FLUID MECHANICS

1. KALI CHARAN NIGAM INSTITUTE OF
TECHNOLOGY, BANDA
LECTURE
ON
NOTCHES AND WEIR
FLUID MECHANICS AND FLUID MACHINE(KME302)
( III SEMESTER )
BY : DEEPAK KUMAR YADAV
ME DEPARTMENT

2. INDRODUCTION
NOTCH : A notch is a device used for measuring for
rate of a liquid through a small channel or a tank.
WEIR: A weir is a concrete or masonary structure,
placed in open channel over which the flow occurs.
It is generally in the form of vertical wall, with a
sharp edge at the top , running all the way across
the open channel.

3. DISCHARGE OVER A RECTANGULAR
NOTCH OR WEIR
The expression for discharge notch or weir is the
same.
Let H = Head of water over the crest
L = Length of the notch or weir.
The area of strip = L×dh
and theoretical velocity of water flowing through
strip=

4. DISCHARGE OVER A RECTANGULAR
NOTCH OR WEIR
The discharge dQ, through strip is
dQ= Cd×Area of strip × Theoretical velocity
Total discharge Q,

5. NUMERICAL
• PROBLEM 1 : Find the discharge of water flowing
over a rectangular notch of 2m length when the
constant head over the notch is 300mm. Take
Cd=0.6.
• PROBLEM 2: Determine the height of a rectangular
weir of length 6m to be built across a rectangular
channel. The maximum depth of water on the
upstream side of the weir is 1.8m and discharge is
2000 lt/s. Take Cd=0.6. [AKTU 2015-16]

6. THANK YOU