[aerohead]

I'm not current on this topic.In years past,experiments with turning vanes succeeded in moving air behind a bluff body,but the downside was that air would separate behind the vanes themselves,for a net overall drag increase.---------------------- In ductwork,vanes can create constant area flow around a corner,with virtually zero turbulence.I use them in my wind tunnel,they work great.------------------ When they're used to create an air curtain over a steep backlite to control back-soiling of the glass,it may be a conscious concession to higher drag for the sake of clear rearward vision.