A 4-door sedan with over 500hp of twin turbo goodness requires cooling hence the heat exchangers in the corners for the front bumper. This is especially true when it can lap the Nurburgring in 7:39. An old co-worker of mine form the turbo industry was out in Arizona for some hot weather testing. He happened to be there at the same time the development team from Alfa Romeo was putting the Giulia through its paces. He got a brief ride in it and he can attest to the claimed 0-60 time of 3.8 seconds. What’s the purpose of the slot above the opening for the heat exchanger?
It should dump air out this little slot on the side of the fender liner which reduces drag. Of course, you can see the louvers in the fender liner to allow the air coming off the heat exchanger to escape.
Looking under the front bumper, you can see the carbon fiber splitter which is active aero. In corners and braking, it drops down to produce up to 220lbs of downforce. On the straights, it tucks up to reduce drag. As is standard on cars designed to go fast, it has the diffuser leading into the wheel well. And of course, as it on basically every car made now, the little aero wheel spat that sticks down in front of the tire to reduce aero drag.
Here is just another view of the diffuser leading into the wheel well. You can see the front sway bar wrapped around the steering tie rod. It looks like the tie rod is pretty horizontal and parallel with the lower suspension arm, so I think that should minimize bump steer.
A small spoiler is used on the rear of the trunk to help with the aero balance. Quad exhaust tips are located in the corners making way for the diffuser in the middle.
The bottom of the car is nearly completely covered and flat to reduce drag. The interesting bits are the sets of turning vanes located near the rear axle line. What do they do? I think they are to spread the underbody airflow more uniformly across the rear diffuser as the airflow can tend to move towards the centerline of the car in this area.