EFFECT OF MOUTHPIECE LENGTH AND POSITION ON THE DISCHARGE COEFPICZENT

This research investigates experimentally the different lengths, positions and direction of
mouthpieces to determine the value of the corresponding discharge coefficient (Cd in order to
specify the orifice characteristics that can be properly implemented in the field of imgation. The .. . .
e;perikents were carr~cd our in the Hydraulic Research lnsti~ute in a two sidcd glass flume (40 m
lone. -, 0.4 m wide and 0.6 rn decol. . 126 rims were executed dunne which the leneth and ~osition of
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the mouthpiece were varied. The tested lengths, with respect to the orifice diameter, were 0.5d,
ld, ISd, 2d, 3d, 4d and 5d, while the tested positions of mouthpieces were fitted either internally
(opposite to the flow direction) or externally (along the flow direction). Supplementary tests (36
tests) were canied out for determining the discharge coefficient of the orifice (without
mouthpieces) to act as a reference to the results using mouthpieces. The discharge was varied
from 5 to 13 Vs with increment of 1 11s. Measurements were carried out using point gauges,
ultrasonic flow-meter, current meters and a digital camera to monitor the flow inside and outside
the tested mouthpieces.
The results were analyzed andrepreseuted. The results revealed that increasing the throat length
results in decreasing the loss coefficient to a certain limit after which "Ca" becomes constant.
Also, the results proved that the discharge coeficient in the case of an internal mouthpiece is less
than that of the case of an'external mouthpiece as the separation increases. It was also found that
lowering the mouthpiece under the free surface causes the increase in the head (H) which produces
'more losses.