Quote:
Originally Posted by S13_marine
If you have no wing, VG's aren't going to do anything. The purpose of a vortex generator is to disrupt airflow, or create turbulance, but in a specific air stream in order to use that air to create a desired effect on another surface. Aircraft use them mainly to disrupt air movment over the wings, creating more air surface to hit the ailerons etc... So, in short, unless you have a rear spoiler or wing, it not gonna do anything but look EVO-ish. But with the right sized vortex generators and an ajustable wing, you'd have a pretty effective way to create more downforce in the rear.
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Vortex generators create a streamwise vortex that energizes the flow to reattach it to a surface. In the case of an aircraft, it's trying to get the flow reattached on the wing at higher angles of attack such that the control surfaces are actually acting in airflow. They typically use dual delta wing shapes with a set ~15 deg angle of attack to the incoming streamline.
As far as your wing needing to be above the roofline - totally false. The flow is not separated from the roofline back when looking at a velocity plot. Yes, a wing 2" off the decklid will not work well, that's common sense and a simple tuft test could tell you that. Once you get about 12" off the deck you're probably going to be in "mostly" clean flow, and above 14" on our cars it's probably going to be almost completely linear and horizontal flow.
You do not need a wind tunnel to do aero work. In fact, some simple tools like a manometer/inches of water pressure gauge, some wool tufts plus tape and a little knowledge will go a LONG way towards helping out aero on your car. I'm betting most people who say you absolutely must have a wind tunnel to do any aero work on a car have never even stepped foot inside a wind tunnel, or have an idea of what really goes on inside one. I use 'em all the time, and I'm saying large general changes are easy to make without analyzing things within a gnat's ass. It's called back of the envelope engineering, and it's more common than you think, and the GOOD engineers can make absolutely amazing observations with some observations and a few simple calculations about what needs to happen(in some cases).