Flow over Rectangular
Introduction:
Weirs are generally used to measure discharge in open channels were accuracy is
required. Weirs are sometimes used in hydraulic engineering to regulate the flow in
rivers and channels.
Discharge over sharp crested weirs is a device used to measure Q accuracy +- 2%
A sharp crested weir is formed from a steel or thin stainless steel (rectangular,
triangular, trapezoidal, V notch).
Objective:
To determine the coefficient of discharge and the head-discharge relationship for
rectangular.
Equipment:
Hydraulic bench, hook and point gauge.
Theory:
The theoretical discharge for rectangular notch is given by
Qtheo = 2/3(2g)1/2 bH3/2
Where;
H: height of flow over notch.
b: the width of the notch.
To obtain the actual discharge, a coefficient of discharge Cd
Qactual = Cd 2/3(2g)1/2 bH3/2
Procedure:
1- Set a slope degree below 2%
2- Fit the rectangular weir plate at the channel discharge end
3- Start the pump and regulate the discharge value in order to reach the required flow
rate
4- Measure the difference between the water surface height (m) against the bed
upstream of the weir plate, and the weir height p (m)
5-Calculating the static head value H (m) by h = H-p, where p is the still height
against the channel bed
6- Measure and record H and Q
Analysis:
Results # 1:
Q
(m3/h)
Table (1): Q & H
Q (m3/s)
H (m)
Results # 2:
Table (2): H3/2-vs-Q
Q (m3/s)
H3/2 (m)