Available Online: http://scholarsmepub.com/sjet/ 373
Saudi Journal of Engineering and Technology ISSN 2415-6272 (Print)
Scholars Middle East Publishers ISSN 2415-6264 (Online)
Dubai, United Arab Emirates
Website: http://scholarsmepub.com/
Experimental Investigation of Flow Characteristics over Crump Weir with
Different Conditions
Dr. Abdul-Hassan K. Al-Shukur, Dr. Mohammed Abbas Al-jumaily, Zahraa Shaker
Department of Water Resource Engineering, University of Kufa, Najaf, Iraq
*Corresponding author
Zahraa Shaker
Article History
Received: 03.09.2017
Accepted: 17.10.2017
Published: 30.10.2017
DOI:
10.21276/sjeat.2017.2.10.3
Abstract: Weirs are the most extensively used hydraulic structures in the different
fields of hydraulics, environmental, irrigation, and chemical engineering, as flow
measuring and flow control devices in open Channels. The object of the present paper
is to study the effect of the geometry of crump weir on the coefficient of discharge
(C
d
) under different flow conditions. The experimental work was conducted in
rectangular laboratory flume; fifteen physical models were used with five upstream
angles (17
o
, 22
o
, 27
o
, 32
o
and 37
o
) and three different crest heights (10, 15 and 20) cm
under free flow conditions. The results show that C
d
value will increase with the
decrease of crest height as well as with increasing flow rate; it is also directly
proportional to the upstream slope and inversely to the downstream slope.
Computational fluid dynamic (FLOW 3D) were used to conduct new experiments.An
empirical relation was obtained to estimate the coefficient of discharge Cd under
different height and upstream slopes crump weirs.
Keywords: weir, angle, flow
INTRODUCTION
Weirs are the most usually hydraulic structures; they have been widely used
for flow measurement in channels and rivers because of its simplicity. There are four
function uses of weirs, namely, water level management, flow gauging, for
environmental aims or for channel stabilization [1].
There are many types of weirs; according to
their geometry (Broad crested weir such as rectangular
broad crested weir, and Sharp crested weir such as
rectangular, triangular, and trapezoidal crested
weir),function(flow gauging, flood control, irrigation),
and flow conditions(free or submerged) [2]. ne of the
interesting types is the triangular short crested weir
(crump weir), which is a special type of broad crested
weir.The Crump consists of two parallel walls with a
specially shaped overflow wall on the downstream side.
The wall top is sloped at 1:2 on the upstream side and
1:5 on the downstream side.
It is very essential to study the behavior of the
flow over the crump weir. A limited number of studies
have been dedicated to the flow over this sort of weirs,
Keller, [3] studied the behavior of crump weir under
different transverse crest slopes, he concluded that for
the was concluded that for the same transverse crest
slope, the structure behaves as one half of flat-V weir at
relatively large heads. Hudson et al., [4] Checked the
calibrations performed on the Crump weirs, he showed
that accurate operation of Crump weirs is feasible in
non-standard Conditions. John Demetriou and Eugene
Retsinis, [5] studied the discharge coefficient for
different bed slope of the open channel; he conducted
three equations for zero, positive and negative channel
slope. Mohd Adib Mohd Razi et al, [6] studied the
relationship between the rate of flow and upstream head
over crump weir besides obtaining an approximate free
surface profile in unsteady open channel flow. Safaa N
Hassan, [7] studied the influence of different quantities
of total solids (TS) on the pattern of flow and
coefficient of discharge in open channels and water
treatment plant for crump weir, he conducted that the
coefficient of discharge changes with the value of the
total solid (TS). In this paper experimental work for a
crump weir is performed, in order to find out the effect
of height and upstream and downstream slope on
discharge coefficient and flow characteristics over the
weir.
EXPERIMENTAL SETUP AND PROCEDURE
The laboratory flume used in this study is a
rectangular flume of 18.6 m long, 0.5 m wide and 0.5m
deep. The flume walls are made from a glass fiber to
provide visual observation, while the bed is stainless
steel. A V-notch sharp crested weir is located below the
outlet of the inlet tank measuring the actual discharge
which passes through the flume section as shown in
figure 1.
Abdul-Hassan K. Al-Shukur et al.; Saudi J. Eng. Technol.; Vol-2, Iss-10 (Oct, 2017):373-379
Available Online: http://scholarsmepub.com/sjet/ 374
Fig-1: The flume
Fifteen different model of crump weir were
used, five upstream angles (17
o
, 22
o
, 27
o
, 32
o
and 37
o
with three crest height for each angle (10, 15 and 20)
cm. The channel was adjusted to the horizontal position.
each model of crump weir were put just 9 meters from
the upstream channel in order to provide sufficient
distance to settle the water and take accurate results.
The flow stability is attained. When the upstream water
level became constant, the parameters required are
measured. The procedures have been repeated for each
crump weir model with different cases. For each type of
the crump weir a series of tests under different flow
rates were conducted. A total of 120 runs were
conducted at the experimental work.
THEORETICAL ASPECTS
Weirs are elevated hydraulic structures used to
measure flow and/or to control the water elevation at
outflows from basins and channels. The crump weir has
a triangular profile as it shown in Figure 2. There are
two different types of flow conditions: the modular flow
condition, and the non-modular flow condition.
Modular Flow occurs when the weir operates under
owned, with high downstream water level low Figure 3.
In this condition, the upstream head is not affected by
the downstream head; therefore it is possible to
determine the flow rate by taking a single measurement
of upstream.
Q
m
C
d
B H
3/2
√
…………….. (1)
Where:
Qm = Flow rate for modular flow (L3T-1)
Cd = Modular discharge coefficient
g = Gravity (LT-2)
B = Breadth of weir (m). b = 0.5 m
H= Total Head upstream of weir crest (L).
While, non-modular flow occurs when the
weir operates drowned, with high downstream water
level Figure (4). In this condition, a single measurement
of upstream head is not adequate to determine the actual
flow because the upstream head is affected by changes
in the downstream head. Then, a dimensionless
reduction factor is required to correct the non-modular
flow:
f = Q/Q
m
,
Where
Q = Flow rate for Non-Modular Flow (m3/s), C
d
is the
discharge coefficient.
By using the data obtained from the laboratory
work and equation 1, the value of C
d
for each model has
been calculated under different flow rates, in order to
discover the outcome of upstream slope and crest height
of crump weir on the value of the C
d
.
Abdul-Hassan K. Al-Shukur et al.; Saudi J. Eng. Technol.; Vol-2, Iss-10 (Oct, 2017):373-379
Available Online: http://scholarsmepub.com/sjet/ 375
Fig-2: crump weir model
Fig-3: Crump weir during modular flow condition (Redahegn, 2009)
Fig-4: Crump weir during non-modular flow condition (Redahegn, 2009)
EFFECT OF DISCHARGE AND CREST HEIGHT
ON C
D
:
The values of C
d
are plotted against the unit
discharge for different weir upstream slopes under the
same weir height as shown in Figures (5, 6 and 7) in
order to explain the variation of C
d
value with the
discharge. It is clear from these figures that there is
Increase in C
d
values with increased flow rate. While
figures (8 and 9) shows that the C
d
value decreases by
increasing crest height.
Abdul-Hassan K. Al-Shukur et al.; Saudi J. Eng. Technol.; Vol-2, Iss-10 (Oct, 2017):373-379
Available Online: http://scholarsmepub.com/sjet/ 376
Fig-5: variation of (C
d
) with (Q
actual
) for the five upstream angle with crest height of 0.2m
Fig-6: variation of (C
d
) with (Q
actual
) for the fiveupstream angle with crest height of 0.15m
Fig-7: variation of (C
d
) with (Q
actual
) for the fiveupstream angle with crest height of 0.1m
Abdul-Hassan K. Al-Shukur et al.; Saudi J. Eng. Technol.; Vol-2, Iss-10 (Oct, 2017):373-379
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Fig-8: variation of (C
d
) with (Q
actual
) for upstream angle 27 degree
Fig-9: variation of (C
d
) with (Q
actua
l) for upstream angle 17 degree
EFFECT OF UPSTREAM AND DOWNSTREAM
SLOPE ON C
D
:
The coefficient of discharge C
d
is inversely
proportional the upstream slope as shown in figures (10,
11 and 12). For the same crest height and flow rate, Cd
value decrease by increasing upstream angle value and
increase by decreasing the same angle. It notices that an
increase in upstream angle (from 27
o
to 32
o
) and (from
27
o
to 37
o
) reducing Cd value about (5.1 % and 7.2 %)
respectively. While reducing upstream angle (from 27
o
to 22
o
) and (from 27
o
to 17
o
) make an increase of Cd
value about (1.5 % and 3.7 %) respectively.
Abdul-Hassan K. Al-Shukur et al.; Saudi J. Eng. Technol.; Vol-2, Iss-10 (Oct, 2017):373-379
Available Online: http://scholarsmepub.com/sjet/ 378
Fig-10: variation of (C
d
) with upstream angles for different discharge and crest height 0.2 m
Fig-11: variation of (C
d
) with upstream angles for different discharge and crest height 0.15m
Fig-12: variation of (C
d
) with upstream angles for different discharge and crest height 0.1m
Abdul-Hassan K. Al-Shukur et al.; Saudi J. Eng. Technol.; Vol-2, Iss-10 (Oct, 2017):373-379
Available Online: http://scholarsmepub.com/sjet/ 379
CONCLUSIONS
The researchers have arrived at the following
conclusions:
1. For the same crest height and flow rate, C
d
value
decrease by increasing upstream angle value and
increase by decreasing the same angle. It notices
that an increase in upstream angle (from 27
o
to 32
o
)
and (from 27
o
to 37
o
) reducing C
d
value about (5.1
% and 7.2 %) respectively. While reducing
upstream angle (from 27
o
to 22
o
) and (from 27
o
to
17
o
) make an increase of C
d
value about (1.5 % and
3.7 %) respectively.
2. An increase in discharge of (-232.9 %) led to an
increasing in C
d
of (172.5, 168.3, 155.2) % for crest
height 20 cm, 15 cm, and 10 cm respectively for
(α= 27
o
, β=11
o
). While for weir with (α= 22
o
,
β=11
o
) the rates of the increase in C
d
value are
(170.4, 167.7, 152.03) % , for weir with (α= 37
o
,
β=11
o
) the rates of the increase in C
d
value are
(173.3, 165.8, 155.2) % , for weir with (α= 32
o
,
β=11
o
) the rates of the increase in C
d
value are
(174.3, 170.7, 165.9) % , and for weir with (α= 17
o
, β=11
o
) the rates of the increase in C
d
value are
(169.7, 163.3, 149.2) % .
3. For the same flow rate and upstream angle, the
coefficient of discharge inversely proportional to
the crest height. An increase in crest height from 10
cm to 15 cm (50% increases) cause a reduction in
Cd value about 29.9%. While anincrease in crest
height from 20 cm to 10 cm (100 % increases)
reducingCdvalue about (45.9 %)
REFERENCES
1. Rickard C., Day R., & Purseglove, J. (2003). River
Weirs – Good Practice Guide. Environment
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Almondsbury, Bristol.
2. Bengtson, H. H. (2011). Sharp-Crested Weirs for
Open Channel Flow Measurement.
3. Keller, R. J. (2015). Sloping Crest Crump W E I
R”, University of Leeds, Copyright ASCE.
4. Hudson, J. A. (1990). Choice and Calibration of
Stream Flow Structures for Two Mountain
Experimental Basins Flow measurement and
instrumentation. IAHS Publ. no. 193.
5. Demetriou, J., & Retsinis, E. (2013). Triangular
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University of Athens, Address: JD Research
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Environmental Engineering Faculty of Civil and
Environmental Engineering University Tun
Hussein Onn Malaysia, 86400 BatuPahat, Johor,
MALAYSIA.
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the Discharge Coefficient of Spillway, Broad
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