Ferrari have brought a dramatic car update to Barcelona, and it appears there was hardly an exaggeration when Arrivabene claimed beforehand that 70% of the car was changed. Clearly, the team has put a lot of effort in getting this update package together, but with the changes so dramatic, Ferrari nonetheless opted for Vettel to run with the updates and Raikkonen without, getting a full race of comparison data.
On Friday, Raikkonen was still seen running Ferrari's new update packages, including a new sidepod shape, featuring a new outer shape over their entire lengths. As is the case with airflow around a forward moving car, the changes start at the front, where the shoulder of the sidepod has been lowered on the outer edges, reducing frontal area and hence drag.
The yellow lines marked on the image show what may be the direction of flow in this area, where it seems like Ferrari aims to guide more air into the lower rear end of the sidepod. It would seem like the team has designed its sidepods to make use of the Coanda effect, where air flowing low above the floor, around the sidepods will be used to help pull air from around the sidepod's shoulder down. While that idea may not be new, it's probably most explicitly used here on the SF15-T.
With more quality airflow potentially available underneath the sidepod's hot air exists, the team also decided to reposition the outlets to be higher above the floor (if not clear, just compare where the sidepod crosses the suspension arms and note how in the new configuration the sidepod's bodywork is all above the rear suspension pull rod). With the aperture around the exhaust pipe also narrower, the total exhaust aperture has been reduced, again for aerodynamic benefit. The higher location of the outlets will meanwhile also reduce the lift generated by the sidepods. In addition to that, the potentially higher speed flow over the diffuser can similarly help increase the efficiency of the diffuser.
While it's difficult to imagine the exact airflow around a Formula One car, the modified sidepod panel and bridge, along with a new tiny vortex generator close to the car's floor (at the SKF logo) indicate that Ferrari are clearly looking at this area to extract more performance from their car.