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Yesterday, I got some tuft testing in on my protege. It basically confirmed what I was thinking, in that there was significant separation at the rear window even at low speeds, ~30mph or so.

I think this was my greatest surprise (such low speed separation), but I was intending on creating some sort of kammback cover anyway, so hopefully that will be completed soon.

Here are some pics, and links to the videos below (the mpeg filenames should be self-explanitory)

http://www.cleanmpg.com/photos/data/533/medium/Tuft_Testing_004.jpg

http://www.cleanmpg.com/photos/data/533/medium/Tuft_Testing_002.jpg

http://www.cleanmpg.com/photos/data/533/medium/Tuft_Testing_001.jpg

http://www.cleanmpg.com/photos/showphoto.php/photo/7063/cat/533

http://www.cleanmpg.com/photos/showphoto.php/photo/7062/cat/533

Interesting. I too have been thinking of Kamm backs.

Have you seen any such data on the Prius? I would expect that Toyota got that one right, and there is smooth flow over the back to the Kamm tail.

I haven't looked for it, but surely it's out there

...this is where the prius guys flood this thread with prius links...

but indeed, the prius is a nice, streamlined car. Every time I see one i get so upset seeing that big ol' windsheild wiper in the middle of such a nice kamm tail.

if my CD wasn't the same as a Prius, I'd be jealous... the low CD was what made me a Subaru XT fanatic.

I sure would like to lower my CD more, but I ma afrid to ruin it..
I need to read up on this tuft testing.. looks like fun!

I'm really curious what the tufts did on the trunk lid. Did flow reattach at the rear edge? That's what you want. It's not as good as attached flow the whole way down, but it's much closer.

I'm not sure how to interpret these. If the tufts lift off and
flap all around, does that mean tons of turbulence and that
you're already past the separation point? Particularly on the
rear ones -- what's to say the air coming over the roof of the
car isn't already screwed up in some fashion?
.
_H*

The flapping tufts mean flow has separated. Most cars of any description have attached flow up the windshield and across the roof. It means the whole back window is too steep and flow separates at the top of the glass. We can hope it reattaches at the trailing edge of the trunk. Otherwise, the car has a wake the size of a hatchback/wagon. :eek:

Mine is probably the same. I can see the patterns in the morning dew - the sides dry out from the vortexes from the sides, but the center stays wet the whole trip - no smooth airflow.

Nice work on the tufts.. :)

You may want to stagger your tufts to avoid interference from one horizontal row to the next, but it looks like your pattern got the idea across. Whenever you tuft, you want to look at as broad (width and depth-wise) an area as possible, obviously without risking a ticket for obstructing your view out the windshield... Also, I would suggest a passenger to video for obvious reasons. Just be careful to maintain your concentration and not get caught up in discussing the test while you drive. Make a good plan that has options depending on the traffic and conditions you encounter, and stick to it. If you need to re-evaluate your plan, stop somewhere to think it through before resuming driving. There are quite a few tuft test videos on the web where they drove the test vehicle past a stationary photographer or alongside a chase car to get a look at areas that can not be seen from inside the car. Intentionally driving in close formation with another vehicle by far carries more inherent risk, and no accident is worth the gas $ you might save, so choose your testing methods cautiously!

http://www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2004/16E_03.pdf

This is a link to a study of sedan airflow and the effectiveness of vortex generators. If I remember right, they found that airflow will generally not stay attached at an angle greater than (I believe) of about 11-12 degrees. The fact that the airflow separated (stalled) at slower speeds around the bends is to be expected.

It is likely you will have some areas directly behind the windshield of un-attached flow, with re-attachment over the rest of the roof. It is unlikely that you will see much, if any attached flow on the trunk deck, except possibly from some "spillage" from the sides

The flapping tufts mean flow has separated. Most cars of any description have attached flow up the windshield and across the roof. It means the whole back window is too steep and flow separates at the top of the glass. We can hope it reattaches at the trailing edge of the trunk. Otherwise, the car has a wake the size of a hatchback/wagon. :eek:

Mine is probably the same. I can see the patterns in the morning dew - the sides dry out from the vortexes from the sides, but the center stays wet the whole trip - no smooth airflow.


"a wake the size of a hatchback/wagon. :eek:"

That's one of my problems with the CRV. Not only is it a squared off right angle off the top,
there's a spare tire hanging on the back for the pressure swirls to grab hold of..

I was wondering about sticking some vortex generator tabs on top of the trailing edge of the roof, but now I read about zig zag turbulator tape being used on aircraft and some cars that seem to do the same job as VGs. Is Zig-Zag tape really that effective?
It just seems so thin, it's hard to see how it would work.

Here's a pic, in case anyone thinks I'm make this up.. :)
http://ecomodder.com/forum/showthread.php/belly-pan-vortex-generators-1209-2.html

http://i17.photobucket.com/albums/b53/edbso/zig-zag.jpg

maybe but is it worth looking so square?