CHAPTER 5 : NON UNIFORM

FLOW IN OPEN CHANNEL

OPEN CHANNEL : A CHANNEL

WHERE THE WATER FLOWS WITH

MAINLY BY GRAVITY FORCE AND

THERE HAS A FREE SURFACE

AND ATMOSPHERE PRESSURE ON

THE WATER.

EXAMPLE

CHAPTER 5

1.Uniform flow

2.Non uniform flow

Steady Uniform Flow

UnSteady Uniform Flow

Steady Non

Uniform Flow

UnSteady Non

Uniform Flow

Rapidly Varied

Flow

Gradually Varied

Flow

TYPE OF FLOW :

CHAPTER 5

Uniform flow

- Depth, discharge & velocity

constant along the length of the

channel

y1 = y2

v1 = v2

v1 v2y1

y2

Q

CHAPTER 5

Non uniform flow

- Depth, discharge & velocity is

different along the length of the

channel

y1 = y2

v1 = v2

v1 v2y1

y2

Q

CHAPTER 5

Steady uniform flow -

- Depth, discharge & velocity is

constant along the length of the

channel and not change with time

Constant

depth

Constant

velocity

CHAPTER 5

UnSteady uniform flow

- Depth, discharge & velocity is

constant along the length of the

river but changed with time

CHAPTER 5

Steady non-uniform flow

- Depth, discharge & velocity is not

constant along the length of the

river and not changed with time

v1 v2y1

y2

Q

CHAPTER 5

UnSteady non-uniform flow -

- Depth, discharge & velocity is not

constant along the length of the

river and changed with time

v1 v2y1

y2

Q

CHAPTER 5

Gradually Varied flow

- Depth, discharge & velocity is

changed slowly along the length of

the river

- Example : Backwater in Sluice gate

v1 v2y1

y2

Q

CHAPTER 5

Rapidly Varied flow

- Depth, discharge & velocity is

changed rapidly along the length of

the river

- Example: Hydraulic jump

v1 v2y1

y2

Q

CHAPTER 5

CHAPTER 5

Specific Energy, E

Total of depth and kinetic energy of

the flow.

E = y + v2

2g

CHAPTER 5

Specific Energy, E

Alternath depth

CHAPTER 5

Specific Energy, E

Example 1:

A trapezoidal channel has dimension

of bottom width 6m and side slope

1:1 flows water at rate 8 m3/s.

Calculate specific energy for the

water if the depth of water is 2m.

2m1

1

CHAPTER 5

Discharge per unit width, q

q = Q

b

Froude Number, Fr

-Used to determine characteristic of flow

* Only for square &

prismatic channel

Fr = v

√(gy)

Fr < 1: subcritical (tranquil) flow

Fr = 1: critical flow

Fr > 1: supercritical (rapid) flow

CHAPTER 5

Subcritical flow

- Deep, calm

Critical depth, yc

Supercritical flow

- Shallow, fast

Critical flow

- Disturbance, small gravities wave

yc

= q2

g

1

3

CHAPTER 5

Minimum energy, Emin

Critical velocity, vc

Emin

= 3

2

yc

vc

= √(gyc)

CHAPTER 5

Example 2:

Water flows in square channel

which the width of the channel is 6m

and the depth of the water is 3m. If

the flowrate is 30 m3/s, calculate:

a. Froude number

b. Type of flow

c. Critical depth

CHAPTER 5

HYDRAULIC JUMP

- THE SUDDEN INCREASE IN

DEPTH OF FLOW IN SHORT

DISTANCE

- THE TRANSITIONAL FLOW FROM

SUPERCRITICAL TO SUBCRITICAL

CHAPTER 5

HYDRAULIC JUMP IN LABORATORY

CHAPTER 5

WHERE HYDRAULIC

JUMP OCCUR?

1. At the bottom of hydraulic

structure which supercritical flow

through into stilling basin.

2. At downstream of flum which the

supercritical flow transit to

subcritical flow.

3. In the trashrack channel

CHAPTER 5

TYPES OF HYDRAULIC JUMP

1. Undular Jump Fr1

1.0 – 1.7

2. Weak Jump Fr1

1.7 – 2.5

3. Oscillating Jump Fr1

2.5 – 4.5

4. Steady Jump Fr1

4.5 – 9.0

5. Strong Jump Fr1

> 9.0

CHAPTER 5

THE APPLICATION OF

HYDRAULIC JUMP

1. As Energy Disperser

2. For Chemical Diffusion

3. For Aeration

4. To increase Flow Level