Schlieren video for testing aerodynamics ?

[RobertSmalls]

No, I hear you, and I'm very much interested in aerodynamics. I just don't know how to go about photographing a car at highway speeds using this technique.

The only Schlieren photos I've seen are of dramatic aero events, like shock waves and sneezes. The result is 2D, and it really would take 3D to properly illustrate the aerodynamic defects of my car, like the side mirrors.

A virtual wind tunnel is where it's at. I'd love to set one up. I don't know OpenFOAM, but if you figure out how to toss a SolidWorks model into OpenFOAM or some other software package, and get a Cd out of it, I'll whip up a 3D model of a car with and without mirrors, with and without side skirts, with smooth wheels, etc. Actually, this paragraph has been kicking around in my head for a few months, and it's probably worthy of its own thread.

[dcb]

It is conceivable to make an inexpensive diy 3d laser scanner, feed that into open foam, and model your car that way.

It is equally conceivable to adjust the computer model till you like the numbers, and have the same laser scanner highlight (directly on the car) the spots where you need to build up and where you need to sand down on your car/plane/boat.

[windrider919]

Schlieren photography is very much used in wind tunnels to show pressure areas and turbulence. It has been used by aircraft and auto companies using scale and life size models to develop the best aerodynamic shape. I first saw it used on a school trip back in 1970 at a NASA windtunnel. Google it and lots of sites are there.

But now it is easier to use CFD computer modeling instead of having to build an actual model or prototype.

Just yesterday I started a thread about we ecomodders doing it for ourselves. Building a model database to test various aerodynamic modifications for validity before possibly wasting money on something that does not work. Model it and then build it right one time.
See:
http://ecomodder.com/forum/showthrea...gram-9944.html

[Cd]

I must remind myself ( again ) to Wiki and Google on a topic before I post. Sorry folks

While I would love to do CFD calculations, I'm not good at all in math.
With this Sclerian technique, I was hoping for a simpler method that would be easy for me to play around with.

I was really just wondering if this sort of thing had been thought of before.


( I had originally envisioned driving a car already tufted past a stationary video camera. The tufts would show the flow on the surface of the car, but the Sclerian effect would show what the wake was doing. )

[Cd]

The last time that I tufted my car, I had intended to have a large vertical piece of cardboard mounted behind the car. As air spilled off the back of the car, the tufted piece of cardboard would show the pattern of my wake.
I ran out of time though ( rain ) .

[andylaurence]

Originally Posted by dcb

It is conceivable to make an inexpensive diy 3d laser scanner, feed that into open foam, and model your car that way.

It is equally conceivable to adjust the computer model till you like the numbers, and have the same laser scanner highlight (directly on the car) the spots where you need to build up and where you need to sand down on your car/plane/boat.

Really? URL! I'd love to get an accurate 3D model of my car. Actually, what'd be great is if I could make changes to the model and upload it to a server somewhere for processing and receive stats back from that (a few images and a CdA). I still have yet to get my head around OpenFOAM and when I do, where do I get an accurate model from?

[Cd]

You can use this laser scanner to 'model' your car in less than a tenth the time it takes to model it freehand ( It will be more accurate as well ).

Post images - we would love to see your progress !

The link : DAVID 3D Scanner

[andylaurence]

That's very cool. There's little evidence of large objects being scanned though, and I imagine the resolution of a car would be low. Still, it's worth a punt! I'll add it to the (long) list of items on my todo list.

[Cd]

If you look at the image gallery, there is a scan of a person from head to toe.
If you took the car in sections, such as doing a fender, you could piece the 3D data together to form the complete model.
The nice thing about 3D modeling is that you can do a copy-flip-attach and mirror the work you have done. You would still have to scan the entire underside though, since it is non symetrical.

Did you notice that the program is FREE for the low res scanning version ? Just a couple of years ago, they were selling stuff like this for over $ 5,000.

[andylaurence]

Yeah, I can't believe it's free software. Brilliant! When I find the time, I'll try it out.