Quote:
Originally Posted by Bicycle Bob
"The air going under the car takes a straighter path to the rear than the air going around or over the car and according to Bernoulli's theorem,it's pressure would be higher than those other two pathways.-------------------------"
If the path for the air from the front stagnation point to the low pressure zone at the rear is very smooth, the pressure difference, along with the restriction from the ground, can move the air as quickly as the air going around. This is one of the major techniques to produce downforce for racing - the venturi bottom.
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I'm in town without the aid of my library(as usual).Relying on memory,and referring to Wolf Hucho's text,under vehicle flow will never reach ground speed velocity for typical passenger vehicles with typical ground clearance.He provides some quanta for anyone wishing to run some numbers.-------------------------- In the case of racing vehicles and record cars,sure,you can "idealize" the bottom of the car.Dr.Michael Seal of Western Washington University created the 100-mpg Viking series of cars with high ground clearance and an inverted airfoil underside to provide downforce.The smooth belly cut drag and the profile helped with added stability.-------------------------------- The other school is to lower the car into the weeds,with ground skirts and tunnel effects with diffusers.Whatever the sanctioning body will allow.------------ This second approach requires ground clearance which would not survive the light of day in day to day commuting.