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Old 07-31-2009, 04:05 PM   #1 (permalink)
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Question Vortex generator? Mystery windshield lip

On my Toyota Previa there is a lip running up either side of the windshield. I have two theories as to it's function:

1) Drip rail to send rain up and over the car and not around the side. To keep rain off the side windows for better visibility.

2) A vortex generator to keep flow attached along the side of the car where the windshield and side pillar meet at a relatively sharp angle.

Looking up from the hood:

the air flows toward the drip rail at about a 35 degree angle.



My proposed fix if it is just a drip rail and not a vortex generator.



Any ideas?

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Old 07-31-2009, 04:11 PM   #2 (permalink)
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Tons of new cars have a really exaggerated version of that. I've theorized it's to direct air over the top of the vehicle and not around the sides, but I honestly have no damn idea. i'll see if the Jetta has in and if so tuft test it.
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Old 07-31-2009, 04:25 PM   #3 (permalink)
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Tuft test. Brilliant. Now where is my knitting...

I can't imagine it's big enough to direct air over the top. The raindrops take a straight line right to the lip.

I imagine the air spills over it, but unless it then goes into a good vortex and not more turbulence it would just produce more drag.
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Last edited by orange4boy; 07-31-2009 at 04:32 PM..
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Old 07-31-2009, 04:26 PM   #4 (permalink)
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My '02 Mitsubishi Galant has them as well. Maybe 1/2" tall. I just always thought someone had their head up their arse.

You may try taping it off first to see what it does.

Don
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Old 07-31-2009, 05:56 PM   #5 (permalink)
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Those are rain gutters. I remember Hucho paid attention to their design when talking about aero details optimization in his book. You can hammer them down, but more convenient would be to fill them with silicone or foam as you suggested.
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Old 07-31-2009, 06:32 PM   #6 (permalink)
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The next windshield guy is going to love you.
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Old 07-31-2009, 06:53 PM   #7 (permalink)
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I may try to cut them off as they are just rubber and this would give the largest profile reduction without the hassles of silicone,tape,foam etc.

Maybe I can plane them off with a wood plane.

Thanks.
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Old 07-31-2009, 07:23 PM   #8 (permalink)
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I didn't notice they were rubber. Just shape them so it makes a nice transition from the windshield to the metalwork and call it a day.
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Old 07-31-2009, 07:30 PM   #9 (permalink)
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Did Hucho say anything about how bad they are aerodynamically?
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Old 07-31-2009, 07:30 PM   #10 (permalink)
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I think we have another mod for the list.

One side done!

Small very sharp stanley 101 plane does the job like buttah! I think this is a type of plastic not rubber. Rubber might have problems of it's own.

I did the calculation and the frontal area adds up to 18square inches. 72 linear inches, 1/4 " depth. so 72*.25=18. Now the air hits at an angle so this may be a bit high. Effective square inches is possibly half that.



The start and end were a little tricky. A few digs but nothing that cant be smoothed

I'm having some success with sandpaper 320 grit to smooth the plastic back. A sharp file works too but is not easy to get close to the work.


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Vortex generators are old tech. My new and improved vortex alternators are unstoppable.

"Itís easy to explain how rockets work but explaining how a wing works takes a rocket scientist."
-Philippe Spalart



Last edited by orange4boy; 07-31-2009 at 07:38 PM..
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