Quote:
Originally Posted by freebeard
Which is to my point. If you have contact with Dr. A. Gaylard ask him this: All talk about boundary layer references free air. The underbody is a plenum with four open sides and two [relatively] moving walls. I know that when testing motor oil (analogizing from engine theory, I know) what they use is two concentric cylinders with an oil film between. The shear forces can tear oil molecules apart.
So the condition in the underbody should be shear forces instead of boundary layer. Or, I'm wrong. Whichever.
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You are implying that the boundary layer under the car extends between the underbody and the road. (That is, it's the shear forces that are most germane.) This is not the case in any modern car that has a smooth underfloor. It may, however, be the case with old cars with rough underbodies that have a very low ride height.
I have bought multiple pitot tubes so that I can directly measure boundary layer thickness, but I doubt I'll be doing that under the car (too easy to lose them over a bump).