Transonic wind tunnels, between , are designed on similar principles as subsonic tunnels but present additional challenges, primarily due to the reflection of

shock wave In physics, a shock wave (also spelled shockwave), or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a me ...

s from the walls of the test section. To mitigate this, perforated or slotted walls are used to reduce shock reflection. In transonic testing, both

Mach number The Mach number (M or Ma), often only Mach, (; ) is a dimensionless quantity in fluid dynamics representing the ratio of flow velocity past a boundary to the local speed of sound. It is named after the Austrian physicist and philosopher Erns ...

and

Reynolds number In fluid dynamics, the Reynolds number () is a dimensionless quantity that helps predict fluid flow patterns in different situations by measuring the ratio between Inertia, inertial and viscous forces. At low Reynolds numbers, flows tend to ...

are critical and must be properly simulated. This often necessitates the use of large-scale facilities and pressurized or

cryogenic wind tunnel In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th International Institute of Refrigeration's (IIR) International Congress of Refrigeration (held in Washington, DC in 1971) endorsed a univers ...

s. These tunnels are crucial for studying aerodynamic properties of objects at speeds approaching and surpassing the

speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elasticity (solid mechanics), elastic medium. More simply, the speed of sound is how fast vibrations travel. At , the speed of sound in a ...

, such as high-speed aircraft and spacecraft during critical phases of flight.

Closed wind tunnel

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.

Transonic tunnel

High subsonic wind tunnels, between Mach 0.4 and 0.75, and transonic wind tunnels, between Mach 0.75 and 1.2, are designed on the same principles as the subsonic wind tunnels. Testing at transonic speeds presents additional problems, mainly due to the reflection of the shock waves from the walls of the test section. Therefore, perforated or slotted walls are required to reduce shock reflection from the walls. Since important viscous or inviscid interactions occur (such as shock waves or boundary layer interaction) both Mach and Reynolds number are important and must be properly simulated. Large-scale facilities and pressurized or cryogenic wind tunnels are used.

References

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Closed wind tunnel

Transonic tunnel

References

See also