Subsonic and transonic wind tunnel

Transonic wind tunnels, between Mach 0.75 and Mach 1.2 (920 and 1,500 km/h; 570 and 910 mph; 260 and 410 m/s), are designed on similar principles as subsonic tunnels but present additional challenges, primarily due to the reflection of shock waves from the walls of the test section.

To mitigate this, perforated or slotted walls are used to reduce shock reflection.

This often necessitates the use of large-scale facilities and pressurized or cryogenic wind tunnels.

These tunnels are crucial for studying aerodynamic properties of objects at speeds approaching and surpassing the speed of sound, such as high-speed aircraft and spacecraft during critical phases of flight.

In a return-flow wind tunnel the return duct must be properly designed to reduce the pressure losses and to ensure smooth flow in the test section.