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Old 01-17-2007, 04:00 AM   #1
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windshield airflow

some ideas i had:
A:
from what i read on the web "a-pillars" apparently create a big vortex at the side of the vehicle wich is said to be responsible for a lot of wind noice (most research seems to be aimed at wind noise reduction) but this vortex probably has a very undesirable effect on drag as well.

i'm wondering if installing vorex generators to the side of the A-pillar might succeed eleminationg this big vorex and at the same time keeping more airflow attached to the side of the vehicle?

B:
also i noticed that most modern vehicles hood curves upward leaving a recessed area for the wipers. on my car the wipers are frightfully exposed to the airflow. i'm considdering inserting a strip of about 5 cm's high in front of them at the rear hood seam, and angleing this strip at the same angle and curve as the windshield...

i realise that the transition hood/fairing should be more smooth but since this is not the case for the original hood/ windshield transition anyway there should be no aeordynamic changes in this respect.

any thoughts on this approach?

(after posting i noticed this post should go under "General Fuel Economy Discussion "....sorry)
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Old 01-17-2007, 07:56 AM   #2
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here's a scematic of what it should look like
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Old 01-17-2007, 08:10 AM   #3
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When VGs are used to promote non-turbulent airflow over a curve, they need to be placed upstream of the separation point. I'm not sure that putting them on the a pillar itself would work because it's probably not far enough upstream from the transition, and also the angle is relatively sharp.

The wiper fairing idea seems OK. I know a few people have done this (or plan to).
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Old 01-17-2007, 08:30 AM   #4
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Quote:
Originally Posted by lunarhighway View Post
A:
from what i read on the web "a-pillars" apparently create a big vortex at the side of the vehicle wich is said to be responsible for a lot of wind noice (most research seems to be aimed at wind noise reduction) but this vortex probably has a very undesirable effect on drag as well.

i'm wondering if installing vorex generators to the side of the A-pillar might succeed eleminationg this big vorex and at the same time keeping more airflow attached to the side of the vehicle?

B:
also i noticed that most modern vehicles hood curves upward leaving a recessed area for the wipers. on my car the wipers are frightfully exposed to the airflow. i'm considdering inserting a strip of about 5 cm's high in front of them at the rear hood seam, and angleing this strip at the same angle and curve as the windshield...


any thoughts on this approach?

(after posting i noticed this post should go under "General Fuel Economy Discussion "....sorry)
Sorry? I posted(still do) under the wrong slots many times...they get read!

First, a comment on your windshield wiper placement...relax! The wipers nest in the stagnant air at the base of the windshield. It's (relatively) quiet down there ... little or no drag. Hint : Watch the raindrops next shower.... Wiggling 'drops aren't pushed by air (no definite velocity), just a bit of chaos. The streaming drops are where the velocity lies... and the drag potential.
Next, a comment on vortex placement .... The side of the pillar(s)? A vortex generator requires energy to spin ! This energy is called "drag". Imagine holding a plastic pinwheel out the window...at the windshield base (or wherever). It will last a micro-second before self-destruction at speed ! Vortex generators do one thing very well! They lighten the wallet!
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Old 01-17-2007, 11:42 AM   #5
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thanks for the advice...
the a-pillar vortex i'm talking about comes from this document :
http://www.exa.com/newsite/PowerFLOW...acoustics.html

the idea of adding VG's to the pillar would be to break this up into smaller vortexes rater than try to keep the air attached to the vehicle directly...

it's just a thought though... and the actual effect of anything would be hard to detect... but i might try to ad some homemade vg's there at some point, just to see what it does ( looking at the shape of aircraft vg's it shouldn't be a poblem to make them inexpensively maybe i'll even use card for testing)...
i added 2 tape covered card fins at the outer edge root of my windshield today.
i noticed an increase in noise at speed and sticking my hand out of the window there seemed to be more airflow beside my window. i won't draw any conclusions from this but it's encouraging to keep trying...
more "testing" to be done
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Old 01-18-2007, 09:22 AM   #6
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Acoustics...

Quote:
Originally Posted by lunarhighway View Post
thanks for the advice...
the a-pillar vortex i'm talking about comes from this document :
http://www.exa.com/newsite/PowerFLOW...acoustics.html
Hi, again!
I just looked at the link you provided...and I see what you're refering to...wind noise (we used to call it "buffeting"). The vortex at the top of the pillar is where the roaring comes from...remember the days of the vent window? they're gone now...the stylists and the beancounters got 'em!
Vehicle drag is always present, especially in the areas of corners. Whenever you separate laminar lines of flow you'll find vortices (and the drag associated with them)! Filling the low pressure zones with air from "somewhere else" works to reduce the low pressure ("Nature abhores a vacuum", right?).
The absolute easy way to reduce these swirls is to slow down... in lieu of / in conjunction with?... that, fill 'em in! Idea: Try filling in the area with a pitot tube arrangement(just a length of plastic tubing)...taken from a high pressure (ram air source ) in the front of the vehicle..., pitot tube protruding a bit from the chaos zones. You might as well use that pressure zone(stagnant air pocket) for something!
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Old 01-18-2007, 01:43 PM   #7
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Quote:
Originally Posted by Ted Hart View Post
remember the days of the vent window? they're gone now...the stylists and the beancounters got 'em!
i think my dad's prevous cars used to have them he used to have them.
he's subsequently owned 3 or 4 opel rekords c coupés... it's also the first car i learned to drive in. http://upload.wikimedia.org/wikipedi...e_vl_green.jpg
(this is just an example the one's i remember where golden-brown and white). the car was very sleek looking,but getting all the weight on the move took quite some energy... fortunately it's appearance caused most drivers to slow down a bit ... the last one started to become impractical as a dayly driver and with no place to store and restore it, it had to go...i think FE was close to terrible as well
Quote:
Originally Posted by Ted Hart View Post
Filling the low pressure zones with air from "somewhere else" works to reduce the low pressure ("Nature abhores a vacuum", right?).
...

interesting... i suddenly got an idea...why not use all the "tubing" that's already on the car? the intake of my heater/ventilator is located as the windows base, probably as the high pressure forces it in... right?... there are also 2 additional outlets on the dash aimed at the side windows to defog them.......they're pretty close to the side mirrors...
it wouldn't be too difficult (al least in theory...) to route this air trough to the side mirrors for example... first of all having cold or warm air come out of the sidemirrors might come in handy in the winter ... but it might also be used to reduce the mirrors wake?perhaps a directable outlet could be interesting too.. of course it might not be a good idea at all but if i can find a relative easy way to try this i might give it a shot...
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Old 02-28-2007, 01:41 PM   #8
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Quote:
Originally Posted by lunarhighway View Post
B:
also i noticed that most modern vehicles hood curves upward leaving a recessed area for the wipers. on my car the wipers are frightfully exposed to the airflow. i'm considdering inserting a strip of about 5 cm's high in front of them at the rear hood seam, and angleing this strip at the same angle and curve as the windshield...
You mean something like this, right?



(Lund Wiper Cowl)

I've wanted to put one of these on a vehicle for years, but will have to fabricate my own since they're mostly made for trucks. Not a big deal, used to working with thermoplastics, but have always wondered if it's a benefit or detriment to airflow. Visually seems like an obvious improvment, but could that big gap that's being created just cause more turbulence? Anyone know?
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Old 02-28-2007, 05:07 PM   #9
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Yeah, I know. It will just fill up with snow.
Can you tell there's a forecast for another 6~8 inches with rain on top to make it really heavy?

Oh, It'll also obscure my state's annual inspection sticker, a legal no-no here leaving me liable to a fine. I don't think a clear one instead of the tinted one in the image above would be acceptable, either.
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Old 02-28-2007, 05:18 PM   #10
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One could also park their wiper blades up and down for a cheapie fix, ie. pull the fuse at just the right moment or add a switch, or get fancy and put the crank on 180 degrees out or somesuch.
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