Ground effect explained | F1 2022 Venturi aerodynamics
Downforce and ground effect explained
The aerodynamic forces: lift and drag.
The picture below shows the main forces acting on an aircraft: lift (L “Lift”), resistance (D “Drag”), weight (W “Weight”) and thrust (T “Thrust”). V indicates the apparent wind direction. We also talked about drag and lift in a dedicated article here.
The procedure by means the plane flies and the race car, despite having a high speed, remains attached to the ground is not so simple; many forces act on the wings of the plane and on the various components of the car: the lift and the force-weight act vertically, therefore their resultant allows the vehicle to be raised or lowered while the resistance and the thrust of the engine act horizontally, therefore their resultant allows the vehicle to go faster or slower.
How do we generate downforce? Not only ground effect.
Lift is not always opposite to force-weight, but it can follow any direction. In fact, in the cruising motion of airplanes generally the lift has the same direction of the weight and in the opposite direction, but when the plane rises or falls in altitude, or when it makes a turn, the lift will tilt with respect to the vertical. In some acrobatic maneuvers, lift can take the same direction as force-weight. In this case the term downforce is used. This force is exploited above all in the automotive sector, when the cars reach high speeds, in order to guarantee the adhesion of the tires to the ground.
The idea therefore is to increase this normal force (called aerodynamic component) by adding it to the static component, given by the weight of the car.
To obtain this effect, special ailerons are applied (both in front of the front and rear on the rear), which exploit the same principle as the wings of the aircraft, but in the opposite direction. When the track engineers change the incidence of the ailerons, they do so to change the downforce according to the characteristics of the track (twisty or not), the required trim or the environmental conditions of the ground (dry or wet).
In addition to changing the impact of the ailerons to change the contribution of the downforce, another method of increasing downforce is to use a flat bottom of the car together with the use of the so-called miniskirts and a rear extractor (the known rear diffuser), so as to create a depression under the car by accelerating the fluid between the ground and the bottom of the car with respect to that above it, always according to the Bernoulli principle.
READ: THE AERODYNAMICS OF A F1 REAR WING – CFD EXPLAINED IN MOTORSPORT
The Ground Effect explained
This stratagem exploits the ground effect, which consists in a modification of the aerodynamic field around the body when it moves close to the ground, and in the corresponding variation of the aerodynamic forces applied to it.
Approaching this body to the ground the aerodynamic field is no longer perfectly symmetrical: a fraction gradually increases overhead with a lower speed (therefore higher pressure) while a smaller percentage passes below, with a higher speed (and lower pressure). In racing cars, however, it is necessary to create downforce and to obtain it from the ground effect, we need to change the shapes of the appendixes so that an air flow passes under the car with a speed greater than that which passes over the car.
Downforce and ground effect in Motorsport. Bottom flat and the take-off risk.
In general, the aerodynamic advantage of downforce occurs mainly in curves, where the inertia forces that cause the centrifugal forces tend to make both the trajectory and the grip unstable; here therefore an increase in the total weight of the car manages to keep it more adherent or flattened on the ground. It also gains stability on the straight: without a rear wing the car would risk taking off. However, the most common disadvantage is that the more the incidence of the ailerons increases, and in general therefore the aerodynamic load and the adherence, the more the aerodynamic drag force increases with a decrease in the top speeds in the straight stretches.
The high risk of “take-offs” due to the design of flat-bottomed cars, however, has suddenly “brought flying races closer …”. We have thus moved on to stepped funds, safer and more efficient.
How the Venturi channel works in F1 2022.
The Venturi effect explained in F1.
The so-called “Venturi effect” is a physical principle according to which a fluid that moves inside a conduit increases or decreases its pressure according to its speed.
This characteristic was discovered in the 19th century by the Italian physicist Giovanni Battista Venturi, during some research on fluid mechanics, and it is still used today as one of the most common methods to measure velocity (Venturi tube).
When a fluid flows inside a duct that shows no leakage, the fluid keeps its mass constant (also called mass conservation principle).
Since we are talking about a fluid in motion we can extend the principle of conservation of the mass, to the flow of the fluid; therefore, if we measure 50 m^3/h of air at the inlet section of the duct, we will measure the same value at the output section.
If we imagine that the conduit does not have a constant section, the fluid passing through it will change its speed according to the passage section in which it is located.
It is easy to imagine the following: if a certain airflow Q ̇, which is constant, is passing through a large opening A0 its velocity v0 will be reduced, whereas if the same airflow Q ̇ I crossing a smaller opening A1 its speed v1 will be higher.
If inside the duct there is no device capable of supplying energy to the fluid, according to the principle of energy conservation, also this value will remain constant between the duct inlet and its outlet.
READ: AERODYNAMIC F1 HISTORY BACKGROUND
In order to better explain this principle it is necessary to consider the fluid that moves inside the conduit as an ideal fluid and apply to it the Bernoulli principle, that says: the sum of the kinetic energy (contribution provided by the velocity v of the fluid ), the potential energy (contribution provided by the change in height h of the fluid) and the pressure p remain constant along the conduit.
But the return to ground effect in 2022 is not going to be as big a shift as those figures would suggest and I’m not convinced we will really see a significant difference.
Overall, the aerodynamic changes have been mainly conceived to reduce the turbulence, in other words improve the wake left behind a car. All these small turning vanes and gizmos we have seen over the last few seasons help improve the downforce levels of the car they are mounted on, but generate dirty airflow for those trying to follow.
The new regulations are focused on cleaner aerodynamic surfaces, which should generate less turbulence. The problem with that is that the following car also has cleaner and less aggressive aerodynamic surfaces to generate downforce from, so it could very easily be a catch-22 situation. This is because it means less turbulence from the leading car, but also less downforce from the following car.