The body of the car is designed to be as close to the ground as possible to increase the velocity of the air flowing below it. Bernoulli’s principle states that a faster moving fluid should be at lower pressure than when it moves at lower speeds, so the lower pressure below the car allows the air above it to push it harder into the ground.

Diffuser directing air flow upwards (http://www.formula1-dictionary.net/diffuser.html) The role of the diffuser is to slow the air below the car down and direct the air upwards to be ‘attached’ to the surrounding air.

Increasing pressure

By expanding the cross-sectional area of the air flow, the speed of the airflow is slowed down, increasing the pressure the air exerts on the surroundings by Bernoulli’s principle. The pressure within a fluid must be continuous, so the air close to the diffuser must be near atmospheric pressure, like the air behind the car. Thus, by increasing the pressure of the air near the end of the car, it means that the air below the body and between the front wing and the diffuser must be at lower pressure, increasing the downforce experienced by the car.

Directing air upwards

The rear wing directs air from above the car upwards and away from the ground, resulting in a region of lower pressure behind the car. Without the diffuser, there will be 2 separate air streams above and below the car. The separated air streams cause a variety of problems in increased drag and reduced downforce, so teams add a diffuser to the end of the car to help ‘attach’ the two streams together and help mitigate these downsides.

Blown diffuser

In a blown diffuser, the exhaust is blown upwards near the diffuser, helping to reattach the air flow and increasing the speed of the airflow below the car, helping ‘blow’ the diffuser to make it more efficient.

Double diffuser

As discussed earlier, there are many advantages to using a diffuser, and having a larger diffuser magnifies the advantages and minimizes the downsides of creating downforce. However, the FIA has imposed a limit on the size of the diffusers at the end of 2008 in an effort to improve overtaking, meaning most teams only had 175mm of space to work with for their diffusers. The double diffuser was an idea to not completely block off the roof of the car, allowing more room for the air to flow and increasing the cross-sectional area of the air flow while technically not adding material outside the regulation limits.