testing aero. of a caravan
 

Ran across these on You-Tube:
https://www.youtube.com/watch?v=karGqjCZOV8

Thats a very dirty wake. Must be room for huge improvement

huge
 

NASA says kill the gap,then boat tail it.

Would a kammback help if boat tail is too long

What about that "part 2" video with the topper? Is that better or worse?
https://youtu.be/sweZltfD-no

I'd go with different. They missed a bet not putting the two videos one above the other and matched in speed.

It's interesting to watch the lines approach from the left. There's some initial noise that damps down to straight lines, but they aren't erased so it obscures the initial approach. There appears to be turbulence building up ahead of the rooftop container, it might be caused by the airgap between the topper and roof.

The topper seems to create a locked in rolling vortex ahead of the trailer, similar to a half-tonneau cover on a pickup.

What do you think about the area above and behind the trailer? With the container the disturbed air rises higher, even out of the rendered flow lines, but it looked somehow more orderly to me.

kammback
 

Technically speaking,a K-form tail (Kamm-back) is just a shortened ideal tail (boat-tail),or vice versa.
Here you can see how Koenig-Kamm experimented with different lengths of this K-form at the FKFS,next door to Daimler-Benz in Stuttgart.
http://i1271.photobucket.com/albums/...titled5_17.jpg

topper
 

My gut feeling is that this is a low-cost,2-dimentional CFD program,that they don't achieve a critical Reynolds number flow,and while interesting to watch,and trends may be reflected,we'd want an expensive,corporate-level,3-D program to provide a more real-world representation of how things would be.
I don't think the streamline filaments would behave the way they're depicted.

above and behind
 

I'm not really convinced that we're seeing flow as it would actually occur.
Here are some comparison images
http://i1271.photobucket.com/albums/...titled10_9.jpg
http://i1271.photobucket.com/albums/...ntitled8_9.jpg
http://i1271.photobucket.com/albums/...head2/2239.jpg
http://i1271.photobucket.com/albums/...head2/2234.jpg
http://i1271.photobucket.com/albums/...head2/2226.jpg
http://i1271.photobucket.com/albums/...ohead2/227.jpg
http://i1271.photobucket.com/albums/...d2/06-2835.jpg
http://i1271.photobucket.com/albums/...Untitled-5.jpg
http://i1271.photobucket.com/albums/...titled8_10.jpg
http://i1271.photobucket.com/albums/...itled10_10.jpg

After watching it, YouTube offered up this gem:
https://www.youtube.com/watch?v=0577mRifVfI

Improved aero over most trailers, but the really interesting thing is the hydraulic lowering by rotating the entire suspension assembly.

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

http://i1271.photobucket.com/albums/...head2/2239.jpg

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.

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

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:

https://upload.wikimedia.org/wikiped...-animation.gif

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


https://upload.wikimedia.org/math/7/...48ee53b56a.png

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

listening
 

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!:thumbup:

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.