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dontlifttoshift
11-14-2012, 10:59 AM
Came across this pic in my quest for useless knowledge today.

Can anyone dechiper this? What do the different colors represent? Some lines are straight and others twirl around, I think I have a grip on it but thought maybe someone smarter than me could make sure I don't interpret it incorrectly.

Thanks!!

dontlifttoshift
11-14-2012, 11:05 AM
duh, forgot the picture......

67502

exwestracer
11-14-2012, 01:04 PM
Just looking at it I would have to say relative air pressures with blue being low and red being high. Green is possibly 1 bar reference? The rear wing either isn't factored in (likely) or they are getting **** for pressure differential...

cornfedbill
11-14-2012, 01:27 PM
Yes, this is the relative air pressure as Ray has pointed out. As you can see, the red indicates pressure against the front of the car. The blue represents the low pressure over the roof that tends to lift the car. Likely the filter removed the lines on top of the wing to make the picture easier on the eyes.

The C6R is one cool ride. Two of my sons used to work at Pratt and Miller, and made body panels for these cars. I had the chance to visit the shop there. It is one awesome toy store!

dontlifttoshift
11-14-2012, 01:55 PM
One thing that really struck me are how far out (forward) the high pressure is in front of the car. It really illustrates how effective a splitter is.

Bill, when you say low pressure that tends to lift the car, do you mean negative pressure?

......is that air being sucked out the rear wheel well?

jpgolf14
11-19-2012, 01:56 PM
One thing that really struck me are how far out (forward) the high pressure is in front of the car. It really illustrates how effective a splitter is.

Bill, when you say low pressure that tends to lift the car, do you mean negative pressure?

......is that air being sucked out the rear wheel well?

Its not negative pressure, but rather a relative pressure. Just like an aircraft wing, if the pressure on the top of the car is lower than the pressure on the bottom of the car, then the difference in air pressure will lift the car. From a lift point of view, the actual value of the pressure is not important, only the difference between the two.

Regarding the front. Yes, because the car is traveling at less than the speed of sound, the air molecules get adjusted by the car. Basically the car is telling the air to get out of the way.

dontlifttoshift
11-19-2012, 03:11 PM
What is the pressure on the bottom of the car, under the car? Should be close to whatever barometric is or am I way off. So the air over the top of the car would be high speed/low pressure?

jpgolf14
11-20-2012, 03:52 PM
What is the pressure on the bottom of the car, under the car? Should be close to whatever barometric is or am I way off. So the air over the top of the car would be high speed/low pressure?

Yes, the air under the car. As you point out the high speed air over the top of the car creates a low pressure.

If we consider the conservation of mass, all the air around the car is conserved, it is not created or destroyed. So the car splits the air flow, some goes over the car, some goes under the car. Basically the airflow that splits apart at the front of the car needs to recombine behind the car. The air traveling underneath the car has a shorter path to the combination point than the air traveling over the car, simply due to the shape of the car. So the air moving over the car has to move faster than the air under the car. Faster flow = lower pressure. Low pressure on the top = lift.

exwestracer
11-21-2012, 06:26 AM
Part of the reason there is so much air "stacked up" in front of the car is the designers are doing everything they can to keep that air from going UNDER the car. Hate to bring NASCAR into a technological discussion..., but watch how those cars run right down to the ground at speed. It's not the air pushing against the front that gives them downforce (well..really it IS) but the LACK of air under the car is what creates the differential pressure.