It occurs when a viscous air blockage under the floor is created at high speed, impeding more air from passing through the floor and, hence, losing downforce which, in turn, increases the clearance height and then it generates a high vertical force again. There are many variables that intervene in this optimization: dimensions of the floor and diffuser, inlet and outlet areas of the floor and diffuser, heights, expansions ratio of the floor and diffuser, etc.Ī bad design in the floor-diffuser assembly can produce the so-called “ porpoise effect”. In order to achieve a high rake angle, it is necessary that both the floor and the diffuser work together optimally and this, logically, is complicated. But this angle has a limit for each car design. The pitch or “ rake” is defined as the angle that the car's floor forms with the asphalt the greater this angle, the greater the downforce the car will generate. This was the reason why the Williams FW07 were more efficient than the Lotus 80, as Patrick Head was the first Engineer who designed the flat floor on both sides and a long diffuser with an angle of maximum 7 to 10 degrees, to keep the boundary layer adhered to the diffuser walls. It is important to indicate that it is NOT necessary to use a curved floor, because the most effective system is to use a flat floor, followed by a diffuser, because it allows a greater stability of the air flow that circulates under the car and maintains a lower average negative pressure. Those values created a great difference in efficiency and from that moment, that radically changed the aerodynamic design of racing cars. The Lotus 79 was a considerable improvement and generated 2.8g to 3g and 3.5g respectively. It should be remembered that before the ground effect was used, F1 cars generated accelerations of approximately 2g while cornering and 2.8g while braking.
Lotus car asphalt 4 Patch#
Furthermore, this force is essential since it compresses the elastic part of the suspension system and consequently compresses the tyres against the ground, increasing the friction force between the contact patch and the asphalt. The downforce generated by the ground effect is very important because it is a force that does not have inertia. Recall that we are dealing with speeds of the car that are of the order of Mach 0.3, so the fluid can be considered as incompressible.Ĭonsidering Bernoulli's Principle, for a constant mass-flow rate, the total energy remains constant along a flow line (or “streamline”) through the duct, so if the cross-section area decreases in one part of the duct, the air speed will increase in that part and, therefore, the pressure will decrease. The mass-flow rate of air entering the conduit will be equal to the mass-flow rate of air leaving the conduit. If there is no opening within that conduit that allows fluid to enter or exit the conduit. The continuity equation describes the uniformity in terms of flow within a duct or tube. The diffuser is in charge of “diffusing” the pressure and increasing it gradually until it reaches the atmospheric pressure value that surrounds the car. The diffuser starts where the flat floor ends, increasing the section or passage area. We must bear in mind that the reason for the Ground Effect occurs for three physical reasons or numerical simplifications of reality: the Bernoulli's Principle, the Continuity Equation and the Venturi Effect (which derives from the two previous ones). This effect, due to the speed of the car that generates a negative pressure in the conduit with respect to atmospheric pressure, is known as the “Ground Effect”. This force is proportional to the static pressure on the surface of the bottom of the car and its two sidepods, multiplied by the total section of that plate.
When a car travels at a certain speed on a fixed surface (asphalt surface of the circuit) in a gaseous medium such as air, and there is a certain clearance distance between both surfaces, there is a significant reduction in static pressure (below the atmospheric pressure) between the duct walls and the circuit surface, which generates a vertical force or “downforce” (DWF) that pushes the chassis down. Figure 1 – Curved floors under the sidepods of an F1 car
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