Mach number

Dimensionless quantity in fluid dynamic

The Mach number (M or Ma), often only Mach (German: [max]), 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 Austrian physicist and philosopher Ernst Mach. M = u c , {\displaystyle \mathrm {M} ={\frac {u}{c}},} where: M is the local Mach number, u is the local flow velocity with respect to the boundaries (either internal, such as an object immersed in the flow, or external, like a channel), and c is the speed of sound in the medium, which in air varies with the square root of the thermodynamic temperature.

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