Aerodynamics

Aerodynamics

Aerodynamics is a large subject to generalize as it encompasses a wide range of techniques and applications. As this site is about Formula 1, this article is mostly about wings, rather than other forms of generating downforce such as tunnels in the case of indycars and airdams and splitters in saloon car racing. Some of these effects are used in one form or another in F1 so they will be covered briefly.

With 2006 cars running the less powerful V8 engines instead of V10 engines, aerodynamics are even more of a factor than ever. The V8 engines require less cooling than the V10s so teams invested a lot of time in reducing elements such as the sidepods and engine air takes to impove the aerodynamics of the cars.

The Bernoulli Principle

The Bernoulli principle has a big role in the operation of the aerodynamic surfaces of an F1 car. The Bernoulli principle is expressed by an equation (known as Bernoulli’s equation) which states that for a given volume of fluid, the total energy remains constant due to the principle of the conservation of energy. This means that When a fluid is in relative motion, the energy is split into the ‘parts’. The sum of these parts will not exceed a certain value which will remain constant as long as the external conditions do not change.

The three parts of the total energy are:

1)  The pressure energy within the fluid.
2)  The movement of the air (kinetic energy)
3)  The potential energy of the air (in this case, elevation)

This can be written as:

p + 1/2 r v2+ rgh = some constant

p = Pressure
r = Density of fluid
v = Velocity of fluid
g = Acceleration due to Gravity
h = Height of fluid above some reference point

Your average track is fairly level, so a race car will not have enough change in elevation to make the potential energy a variable, so we take this potential energy as a ‘constant’and therefore are able to remove it from the equation. This leaves us with:

p + 1/2 r v2 = some (other) constant

We can rewrite this as:

p + q = H

p = static Pressure
q = 1/2 rv2 = dynamic pressure
H = some (other) constant

This basically means that if the dynamic pressure increases, the static pressure has to decrease and if the dynamic pressure decreases, the static pressure will increase. This means that if we speed up a fluid, the pressure will fall.

Wings

We shall start by looking at a wing cross-section designed as it was meant to be used – to produce lift on an aeroplane. As the wing moves through the air it splits the air into two streams. One stream travels over the wing and one travels under the wing. Because of the way the wing is shaped, the distance across the top of the wind is greater than the distance across the bottom of the wing. This causes the air flowing over the wing to move faster than the air flowing under it.

As we have seen above, Bernoulli’s equation states that a faster moving fluid has a lower pressure than a slower moving one. This means that the faster moving air above the wing has a lower pressure than the air flowing under it. This pressure difference causes the wing to move towards the area of low pressure i.e. in an upwards direction. This phenomenon is known as lift and this is what keeps planes from falling from the sky. The lift on a wing is proportional to its’ area – the larger the area, the more lift is produced.

An inverted wing is used on racing cars. An inverted wing is basically a standard wing fitted upside-down. This means that the lift that is produced is in the opposite direction to a standard wing – this type of lift is known as ‘negative lift’, otherwise known as downforce. This downforce forces the car onto the road which in turn forces the tyres down onto the road with a lot more force than the weight of the car alone. The grip that tyres can produce increases roughly in a linear manner with increasing load (downforce in this case). Therefore with the increase in downforce, the load on the tyres increases meaning that the grip the tyres have is increased proportionately. This allows the drivers to go faster around corners than in a car without the downforce and produces significant time savings.

Usually, two wings are used – one at the rear and one at the front. This is done to balance the forces so that the grip is roughly equal at both ends of the car otherwise the handling of the car would be terrible, especially at higher speeds when maximum downforce is achieved.

Lift and Drag

A very important aspect of aerodynamics and wings to remember is, as mentioned, the dependence on speed. Speed has an effect on both the lift developed by the wing and also its drag. Drag is the resistive component of the lift force.

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