بررسي خصوصيات هيدروليكي سرريزهاي استوانه اي و تاج دايره اي

Characteristics of circular-crested and cylindrical weirs

Circular-crested and cylindrical weirs are used for flow measurement and have wide applications in hydraulic engineering. They can also be used to control the water level in farm ponds and reservoirs. The advantages of the circular-crested and cylindrical weirs compared to other weirs include the stable overflow pattern, the ease to pass floating debris, the simplicity of design, the higher discharge coefficient and the associated lower cost. In this study, the hydraulic characteristics of circular-crested and cylindrical weirs such as the coefficient of discharge, the relative depth over the crest and the energy loss were investigated. A total of eighteen physical models, divided in five groups were tested. It is found that the coefficient of discharge of cylindrical and semi-cylindrical weirs increase when the relative total head is increased. It is also shown that in circular-crested weirs the variation of upstream and downstream slopes do not change the coefficient of discharge for a specific relative total head. The head loss for cylindrical weir is more than that of semi-cylindrical for a specific relative total head. For all the models head loss increases when the downstream slope is increased. The relative flow depth over the crest is 0.7 for cylindrical and semi-cylindrical weirs. The relative flow depth over the crest increases a little for relative total head greater than 0.6 when the upstream slope is increased and does not change with the downstream slope.