Is circulation real?

In case you didn't notice, I was answering a post from Alan Catteliot.

 

Ah, sorry, didn't spot that. Makes more sense now.
Any update on the text request?

 

Finally finished the simulation These are the results
The setup is as follows:

1. The wing chord is 2 metres,
2. The free stream velocity is 10 m/sec.
3. The smoke lines represent a 100ms "puff" so are 1 metre long in the free stream.
4. The frames are spaced at 50 ms.
5. The upper stream and lower stream start and end positions are based on the data supplied by @Doug Halsey
6. The simulation granularity is 0.1 ms, and runs until the tail of the free stream puff clears the trailing edge, which is 3,000 cycles, or 300 ms

The upper and lower streams are slightly delayed to match the Babinsky video



My initial observations from comparing this with the Babinsky experiment are:

1. The upper stream, as expected, goes faster than the free stream and reaches the trailing edge (TE) sooner than the freestream in frame 4.
2. The lower stream runs slower than the free stream, but not as slowly as the experiment as it reaches the TE before frame 7 while the tail of the free stream is just clearing the TE.
   
   What do you think?
   

 

The lengths of the smoke trails are not constant, as it should be if the medium is incompressible ( or almost ... ) The mass conservation is not respected in your simulation. It is the result of the "mapped" velocity field over a 1D displacement of the pixels. I don't really understand how you draw conclusions from the comparison of Babinsky's video with this kind of simulation.

What is to be understood, in the end ?

 

I think you are misinterpreting the effects of the conservation of mass in an incompressible fluid. If the "tubes" containing the fluid (the smoke) change velocity (as per @Doug Halsey's data ), then the front of the tube is moving at a different speed to the back of the tube and so, to conserve the volume (and mass) their change in length has to be compensated by a change in diameter.
[EDIT] Think about a tube of toothpaste: you have to squeeze the tube to make the paste move out of the end.[/EDIT]

Yup, that's exactly what it is intended to be.

I haven't drawn any conclusions yet. I have simply pointed out some observations.

To visualise the application of @Doug Halsey's data in order to compare it with Babinsky's experiment.
[/EDIT] And to explore @latestarter's observations about the bulges in the front line of the smoke trails. [/EDIT]

 

I have retrieved this reading list from the 2022-23 undergraduate aerodynamics course at Sydney University:

The list at the University of NSW is a subset of this list.
Is the one text that in your opinion best explains the foundations of aerodynamics on this list?
I am trying to get on the same page as you, but that's not possible until I know which book you're reading .

 

But none of your filament change their supposed "diameter", in the picture you gave. I understand the picture of toothpaste, but again, this is a lot of imagination to compare this with Babinsky video. Good luck.

None of them....Cultural gap I think. Our educative programs are more centered on the theory than on the application...

Used in University LANDAU & LIFSCHITZ VOL6 : https://phys.au.dk/~srf/hydro/Landau Lifschitz.pdf
Used in Aeronautic High School ASYMPTOTIC ANALYSIS AND BOUNDARY LAYER, COUSTEIX : Asymptotic Analysis and Boundary Layers https://link.springer.com/book/10.1007/978-3-540-46489-1

 

It was a one-dimensional representation of @Doug Halsey's velocity data.

I am looking for the text covering the "foundations of aerodynamics".

 

In english, "the Anderson" FUNDAMENTALS OF AERODYNAMICS was generally used as a reference.

 

It is certainly on many course lists, but I am interested in the text that @Doug Halsey follows when referring to the foundations of aerodynamics.

 

I think this is a step forward.
You have re-presented the data so it is no longer a subjective debate about is or is not a particular pocket of air changing speed.
It accords with my viewing of the Babinsky video and my query about the "S" shape.
The luke warm reception may be down to this debate going on for a couple of months.
At face value it seems more in line with Doug and Alan's view than your previously expressed opinion.

 

This post is to emphasize more strongly that the streamlines at the top or bottom of the screen in Babinski's video cannot be considered to be the undistrubed freestream. In the quoted post, I mentioned only the possibility that they were too close to the tunnel ceiling and floor. In this post, I show (for the upper one) that they are also too close to the lifting airfoil.

I modified the code that I used to calculate the airfoil's velocity distribution to also calculate velocities out in the flowfield. The figure below shows the results. The blue curve is for a line that's about the same height as the top streamline in the video. It should be clear that its velocity is significantly perturbed by the presence of the airfoil, reaching values more than 10% greater than freestream in some places.

I don't think there's anything shown in the video that allows us to accurately determine the speed of the oncoming freestream, although the figure could possibly be used to get approximate values.

 

I still maintain that the professor of aeronautics at Cambridge probably knew how to run a wind tunnel experiment.
Since you have declined to reveal your source of truth about the foundations of aerodynamics, I am unable to interpret your figure.

 

Knowing how to run an experiment and knowing how to interpret the results are two entirely different things as you can attest. You can beat a dead horse to water but you can't make it think.

This is pretty much shouted out, so perhaps it should be closed by the admin.

 

@Doug Halsey continues to protect his source.