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Mach Number
Assess compressibility effects from the ratio of flow speed to sound speed.
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Machcompressiblespeed of sound
formula
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M = U / a, a = sqrt(gamma R T)a — sound speed
346.0 m/s
M
0.983 · Transonic
M < 0.3 incompressible, 0.3–0.8 subsonic, 0.8–1.2 transonic, 1.2–5 supersonic, > 5 hypersonic.