Rex, the tire is embedded in the surface. This is a 2D slice where the air can get around the tire but not under it. So you were wrong about the tire in the surface but right about the flow around the tire! Good eye! The 'jets' and vortices around the bottom were first identified by Fackrell and Harvey in 1973.
For an up to date study see: SAE 2007-01-0107, Fig 12 & 13 (SP-2066).
Regarding Sr. Bernoulli, he discovered that there is a relationship between pressure and velocity. (This is conditional but for our uses and understanding we'll let the PhD's worry about that!) The problem is the way we are taught his principle. All any fluid ever wants is to not be disturbed in any way. A bunch of Utah air molecules are banging off each other in a random, happy manner and reach this steady state condition that we call pressure. And then along comes a bunch of land speed racers to stick a lot of funny looking objects in the breeze and upset their randomness!
All the velocity changes we see are a result of the pressure differentials that result from an object moving in a fluid or a fluid moving around an object. Force, velocity and acceleration are all vectors which just means they have magnitude and (3D) direction. The force on the now not so random air molecules tells them which direction they are going to go, how fast they will go and how quickly they will get there. But it is a one-way relationship - pressure can change velocities but velocity does not change the pressure! Pressure is a force - velocity is not! However, for simple shapes like a venturi we can calculate the pressure if we know the velocity because they are joined at Sr Bernoulli's hip!
Not everyone buys this idea but it's my story and I'm sticking to it! BTW: These guys helped me confirm my suspicions: Understanding Flight, Second Edition by David Anderson and Scott Eberhardt. If you start to think about fluid flow strictly in terms of pressure differential little lights will start coming on. When I ask what do you measure on a flow bench the usual answer is CFM. Actually you measure pressure differential and you calculate CFM or velocity or density or ....
Buddy, the fender question is an old one. Flow around an open tire is very complex and is being studied and restudied all the time. If the tire is open the first thing is to make it smaller, then put discs on it and lastly maybe get the tire guys to make it more aero in cross section otherwise they are just in the wind! I would put a fixed aero fender around it. The fender may have slightly more frontal area but it will be cleaner and more slippery. Remember the pressures on the body will talk to the pressures on the tire or fender, too. A partial fender behind it would give a partial improvement. In an open fender the ratio of the fender volume to tire volume is the key factor. In other words make the inner fender as close to the tire as you can. You old salt dogs got any usable comments on salt packing in the wheel wells?
Here is a rotating wheels video:
http://www.deexchange.com/video/cfd-for-dexMotorcycle liner aka long, round fender with two wheels. (Bonus link there to a scoop concept at 300 mph.)
I will be doing some studies for Buddy and Sparky. Thank Sparky for the tires shots here! Wendy Jeffries has asked me to do some articles for Bonneville Racing News about what it is I do. Buddy and Sparky have agreed to share some of their results for the articles. I hope you will enjoy them! I feel like this was the first chapter.
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