Mach Number in Compressible Flow

The Mach number (M) is a critical dimensionless parameter used to describe fluid flow characteristics, especially in compressible fluids.

It is defined as the ratio comparing the speed of an object moving through a fluid to the speed of sound in that fluid.

Specifically for compressible flow, the Mach number is calculated as:

$ M = \frac{v}{c} $

Where:

• $v$ represents the local flow velocity.
• $c$ represents the local speed of sound in the fluid medium.

This ratio helps categorize flow regimes: subsonic (M < 1), sonic (M = 1), and supersonic (M > 1).

Option 1 correctly states that the Mach number is the ratio of flow velocity to the speed of sound.