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They're vortex generators. It is considered by some, myself included, to be a fad device. The most effective aspect of the design is to make money for the people selling them. They have legitimate uses on aircraft, but on ground transport no one has really shown them to have a great effect, if any.
They are purported to help maintain attached flow longer to help reduce drag, or to allow the air to fill in the void behind a vehicle faster thus reducing drag.
2 basic things working against them are:
They are purported to create a turbulent boundary layer which helps to create attached flow...well, all ground vehicles have a continuous turbulent boundary layer, there really isn't laminar flow on ground vehicles. And that's OK.
There is a huge volume of air that is affected by the passing of a vehicle through it, it is NOT just the air rushing over the 2 inches above the surface of the vehicle that is moved about but several 10's of feet of air around it and many hundreds of feet behind that all matter. The VG's are essentially blades of grass in a hurricane breeze and really cannot alter enough of the flow of air in such a way as to make a difference.
Search "vortex generators" here in ecomodder, the subject has been thoroughly hashed out several times.
Like HHO, this is a subject of often contentious debate. I only hope it leads you to further try and learn the basics of aerodynamics so you can understand that these are kazoos trying to be in the Philharmonic.
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