Fluid Mechanics Lab
Submitted By:
M.Usman Nisar
Asad Iftikhar
Hassan Jan
Annas Khan
Ali Taimoor
Mosaeeb Zaman
Table of Contents
TITLE: FLOW OVER WIERS....................................................................................................................3
ABSTRACT:...........................................................................................................................................4
OBJECTIVE:..........................................................................................................................................5
INTRODUCTION:..................................................................................................................................5
THEORY:..............................................................................................................................................5
TECHNICAL SPECIFICATIONS:..............................................................................................................7
EXPERIMENT:......................................................................................................................................9
AIM:....................................................................................................................................................9
PROCEDURE:.......................................................................................................................................9
OBSERVATIONS AND CALCULATIONS:.................................................................................................9
CONCLUSION:....................................................................................................................................10
Flow over weirs
Abstract:
This report depicts the study of flow over weirs. In this experiment we studied basically flow over two
weirs. First one is rectangular shape and the second one is v shape. Initially we calculate the flow rate
over these weirs which is the actual flow rate and then we calculate the flow rate by the given formula
and in the end with the help of above mentioned flow rates we calculated the discharge coefficient.
Objective:
Our objective is to study the effects of different weirs that are produced on our flows.
Introduction:
What is weir?
A weir is a barrier across a river designed to alter its flow characteristics. In most cases, weirs take the
form of obstructions smaller than most conventional dams, pooling water behind them while also
allowing it to flow steadily over their tops. Weirs are commonly used to alter the flow of rivers to
prevent flooding, measure discharge, and help render rivers navigable
Theory:
The theoretical discharge for the rectangular weir is given by
Qtheo= (2/3) (2g)(1/2)x B x H(3/2) (1)
And for Vee notch is given by:
Qtheo= (8/15) x (2g) (1/2) x tan(θ/2) x H(5/2) (2)
Where
B = Breadth of rectangular notch
H = Height of flow over notch
θ = Angle of Vee notch
g = Gravitational acceleration
To the contraction of the flow area downstream of the notch, the actual discharge Q is considerably less
and may be expressed as:
Qact = Cd x (2/3) x(2g)(1/2)x B x H(3/2) (3)
Qact= Cd x Qth (4)
Where Cd : the coefficient of discharge for the rectangular notch. And expression for Vee notch:
Qact= Cd x (8/15) x (2g) (1/2) x tan(θ/2) x H(5/2) (5)
Qact= Cd x Qth (6)
Weirs are normally categorized by their shape as either sharp-crested or broad-crested. This laboratory
experiment focuses on sharp-crested weirs only. Two different types of weirs will be introduced, The V-
notch weir and the rectangular weir (horizontal weir with end contractions). Figure 8 represents the
rectangular weir while figure 9 represents a Vee notch weir.
Rectangular Weir Vee Notch Weir
TECHNICAL SPECIFICATIONS:
Dimensions for the following Weirs are given below. Following diagram shows the rectangular weirs one
with broad face and the other one is narrow rectangular weir. Technical data is given in the table.
Broad rectangular weir and Narrow rectangular weir
Types Broad rectangular weir Narrow rectangular weir
Breadth 2” 1”
Depth 3” 3”
Technical data for v type weirs
The V type Weirs (a angle 90o and b angle 42o)
Experiment
To determine co-efficient of discharge of flows over V shape and rectangular shape weirs.
Procedure:
First insert the V shape weir in the passage of flow at its proper place and fix it tight by using
thumb nuts.
Position the hook and point gauge, mounted on the instrument carrier, on the side channels
adjacent to the weir plate.
Now start the pump and allow the water to enter into the channel by opening the control valve.
Now let the water come to the level of plate and when water start flowing over the plate close
the control valve and let the water to stabilize itself.
Set the height gauge to a datum reading using the top of hook.
Allow the water to the channel and adjust the flow control valve to obtain heads H increasing in
steps of about 1cm.
For each flow wait until the conditions become steady and note the readings of height H and
volume V using volumetric tank and calculate the flow rate.
Take at least three readings.
Observations and Calculations:
Sr # Time Qact H Qtheo Cd
(sec) (m3/sec) (m) (m3/sec)
1 9.1 3.23e-4 0.076 4.54e-3 0.05
2 8.9 4.43e-4 0.084 6.39e-4 0.74
3 7.5 5.55e-4 0.091 7.10e-3 0.09
Conclusion:
After performing the experiment and on behalf of readings we obtained value of discharge co-efficient is
very small which indicates that our practical results are quite close to the the ideal ones.
