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Old 10-22-2020, 09:02 AM   #1 (permalink)
Vman455
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Negative pressures on forward-facing surfaces

I read something interesting the other day about the non-intuitive nature of aerodynamics: It is possible, the author claimed, to shape the front of a car such that most of the surface is exposed to negative differential pressure and thus contributes thrust. Most people, he went on, don't see how this could be since they think, intuitively, that air behaves the same as a moving solid would, "hitting" the front surfaces exposed to flow and thus exerting positive differential pressure on them.

Well, could that be true?, I wondered. In order to find out, I took some centerline pressure readings on the front of my car, which is just the sort of continuous curve the author recommended. The results:



Yes! In fact, the pressure is below atmospheric from just above the emblem, all the way up the hood, and then across the upper part of the windshield.

I used a digital manometer and pitot tube ($50 on Amazon), 40 feet of clear vinyl tubing, one of my new Scanivalve pressure patches (less than $10), and some painter's tape to gather this data.

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