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Old 12-11-2008, 08:39 AM   #1 (permalink)
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interesting find while simulating wheel dams

since i'm still messing about with different wheel dam configurations i decited to run a few things trough flow illustrator... i know it's not the most scientiffic, but it's the best i got and it gives some sort of impression on what might happen.

i ran several different variations on the dams i have on right now, but the resulys all looked about the same, especially all seemed to have turbulent tails...

anyway just before i was about to quit i wondered what would happen if there was a hole in the dam. especially ford seems to have two wheeldams on their new models with a slot in between the two dams.

as inaccurate as it might be the difference was quite big, especially compared to all the weird compound dam things i had tried... i simply "drew" a hole in the dam and the turbulence behind the wheel setteled much quicker. in fact the turbulence in the simulation without the hole never setteled while the sim with the hole became perfecly smooth alfwat trough the 30 second render.






i'm considdering makeing the slots in my (custom) dams, but i'd like to know if anyone would be able to explain this or perhaps run a better simulation

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aer·o·dy·nam·ics: the science of passing gass

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Old 12-11-2008, 08:59 AM   #2 (permalink)
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I'm not sure I quite understand what you are working on....do you have a picture of your car?
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Old 12-11-2008, 09:40 AM   #3 (permalink)
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sorry perhaps i should have explained things a bit better, the big black opject represents the left front tire, seen from above and the curved limes represent dams intended to divert air away from the tire and the wheelwell behind it.

these dams are quite common on almost every curent vehicle.
some are straight and only cover the tire or the suspention on some cars i've obseved these dams curve inwards near the center... mostely bmw's audis, and the new ford mondeo have this layout. the ford seems to have two separate dams however separated by a gap of about a cm.

what i did was extend the weel whell liners in from of the tires with a strip cut from a cheap plastic bucket, handy as this already has a curve in it.

i had planned to use the leftover bits of the bucket to make small curved dams in front of these dams but when simulating this they didn't seem to produce something that was vastly different from the first movie.

but when i added the gap this changed the behavior drasticly as you can see in the movies.

based on this simulation one might conclude a gap between the portion in front of the tire and the curved portion would be a good idea.

my theory is that he full dam acts as a single vortex generator while the split dam might act as two vortex generators produceing counter rotating vortices.
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Old 12-11-2008, 11:25 AM   #4 (permalink)
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I think you probably need to simulate the wheel wells to get an accurate estimate of aerodynamics.
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Old 12-11-2008, 11:29 AM   #5 (permalink)
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This seems like a similar phenomenon to what these guys are claiming:

Oval Concepts TT Fork
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Old 12-11-2008, 12:15 PM   #6 (permalink)
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Quote:
I think you probably need to simulate the wheel wells to get an accurate estimate of aerodynamics.
yes but how?

this simulation is 2d, so it's really a slice taken just below the cars under surface... normally it would be just a slice of wheel, but the add-on dams also intersect this plane and they appear as lines... nothing else sticks out into this slice of air, so there's nothing else drawn. i do want to divert air around the open wheelwell above the plane, as this is what oem airdams on some other cars seem to do.

so i want the majority of this flow to go around the area below the wheelwell, even when this is not moddeled.

i know interacting airflow can create flow patters wich are vastly differnent than what happenes with individual components, but i think it can be interesting to isolate certain things, like the dam/wheel, interaction and than try to guess what happenes when this would be integrated in whats aleady there.

that bike fork is interesting!... i think most objects in the end function as crude vortex generators so i think most drag reduction solutions are a matter of countering the bad vortices and enhanceing the good ones
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Old 12-11-2008, 02:09 PM   #7 (permalink)
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Very interesting find

Now the question is would it be better to have it curve around to the inside of the car or around to the outside? Also what affect does modeling both front tires have on the airflow? You might try modeling all 4 wheels and run a few tests.
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Old 12-11-2008, 04:31 PM   #8 (permalink)
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FYI, hole in the front tire air dam of a 2007 (I think) Toyota Camry Hybrid.

I suspect it's there for brake cooling though.



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Old 12-13-2008, 02:31 PM   #9 (permalink)
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i finally found a good picture that shows the mondeo dams.




an itneresting point to note is how the dams on the left look like theyre inline, while the ones on the right show the inner component is angeled backwards... shows how deceptive pictures can be

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