The sliding side skirts used in the late 1970’s to early 1980’s helped to seal the underbody duct, preventing this flow ingress from the sides - which helped to maintain a low pressure under the car.
With the underbody this means the large flat area will experience an increase of pressure towards the centre of the floor, reducing downforce. Naturally air pressure wants to return to an equilibrium state, with higher pressure regions migrating towards lower pressure ones (filling the relative vacuum). a relative vacuum) sucks the car into the ground (downforce), because downforce is equal to the integral of pressure over the planform area ( ) of interest The Venturi effect is the key downforce generating ground-effect for a Formula 1 car, the negative pressure created (negative only when compared to the atmosphere, i.e. This is derived from the Bernoulli equation where the increase of dynamic pressure (q) will cause a reduction of static pressure, , The Venturi effect tells us that static pressure (p) will be reduced when the air is accelerated (i.e. The contracted volume (where ) between the car and the ground will cause the air to accelerate. Where is the density of air (which is constant when air is incompressible), U is the velocity of the air, and S is the cross sectional area of the duct. As air behaves like an incompressible fluid at low Mach numbers, the mass of the airflow ( ) travelling through a duct will be conserved , The underbody behaves like a convergent-divergent duct, contracting air under the car, before expanding it again with the rear diffuser. The way these important surfaces affect downforce is detailed below: Approximate distribution of aerodynamic downforce and drag for a modern F1 car UnderbodyĮven with the mandatory flat floor and step plane the underbody and rear diffuser are the largest contributor to overall downforce, producing between 60-65% of the car’s downforce. The main mechanism for downforce on a Formula 1 car is ground-effect, with all surfaces affected by the car’s proximity to the ground. Starting when wings had to be fixed to the sprung part of the car - initially wings were fixed directly to the suspension uprights which resulted in a number of high profile accidents - followed by the ban on sliding skirts, the mandatory flat floor between the axle lines, shorter diffusers, taller wings, shorter wings, longer diffusers, step planes, wooden skid planks - the list goes on. The exact size, position, and shape of the downforce producing surfaces are dictated by regulations, initially by FISA and by the FIA themselves since 1993.
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