Flow Illustrator Stand Alone Version (Windows Only)

[GMPG]

Chaz,

Could you give your thoughts on the images of my Sunfire that Sven ran for me? I'm on a Mac and don't have a windows machine available to run F-I on so I haven't been able to play around with the software yet and gain any insight into interpreting the images.

Any thoughts on what the flow points to or ways I could improve the outlines for better results would be great. Better as far as compatibility with F-I that is.

Thanks,
GMPG

[ConnClark]

Originally Posted by Sven7

I'll speak for myself because ConnClark surely has something to say about it too. (CC, what do you do for a living, if I may ask?)

Engineering. Mostly in electronics.

I have "calibrated" it based on ChazinMT's recommendations but noticed slight discrepancies between the data and my tuft testing. Not sure what to do about that, but once you get it locked in it should be pretty accurate for most tests, right?

The answer is no.

Here are a few quotes from the author of Flow Illustrator

"I (S.Chernyshenko) am often asked how to use Flow Illustrator for research. The short answer is that you cannot do this. "

"Flow Illustrator is optimised for speed and robustness, with accuracy being traded in. Treat the movies as artist impressions. The artist is you. This means that, however 'correctly' you select the parameters, the results will be inaccurate."

"Realistic conditions for flows past, for example, cars correspond to very high Re (like 10000 or more). However, if one ignores small-scale turbulent fluctuations always present at such high Re (which one has to do in Flow Illustrator since the characteristic length scale of those fluctuations is typically smaller than the pixel size) one should introduce so-called turbulent viscosity. In Flow Illustrator the effect of turbulent viscosity can be crudely modelled by decreasing Re. Re calculated using turbulent viscosity instead of laminar viscosity is called effective Re. Very crudely, for bluff bodies (like cars, or any body the flow past which is separated) effective Re, if based on the body largest cross-section dimension, is usually between 100 and 1000. Note that the laminar, numerical, and turbulent viscosities differ not only in magnitude but in many other respects, so that one can never be accurately modelled by the other. "


Flow Illustrator More Info page

I have no training outside Phil's lectures and other things on this site. I don't have the money for Hucho's book so it's mostly just studying what people say and studying tuft and smoke images (including independent "research" via tuft testing on the Probe). Still, when CC says "99.9%" of people don't know what to look for, I would wager that that other 0.1% is the members on this site, reading this thread, and using the software. If not us, who?

Curious to see what others say.

Let me quote the author of Flow Illustrator one more time. "So, if, for example, you want to have a realistic movie of the flow past a particular vehicle moving at 80Km/h, you should somehow imagine first what that movie should be like. For this, one probably has to take a few years university course in aerodynamics, then do a PhD in car aerodynamics, and perform a number of experiments with visualisations and so on - that is to become a specialist in the field. Once you know, what the movie should be like, you can play with Flow Illustrator's parameters until what it gives you looks realistic. "

Since it requires for a person to know what the actual output to look like to get something representative of reality this renders this software useless for experiments. So unless the members on this site, reading this thread, and using the software have a PhD in car aerodynamics and are a specialist in the field, every image produced by this software is what they want to see and not a real representation of what can be expected in the real world.

[99metro]

Awesome proggy. I think I got my first aero mod figured out. Thanks!

[aerohead]

Originally Posted by ConnClark

Engineering. Mostly in electronics.

The answer is no.

Here are a few quotes from the author of Flow Illustrator

"I (S.Chernyshenko) am often asked how to use Flow Illustrator for research. The short answer is that you cannot do this. "

"Flow Illustrator is optimised for speed and robustness, with accuracy being traded in. Treat the movies as artist impressions. The artist is you. This means that, however 'correctly' you select the parameters, the results will be inaccurate."

"Realistic conditions for flows past, for example, cars correspond to very high Re (like 10000 or more). However, if one ignores small-scale turbulent fluctuations always present at such high Re (which one has to do in Flow Illustrator since the characteristic length scale of those fluctuations is typically smaller than the pixel size) one should introduce so-called turbulent viscosity. In Flow Illustrator the effect of turbulent viscosity can be crudely modelled by decreasing Re. Re calculated using turbulent viscosity instead of laminar viscosity is called effective Re. Very crudely, for bluff bodies (like cars, or any body the flow past which is separated) effective Re, if based on the body largest cross-section dimension, is usually between 100 and 1000. Note that the laminar, numerical, and turbulent viscosities differ not only in magnitude but in many other respects, so that one can never be accurately modelled by the other. "


Flow Illustrator More Info page




Let me quote the author of Flow Illustrator one more time. "So, if, for example, you want to have a realistic movie of the flow past a particular vehicle moving at 80Km/h, you should somehow imagine first what that movie should be like. For this, one probably has to take a few years university course in aerodynamics, then do a PhD in car aerodynamics, and perform a number of experiments with visualisations and so on - that is to become a specialist in the field. Once you know, what the movie should be like, you can play with Flow Illustrator's parameters until what it gives you looks realistic. "

Since it requires for a person to know what the actual output to look like to get something representative of reality this renders this software useless for experiments. So unless the members on this site, reading this thread, and using the software have a PhD in car aerodynamics and are a specialist in the field, every image produced by this software is what they want to see and not a real representation of what can be expected in the real world.

This was the premise for the 'Template'.It satisfies all the criteria for attached flow in the real world the phDs worked in.
We can all get a phD or we can learn from empirical results which they've published about over the last 90 years.

[99metro]

The following is just my opinion and to be taken as just that.

I understand the extreme limitations of this program. I can basically use a cardboard cutout, non-3D version of something and get a jist of what's going on. Just a sliver down the middle. There are lots of dynamics with flow from so many angles that this program can't show that would greatly affect this sliver of a flow. But I think I can use this as a tool along with independent experiments to help visualize a path to take.

Tuft testing is great for near-car wind flow dynamics, but this program makes me realize even more the importance of flow going on 10 feet or more behind me. Tuft testing with 10 foot streamers behind the vehicle ought to be added to any aero experiments along with near-car tuft testing. It would sure be cool to see if the aero experiment resulted in even flow past the vehicle or if it resulted in a worse situation.

[Sven7]

Originally Posted by 99metro

Tuft testing with 10 foot streamers behind the vehicle ought to be added to any aero experiments along with near-car tuft testing. It would sure be cool to see if the aero experiment resulted in even flow past the vehicle or if it resulted in a worse situation.

I think I know what I'll be doing over winter break

[CigaR007]

I was reading on MAF sensors (Mass flow sensor - Wikipedia, the free encyclopedia) and found this gif animation to be quite interesting.



So I tried to re-create it using using Flow Illustrator. Here's what I obtained.

http://www.youtube.com/watch?v=J9AifF61XGM

From the looks of it, you can see that the "wake" pattern seems to be the same. Pretty sure that it can be even closer with some further tweaking of the velocity and viscosity.

So, it is possible to simulate with a certain precision, but as stated previously, it requires you to know what the flow should look like. Quite an interesting result nonetheless !

[aerohead]

Originally Posted by 99metro

The following is just my opinion and to be taken as just that.

I understand the extreme limitations of this program. I can basically use a cardboard cutout, non-3D version of something and get a jist of what's going on. Just a sliver down the middle. There are lots of dynamics with flow from so many angles that this program can't show that would greatly affect this sliver of a flow. But I think I can use this as a tool along with independent experiments to help visualize a path to take.

Tuft testing is great for near-car wind flow dynamics, but this program makes me realize even more the importance of flow going on 10 feet or more behind me. Tuft testing with 10 foot streamers behind the vehicle ought to be added to any aero experiments along with near-car tuft testing. It would sure be cool to see if the aero experiment resulted in even flow past the vehicle or if it resulted in a worse situation.

I know that BMW has included very long streamers during photo sessions within their wind tunnel.
Attaching a 'rake',with attached streamers ahead and to the sides of a vehicle would allow for visualization of the outer flow field.
The streamers would need to be of the lowest mass possible to counteract gravity's attempt to 'ground' them.
Aerodynamicists have resorted to helium-filled bubbles for neutral-buoancy in attempts at 3-D flow visualization.
Smoke seems to remain the 'KING' for visualization.

[Cd]

Originally Posted by GMPG

Chaz,

Could you give your thoughts on the images of my Sunfire that Sven ran for me? I'm on a Mac and don't have a windows machine available to run F-I
Thanks,
GMPG

Unfortunately I too have a Mac ( oh why did i ever buy this overpriced thing ) I run F-I on my MBP on the Windows partition and it works fine !
It's just a major pain to switch back and forth.

Surely you have an old edition of Windows laying around eh ?

[Cd]

For doing tuft testing behind the cars wake, why not attach a flat rigid extention of cardboard or coroplast or whatever and 'sew' some yarn through it.

You could have it extend out several feet and the tufts would show the direction of the flow within the wake.