Characteristic Mach Number

where   M*  is the characteristic Mach number ( No unit)

M is the Mach Number ( No unit)

γ is the ratio of specific heat (No unit)

M = V/a* = V/(γ×R×T* )^0.5

where V is the local flow velocity (m/s)

T∗  is the temperature at sonic condition (K)

R is the specific gas constant (0.287 KJ/kgK)