The underfloor has historically played a large role in producing downforce for Formula One cars, but a series of regulations to reduce the downforce of the cars have reduced the extent of the downforce. Nevertheless, teams still create ingenious aerodynamic solutions to maximise the downforce produced.

Historical: Skirts

Skirts were a popular aerodynamic solution, particularly in the 1980s, to generate large amounts of downforce. The skirts seal off the underneath of the floor from the outside, permitting ground effect solutions like venturi tunnel esque designs to arise.

Current: Vortex Generators

With the banning of skirts, teams can no longer utilise ground effect principles to produce large amounts of downforce. However, instead of using physical skirts, they create an aerodynamic ‘skirt’ using vortices produced by slots in the floor.

These slots produce vortices that prevent airflow from outside from entering the underfloor, and also preventing the air from leaking out. As a result, the design objectives of a skirt is met, without a physical aerodynamic device.

References

https://www.formula1.com/en/latest/article.tech-tuesday-the-lowdown-on-2018%27s-key-aerodynamic-developments.2N1IxDVHjGSaiAaO4cGYIW.html