Quote:
Originally Posted by JulianEdgar
I just saw this.
As with Aerohead's comment on the thickness of the boundary layer being of no consequence, it is also wrong.
If you wish to see this for yourself (anyone) just measure some pressures on real cars on real roads. On many cars, as indicated by the experts quoted above (surprise, that!), base pressures do not "mimic that at the separation line".
Here's a real life example from my measurements (side/wake and then centreline/wake):
...and from car company measurements (centreline/wake):
It's a good example of Aerohead just repeating what he has said before, and utterly ignoring any credible information that doesn't match his existing beliefs.
I know it's quite silly of me, but I was actually looking forward to Aerohead commenting on this thread, and potentially building on the latest information from some of the best car aero experts in the world. Especially, when there is so little on this specific subject in the textbooks - and it so strongly relates to our number one topic of reducing drag.
But I should have guessed that instead he'd just repeat same-old, same-old, complete with mistakes. Then, subsequently, defend those mistakes to the death, irrespective of any evidence brought to the contrary.
[Shrug] For everyone else, look and learn - I certainly am.
(And from Adrian Gaylard today in response to a last question from me:
Classically we’d think of the pressure gradient driving the boundary layer, which is essentially the way adverse pressure gradient driven separation is described. But energy loss at the surface generates the boundary layer. There’s usually more than one thing happening.) |
1) The Mercedes is not a 'full' body, with respect the 'entire' body it's derived from.
2) Your measurements, while representative of the given length of the Mercedes, would, in no way, reflect the context within which my comment was prefaced.
3) If 'half' of the Mercedes weren't missing, you'd be left with the thickest boundary layer and lowest drag, represented in the pressure profile of the missing body.
4) 'many' cars does not constitute 'all' cars. Measure a 'Kamm-back' and report back.( Renault Vesta-II, Mercedes-Benz Bionic Boxfish, Mercedes-Benz IAA, with tail extended etc..)
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Is Gaylard going to retract his ' flow separation due to the adverse pressure gradient' quote from page- 59 of his Doctoral Thesis?
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Viscous shearing forces, fed by momentum interchange from the local streamline does generate the TBL. That's classical boundary layer theory.
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An EcoModder's best dream come true would be to have the 'BIGGEST' boundary layer imaginable!