Above what Mach number must compressibility be considered wh

Above what Mach number must compressibility be considered when calculating flow properties? Why?

Solution

As we know Compressibility is a physical property of the fluid, and is very highly related to fluid flow. As fluid with Mach Number less than 0.3 is considered out to be incompressible and above 0.3 is considered to be compressible.

Reason : Air has a high compressibility and for flows with Mach numbers less than about 0.3 the pressure forces are sufficiently small that the air density doesn\'t change and hence the flow is incompressible.