Dusty car base areas

[aerohead]

Originally Posted by JulianEdgar

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

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.'

[JulianEdgar]

Originally Posted by aerohead

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.

[aerohead]

Originally Posted by JulianEdgar

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

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.

[JulianEdgar]

Originally Posted by aerohead

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.

[aerohead]

Originally Posted by JulianEdgar

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 ( 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.

[Cd]

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.

[aerohead]

Originally Posted by California98Civic

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.

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.

[aerohead]

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.

[freebeard]

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.

I've seen this.

It's why air curtains work.

[Phase]

I’ll just add mine again