An introduction and a "video"

[autogyro]

Hi
This is my first posting, but I've been a member for sometime, and thought I should share some stuff I've come by.
First the video:

I can't add links yet (I fail to understand this policy), but you can search YouTube under autogyro46.
The shape is shown in the attachment.

This is the start of a crazy project which should soon result in a 1/4 scale model, using a roof-rack "wind tunnel"*, for which I'm developing some laptop based instrumentation. Then, who knows, full scale?

I suspect many of you have already used Flow Illustrator, and therefore need no introduction. For those of you that haven't, it's a revelation! This particular model was first developed in JavaFoil, another free download, and tranferred in a .bmp file to Flow Illustrator.
( Yes you can achieve low CD values "on paper". I have a copy of Morelli's two seminal articles which, if you read between the line have a lot of useful info.)

Although both of these tools are only 2D, (not to mention paper!) they are very revealing, showing how difficult it is to prevent flow separation.
All this will probably be put into a CFD program like Symscape, certainly before I go to full scale. I'm trying to avoid really expensive mistakes.

Thanks everyone.

*There's a discussion of this topic on another forum, EngTips, under "roof-rack wind tunnel" for anyone who's interested. Re the instrumentation, that a work-in-progress, too, but should be up and running soon. If anyone's interested let me know.( BTW: instrumentation is what I do in "real life")

[ChazInMT]

Hey Autogyro, just looked at your video, and 2 things jumped out at me initially.

1st, Your shape is below the plan taper in the back, this will be the biggest problem with it, also, not sure why you have so much air being jammed under the car in front with the shape you have.

2nd, Using a value of 10M for Re seems a tad high according to the "more info" stuff on the flow illustrator web site, 100-1,000 should be the Re settings.

Much discussion by others is sure to follow, hope this doesn't discourage you, keep learning.

Here's a link to your vid.
Espadon12c Re10M Flow illustrator - YouTube

[aerohead]

At 1/4-scale you'll need a minimum 80 mph to fix your Cd / turbulent boundary layer.
The 2-D simulation won't help as a predictor for 3-D behavior,especially the wake.
Edge radii for the greenhouse is an extermely important parameter with fastback architecture,it's a pity that the really good Navier-Stokes equation with spherical coordinate system software is beyond the reach of mortal men.
Best to you! Looks like a fun project.

[autogyro]

Thanks guys
First @chaz
1.In fact this shape was the result of a whole lot of iterations on F.I. There were others that performed differently, but the thing about this one was the thin attached top boundary layer at the end of the clip. The airflow seemed to really like the big radius, although it took awhile to "settle in". That's the second big revelation. Airflow patterns do not equillibrate instantly.
2. See the comment below yours. An overall length of 4.5m @ 30m/s gives that 10 X10E6 Reynolds. It seems to works fine
BTW the pressure coefficients in this 2D model are very close top and bottom over the first 10% of the chord. I have a different F.I. simulation with the same nose that show no separation. Haven't figured that out.
@Aerohead: I guess I tried to address your comments in the above. 30m/s (67.1MPH) i took to be a bare minimum to get an acceptable Re with a reasonable scale model size. It's a figure that gets cited a lot in Katz's book, which is why I went with it. Not to mention the, ahem, legal issue.
On your second point....aaahh,sigh. I haven't heard anything either way about Symscape/Caedium, but if it doen't work out, I haven't lost my shirt. I have great hopes for it.

[some_other_dave]

If you look closely, in the middle of the video you can see one of the "particles" in the "air" going forward under the form, just about all the way to the front. I thought that was an interesting flow reversion--but one that is not likely to happen if you used a moving ground plane.

-soD

[autogyro]

Yeah, I noticed that too. It can only mean a positive pressure gradient on the underside going back to front, to which I can only say..HUH?
I think the snowflakes are on of the best features of F.I.

[user removed]

Caproni-Campini N1 CC 2

regards
Mech

[euromodder]

I Think that's gone in the wrong thread, Mech