Is circulation real?

[DogCavalry]

Prandtl said nothing of the sort.

Oh, @jehardiman got there fustest with the mostest, as a great general once said.

Ok, from a different direction, as Wagner demonstrated in his work with Indicial response at T=0 following a perturbation, lift is already equal to 50% of what it will be when circulation is fully established, when there is no circulation whatsoever. Lift asymptomatically approaches it's full value over distance traveled, as circulation is induced by the forces acting on the free stream fluid by that lift. It was empirically demonstrated that Cl is close to it's full value after 7-8 chords travel.
Since a SPP travels about 1⅓ chord after the trailing edge enters the water, before the leading edge exits, there simply isn't the time for circulation to develop.

And what about the other examples I provided? The bottom of a planing hull can hardly be considered to have generated circulation, yet a good hull under good conditions can have an excellent lift to drag ratio. To say nothing of any body travelling faster than the speed of sound in it's medium. The wing of an aircraft above mach 1 also generates all the lift one could possibly want, with circulation no where in sight.

 

[sandhammaren05]

randtl wrote out the entire theory after Lanchester had stated the ideas 10 yrs. earlier. The work is precise, there is nothing heuristic about it. There is no reason to ponder Lerbs or anything in sname. Just a bunch of detailed repetitions with change in the basic idea: circulation causes lift.

 

[jehardiman]

randtl wrote out the entire theory after Lanchester had stated the ideas 10 yrs. earlier. The work is precise, there is nothing heuristic about it. There is no reason to ponder Lerbs or anything in sname. Just a bunch of detailed repetitions with change in the basic idea: circulation causes lift.

Did you even read this? ...."wrote out the entire theory"....

 

[DogCavalry]

Well, I don't think this is going anywhere.

 

[sandhammaren05]

Did you even read this? ...."wrote out the entire theory"....

Theory of lift plus calculations, after he'd described how it works. I also recommend his 2D shot of flow visualization of the (horses shoe) vortex formation on the leading and trailing edges before lift is developed.

 

[DCockey]

"all models are approximations. Essentially, all models are wrong, but some are useful. However, the approximate nature of the model must always be borne in mind" In George E.P. Box, Norman R. Draper, Response Surfaces, Mixtures, and Ridge Analyses (2nd ed. 2007), 414 George E.P. Box Quotes - 9 Science Quotes - Dictionary of Science Quotations and Scientist Quotes https://todayinsci.com/B/Box_George/BoxGeorge-Quotations.htm

 

[sandhammaren05]

"all models are approximations. Essentially, all models are wrong, but some are useful. However, the approximate nature of the model must always be borne in mind" In George E.P. Box, Norman R. Draper, Response Surfaces, Mixtures, and Ridge Analyses (2nd ed. 2007), 414 George E.P. Box Quotes - 9 Science Quotes - Dictionary of Science Quotations and Scientist Quotes https://todayinsci.com/B/Box_George/BoxGeorge-Quotations.htm

Hydrodynamics is the continuum statement of Newton's second law. This is not like a model. Circulation is conserved. Circulation cannot end in mid-stream, it can only end on a solid surface or other boundary like a discontinuity between two different flow strams (or water and air). The tip vortex from a wing, shown in flow visualization, extends over the wing (providing the lift) and ends on the fuselage. Prandtl's 1930s era flow visualization is valuable: in the rest frame of the fluid it shows the horse shoe vortex forming near the leading edge and near the trailing edge. This vortex extends around the wing tip and ends on the fuselage near both the leading and trailing edges. As the wing speed increases the trailing vortex slides along the fuselage, because it experiences a downward lift and is not 'pinned'. It slides and finally slips off the fuselage to form the tip vortex , which experiences no lift because it moves without hindrance in the free stream. There is no substitute for circulation conservation.

Prandtl's flow visualization photo can be seen in von Karmann's 'Aerodynamics', Dover.

 

[sandhammaren05]

Prandtl said nothing of the sort.

Oh, @jehardiman got there fustest with the mostest, as a great general once said.

Ok, from a different direction, as Wagner demonstrated in his work with Indicial response at T=0 following a perturbation, lift is already equal to 50% of what it will be when circulation is fully established, when there is no circulation whatsoever. Lift asymptomatically approaches it's full value over distance traveled, as circulation is induced by the forces acting on the free stream fluid by that lift. It was empirically demonstrated that Cl is close to it's full value after 7-8 chords travel.
Since a SPP travels about 1⅓ chord after the trailing edge enters the water, before the leading edge exits, there simply isn't the time for circulation to develop.

And what about the other examples I provided? The bottom of a planing hull can hardly be considered to have generated circulation, yet a good hull under good conditions can have an excellent lift to drag ratio. To say nothing of any body travelling faster than the speed of sound in it's medium. The wing of an aircraft above mach 1 also generates all the lift one could possibly want, with circulation no where in sight.

I don't know where all the confusion comes from. What Wagner ref. do you mean? I add that I have no interest in unsteady flows at large attack angles. I'm interested in steady flow at small attack angles.

A vortex sheet forms on the planing hull bottom and extends backward as the wake on the water surface after the trailing vortex is shed (that's when the entire transom becomes dry). A vortex sheet is a velocity discontinuity, and is described mathematically by a density of vortex lines transverse to the flow direction. The velocity discontinuity gives you half the circulation you would get from both sides of the mean camber surface. There is nothing difficult about any of this.

Where in hydrodynamic theory is there any case with flow equation from where large L/D is generated without circulation-?!

 

[DogCavalry]

Wagner did his work in the 20's. Before that, Prandtl et al's work on circulation was just a preliminary description. Like the underpants gnomes.
Step1: no circulation
Step2: ......
Step3: circulation!

 

[DogCavalry]

I don't know where all the confusion comes from. What Wagner ref. do you mean? I add that I have no interest in unsteady flows at large attack angles. I'm interested in steady flow at small angles of attack.

Where in hydrodynamic theory is there any case with flow equation from where large L/D is generated without circulation-?!

Sorry, nope. You made a blanket statement. 'Lift only come from circulation.' No half-**""" waffling. And I've provided a bunch of examples. You have a notion lodged in your head, and no amount of reality will help you get it out.

I'm going to talk with @jehardiman .

 

[sandhammaren05]

I'll try to take a look when I find time, but I'm not interested in large angles of attack (stall).

 

[Alan Cattelliot]

Hi All,

Very interesting to see this topic poping out. Indeed, there is a growing number of people, in the aeronautic field, who are, like you all, putting in question the paradigm of the circulation.
For those who are interesting in going deeper in the subject, I may recommend :

https://www.csc.kth.se/~cgjoh/newtheoryflight.pdf

Besides, I also recommend a carefull reading from those who think that everything has been already said on the "Circulation Theory".

Cheers,

 

[Doug Halsey]

Hi All,

Very interesting to see this topic poping out. Indeed, there is a growing number of people, in the aeronautic field, who are, like you all, putting in question the paradigm of the circulation.
For those who are interesting in going deeper in the subject, I may recommend :

https://www.csc.kth.se/~cgjoh/newtheoryflight.pdf

Besides, I also recommend a carefull reading from those who think that everything has been already said on the "Circulation Theory".

Cheers,

I don't see any mention of publishing or peer review. What about it makes you recommend it?

 

[jehardiman]

I don't see any mention of publishing or peer review. What about it makes you recommend it?

Apparently they are computational mathematicians who write textbooks

Johan Hoffman; Courant Institute of Mathematical Sciences, New York University, New York, USA; presently KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden

Claes Johnson; Department of Computational Mathematics, Chalmers University of Technology, Göteborg, Sweden; presently School of Computer Science and Communication, KTH Royal Institute of Technology, 10044 Stockholm, Sweden.

Computational Turbulent Incompressible Flow: Applied Mathematics: Body and Soul 4
by Johan Hoffman and Claes Johnson | Jan 5, 2007

Dreams of Calculus: Perspectives on Mathematics Education
by Johan Hoffman, Claes Johnson, et al. | Aug 17, 2004

The Secret of Sailing (Draft)
by Claes Johnson | Oct 1, 2014

Methods in Computational Science
by Johan Hoffman, | Sep 1, 2021

 

[Alan Cattelliot]

Hi,
Thank you Jehardiman ! They are real true theoricists of flight. I have read also read reviews from this article, arguing about definitions, but not formulas.

I studied aerodynamics and make my application in the DMAE, ONERA, France. My master was D. Cousteix, one of the well known experts in the boundary layer theory. Believe me it is also quite a shock to me to discover a very well documented and concurrent theory, that throw away wall boundary conditions, and their very difficult closing equations.

I came across this paper doing some research on the subject, and in the same time, one friend of mine developing commercial aircrafts just show me the same paper, very excited.

It happens that this new theory has been put in test un-officially by CFD engineers, at work. The idea of being able to compute, in no time, aerodynamical coefficients, for sure, would be handy ! And the results were astonishing. Although the precision is not sufficient enough for the resulting data to be put in an flight aerodynamics database, one should be able determine, very efficiently, the general arrangement of an airplane. And it's working !!!

I have myself conduct an experiment, years before, at the Department of High Energy, in the University of Rennes, France. After the experiment was made, I had no time to publish the results, so I use an inviscid numerical code to simulate the fall of paper sheets, for comparison with experimental measures. I was very surprised at this time to get close results that way, but till today, I did not re-open the case.

Cheers,