testing aero. of a caravan

[freebeard]

That's actually kinda neat. The lowrider and extreme camber crowds will see the utility. Lay frame.



This is quite literally the proverbial 'blue smoke and mirrors', but what it puts me in mind of is polarized light. If you have a material that varies in thickness between two polarizing filters at an angle to each other white light gets bent into various colors. Water might work better than air. Even if the wavelength only varies by a few angstroms a high resolution capture with false color imaging should allow you to view a run from some narrow angle.

Circular water tunnel and orbiting polarizer. Filters displaceable in the longitudinal direction for 3/4 front and rear views.

[freebeard]

Originally Posted by myself

...polarized light...

Replying to myself again. I can't link into the middle of a Youtube video, but at 8m08s in it talks about Boeing's wind tunnel with an array of 100 microphone that listen to the air flowing over the aeroform.

https://www.youtube.com/watch?v=D43tP4PtPLU

[gone-ot]

Originally Posted by freebeard

Replying to myself again. I can't link into the middle of a Youtube video, but at 8m08s in it talks about Boeing's wind tunnel with an array of 100 microphone that listen to the air flowing over the aeroform.

There's a formula for estimating the sound (HZ) waves created by air turbulence over smooth surfaces...works on the nutating (left/right and up/down) wanderings of the air pressures as they are created within the air turbulence. I'd guess that's what the microphones are listening for.

This Wiki illustration shows *how* this sonic (Von Karman vortex) nutation occurs:



from this Wiki page: https://en.wikipedia.org/wiki/K%C3%A..._vortex_street




where "ƒ·d/V" is called the "Strouhal Number" and:

f = vortex shedding frequency
d = diameter of cylinder
V = flow velocity

A published UK workshop presentation: http://wwwf.imperial.ac.uk/ssherw/bb..._Meneghini.pdf

...and a NASA paper: https://info.aiaa.org/tac/ASG/FDTC/D...-1218-1989.pdf

[aerohead]

In the movie,"Who Killed the Electric Car," there is a brief sequence shot inside the GM wind tunnel,of Dr.Paul MacCready 'listening' to the boundary layer of the GM/AeroVironment 'Sunraycer' electric race car.
Paul was using the static pressure tap of a Pitot tube with a stethoscope to hear the 'rustle' when the LBL transitioned over to TBL.Clever!
Perhaps unidirectional microphones can discern the same thing.Cool!

[freebeard]

The Boeing wind tunnel has 100 microphones (on at least one traveling pickup) so they can create a virtual three-dimensional model of the sound waves. They demonstrate that the areas of concern are the landing gear and control surfaces, especially in the gaps that open up when a flap or elevron articulates.