Aerodynamics of F1
It has now been more than 70 years since F1 first started and with growth in engine technology, the rules on the power units f an F1 car have become quite strict giving aerodynamics engineers a lot to play around to improve the performance of the car. Today we’ll be looking at the aerodynamics in an F1 car. Topics that I’ll be covering today:
1. Downforce and the ground effect
2. Front wing
3. Rear Wing
Lift is generated in an aircraft by accelerating the air above the wings and thus creating a low pressure area above the wing and creating an area of slow moving air below the wing creating a high pressure area. This imbalance in pressure creates lift. A F1 car works on the exact opposite principle and is essentially an inverted wing. A F1 car tries to create a low pressure region below the car and a high pressure region above the car to increase the downforce. Now, you must be wondering that why is downforce given so much importance rather than reducing the drag force? Increasing the downforce improves the stability of the car and keeps it closer to the ground thus increasing its speed and traction around corners.
Fdown = 0.5DClAV²
Where, D= density of air
Cl=Coefficient of lift
V= velocity of object
So, a F1 car at 100mph will produce roughly 750kg of downforce. Interestingly, lower weight limit of a F1 car is 743kg so you could in theory drive the car upside down.
Ground effect – where the pressure of air under the car is lower than the pressure above the car, creating a sucking effect that pushes the car to the ground.
(IMAGE SOURCE- https://www.totalsimulation.co.uk/secrets-formula-1-part-3-role-front-wing/)
The front wing is a very important aerodynamic device in a F1 car. It has 2 main purposes, first to generate downforce and second to manipulate the flow to the rest of the car by controlling the vortices over and under the vehicle.
Endplates are one of the most important aspects of the front wing. They control the flow of air around the Formula One car by redirecting the airflow around the tires. This minimizes the overall drag resistance produced and facilitates the airflow to continue back to the side pods and the car floor. In addition, the tips of the front wings coincide with the ends of the tires. This creates unnecessary turbulence in front of the wheels and increases drag. Hence, the inside edges of the end plates are curved to ensure that the air flows around the tires.
(IMAGE SOURCE- https://www.simscale.com/)
F1 front wings are sharply pointed and fine edged, to promote the creation of turbulent vortices, which the cascade elements direct underneath the floor of the car. Designers want to create vortices that they can control, but without endplates, both on the front wing and rear wing, uncontrollable vortices are produced, which add to the drag coefficient of the car but don’t increase downforce production, so are undesired. The fast moving vortices now travelling underneath the car are of higher speed and lower pressure than the air going over the car, thus increasing the downforce-ground effect.
(IMAGE SOURCE- https://www.totalsimulation.co.uk/secrets-formula-1-part-3-role-front-wing/, LABELS- self)
(f1 rear wing. Source- https://www.presticebdt.com/. Labels-self)
The rear wing is among the most regulated aerodynamic device of a Formula One car. Teams will have track specific rear wings depending on how much downforce is required on a particular track. The FIA allows a span of 101cm for the rear wing and an additional 5cm for each of the endplates. The end of the rear wings is designed and finished within these 5 cm on either side. The rear wing has to be 35cm in front of the rear tip of the car and have to be 22 or less cm deep.
The rear wing of a F1 has the aim to generate downforce to counterbalance the downforce produced by the front assembly. In fact, the force distribution alongside the vehicle determines the overall balance of a car. The rear wing of a F1 generates about ~10% less downforce than the front wing. The rear wing works quite differently than the front wing as it can’t exploit ground effect and work with disturbed flow.
(Airflow over the rear wing. Source- https://www.presticebdt.com/the-aerodynamics-of-f1-rear-wing-cfd-explained/)
1. A main plane: the thicker profile of the rear wing assembly. This part remains fixed when DRS is open.
2. the smaller profile which acts as a slotted flap increasing downforce and preventing flow detachment. This part is moved and opened by the DRS system.
3. Middle trim: this part of the endplate, is sometimes trimmed in order to better drive the flow coming from the wheels and the bodywork.
4. Bottom trim/louvers: These louvers located in the lower part of the endplates are designed to work efficiently with the rear diffuser and exhaust gas.
DRS stands for drag reduction system, it was introduced in f1 in 2011 in order to improve overtaking. It is a device that allows the reduction of the downforce acting on the vehicle with less adherence to the track and therefore an increase in speed, but also with a decrease in stability.
(Image source- https://www.presticebdt.com/)
The addition of the flap has the aim to increase the overall camber of the main wing, leading to an increased downforce and preventing flow separation.
When the airflow approaches the rear wing with DRS in closed position a large high pression area is generated on the upper side of the wing-flap profile, while a suction area is present underneath the profile. A qualitative effect of DRS effect on F1 aerodynamics is reported on the following image. The red colors identify a high pressure region while the blue one a low pressure area.
(pressure difference when DRS is opened or closed. Source- https://www.presticebdt.com/)
When the DRS system is activated, the high pressure on the upper profiles greatly declines. The reduced pressure means a reduced downforce and drag. By enabling the DRS system, a F1 car can have over 10 km/h gain. However, the overall impact of DRS on car performance are greatly influenced by the profile chosen as main wing. For instance, when low angle of attacks and low downforce profiles are used , also the effectiveness of the DRS system is reduced.
The diffuser is an area of bodywork at the rear of the car and the air flowing below the car, exits through the diffuser on the rear of the car. Although wings and diffusers work similarly, they are based on different concepts. 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, which states that where speed of the fluid is higher, pressure must be lower. Therefore the pressure below the race car must be lower than the pressure at the outlet since the speed of the air below the race car will be higher than the speed of the air at the outlet.
The diffuser in itself doesn't produce a reduction in pressure. The role of the diffuser is to expand the flow from underneath the car to the rear, decrease the flow's velocity from inlet of the diffuser to outlet (so that at the outlet the flow velocity is similar to the free stream velocity), in turn produce a pressure potential, which will accelerate the flow underneath the car resulting in reduced pressure and as such, a desired increased downforce generation.
The addition of the vertical ‘fences’ to a diffuser help to optimize the diffusers efficiency by ensuring that the air is only drawn only from the underbody and does not spill in from the upper body surfaces.
(Pressure on the underside of a diffuser. Source-- https://www.racecar-engineering.com/)
shows the pressure coefficient of a generic diffuser design, with blue representing lowest pressure areas and red highest pressure. This clearly illustrates the reduction in pressure at the throat area as the velocity increases and the subsequent reduction in pressure for the underfloor as the diffuser sucks the car to the ground.