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Old 06-26-2019, 11:10 AM   #46 (permalink)
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moving floor

Originally Posted by NeilBlanchard View Post
To accurately measure the drag of a car, it has to be on the ground. So, raising the car is not what you want to do.

I am talking about the effect the moving belt (and its surface texture) has in the wind tunnel. It would accelerate the air in the boundary layer, in the direction of the air in the "middle" of the tunnel. And this would lower the pressure of the boundary air at the front of the belt.

By vacuuming air out of a slot at the front of the belt - this would further lower the pressure there. And it would reduce the amount of air that would be accelerated by the belt. Which is "artificially" affecting the air pressure under the front of the car.

My take is that air would need to be ADDED at the front of the belt; not removed - to offset the effect of the moving belt.
*A consideration is how far away from the settling chamber,or tunnel jet,does the moving road begin.There could be hundreds of feet of tunnel floor,wall,and ceiling for boundary layer growth before the air ever gets close to the test section and moving floor.That would have to be managed.The boundary layer could be as thick as on a short railroad train.
*Since the moving floor does not span the entire width of the test section,you'd have a differential floor boundary layer thickness,depending on location.
*If the belt is moving at exactly the same velocity as the airflow,that's one thing,if not,compensation must occur.
*And the Bernoulli effects of a 'blown' jet could perturb the streamline filaments you've spent $millions to create for your 'source',demanding vigilance with air management.
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