1288 upvotes, 14 direct replies (showing 14)
View submission: How does adding texture to a surface reduce drag?
Actually, it is not like golf balls. The mechanism used by golf balls and other turbulent trips are designed to increase the pressure recovery around a body and thus reduce its profile drag (what people generally refer to when talking about how different shapes have different drag like this overview[1]).
1: http://www.aerospaceweb.org/question/aerodynamics/q0231.shtml
However, the "shark skin" or other micro/nano surface structure materials reduce the skin friction [Marine drag reduction of shark skin inspired riblet surfaces[2]]. This is more like the normal friction people think about between two objects. The small structures promote imperceptible boundary layers that effectively make the overall surface "smoother".
2: https://www.sciencedirect.com/science/article/pii/S2405451816300484
These same structures can also make surfaces super-hydrophobic like a lotus leaf[3]. This has the added benefit of not only reducing skin friction, but also adds a self-cleaning effect (getting dirty adds drag).
3: https://en.wikipedia.org/wiki/Lotus_effect
Comment by Long_Educational at 19/10/2021 at 02:36 UTC
265 upvotes, 6 direct replies
A lot of the fuel efficiencies cited in the Boeing 737 Max was due to the reduction of drag by going with a composite single piece construction for the wings and fuselage, removing the need for rivet fasteners. I'm sure even more could be gained through the use of advanced coatings.
Comment by tryid10t at 19/10/2021 at 02:09 UTC
23 upvotes, 2 direct replies
So, is it creating tiny vortices? Is this just a smaller concept of the tailgate up/tailgate down concept? Sorry that's the best way I can describe it.
Comment by Bissquitt at 19/10/2021 at 05:46 UTC
18 upvotes, 3 direct replies
From my brief reading (lotus leaf) it appears that this effect is unique to H2O (I know hydrophobic literally means water, but many people use it as "liquid resistant" as short hand) If another liquid without the unique surface tension properties of water were poured on the surface, I don't believe it would have the same effect. This may seem obvious, but I find it helpful in understanding it doesn't repel water because it's a liquid, it repels water because its H2O.
Comment by maglax at 19/10/2021 at 15:10 UTC
3 upvotes, 1 direct replies
Being hydrophobic should inhibit ice as well? Passive deicing should save weight and fuel?
Comment by [deleted] at 19/10/2021 at 13:22 UTC
2 upvotes, 0 direct replies
I was thinking it was a lot like say you're on a motocross bike, and you travel along at such a speed oflver a series of bumps that you spend most of the time in the air. You have the right combination of speed and bump distance where you are just sort of lightly kept suspended. (The air doesn't have much gravity pulling it to the fuselage.) And so bumps keeping you at bay means you're less in contact with the surface. But they'd need to be properly designed bumps, otherwise the friction would be worse.
Is it something like that?
Comment by NaBrO-Barium at 19/10/2021 at 13:49 UTC
2 upvotes, 1 direct replies
My biggest question with modifying the surface at nanoscale is how durable is it? Would this hold up to ice, birds, or anything else it might come into contact with during flight?
Comment by VirtualMachine0 at 19/10/2021 at 15:16 UTC
2 upvotes, 0 direct replies
Actually, it is not like golf balls.[...] The small structures promote imperceptible boundary layers that effectively make the overall surface "smoother".
I thought that was the mechanism the golf ball dimples used, though; holding a better boundary layer to the surface to promote a sort of virtually smoother surface. Thus getting more air to the rear of the ball faster, decreasing that negative pressure zone.
Comment by [deleted] at 19/10/2021 at 19:03 UTC
2 upvotes, 0 direct replies
If I recall correctly, the Soviets accidentally got a similar improvement when they constructed the MiG-29. Due to lower tech construction techniques, the surface wasn't as polished, but it ended up netting a surprise improvement in drag.
But, I could be remembering that all wrong, it's been decades.
Comment by PoliticalAnomoly at 19/10/2021 at 19:14 UTC
2 upvotes, 0 direct replies
Speaking of lotus leafs and drag, I used to be a waterproofer by trade and once learned about a product called Stocoat Lotusan. If memory serves, it is a building coating material that essential allows any dirt and dust accumulated to be easily rinsed from the surface because basically nothing really sticks to it.
Comment by [deleted] at 19/10/2021 at 07:03 UTC
4 upvotes, 0 direct replies
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Comment by Cybersad3021 at 19/10/2021 at 14:06 UTC
1 upvotes, 0 direct replies
That's good and all but hydrophobia is a serious world problem we need to address.
Comment by [deleted] at 19/10/2021 at 11:52 UTC
0 upvotes, 1 direct replies
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Comment by apu74 at 19/10/2021 at 04:37 UTC
1 upvotes, 0 direct replies
Do you think something like this would help with reduced heat transfer from the medium to the body?
Comment by [deleted] at 20/10/2021 at 06:39 UTC
1 upvotes, 1 direct replies
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