Open Channel

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Engineering and Design Department  
Civil Engineering with Sustainability 
CE2001 Fluid Mechanics and Hydraulics 
Specific Energy of flow in Open Channels Experiment  
 
Lecture’s: Dr Robin Wakelin 
 
Group Number: 1 
Group Members: 
 Omar Abo Madyan, Blain Davis, Joshua James,  
Alisa Magar, Christopher Peckham, Tun Soe 
 (15% of module mark) 
Submission deadline: 12am, Monday, 28th/January/2013 
Student name: Omar Abo Madyan 
Student ID: 1114107

Abstract
The experiment conducted was in order to find the relationship between the specific energy and the depth in an open channel flowing through an undershot weir, in order to understand the behavior of a flow at different depths, allowing for accurate engineering and designing of open channels. Depth measurements where taken at up-stream and down-stream for several weir openings in order to generate a specific flow open channel diagram, which will contribute to the analysis of open flow channels. In many cases the major features can be expressed in terms of only a few variables, whose behavior can be described adequately by a simple theory. The principal forces at work are those of inertia, gravity and viscosity, each of which plays an important role. The flow rate was constant throughout the experiment at 4.98 l/s, and values for Ec and yc where calculated at 0. 04560 and 0.03040 respectively.

Table of contents:

Abstract---------------------------------------------------------------------------------------2
Introduction----------------------------------------------------------------------------------4
Theoretical background--------------------------------------------------------------------5
Methodology----------------------------------------------------------------------------------6
Results -----------------------------------------------------------------------------------------7
Conclusions, discussion---------------------------------------------------------------------8
References-------------------------------------------------------------------------------------9

1. Introduction
Open-channel flows, a branch of hydraulics, is a type of flow with a free surface (interface between water and air), and are mostly characterized as turbulent flow but, it can be classified based on the flow depth according to time and position (Steady flow, Unsteady flow, Uniform flow, Non-uniform flow). The viscosity of the liquid and internal forces such as friction causing energy loss affects the behavior of the flow along with the channel capacity and slope, which highly influence the flow.

The experiment conducted was in order to determine the relationship between the specific energy and the depth of flow in a rectangular open channel flowing through an undershot weir as illustrated in the figure below: -

Figure 1

The total energy of the flow in a channel with a bed as datum, can be expressed based on Bernoulli’s energy equation as:
E=y+ν22g=y+(QA)22g

E=Total energy above the channel bottom, termed, specific energy. y= depth of flow; v= velocity of flow, Q=discharge
A= cross sectional area, g=gravitational constant (9.81m/s2)

For a Rectangular channel, where q=discharge per unit length

QA=bqby=qy ∴E=y+q22gy2

Hence from these equations, a specific energy curve can be generated (figure 2), it represents the max possible discharge for a given E (i.e. most efficient flow condition), it also enables determination of Q as yc and VC can be calculated readily making the diagram a critical tool for solving open channel flow problems and assessing flow behavior especially in rapidly varied flow problems.

2. Theoretical background

Figure 2
Figure 2

Features of Specific Energy Curve (figure 2)
* A plot of E against y gives a curve with 2 asymptotes–one on the E axis and the other on a 45-degrees line passing through the origin (i.e....
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