The diffusers are critical for the aerodynamic efficiency of modern F1 cars and the Mercedes W09 has one of the most developed and the detailed diffusers that has serrated gurney tab in its middle section.
For 2017 F1 season, the rules for bodywork and floor dimensions changed, so the diffuser became about 2.2 times bigger. As the downforce generated from the floor and the diffuser is most efficient (less drag for the same amount of downforce), this area gets much attention from all teams.
The teams use the maximum width and height for their diffuser, but sacrifice the maximum volume to make the edges round and thus to help to make the diffuser virtually bigger.
Curved edge fins, which became common in the last year in Formula 1, are often multiple, such as bird wings, and continue to the upper edge of the diffuser.
The entire width of the Mercedes diffuser is equipped with two horizontal flaps (like Gurney tabs) which become curved at their tips (turquoise).
At the place where the vertical rear wing endplate end, the double flaps become single while in the area below and around the rear crash structure (middle) Mercedes added toothed gurney tab and paired it with an almost vertical flip up (orange) continue. Above the orange flap, each side of the crash structure has one small horizontal flap.
Micro aerodynamics in this part of the car helps control the airflow on this very important and sensitive place and connect the air flow that travels to the rear wing with the one traveling over the top and into the diffuser itself.
Interestingly, Mercedes separated curved edges from the diffuser structure, which ends quite straight and vertically (pink), and the vertical fences, which serve to control the airflow in the diffuser and help its expansion, are vertically cut.
The Mercedes gearbox (below the rear crash structure) is somewhat narrower than last year which brings a little bigger volume of the central part of the diffuser.
Notice that the central exhaust pipe is tightly wrapped with a carbon fiber cover (yellow), which reduces turbulence caused by the cover, and the smaller, lateral wastegate exhaust manifolds are outside the cover.
The narrowly wrapped engine cover around the central exhaust pipe on each side extends into two circular cooling outlets, through which hot air goes out. Their shapeis circular because fluids better follow curved contours (like in pipes).
Circular cooling outlets help to provide a better heat extraction from the engine compartment so the outlets can be smaller, reducing the negative aerodynamic impact on the rear of the car.