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Old 12-07-2020, 10:44 PM   #1 (permalink)
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Tufts

Someone asked the other day whether tufts were still used in wind tunnels. The professional aerodynamicists I have communicated with have all suggested that tufts are still very useful, and the other day I noticed in a tech paper on the Porsche Taycan that they'd run a tufted pic. Pity it's not the rear three quarters, but you can't have everything.


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Old 12-10-2020, 01:31 AM   #2 (permalink)
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In fact, as a zero-cost technique, I continue to believe that tuft testing on the road is much underestimated by most people.

It's a bit like using a microphone on the engine block to listen for detonation when changing ignition timing. It's not just binary (it is detonating or is not detonating) but as you become more skilled at listening, it's more the "degrees of closeness to detonating".

Same with tufting: you get a feel for how close to separation is the flow.

But I remain a fan of still photography from the side of the road (or from a tracking car), rather than introducing potentially flow-disturbing car-mounted video cameras into the mix. (But I think there is plenty of potential from drone cameras - I have an agreement with my 16 year old son to, some time, do some drone pics of the wakes of various cars on local dirt roads, using his drone.)

Because in the past people have poured lots of shiXX on me for using tufts (but note: not in this group) I have always made a point of asking nearly every professional aerodynamicist that I come in contact with what they think of tuft testing - and every single one has been positive about it.

So that's good enough for me!
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Old 12-10-2020, 06:16 PM   #3 (permalink)
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We needed a quick validation of where the vortex that was shedding off the barge board was indeed going, so we whipped out the tufts. These are particularly long and we also had a string-on-a-long-stick in play (you can see it poking in from the bottom of the frame). This was 2007 when developing the Super League Formula single make series car. Only time I've ever done wool tufts on a scale program.



For on surface flow visualization our preferred method is flow-viz fluid. Flow vis is a liquid concoction and the recipe is typically a highly guarded secret between outfits. Ours was a mixture of oleic acid, tempra paint (glow in the dark if I remember correctly), and paraffin oil, though for the life of me I can't find the exact ratios. 2006, Panoz DP01 Champ Car development:
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Old 12-10-2020, 07:12 PM   #4 (permalink)
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For the fluid Rob Palin (ex Tesla) suggested light grade engine oil and chalk dust. I've tried it but it's hard to get good results on panels that aren't horizontal.
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Old 12-10-2020, 09:20 PM   #5 (permalink)
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Quote:
Originally Posted by JulianEdgar View Post
For the fluid Rob Palin (ex Tesla) suggested light grade engine oil and chalk dust. I've tried it but it's hard to get good results on panels that aren't horizontal.
Yes, oil can be problematic because once you stop forward motion gravity takes hold. That's the beauty of flow-viz solutions; the carrier liquids are ratio'd to evaporate leaving the tempera paint base, which then in theory can be wiped off as it's just residue.
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Old 12-10-2020, 09:34 PM   #6 (permalink)
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Why doesn't every car have a permanent tuft attached to hood center, for situational awareness concerning crosswind conditions?

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