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Old 02-24-2011, 11:07 PM   #133 (permalink)
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Originally Posted by NeilBlanchard View Post
...The atmospheric pressure can push air at a certain rate, and given a little longer time (i.e. at a lower speed) then wouldn't a steeper trailing angle work just as well at low(er) speeds?....
Hi Neil,

As you move through the air faster, and the air is split apart by the moving body, the local pressure at the split area is also higher.

As the body passes and the air starts moving back to it's original spot again, the higher local pressure can move the air back to it's original location faster because of the higher local pressure.

There are limits to this of course, but the speed in which the air moves back again is not proportional to the speed at which the body moves through the air.

BicycleBob and AeroHead have elaborated on this before.


Not quite applicable, but I typically use subsonic orifices to calibrate equipment on occasion and it's interesting to note that the air velocity increases due to inlet pressure are not linear at subsonic values.

If you double the inlet gage pressure to the orifice, the resultant flow rate is only increased about 50%, not double like you would expect. As you get towards sonic flow this ratio slows down even more.


Last edited by 3-Wheeler; 02-25-2011 at 01:26 PM..
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