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Subsonic, Supersonic, Transonic, and Hypersonic Wind Tunnels: What’s the Difference?

Subsonic, supersonic, transonic, and hypersonic wind tunnels:

If you’re looking to build an aircraft, you’ll need to know what kind of wind tunnel is right for your application.

Subsonic wind tunnels are designed to test models at speeds up to Mach 0.3 (approximately 230 mph). Subsonic tunnels can also be used for testing missiles and missiles systems.

Supersonic wind tunnels are designed to test models at speeds between Mach 1 (1,235 mph) and M∞ (the speed of sound). Supersonic tunnels are typically used for testing supersonic aircraft and rockets.

Transonic wind tunnels are designed to test models at speeds between Mach 0.5 (approximately 622 mph) and M∞. Transonic tunnels are typically used for testing cruise missiles and other high-speed aircraft.

Hypersonic wind tunnels are designed to test models at speeds above M∞. Hypersonic tunnels are typically used for testing hypersonic aircraft such as space shuttles or ballistic missiles.

Here’s a table to differentiate each type of wind tunnel further more:

 SUBSONIC WIND TUNNELTRANSONIC WIND TUNNELSUPERSONIC WIND TUNNELHYPERSONIC WIND TUNNEL
Increases the speed byIncreasing the blowing pressureA downstream test section “extension” with adjustable pressure flaps works in unison with other wind tunnel componentsExpanding the channel area downstream of the throat to accommodate the increased volumeContracting the flow until it chokes in the throat of a nozzle. We then diffuse the flow which increases the speed supersonically. 
ChokingChoking may be delayed by using a liner with slightly divergent walls.The choke works in concert with the stagnation pressure control valve to achieve and maintain target airspeed.Compressible flows experience mass flow chokingwe contract the flow until it chokes in the throat of a nozzle. 
Mach number   Speed regimeM<0.80.8< M<1-1.21-1.2<M<5M>5
LinersParallel-sided linersSpecial liners are requiredA Mach liner is fixed in the bottom of the test sectionLiners with very narrow throats are required
Working fluidIncompressible for low speed subsonic and compressible for high speed subsonicCompressibleCompressibleCompressible
Shockwaveseffects of shock waves for this flow are commonly not consideredSonic pockets are initiated as soon as the local Mach number reaches one and subsequently terminates in the downstream with a shockwaveNotable in this regime is the appearance of shock wavesOblique shock shift closer to the object’s surface