The Indianapolis circuit is certainly not the easiest one for the race engineers that work on the car specifications and adjustments during the race- weekend. It is necessary to find a lot downforce on the infield and keep a high topspeed as well.
Some teams made remarkable aerodynamic changes but mostly only concerned some front and rear wing changes.
Prost Grand Prix for instance kept the double front wing from previous races as we had already seen in Hungary. The upper element is actually working as the lower, but there is an extra function to it. All air passing under it is automatically curved up before it touches the lower element. The front wing endplates were also changed compared to Monza, and looked again a lot like Ferrari's design. Still something that has been appearing at Prost are these thick end plates. Compared to Ferrari's, they might be twice as thick. You may ask why, well it may be for stability and weight. The little more drag it generates, it produces less vibrations also because it is a little heavier. Replacing the weight to the front that is called, and because this is the point the most in front of the car, it might be one of the best solutions ever to replace some car weight to the front.
McLaren has also been working at the front wing. It is a little les smoothly curved, but there is more some kind of the stiff part fitted to each other. The centre part seems to be less curved than before, and the outer parts are like the continuation of it, but sloping upwards to the outside. The end plates were not changed a lot compared to Monza, as we expected from McLaren. Ferrari on the contrary did change its front wing as usual, especially the end plate and experimented further with small flaps on the inside of the wing plate.
The top 3 also made some changes to the rear main aerodynamic parts. As the picture of Williams shows, they have added an standing element that somehow splits the air going up over the flap up from the molecules gliding to the rear wheel immediately. This is quite interesting to understand. The bottle effect of the car pull the air to the center of the car towards the diffuser. Part of that air doesn't make it to the diffuser and is flipped up by that large white flap. That air is pushed away by some air that flew over the sidepods. So That explains a little loss of downforce, as some air will be pushed to the outside of the car, and thus hitting the rear wheel. The newly added standing flap prevents air floating away from the slope that pushes the air over the rear wheel. (see picture below)
Ferrari added a small fence on the outer edge of the rear wing endplates, creating a small amount of extra underpressure under the rear wing. It's an addition of a little drag and a little downforce (picture above).
McLaren dug up an old flap as seen a season ago. Apparently the new design did not fit the circuit very well. (picture above)
BAR showed up at Indianapolis with a new big Sponsor. The logo of EA sports, a very famous pc gaming manufacturer can now be seen on the bonnet of the British American Racing car. They also reintroduced the midwing for maybe the fifth time this season. They seem to have a lot of problems with their aero package, and first of all on circuits with a highly differing circuit characteristics. They cannot find a good combination between drag and downforce, where we may conclude that BAR has not been doing a good job designing its wings and other aero package elements.