بررسي آزمايشگاهي خصوصيات جريان بر روي ضريب دبي سرريز مركب لبه پهن مستطيلي

Experimental investigation of flow characteristics on discharge coefficient over compound rectangular broad-crested weir

Compound weirs are composed of two sections: 1.Lower entrance section 2.Upper entrance section. Lower entrance section is designed in different shapes such as rectangle, trapezoid, ... and it works singly in low discharges. Flow discharge is measured accurately and sensitively according to weir shape in such a condition. In high discharges, upper entrance section prevents water surface from having remarkable increase at upstream of weir and provides the possibility of discharge measurement with acceptable accuracy. In this study, flow over 15 rectangular broad-crested weirs was simulated with different sizes in central width of weir, height and length of weir using experimental models and the effects of these parameters on discharge coefficient, velocity coefficient, and modular limit were investigated. Results show that with increasing dimensionless parameter: head to weir length (h|/L), discharge coefficient (Cd) increase, in other words, Cd in single section (hi/L)<0.24 is lower than compound weir section. Also this condition for hi/p<0.94 (p is weir height) is true. In compound weir condition, reduction in central cross section width and weir height causes to increase modular limit.