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Originally Posted by freebeard
My disappointment was that the digram you showed and ask us to imagine 3D showed the flow over and under the car but it was all about side pressures.
There is a silent minority at Ecomodder who hold that the air is standing still and it's the vehicle that is moving. 
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.
I have an idea for easy 3D diagrams, maybe I can prepare an example. |
Excellent points.
Regarding moving air Vs moving object, I've tried to discipline myself several times on this topic but continue to fall short. I can get half way there if I try, but only for short periods of time.
1. When imagining pressures at the front of the car I can successfully imagine the air being still and the car slamming into the air molecules.
2. When imagining drag pulling back on the moving body/car
parasitic, vortexes, and low pressure described in opening post of this thread.
All other times I revert into thinking the air is moving, and my obsession with wind tunnel images with smoke doesn't help me there.
Regarding air pressures under the car, just use them so they aid handling at speed. Accept that it will be there, and manage it.
Car Aerodynamics Basics and How-To Design Tips cont…
https://www.buildyourownracecar.com/...-and-design/4/
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Diagram AD8. The Venturi tunnel shape increases the velocity of the mass of air flowing through it, lowering the pressure and generating downforce.
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The pressure differentials at stern of moving vehicle result in unwanted turbulence and vortex formation.
I think information is out there, we just gotta remember where we have posted it before.
