.... Sorry for that, I didn't mean being controversial. I admit there is a lot of very strange theories circulating with the help of internet and wonderfull content creator bots.
I'm just tchating here, and to my applications, the vortex theories are very handy to use both in structural and aero/hydro calculations, making design loop more consistent.

Cheers,

 

[DogCavalry]

There is also this article that poses the issue in readable terms, with figures :
No One Can Explain Why Planes Stay in the Air https://www.scientificamerican.com/article/no-one-can-explain-why-planes-stay-in-the-air/

Yup. That's swill.

 

[patzefran]

Yup. That's swill.

Bernoulli must be turning in his grave !

 

[patzefran]

Obviously, I was talking about the article !

 

[Alan Cattelliot]

Was it Einstein who said :
The theory is when one knows how it works, but do not know why.
Practice is when you know why things work, but not how.

 

[DogCavalry]

@Alan Cattelliot thanks, it is gracious of you to provide the link, and join the conversation, but the author of that article would have to sell a kidney on the black market to buy a clue. They have absolutely no idea what they are talking about. None whatsoever.

 

[Alan Cattelliot]

Okay... As Bernoulli won't take part in the conversation, nor Stokes, then I guess we are bound to put tape on our wind tunnel models, to match the Finite Element models, which are not sufficient to accurately predict at first guess the re-circulation pockets locations....

 

[jehardiman]

Alan, some of this field has been plowed before. Go use the search function for Leo Lazauskas with turbulence. Most people believe that the forces are caused by energy transfers between the body and the fluid. But EXACTLY how that happens is the hard part. Different regimes respond to different methods.

 

[Alan Cattelliot]

I don't know what is your point here ? I see the CFD calculations of Leo Lazauskas. One is probably derived from Mitchell's equation. The other may be something else.
I see very beautiful colors, that's nice !
CFD = Colorful Fluids Dynamics...
Because the world is better seen in color....

We all know from the very intensiv work of validation on XFoil, that a panel method can always be enhanced by addition of complementary models that manage turbulence, parietal friction, or time dependency as uncoupled or weakly coupled equations.

Should we say that, the existence of other methods -say all the methods that do not use integral formulation, like derivatives or statistics methods, clearly shows that the concept of circulation is only a mathematical tool use for computation, among others ?

Most of the time, I sail in two places. Bay of QUIBERON and LA ROCHELLE (France). Windfinder gives the best predictions for sailing in QUIBERON, while Windguru's forecasts are more often good in LA ROCHELLE. Still, none of them is able to explain why or how are the clouds forming in the sky.

We may deal with a very similar situation regarding our discussion about the true reality of the circulation, with respect to the physical phenomenon that lies under our observations.

Renée Descartes ( Mathematician and philosophe ) : Je Sais que je ne sais Pas.

 

[philSweet]

We all know from the very intensiv[e] work of validation on XFoil, that a panel method can always be enhanced by addition of complementary models that manage turbulence, parietal friction, or time dependency as uncoupled or weakly coupled equations.

Should we say that, the existence of other methods -say all the methods that do not use integral formulation, like derivatives or statistics methods, clearly shows that the concept of circulation is only a mathematical tool use for computation, among others ?

It really has nothing to do with integral methods per say. Circulation can be regarded as a property of fluids, just like pressure. In the realm of continuum mechanics, the circulation-lift relationship is effectively one of the constitutive equations. To fault circulation for failing to predict flow evolution is rather silly. It's failings are shared by all the other equations that constitute continuum theory. I have never understood why circulation theory gets all the attention. Why not go after pressure with the same zeal? If we got the pressures right, circulation would be golden - no?

The constitutive equations of continuum theory can all be developed independently from statistical mechanics and the continuum theory constraints. They are part and parcel of the theory. You can't opt out of an equation that is theory consistent and you can't blame just one of them for a failure of the model.

The circulation-lift relationship just comes with the territory. You are free to ignore it, but arguing about it while at the same time accepting the other tenets of the theory isn't rational. We can certainly choose all manner of ways to measure and report it, just as we do with pressure. Defining an equivalent Greens Integral, where appropriate, is just one way.

 

[Alan Cattelliot]

Ok, Phil, I agree that my comments are lacking some partiality, but nevertheless, I really don't get why you begin your reply saying that this has nothing to do with Integral methods, while finishing your comment talking about the Greens Integrals. Please take a look on how Wikipedia explains the basis of the notion of circulation.
The issue, when summing along path or surface (in case of radiations for instance), is to be sure that the inner domains does not contains any singularity that we wouldn't have taken care of. The field of mathematics that applies is then the theory of distributions, which goes with the asymptotic functions theory. What is said, basically, is that if you missed the knowledge of a singularity, then your integration, with Green Functions or others, won't give the awaited result, which is : being able to predict, at first guess, the parietal friction of ... Let's say... An America's cup bulb. First guess !! No calibration.

 

[DogCavalry]

The reason why models don't give perfect answers is not a failure of the model, or the theory, or anything else amenable to intelligent effort. It's because problems in fluid dynamics are incredibly sensitive to initial conditions. So much so that there's no particular reason to ever expect really good simulation. And by that I mean a simulation where a vessel designed solely digitally would perform precisely as designed without any reference to the vast body of existing empirical knowledge.