Dusty car base areas
 

Toyota RAV 4 Hybrid:

https://i.postimg.cc/8cpFLpLP/IMG-1139.jpg

Toyota Land Cruiser Prado:

https://i.postimg.cc/KYt4VkN8/IMG-1249.jpg

Land Cruiser Prado showing interesting roof separation - airflow tripped by panel margin:

https://i.postimg.cc/CxPWgmcv/IMG-1091.jpg

And, then, on another occasion, you can see that on the same car the airflow remains attached across the upper surface of the rear spoiler:

https://i.postimg.cc/4xnM4p7B/IMG-1248-cropped.jpg

(The owner gets their car serviced at the local garage, that I walk past frequently.)

And another - very 'feathery' separation line down the side.

https://i.postimg.cc/FzydwPQz/IMG-0665-cropped.jpg

Lack of attached airflow under rear 'wing' - that's really acting as a spoiler. (Or as a partially stalled wing, I guess.)

https://i.postimg.cc/TwWC5Xns/IMG-0167-1.jpg

I have tons of photos like this of my car from the El Mirage dry lake bed here in Southern California.

In these, I like the contrast in the dust patterns between the first Toyota pic and the blue Peugeot. Seems the Toyota people got much better results for the flow along the sides of the vehicle.

EDIT: or maybe the Peugeot was traveling at a yaw angle to the wind.

Blue car is a Holden Astra (same as Opel Astra). Yes, RAV 4 hybrid is amazingly clean down the sides.

This is my favorite dust picture:

https://ecomodder.com/forum/member-f...4-hpim1176.jpg

...because it shows the various vortexes on an open wheel, Outward at the bottom and rearward at the center and top. The wheel carrying dust forward of the centerline is just icing on the cake.

Yes it's interesting, but for me at least, doesn't help at all in our modifying cars. On the other hand, dust deposition on road cars is a very powerful tool in seeing aspects such as separation lines, changing airflow behaviour on different days (eg the Prado), etc.

You have shared this photo a bunch of times, and I never regret the repeat. One of the best shots ever taken for seeing aspects such as separation lines, visualized here beautifully over the front tire and aft of the passenger compartment. You can see the recirculation zone behind the tire recapitulated behind the car and easily connect the principle to the dust sticking on the base area. Would be an excellent teaching tool. In fact, next time I am at El Mirage, I'll see if I can get still shots of dust deposits on one of the roadsters that can compare to this.

feathery
 

This area may denote the 'bistable' flow Hucho attributed to angles within the 28-degree-to 32-degree range, where the separation line jumps between a fastback and squareback wake pattern.
Something perhaps which showed up in an anechoic / accoustic wind tunnel as 'booming.'

The rear hatch angle is nowhere in the range you have described.

https://i.postimg.cc/HWvQsDbD/rt-i-h...-s-r-00-65.jpg

hatch angle
 

I'm referring to the sides. They're unbounded by 'burst edges' which might 'fix' the separation line.
We don't have an overhead view.

In that case you're confused, I think.

Hucho's reference to bistable flow (in your words - 28-degree-to 32-degree range, where the separation line jumps between a fastback and squareback wake pattern) is nothing to do with boat-tailing, it's to do with the vertical angle of the rear hatch.

The lack of separation edge is obviously causing the feathery side separation - nothing to do with hatchback versus squareback flow patterns.

bistable
 

Bistable ( Hucho's word ) would not be limited to the rear slant angle.
Separation and re-attachment, or the lack thereof may occur anywhere in the aft-body.
While it's inefficiency may be absorbed within the confines of the specification of the vehicle, drag-wise, it may turn out to be objectionable, noise-wise, requiring a change to body tooling in order for noise abatement, something enforced in the USA.

Saw this today. Of note, is how that the dust shows detached flow just behind the emblems on the door, yet it does not show any just behind the wheel on that fender flare.
The air is such a mess there that I would speculate that it just causes the dirt to stick there regardless.

https://ecomodder.com/forum/attachme...1&d=1677778239

'dust'
 

When NASA was conducting their truck aerodynamics testing at Edwards Air Force Base, they used diatomaceous earth to help visualize the airflow dynamics.
In college, the Lubbock, Texas area provided many, low traffic caliche roads , with silt so fine that, generating high-contrast separation lines were a no brainer. Very much like El Mirage Dry Lake, California, near Adelanto, where we used to race motorcycle T-T scrambles.:)

'RAM side soiling'
 

If you'll tail the truck during the rain event, you'll witness a horizontal geyser exploding out each side of the truck. At the rears as well.
The soiled water has much higher density than the air in the same area, and indicates telltales a little different than what the air would.
Capillary action allows the watermark some contiguous streaking which would also not be present in the airstream.
Analyzing the reattachment point behind the emblems, based upon their thickness would be qualitatively instructive.

I've seen this.

It's why air curtains work.

I’ll just add mine again

What do you think makes the vertical striatioins under the spoiler and tail lights and along the bottom?

The only thinbg I can thing of is inverse Cymatics.
The buffeting air is vibrating instead of the car. A tiny sucking sound.

I would guess those marks are owner generated. I get them on the golf because you have to handle the rear hatch to get it open to load.

Under the taillights?