Originally Posted by Crazy_pilot
I love seeing that some research has actually been done here to substantiate the theory of VGs. I'm scratching my head a bit though (and this is just curiosity, not criticism), because in order for vortex generators to do what they're supposed to, shouldn't they be oriented at an angle to the relative airflow, as they are on airplane wings? If the vanes are mostly aligned with the airflow, where does the vortex come from? I would really like to see a car driven with a fully tufted rear windshield to see the airflow with and without VGs attached. The theory is sound, but I don't know if it's being applied correctly in most of these aftermarket parts.
The vortex is formed as the air flow separates from the tip of the vertical triangular. As the air travels over each triangular piece it has to not only change direction, but also changes in magnitude. This causes the turbulence to occur at the very ends of the tips and causes the entire flow to turn turbulent as a result of molecular interaction of air molecules. Similar to what you see at the tip of the airplane wing, but in a much smaller scale (also wings are perpendicular and not vertical but the results are the same).
As for testing, you and me both! Problem is that to have a wind tunnel large enough to test something like accurately would cost more then the manufacture could ever re-couple from selling the product. So most of this testing is done in CFD due to cost.
With that being said, I know that Mitsubishi did a large amount of testing with this(EVO images were actually from MHI) to make improvements to the EVO IX over the EVO VIII in terms of aerodynamics and was implemented in the MR models as well.
Hope this helps a bit.