First I'd like say that since this is going to be a long post I might forget something or might make some slight errors
Well lets start by some important information conserning fluids.....which help to understand how the underbody works.....
First....Bernoulli's law (principal, whatever you call it
) in a general way states that the fast the air flows the lower the pressure of that airflow is.
Now Venturi states that if the amount of fluid passing through a determined area stay constant even with "channel decreases in size"
Example: V1 * A1 = V2 * A2.....so if
V1=1 A1=1
V1*A1=1
so if A2 is smaller then A1....the speed will have to go up!
V2=2 A2=0,5
V2*A2=1
And lets not forget that fluids always flow from a high pressures to low pressures!
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Now the the explanation..the underbody can be cut into 3 parts....the intake, the plane and the diffuser.
First lets look at the underbody as a whole object...the main idea of the underbody is to make air pass as fast as possible under the car, creating a low pressure system under the car...this will create 2 situtations...first the air moving around the car will tend to move to the lower pressure under the car but since the bodywork is in the way...the motion of air will push the car down! The other situation is more or less what happens with a vacum cleaner when you put the nozzle to the ground....it will tend to stick to the ground.
Now lets look at the intake....the intake of the underdosy has to be designed in a way the will produce an aceleration of the airflow that goes under the car....so one of the best ways of doing is by creating a small venturi tube....where V1 is the speed of the undisturbed air coming from under the front wing and A1 is the width of the intake the high from the tip of the intake to the ground......then the intake is pointed down....this will make the high to the ground slightly smaller so the air will tend to speed up in order to keep a constant airflow! This will produce the first aceleration under the car! (this part is well explained in the April issue of Racecar engineering magazine)
Now the plane....this part of the diffuser doesn't have a very important job in the downforce creating process!So lets skip it!
Now looking at the diffuser....the diffuser is basicly the oposite of the intake...so the area will be increased drasticly....but!!! (I love this word
)....if you've been paying attention you'll know that due to the Venturi effect the airflow will slow down with the increase of area....which won't help the low pressure system under the car....but with the drastic increase of volume the airflow will slow down....but the density of the air will decrease and there is a pressure drop in the diffuser...this will also help creating and maintaining the low pressure system under the car, which since it's a lower pressure then in the plane area of the underbody, will speed up (a sucking effect) the air in the plane (cause the pressure in the plane it higher then in the diffuser).
I have left out some info cause to get a general picture of how it works isn't very important! But the info I left out is basicly info conserning the lose of performance in the underbody, basicly in the plane area.
It's very easy to explain with a piece of paper and a pen...where I can draw it and explain with the correct formulas....but writting it is slightly harder....but I hope it gives you a slightly more indepth look at the diffuser. If anyone has something to add...go ahead....and if someone doesn't understand something....just let me know and I'll clarify it!
About the book Stik recomends it's written by Joseph Katz...it's a fantastic book...and very easy to understand I read it for the first time when I was 15 and understood almost everything!
