Scale model RAM pickup smoke flow

[kach22i]

Originally Posted by aerohead

Here's a second video by same folks.
You'll notice the separation behind the 'aeroshell'.
Then, when smoke is introduced into the wake, the smoke momentarily indicates the outline of the preferred contour for fully-attached flow.

Yes I see that.

However at the 1:50 mark they put in a version of an aeroshell that does not perform very well.

From I can tell the air should remain attached for over half the arc, but does not. Why is that? The space between cab and gap just too disruptive?

[aerohead]

Originally Posted by kach22i

Yes I see that.

However at the 1:50 mark they put in a version of an aeroshell that does not perform very well.

From I can tell the air should remain attached for over half the arc, but does not. Why is that? The space between cab and gap just too disruptive?

One guess is that, because it's a 'small' model, and would need to be equivalent to at least 20-mph at full-scale to have a chance for attached flow, that it's demonstrating a sub-critical Reynolds number and a laminar boundary layer, just like a golf ball without dimples.
1/4-scale is the minimum a car company will use for wind tunnel testing.
1/24th-scale would require a minimum 420-mph air velocity, and you'd be experiencing supersonic shockwaves.