Mach Number
Mach Number
The Mach number tells you whether compressibility matters: below ~0.3 a flow is effectively incompressible, near 1 it is transonic.
The Mach number is M = v/a. where v is the flow speed and a the local speed of sound.
Inputs
v := 250 m/s=250 m/s
a := 340 m/s=340 m/s
Divide the speed by the speed of sound.
M := v/a=0.74
Results
Below Mach 0.3 density changes are negligible; above Mach 1 the flow is supersonic and shock waves form. This single ratio decides which aerodynamic model applies.
Assumptions & limitations
- Local speed of sound for the actual temperature.
- Single-phase gas flow.
- Speed and sound speed in the same frame.