Mythbusters - dimpled car
Discussion
Just been watching the new episode of Mythbusters, where they put golf ball style dimples on a car, and achieved an 11% reduction in fuel consumption. I wonder if any car manufacturer will pick up on the idea ( though obviously using something a tad lighter than the half tonne of clay they used on the show )
And they missed a major opportunity - they didn't use a Golf
And they missed a major opportunity - they didn't use a Golf
Where did they put the dimples? On a golf ball it's the rear face that's more important, the dimples cause turbulence in the boundry layer which keeps it attached longer, so you get a smaller wake behind the ball, and thus less drag. The equivilent on a car would presumably be the flow from the roof on to the rear windscreen, and a lot of manufactuers put spoilers her to reduce the drag anway.
BIANCO said:
It’s the same affect that these modern swimsuits use which copy shark skin. I remember a program a few years ago which they put a film over a plane designed on the same principals and it did make it more efficient. Cant remember by how much though.
The problem was apart from cost of making and installing it in the first place. Was that the faster you go the smaller the dimples need to be so if you don’t consistently clean them they get filled with dirt and the efficiency decreases.
The shark skin effect and dimples are different.The problem was apart from cost of making and installing it in the first place. Was that the faster you go the smaller the dimples need to be so if you don’t consistently clean them they get filled with dirt and the efficiency decreases.
Edited by BIANCO on Tuesday 27th October 02:02
The shark skin effect is for streamlined bodies and basically constrains the boundary layer to channels (so it can't travel perpendicular to the flow), thus reducing turbulence and thus skin friction drag. They are also used on walls on some wind tunnels in order to reduce turbulence.
Dimples are for bluff bodies such as gold balls where form drag is much greater than skin friction drag - they purposefully generate turbulence in order to reduce drag by delaying the separation point and thus reducing the wake (as already mentioned).
The problem with both is that their effectiveness is highly dependent on the boundary layer size which in turn is highly dependent on the Reynolds number of the flow, which in turn is highly dependent on the speed of the body. So something that travels over a large range of speeds (eg. a car or plane) would need adaptable dimples or shark skin for it be really viable - obviously the manufacturing costs for this far outway the benefits.
navier_stokes said:
BIANCO said:
It’s the same affect that these modern swimsuits use which copy shark skin. I remember a program a few years ago which they put a film over a plane designed on the same principals and it did make it more efficient. Cant remember by how much though.
The problem was apart from cost of making and installing it in the first place. Was that the faster you go the smaller the dimples need to be so if you don’t consistently clean them they get filled with dirt and the efficiency decreases.
The shark skin effect and dimples are different.The problem was apart from cost of making and installing it in the first place. Was that the faster you go the smaller the dimples need to be so if you don’t consistently clean them they get filled with dirt and the efficiency decreases.
Edited by BIANCO on Tuesday 27th October 02:02
The shark skin effect is for streamlined bodies and basically constrains the boundary layer to channels (so it can't travel perpendicular to the flow), thus reducing turbulence and thus skin friction drag. They are also used on walls on some wind tunnels in order to reduce turbulence.
Dimples are for bluff bodies such as gold balls where form drag is much greater than skin friction drag - they purposefully generate turbulence in order to reduce drag by delaying the separation point and thus reducing the wake (as already mentioned).
The problem with both is that their effectiveness is highly dependent on the boundary layer size which in turn is highly dependent on the Reynolds number of the flow, which in turn is highly dependent on the speed of the body. So something that travels over a large range of speeds (eg. a car or plane) would need adaptable dimples or shark skin for it be really viable - obviously the manufacturing costs for this far outway the benefits.
Pics and video of the car from Mythbusters is here http://www.autoblog.com/2009/10/22/mythbusters-gol...
Hammerwerfer said:
TheEnd said:
I think they call it a Rabbit in the US, so the Golf link is lost.
The Mk I was called a Rabbit. Since the intro of the Golf II in 1985 it has been called a Golf in the USA as well.navier_stokes said:
The shark skin effect and dimples are different.
The shark skin effect is for streamlined bodies and basically constrains the boundary layer to channels (so it can't travel perpendicular to the flow), thus reducing turbulence and thus skin friction drag. They are also used on walls on some wind tunnels in order to reduce turbulence.
Dimples are for bluff bodies such as gold balls where form drag is much greater than skin friction drag - they purposefully generate turbulence in order to reduce drag by delaying the separation point and thus reducing the wake (as already mentioned).
The problem with both is that their effectiveness is highly dependent on the boundary layer size which in turn is highly dependent on the Reynolds number of the flow, which in turn is highly dependent on the speed of the body. So something that travels over a large range of speeds (eg. a car or plane) would need adaptable dimples or shark skin for it be really viable - obviously the manufacturing costs for this far outway the benefits.
Top post. The shark skin effect is for streamlined bodies and basically constrains the boundary layer to channels (so it can't travel perpendicular to the flow), thus reducing turbulence and thus skin friction drag. They are also used on walls on some wind tunnels in order to reduce turbulence.
Dimples are for bluff bodies such as gold balls where form drag is much greater than skin friction drag - they purposefully generate turbulence in order to reduce drag by delaying the separation point and thus reducing the wake (as already mentioned).
The problem with both is that their effectiveness is highly dependent on the boundary layer size which in turn is highly dependent on the Reynolds number of the flow, which in turn is highly dependent on the speed of the body. So something that travels over a large range of speeds (eg. a car or plane) would need adaptable dimples or shark skin for it be really viable - obviously the manufacturing costs for this far outway the benefits.
You are starting to see these on cycling time trial helmets:
http://gearjunkie.com/lazer-time-trial-bike-helmet
Apparently they can improve output by several watts of power.
http://gearjunkie.com/lazer-time-trial-bike-helmet
Apparently they can improve output by several watts of power.
ker knocked her up?prand said:
You are starting to see these on cycling time trial helmets:
http://gearjunkie.com/lazer-time-trial-bike-helmet
Apparently they can improve output by several watts of power.
"the Tardiz — which is an acronym for “time and relative dimensions in space”http://gearjunkie.com/lazer-time-trial-bike-helmet
Apparently they can improve output by several watts of power.
Well, it would be if it wasn't for the fact "space" doesn't start with "z"
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