Sorry for being confusing.
What I'm wondering is if a 'fence' was directly in the path of air that is headed to a low pressure area and the fence is able to redirect and straighten it, would you still have some spillover that would trip over the fence and go turbulent.
And Julian, yes, I meant air separating and then going turbulent.
BTW, I recently came across your A pillar " side curtain " video.
This is just what I was after, since I am trying to change the direction of tufts on the sude of the car.
I'm already making plans to create some.
So I'd like to ask what is happening around the sides of our cars' A pillar windows as the tufts point towards the roof, rather than straight back.
I know this is due to the tufts being pulled to where there is a change in air pressure ( low pressure, correct ? )
But if the tufts are pointed straight up to the roof, but are steady and not fluttering, this seems to show that the airflow is attached - but since they are pointed away from the rest of the flow, is this a sign that this is a problem area that could be corrected ?