Quote:
Originally Posted by Vman455
Now that's interesting!
I measured pressures down the side of the car and in the wake with air curtain ducts (front and rear, but a different design from Julian's, made of sheet metal). I found no change on the doors and wake (both directions showed exactly the same pressure with and without ducts), but a +10 Pa difference on the (tapered) bumper cover behind the rear wheels. Fuel economy testing suggests that overall the ducts are reducing drag slightly; I wonder if this is how?
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Yes, very interesting - and thanks for reminding me.
But if we look at the angle of that rear bumper taper, and do a forward force triangle diagram from that increase in pressure, it has to be really tiny ie the taper wouldn't be more than about 10 degrees, would it?
But I can certainly see a change in pressure there having an influence on the
wake pattern.
I posted my video to Linkedin, and I have some contacts there who are professional aero people - both CFD and wind tunnel. I've asked if they have any ideas about the relationship between side pressures / degree of attachment and resulting drag.
I just always took it on face value that 'improved side flow attachment = lower drag' but like all aspects of car aero, the more you think about it, the less you realise you know.