7.1 INTRODUCTION
Wind tunnels provide controlled air streams to study aerodynamic and fluid
flow phenomena. They are frequently used to replicate the actions of an object
flying or moving in an air stream, such as airplanes or vehicles. Table 7.1 lists
several types of wind tunnels. Most wind tunnels are designed to have a
uniform velocity profile in the test section at a low turbulence level. The testing
object is placed in the test section for flow visualization and quantitative
measurements such as lift and drag forces. To create an air flow, electric fans
are usually used to blow air in or out of the tunnel. In large wind tunnels for
testing real-size airplanes, rockets, or cars, powerful fans are required to
generate a wind speed comparable with real conditions.