A-Pillar Aerodynamics

[140Airpower]

I have noticed that cars are tending to have recessed windshields these days. The A-pillar is broader than previous habit. It appears that the A-pillar will guide air flow around and keep it attached. My question is this, does recessing the windshield by about 1 inch allow this to work?
I had formally believed you would need a slat to take the air flow off the windshield, turn it an lay it onto the side glass.

 

[GregLocock]

I think you need to recalibrate your ruler. Just checking on a Mundano, the recess is of the order of 3mm beneath the surrounding sheet metal.

Quite how they manage to get the airflow to remain attached around the A pillar is not known to me, and is something that has only become common in the last 20 years.

Cheers

Greg Locock


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[140Airpower]

Greg, some are recessed as deep as an inch or more at the bottom, tapering to just shy of flush at the top. I don't know that the flow stays attached to the A-pillar all the way around. I know that you can make an A-pillar fairing that sticks up several inches and dams the windshield air forcing it to spill over the fairing and follow its surface around. I was skeptical that a small recess would do it. Nevertheless, the A-pillar treatment is different these days from years ago.
I also believe that a slat will do the job, but nobody uses one.

 

[GregLocock]

Ah OK, yes I think I've seen that style. It may be acting as a splitter I suppose. Alternatively in days of yore people would deliberately 'trip' the airflow to 'energise' the boundary layer which helped it attach rather than separate. I use quotes as that was the terminology used but haven't heard an aero guy ever say the same sort of thing.

Cheers

Greg Locock


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[140Airpower]

Greg, I looked up some info and found some discussion of A-pillars. It seems what they are doing is effective at reducing wind noise by as much as 10dB or more. The windshield is recessed, increasing the influence of the A-pillar shape. The A-pillar is broader and the flow stays attached farther around the curve, but far from all the way. The mirror is also critical for noise. Separating it a little farther out from the body helps. Look at this:

http://www.srcosmos.gr/srcosmos/showpub.aspx?aa=14847

 

[GregLocock]

That's a nice paper.

Cheers

Greg Locock


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