You must have been heard about some terms or words like supersonic, hypersonic etc. But do you know, what exactly are they and from where they come? Don’t worry I’m here to explain all about this. So today in this article I will discuss, What is Mach Number? Classification of Mach number regimes. So don’t waste any time further, let’s get started.
What is Mach number?
In fluid dynamics, Mach number is the ratio of the velocity of a fluid to the velocity of sound in that fluid. It is named after an Austrian physicist and philosopher Ernst Mach. It is a dimensionless quantity. It is represented by M or Ma.
M= The Mach number
u= The local flow velocity
c= The speed of sound
If an object (generally aircraft) moves through a fluid, the Mach number is equal to the velocity of the object relative to the fluid divided by the velocity of sound in that fluid. The Mach number is usually used to determine the approximation with which a flow can be treated as an incompressible flow.
The medium can be a liquid or a gas. The boundary can be traveling in the medium, or it can be stationary while the medium flows along it, or they can both be moving with different velocities; what matter is, their relative velocity with respect to each other.
Classification of Mach number regimes
While the terms subsonic and supersonic, refer to the speeds below and above the local speed of sound respectively. Scientists and Physicists often use the same terms to talk about particular ranges of Mach values.
Subsonic: The subsonic speed range is that range of speeds within all of the airflow over an aircraft is less than Mach 1. It is often less than 0.8. Generally, the passenger’s airplanes fly at this speed.
Transonic: The transonic speed range is that range of speeds within which the airflow over different parts of an aircraft is between subsonic and supersonic. So the regime ranges from 0.8 to 1.3.
Supersonic: The supersonic speed range is that range of speeds within which all of the airflows over an aircraft is more than Mach 1. But airflow meeting the leading edges is initially decelerated, so the free stream speed must be slightly greater than Mach 1 to ensure that all of the flow over the aircraft is supersonic. It is commonly accepted that the supersonic speed ranges from Mach 1.3 to 5.
Hypersonic: The hypersonic speed range is that range of speeds within which all of the airflows over an aircraft is more than Mach 5. The X-15, at Mach 6.72 is one of the fastest manned aircraft made of titanium skin. It is commonly accepted that the hypersonic speed ranges from Mach 5 to10.
High-hypersonic: The high hypersonic speed range is that range of speeds within which all of the airflows over an aircraft is more than Mach 10. The NASA X-43, at Mach 9.6 is one of the fastest aircraft. It is commonly accepted that the high hypersonic speed ranges from Mach 10 to 25.
Note: Our Indian Air Force also has a number of fighter aircraft like Jaguar, MIG-29, MIG-27. Mirage-2000, SU-30 MKI and MIG-21 BISON having Mach number range from 1.3 to 2.35. If you want to know more about these aircraft then check out this link.
So I hope you got the basics of Mach number and how its classified into different categories. If you still want to ask any question regarding this then you can ask in the comment section below.