Performing an aerodynamic measurement in the wind tunnel is complex because the test conditions have to resemble real conditions. However, the wind tunnel is a privileged space that allows us to know the projected resistance on a car at different times. Large automobile manufacturers, for the most part, have their own wind tunnels. In them, the air is mixed with the fog to make an exact measurement of the course of the air current, which can be better observed.
Most wind tunnels are built as a rectangular corridor in which the air blows through a flow straighter and a nozzle from the front of the car, this air will be driven to the rear wall of the tunnel. The air flow rate in wind tunnels can reach up to 300 kilometers per hour.
To carry out the measurement process, the car is maintained on a rotary platform to rotate the car and place the nozzle in the right way with the aim of simulating lateral wind. On the gieraratory platform a running ribbon located under the car is launched to simulate the movement of the wheels and the driving surface. In addition, a scale is installed on the measurement point. This measures all the forces and impetus suffered by the car because of the wind, such as the elevation of induced resistance and lateral and longitudinal forces. Using these values, the CD value is calculated (value that represents the friction force on a car caused by the air and that is composed of different forces).
