A fluorescent powder that is mixed up with a light oil, usually paraffin, and is painted liberally on to the car
Then when the car goes out and as it’s moving up to speed and going through a cornering condition, the paint dries as the oil evaporates and you end up being able to visualise, very clearly, what sort of flow structures you've got.
Sometimes flow-vis will just be painted on a small portion of the car, to observe the airflow in a particular area, but sometimes you’ll see cars covered in flow-vis
Aero Rakes
A series of ‘pitot tubes’, which are sensors designed to measure the airflow off of the body structures.
By measuring the dynamic pressure, they can get an idea of the flow structures that are coming off things like the front wing, and the front wheels
There’s a whole host of different shapes of aero rakes, some quite tall, some very wide and some (like the Ferrari below) which look particularly interesting.
Watch out for
Lap count - I personally think this to be far more important than lap times. If a team can get undisturbed running for the 3 days it’ll be ideal.
High winds - this is common with the Bahrain circuit, and it’s a good chance to see how the cars handle under less than ideal conditions.
Team/driver behaviour - the teams behaviour and body language can always be an interesting thing to observe, especially in regards to car performance.
Personally I don’t read too much into lap times themselves because you don’t know how much fuel cars are carrying or what engine modes they are using. I find testing more interesting to have a look at how the cars handle and also to observe body language.
Schedule
Each day will be split into 2 sessions (so over the course of the test there’ll be 6 sessions all together)
The track will open for running from 7am GMT until 11am GMT for the morning session
The afternoon session will run from 12pm GMT to 4pm GMT
The teams will announce their driver split in due time