local Mach number

Mach waves can be used in schlieren or shadowgraph observations to determine the local Mach number of the flow.

Real choke phenomena is a function of compressibility as measured by the local Mach number within an area restriction within the centrifugal pressure stage.

Increasing the number of blades also decreases the amount of work each blade is required to perform, limiting the local Mach number - a significant performance limit on propellers.