A wind tunnel is used to investigate and measure the aerodynamic and aero-acoustic properties of objects.
Probably the best known are the wind tunnel tests of airplanes and cars. While low air resistance and optimum lift values should be achieved for cars, significantly more aspects play a role for aircraft: in addition to the air resistance and lift, there is also sub-surface profile, stability, control etc. Railway trains and ships have also been tested in wind tunnels.
What is important is also the investigation of structures such as high-rise buildings, chimneys and bridges. It must be ensured that these can withstand the wind pressure during storms and especially the wind forces and do not experience critical vibrations alongside natural vibration. To be able to correctly simulate wind current, the entire surrounding area may have to be modelled.
Only on rare occasions can objects be tested in the wind tunnel in their actual size, cars are an exception here, as they are not too big and the relatively low air speeds allow sufficiently large wind channels.