Characteristics of flow over normal and oblique weirs with semicircular crests

الملخص EN

In this investigation, the characteristics of free flow over normal and oblique weirs with semicircular crests are studied experimentally.

For this purpose, forty eight weir models were constructed and tested.

The first twelve models were normal weirs in which the crest radius was varied three times ; 5cm, 7.

5cm and 10cm.

For each crest radius, the weir height was varied four times ; 35cm, 30cm, 25cm and 20cm.

The remaining models were oblique weirs.

The oblique angle was varied three times ; 60°, 45° and 30°.

In weirs of the same oblique angle, the crest radius and weir height were varied similarly to those of normal weirs.The experimental results showed that for normal weirs, the discharge coefficient (Cdw) increases with the increase of head to crest height ratio (h / P) for the same height of weir.

In case of oblique weirs, it was found that (Cdw) decreases with the increase of (h / P) values and weirs of small oblique angle give high values of (Cdw ).For normal weirs, the discharge magnification factor (QNC / QNS) and performance increase as values of (h / P) increase.

Normal weirs of semicircular crests perform better than those of sharp crested weirs for all values of weir height and crest radius tested in this study.

While, for oblique weirs the discharge magnification factor (QOB / QNS) and performance increased with the decrease of (h / P) values.

As (h / P) value approaches zero, the discharge magnification factor approaches the length magnification of the weir.

Weirs of small oblique angles give high discharge magnification factor and high performance.

A simple procedure was applied for the hydraulic design of oblique weirs.

The design method yields the final dimensions of a weir and predicts its headdischarge curve for the whole range of operation.