So we have all seen various teams use various methods, usually consisting either of vortex generators or aerodynamic slots (look like small wings over the front portion of the sidepods), to maintain flow attachment over the top of the sidepods.
Keeping the flow attached has benefits twofold;
1. Reducing drag
2. Reducing turbulent airflow to the rear of the car aiding in the production of downforce.
Included in the link is a bit of information on a similar concept for an aviation application on a C-130 Hercules military cargo plane.
http://aviationweek.com/technology/drag ... 22ad345230