Will these strakes cause more drag ?

[JulianEdgar]

Originally Posted by Cd

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 ?

There's not a lot on the literature about A pillar flow, and the tests you've cited that I did are the only ones I have done with A pillars (except I also filled the windscreen step by placing tape over it, and it didn't help flow on the side glass). But two points:

- Rob Palin (ex Tesla) told me they spent a lot of time in the wind tunnel smoothing the flow of the Tesla Model S around the A pillars.

- I see the tuft pattern as being indicative of the generation of trailing vortices coming off the A pillars. Normally, you can see a re-attachment line on the side glass a bit behind where this 'vertical' tuft behavior is occurring. Using the eroding clay technique allows you to map the separation and attachment quite accurately.

[JulianEdgar]

Originally Posted by JulianEdgar

There's not a lot on the literature about A pillar flow...].

I actually wondered if I had this right and went and looked at the Aerodynamics of Road Vehicles (5th ed). It says in summary:

"A complete investigation of the flow around the windshield of a real car and its surroundings still does not exist..." (Page 273)

What it does say about reducing A pillar drag is all about smoothing airflow around the pillar ie making it as a large a radius as possible to prevent separation. Any material on 'steps' etc is about preventing water flow from the windscreen onto the side glass.