EXPERIMENTAL INVESTIGATION OF FLOW CHARACTERISTICS OVER SEMI-CIRCULAR BROAD CRESTED WEIR MODELS
EXPERIMENTAL INVESTIGATION OF FLOW CHARACTERISTICS OVER SEMI-CIRCULAR BROAD CRESTED WEIR MODELS
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Date
2014-09
Authors
ABDULLAHI, UMAR
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Abstract
The overflow characteristics of semi-circular crested weir models were investigated. Twelve
models were fabricated and tested. The models were categorized into two groups; normal weirs
and oblique weir models. Both group of model had constant weir height and had the crest radius
varied three times; 5cm, 7.5cm and 10cm. However, for the oblique weir, the oblique angle was
varied three times; 60o
, 30o
and 15o
. From experimental results, it was observed that for normal
weirs, the coefficient of discharge (Cd) increases with corresponding increase in head to crest
height ratio (h/P). There were increases in Cd by 3.75%, 3.11% and 3.12% for 5cm, 7.5cm and
10cm normal weirs respectively. However, the oblique weirs showed corresponding increases of
(Cd) with the increase of (h/P) values; while the highest Cd values were obtained with weirs of
small oblique angle (α =15o
) for all crest radius tested. There were increases in Cd values by
0.4%, 4.8% and 4.86% as the oblique angle was varied from 900
to 600
, 600
to 300
and 300
to 150
respectively. For normal weirs, the performance in terms of the discharge magnification factor
(Qac/QNS) increases as (h/P) values increases. Hence, for all values of crest radius tested, normal
weirs of semicircular crests had performance better than those of sharp crested weirs. While, for
oblique weirs the performance in terms of the discharge magnification factor (Qac/QNS) increases
with the increases in (h/P) values for all oblique weirs tested, hence, Weirs of small oblique
angles give high discharge magnification factor and performance. Therefore, the model with
radius 5cm and oblique angle 15o was selected as the most efficient with a discharge coefficient
and magnification factor of 0.885 and 1.326 respectively. Expression for determining the flow
rate over the semi-circular weir was developed through dimensional and regression analysis
respectively. Similarly, linear and non-linear equations for estimating the discharge coefficients
of the weir models were developed. It was found that the flow rate equation developed had correlation coefficient of 0.986 with maximum error of 1.4%. Also, the linear and non-linear
equations developed had correlation coefficients of 0.664 and 0.574 with maximum errors of
33.5% and 42.6% respectively. Finally, the mathematical models developed for computing the
discharge coefficient can be used for design of normal and oblique semi-circular crested weirs.
Description
DEPERTMENT OF WATER RESOURCES AND ENVIRONMENTAL ENGINEERING,
FACULTY OF ENGINEERING
AHMADU BELLO UNIVERSITY, ZARIA NIGERIA.
Keywords
EXPERIMENTAl,, INVESTIGATION,, FLOW CHARACTERISTICS ,, OVER SEMI-CIRCULAR ,, BROAD CRESTED,, WEIR MODELS.