Question Details

For a hydraulic jump formed in a rectangular horizontal channel, the sequent depth ratio is 2. The Froude number of supercritical stream is

Options

A

√3

B

√5

C

√6

D

√8

Show Answer

Correct Answer :

Option A

√3

Solution :

The correct option is √3.

Understanding the concepts:
A hydraulic jump occurs when a supercritical flow (high velocity, shallow depth) encounters a subcritical flow (low velocity, deep depth), resulting in an abrupt rise in the water surface. The depth before the jump is called the initial depth (y1) and the depth after the jump is called the sequent depth (y2). The ratio of these depths is the sequent depth ratio, y2y1.

For a horizontal, rectangular channel, the relation between the sequent depth ratio and the Froude number of the incoming supercritical stream (F1) is given by the Belanger equation:

y2 y1 = 1 2 - 1 + 1 + 8 F 1 2

Step-by-step Derivation:
We are given that the sequent depth ratio is 2:

y2 y1 = 2

Substitute this value into the Belanger equation:

2 = 1 2 - 1 + 1 + 8 F 12

Multiply both sides by 2 to clear the fraction:

4 = - 1 + 1 + 8 F 1 2

Add 1 to both sides of the equation:

5 = 1 + 8 F 1 2

Square both sides of the equation to eliminate the square root:

25 = 1 + 8 F 1 2

Subtract 1 from both sides:

24 = 8 F1 2

Divide both sides by 8:

F 1 2 = 3

Taking the square root of both sides gives the Froude number of the supercritical stream:

F1 = 3

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