Aero rake
An aero rake is a frame of pressure sensors fitted to a car in testing or practice to measure the airflow coming off it.
Also called aero rakes, aerodynamic rake, kiel probe rake, pitot rake
The grid holds dozens of small probes, each reading air pressure and direction at one point. Sampled together across a plane — usually behind a front wheel or above the floor — they map the wake the car is actually producing, at a level of detail no amount of trackside observation can give you.
The point is correlation. A team's wind tunnel and CFD models predict a certain airflow; the rake measures what the real car does at real speed. Where the two disagree, the model is wrong, and every simulation built on it is wrong too. That is why rakes appear in pre-season testing and on Friday practice runs whenever a significant new part is bolted on.
Not to be confused with rake in its other sense — the nose-up attitude of the car, set by running the rear ride height higher than the front.