Question

When flow is compressible, mach number is the ratio of :-

• A. Flow velocity to speed of sound.
• B. Static head to velocity head.
• C. Potential energy to kinetic energy.
• D. Static to stagnant pressure.

Hint:

The Mach number is also a measure of compressibility. In gas dynamics, flows with \( M < 0.3 \) are often treated as incompressible because density changes are negligible.

Answer 1

The Correct Option is A

Concept: The Mach number (\( M \)) is a dimensionless quantity representing the speed of a fluid flow relative to the speed of sound in that specific medium.

Step 1: Mathematical Expression.
The formula for Mach number is: \[ M = \frac{v}{c} \] Where:
• \( v \) = Local flow velocity.
• \( c \) = Local speed of sound in the medium.

Step 2: Classification of flow.
Based on the Mach number, flow is classified as:
• Subsonic: \( M < 1 \)
• Sonic: \( M = 1 \)
• Supersonic: \( M > 1 \)