Reducing skin friction question.
Discussion
Watching the olympic swimming I noticed a few of the swimsuits seem to be designed to trap a layer of water on the surface of the suit and reduce friction by having water then flowing over water rather than the suit material.
Animals like sharks and fish seem to have rough skins which I thought did the same thing by trapping a layer of water on the surface of the skin and again reducing friction.
Why doesn't this work on aircraft or racing cars where a rough rather than smooth surface could trap a layer of air on the surface making air flow over air and reduce skin friction?
Animals like sharks and fish seem to have rough skins which I thought did the same thing by trapping a layer of water on the surface of the skin and again reducing friction.
Why doesn't this work on aircraft or racing cars where a rough rather than smooth surface could trap a layer of air on the surface making air flow over air and reduce skin friction?
El stovey said:
Watching the olympic swimming I noticed a few of the swimsuits seem to be designed to trap a layer of water on the surface of the suit and reduce friction by having water then flowing over water rather than the suit material.
Animals like sharks and fish seem to have rough skins which I thought did the same thing by trapping a layer of water on the surface of the skin and again reducing friction.
Why doesn't this work on aircraft or racing cars where a rough rather than smooth surface could trap a layer of air on the surface making air flow over air and reduce skin friction?
I used to know and then I forgot. Animals like sharks and fish seem to have rough skins which I thought did the same thing by trapping a layer of water on the surface of the skin and again reducing friction.
Why doesn't this work on aircraft or racing cars where a rough rather than smooth surface could trap a layer of air on the surface making air flow over air and reduce skin friction?
I'll try to find out....I remember quite a few years ago, when some timetrials/sprint cyclists wore dimpled helmets (like big golf balls) but they're all pretty much smooth domes again now.
Perhaps it's a scale thing. Small golf ball with small dimples=better aerodynamics. Big object with big/or small dimples=worse or no better aerodynamic benefit.
Perhaps it's a scale thing. Small golf ball with small dimples=better aerodynamics. Big object with big/or small dimples=worse or no better aerodynamic benefit.
Well I'm no thermodynamicist, but perhaps it's because fluid molecules are actually touching each other, whereas gas molecules are not and bounce against each other instead. So in the case described, it makes sense to have the gas molecules move as cleanly as possible, but with a fluid, you want the molecules moving against other fluid molecules rather than solid molecules (eg skin). Maybe.
Edited by Neil_H on Wednesday 13th August 12:54
Effects like this don't scale with physical size and velocity or apply equally to fluids of different viscosity and density. See Reynolds Number. So an effect which works in water for .2mm denticles on the skin of a 2m long shark cruising at 5 mph might not work on a 4m long racing car at 180mph. As I understand it, however, similar effects are exploited in the surface treatments of fast jets, using fine grooves rather than teeth.
Some stuff here:
http://www.stanford.edu/group/ctr/articles/tackle....
Some stuff here:
http://www.stanford.edu/group/ctr/articles/tackle....
dave_s13 said:
I dunno, but if you rub olive oil on your nipples before going for a run it stops them getting sore 
It probably has something to with the laws of thermodynamics and such and will have been thought of and dismissed, several times, by minds far greater than mine, or yours.
Apparently man-fat works very well on ladies nipples too It probably has something to with the laws of thermodynamics and such and will have been thought of and dismissed, several times, by minds far greater than mine, or yours.
The suits they are all wearing are speedo LZRs - they reduce friction in the water and also provide compression, i.e they stop your skin wobbling around (hard to explain, video of it on youtube)
Im not 100% on the science of dimples, but i know its something to do with helping smoth turbulent airflow.
Zipp (who make bike wheels) dimple the rims and hubs of their wheels to aid aerodynamics. As for helmets, the majority are dimpleless as the airflow around your head is laminar on a bike, and they dont have a great benefit.
Golf balls, its a distance thing as far as im aware - they fly around 3-4 times as far as a non dimpled ball.
Engineer and triathlete geek
Im not 100% on the science of dimples, but i know its something to do with helping smoth turbulent airflow.
Zipp (who make bike wheels) dimple the rims and hubs of their wheels to aid aerodynamics. As for helmets, the majority are dimpleless as the airflow around your head is laminar on a bike, and they dont have a great benefit.
Golf balls, its a distance thing as far as im aware - they fly around 3-4 times as far as a non dimpled ball.
Engineer and triathlete geek
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