[aerohead]

It seems that the only explanation for drag reduction would be a higher base pressure.Perhaps the VGs create a "more" homogeneous wake,of smaller vortices,or "micro" vortices,which viscous-attrition can erode quicker,converting kinetic energy into static pressure.Maybe Santa Claus will bring ecomodder.com a BIG windtunnel where we can do easy flow imagery and force measurements!