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Old 06-08-2021, 09:37 PM   #561 (permalink)
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I know in the Darko wind tunnel they put a metal mesh upstream that affected the attachment through the throat.


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Old 06-09-2021, 01:59 PM   #562 (permalink)
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what works

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Originally Posted by freebeard View Post
There's got to be a line somewhere between what works and what doesn't. So -- 1/4 to 1/5th for air and 1/8th for water?
If anyone here has Hucho with them, he made a comment regarding the development of the Vanagon.
Minimum leading edge radii required to guarantee attached forebody flow on the scale model were found to be excessively large when in full-scale, even though they had the Reynolds number dynamic similarity covered.
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Old 06-09-2021, 02:02 PM   #563 (permalink)
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mesh

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I know in the Darko wind tunnel they put a metal mesh upstream that affected the attachment through the throat.

My thought is that, the mesh was just there to protect the flow-straightener egg-crate from damage, should some random jetsam get in there.
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Old 06-09-2021, 06:30 PM   #564 (permalink)
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The guy running it said some thing about attached turbulence in the test section before they added it.
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Old Yesterday, 10:05 AM   #565 (permalink)
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before they added it

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The guy running it said some thing about attached turbulence in the test section before they added it.
Seems like any turbulence attributed to the screen would be insignificant compared to the turbulence created within the deep, egg-crate flow straightener at the jet.
Gary Eaker could probably tell us about that.
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Old Yesterday, 10:31 AM   #566 (permalink)
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about scale models.......................

I went back through Hucho.
What I was remembering, turned out to be about the 1951 VW microbus, compared to the 1969 Vanagon.
Pawlowski published on minimum leading edge radii requirements in 1930.
Lay's research in 1933 confirmed the efficacy of Pawlowski's work.
M'o'ller, in 1951, did not use Pawlowski's geometry for the VW bus.
It turned out that, the 1951 design would have had no greater drag, if the front radii had been just a fraction of what was used.
--------------------------------------------------------------------------------------
With respect to scale models:
Hucho suggests that anything below 1/4-scale would be good only for 'qualitative' investigation. You would not be able to do 'quantitative' work below that 'size'.
In the United States, the typical minimum model scale is 3/8ths, as of 1986.
Hucho said that 1/4-scale results are identical to 1:1-scale.
In 1991, Texas Tech University was using 1/24-scale in their small water tunnel, for food coloring-injected flow imaging. Only.
For underwater tow-testing and actual drag measurements from an overhead gantry bridge- supported sting, they used a 3/8-scale model, and SCUBA divers for close observation and image capture.
Ford paid $ 68,000 for a highly accurate 3/8-scale Ford Taurus model, with clear plastic hood ( bonnet ), complete with all engine bay structures, to develop CFD code. Model velocity was 2-mph.

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