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Old 06-26-2019, 07:15 PM   #49 (permalink)
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Originally Posted by NeilBlanchard View Post
At the front of the belt, the boundary layer of air IS stationary - so the moving belt would accelerate it.

If there was a streamlined plate that had a moving belt, was raised up and was in contact with the wheels, then that might improve the "accuracy" without additional measures to try to correctly mimic a rolling car on a road?
Only the 'layer' of air in contact with the floor; above that, there is a velocity gradient and at the top of the boundary layer, the velocity is the same as free stream velocity.

I think I see what you're saying now--the transition from the stationary flow to the moving belt, where the belt speed is the same as free stream velocity (we aren't talking about testing cars at 160 mph here...). But that's precisely why a suction slot is needed to vacuum off that boundary layer; you just get rid of it to ensure you have one boundary layer forming under the car as in a real car on a real road. I suppose you could elevate the moving belt to get it above the boundary layer over the stationary floor, but as aerohead mentioned, then you run into the issue of the airflow accelerating over the shoulder you've introduced by raising the belt and roller.
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