The “thing” on the truck, let’s call it duct because basically that’s what it is, is to reduce drag and avoid separation. The flow passing parallel to the truck side, on the outer side of the duct creates near the outlet a drop in pressure, sucking the flow from the stagnation area at the sides of the radiator inlets. A similar function have the ducts you could see just in front of rider’s hands on fairings of Aprilia 250 race bikes couple of years ago (not sure if they still use them actually) and in some production bikes.
The fin on the RA106 is, presumably, mainly to split the “clean” flow passing on the inner side of the front wheel from the “dirt” flows, the one downstream the wheel and the (hot and full of carbon residues) brake cooling flow expulsed from the outer side of the rim. Nevertheless remember that basically no part of the car has only 1 function, it’s difficult, make it impossible, to describe accurately why they came up with that particular shape without knowing the details of the flow in that area.
Apex wrote:
The next person who says 'manage' or 'condition' airflow needs a solid kick!
If you think that’s bad, you should hear “our virtual technical commentator” on Italian tv. For that Honda fin he would show a 3d model having a vague resemblance with the car (mainly thanks to livery) and would probably say something like : “that innovative element, fundamental factor in the ultimate design, eventual result of extensive testing in highly developed wind tunnel facilities, activates precious synergies enhancing the aerodynamic potential performance of the whole car.”
