Part 1: Downforce Generation

Bernoulli's Equation

Low speed fluid flow along single or multiple streamlines is interpreted in Figure 1. The presumptions regarding the application of Bernoulli's equation to this scenario are listed in the figure. In this situation, there exists a relationship between velocity, density and pressure. As a single streamline of fluid flows through a tube with changing cross-sectional area, (for example an F1 air inlet), its velocity decreases from station one to two and its total pressure equals a constant. With multiple streamlines, the total pressure equals the same constant along each streamline. However, this is only the case if height differences between the streamlines are negligible. Otherwise, each streamline has a unique total pressure.

As applied to flow along low speed airfoils (i.e. F1 downforce wings), airflow is incompressible and its density remains constant. Bernoulli's equation then reduces to a simple relation between velocity static pressure.

This equation implies that an increase in pressure must be accompanied by a decrease in velocity, and vice versa. Integrating the static pressure along the entire surface of an airfoil gives the total aerodynamic force on a body. Components of lift and drag can be determined by breaking this force down.

In order to discuss lift and downforce, it may be helpful to provide an additional explanation of the relationship that occurs with the above form of Bernoulli's equation. If a fluid flows around an object at different speeds, the slower moving fluid will exert more pressure on the object than the faster moving fluid. The object will then be forced toward the faster moving fluid. A product of this event is either lift or downforce, each of which is dependent upon the positioning of the wing’s longer chord length. Lift occurs when the longer chord length is upward and downforce occurs when it is downward.

Concept of Downforce

Downforce is a downwards lift force created by the aerodynamic features of a vehicle. If the vehicle is a car, the purpose of downforce is to allow the car to travel faster by increasing the vertical force on the tires, creating more grip.

The same principle that allows an airplane to rise off the ground by creating lift from its wings is used in reverse to apply force that presses the race car against the surface of the track. The creation of downforce by passive devices can be achieved only at the cost of increased aerodynamic drag (or friction), and the optimum setup is almost always a compromise between the two. The aerodynamic setup for a car can vary considerably between race tracks, depending on the length of the straights and the types of corners. Downforce increases with the square of the car's speed and requires a certain minimum speed in order to produce a significant effect. Some cars have had rather unstable aerodynamics, such that a minor change in angle of attack or height of the vehicle can cause large changes in downforce. In the very worst cases this can cause the car to experience positive lift, not downforce.

Most racing formulae have a ban on aerodynamic devices that can be adjusted during a race, except during pit stops.

The downforce exerted by a wing is usually expressed as a function of its lift coefficient:

In certain ranges of operating conditions and when the wing is not stalled, the lift coefficient has a constant value: the downforce is then proportional to the square of airspeed.

Quick overview on F1 car parts & downforce generation

In-depth look in Part 3 of our blog series :)

At the rear, the main sources of downforce are rear spoilers, wings and diffusers. A spoiler is a simple plate placed somewhere on the car body so that it can interfere or “spoil” the flow around the vehicle, creating a controlled separation of the flow in a desired place. This is done because fast, smooth airflow leads to positive lift, so by spoiling this flow the lift is either reduced or maybe completely canceled out. As can be seen in the picture, the spoiler causes separation in the rear of the car, creating turbulence just before the flow, this turbulence causes the flow to move more slowly, therefore reducing the low pressure in the area just in front of this spoiler. Therefore, lift on the rear portion of the car is eliminated. Properly designed, a rear spoiler will create downforce on the rear part of the car.

Note that wings are similar to spoilers and serve the same function, the key difference is that spoilers are an integral part of the car while wings have a space between themselves and the body.

The diffuser is an area of bodywork at the rear of the car. The air flowing below the car, exits through the diffuser on the rear of the car. The diffuser is usually found on each side of the central engine and gearbox fairings and is, by the rules, located behind the rear axle line.

The diffuser creates nearly 50% of the car’s downforce. A diffuser serves to eject air out from the underside of the car. This pulling action increases the velocity of the air below the car, so that the more slowly moving air above the car will push the car into the ground. The suction effect is a result of Bernoulli's equation.

At the front of the car, the main sources of downforce are front spoilers, canards (called also dive plates), vortex generators and a front diffuser. The front spoiler and diffuser block air from flowing into the underside of the car, instead diverting it to the side. They are similarly-shaped to their back counterparts.

Canards and vortex generators are small fin-like attachments to the front corners of the car. The inclination of these plates creates downforce on the front of the car, though in small amounts. The same devices can be used in other parts of the vehicle; however, care must be taken so that the leading edge vortices do not affect the operation of the rear wing or other aerodynamic devices. These dive plates are more trimming devices than anything else, they are too small to generate large amounts of downforce; instead, they are used to set up the vehicle handling before a race.