Civil Engineering - Hydraulics - Discussion

M<<<1-ultrasonic.
M<0.4-COMPRESSIBILITY is neglected.
M<1.1-transonic.
M<1- subsonic.
M=1-sonic.
M>1 supersonic.
M>5- hypersonic.

Subsonic Flow: When the fluid velocity is lower than the acoustic speed (M<1) then the fluid flow is called as subsonic. However Mach number of the flow changes while passing over an object or through a duct. Hence for simplicity, flow is considered as subsonic if Mach number is in the range of 0-0. 8. All small amplitude disturbances travel with acoustic speed and speed of the flow in the subsonic regime is less than acoustic speed hence presence of the disturbance is felt by the whole fluid domain. Therefore subsonic flow is pre-warned or prepared to face the disturbance.

Transonic flow: When the flow Mach number is in the range 0. 8-1. 2 it is called transonic flow. Highly unstable and mixed subsonic and supersonic flows are the main features of this regime.

Sonic flow: When flow Mach number is 1 it is called sonic flow.

Supersonic Flow: When the flow Mach number is more then everywhere in the domain then it is called as supersonic flow. This flow is not pre-warned since the fluid speed is more than the speed of sound.

Hypersonic Flow: As per the thumb rule, when the flow Mach number is more than 5 then it is called as hypersonic flows. This is not the fixed definition for hypersonic flow since hypersonic flow is defined by certain characteristics of flow.

Mach number Less than 1 is sub sonic.
Mach number Equal to 1 is sonic.
Mach number Greater than 1 is sonic.