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Author Topic: Would dimples on planes make them more aerodynamic  (Read 1543 times)

Offline thedoc

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Kevin Fitch asked the Naked Scientists:
   Why aren't boats and planes dimpled? My understanding is that dimples on golf balls reduce drag to let the fly farther from the same whack. Wouldn't it make sense to use the same trick to reduce drag on vehicles?
What do you think?
« Last Edit: 25/02/2016 13:50:01 by _system »


 

Offline alancalverd

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Re: Would dimples on planes make them more aerodynamic
« Reply #1 on: 25/02/2016 15:55:33 »
"Turbulators" are sometimes used on aircraft wings to reduce the stalling speed and increase the stall angle of attack. Very useful for bush pilots and agricultural aircraft where you want to minimise takeoff and landing runs, but the additional drag at high cruising speed limits their application in fast jets.
 

Offline evan_au

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Re: Would dimples on planes make them more aerodynamic
« Reply #2 on: 25/02/2016 17:02:01 »
Sharks have a very rough, textured skin, that seems to reduce their water turbulence and allows them to swim faster than you would expect from a smooth skin.

See, for example: http://www.eurekamagazine.co.uk/design-engineering-news/shark-skin-coating-could-reduce-aircraft-drag/47967/

Dolphins, when swimming at high speed also seem to develop tiny dimples in their normally smooth-looking skin.
https://www.newscientist.com/article/dn13693-shape-shifting-skin-to-reduce-drag-on-planes-and-subs/

Due to the very different viscosity between water and air, you would expect any dimples to be quite different sizes.

It's not clear how much of this improvement is due to the texture of the surface, and how much is due to it being an "intelligent" surface which can sense eddies forming, and trigger tiny muscle movements to counteract the developing vortex.
 

Offline wolfekeeper

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Re: Would dimples on planes make them more aerodynamic
« Reply #3 on: 06/03/2016 00:45:26 »
Golf balls are spherical, but spheres actually aren't very aerodynamic; teardrop shapes give much lower drag because the air can curve around the surface and get behind the object better and reduce the partial vacuum that forms there.

The dimples on golf balls cause turbulence, and the swirling allows the air to 'turn the corner' around behind the golf ball better and reduce the drag. The number, size and position of the dimples are carefully arranged to cause enough turbulence to help, and not so much that the turbulence generated wastes too much energy.

Shapes like boats and aircraft are already much better shapes aerodynamically, and reducing turbulence as much as possible is usually a better plan.
 

Offline Space Flow

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Re: Would dimples on planes make them more aerodynamic
« Reply #4 on: 06/03/2016 03:14:53 »
It also has a lot to do with speed. Generally increasing speed of a sphere through a medium goes through different profiles of air disturbance. At golf ball speeds there exists a certain window just after the threshold between "Laminar Separated" flow speeds and "Turbulent Separated" flow speeds where the drag coefficient for a dimpled surface falls well below the previous stage. Golf balls take advantage of this window. 
There is a mathematical relationship that gives a range of Reynolds numbers where this phenomenon can be taken advantage off. 
The mathematics is beyond me, but I'm fairly sure that if such advantage could be had, the engineers and designers would be aware of it and factor it in to their designs. 
At least you would hope so. I'm certain a large percentage would play golf...
 

Offline alancalverd

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Re: Would dimples on planes make them more aerodynamic
« Reply #5 on: 06/03/2016 09:57:21 »
Experimental fact: old aeroplanes acquire dimples known as "hangar rash" from  minor bumps and scrapes. You can eliminate the effect of engine ageing by comparing the performance of gliders, and it turns out that new, smooth metal goes faster and further than old wobbly stuff.
 

Offline wolfekeeper

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Re: Would dimples on planes make them more aerodynamic
« Reply #6 on: 07/03/2016 01:54:00 »
There does seem to be some evidence however, based initially on examining whale fins and wind tunnel testing, that quite big bumps on the leading edge of wings can be desirable though, at least at some reynolds numbers.

http://www.gizmag.com/bumpy-whale-fins-set-to-spark-a-revolution-in-aerodynamics/9020/

Basically, it looks like putting bumps there can give more lift/drag at high angles of attack, and can reduce span-wise flow along a wing.
 

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Re: Would dimples on planes make them more aerodynamic
« Reply #6 on: 07/03/2016 01:54:00 »

 

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