Question

Arrange the following flow types in increasing order of specific energy :
A. Sub critical flow
B. Critical flow
C. Supercritical flow
Choose the correct answer from the options given below :

• A. $C < B < A$
• B. $A < B < C$
• C. $B < A < C$
• D. $A < C < B$

Hint:

The "Critical" state is always the point of "Minimum Energy" ($E_{min}$). This is a fundamental property of open channel hydraulics.

Answer 1

The Correct Option is C

Concept: Specific energy ($E$) is the energy of flow per unit weight of water with respect to the channel bottom. The specific energy curve (E vs. y) shows that for a constant discharge, there is a minimum energy level.

Step 1: Identify the minimum energy state.
By definition, the minimum specific energy for a given discharge occurs at the Critical flow (B) state ($y = y_c$). Therefore, B must be the first in an increasing order list.

Step 2: Compare Subcritical and Supercritical energy.
For any specific energy greater than $E_{min}$, there are two possible "alternate depths":
• A high depth ($y > y_c$) representing Subcritical flow (A).
• A low depth ($y < y_c$) representing Supercritical flow (C). Since $E_{min}$ (Critical) is the absolute lowest, B is at the start. In a typical specific energy diagram, as we move away from $E_{min}$, both subcritical and supercritical flows have higher energy.