Quote:
Originally Posted by MazdaMatt
2.5 degrees steady? could it not curve upwards? ie, if i did make it curve upwards, would flow disconnect at the 2.5* point of the curve?
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I don't think you want to curve it upwards. A diffuser is different from the roof surface or top plane of a boat tail in which you are fighting flow separation only. In a diffuser your main boogeyman is flow reversion because you are typically flowing into a negative pressure gradient. This is because assuming you have an effective front air dam and belly pan ahead of the diffuser the air pressure underneath the car is lower than the air pressure in the wake, but we all know because the vehicle is moving relative to the road air will indeed flow against the negative pressure gradient and the diffuser needs to be very shallow to make it happen cleanly.
Take a look at some of the touring race cars, specifically I'm thinking of the Corvette C6R, had a very prominent diffuser. In many of these vehicles I think they're going for downforce since the diffusers typically have a horizontal plane or splitter on the bottom.
I was behind a Prius in line for a tollbooth today and noticed that the lower edges of the rear fenders/bumper cover behind the tires act as quasi-diffusers. It's only missing a few vertical sails and a smooth taper under the car away from being a better diffuser.