ارزيابي جريان بر روي سرريز لبه تيز مركب مثلثي - مستطيلي

Flow over Sharp-Crested, Truncated-Triangular Weirs

Truncated weirs are used to measure flow rate and control water surface upstream, in irrigation canals and laboratory flumes. The main advantages of such weirs are the ease of construction and the capability of measuring a wide range of flows with sufficient accuracy. The hydraulic performance of truncated weirs has not been widely investigated, and not sufficiently documented in the literature. This paper presents the results of an analytical and experimental study on flows over sharp-crested, truncated-90° triangular weirs with different side construction ratios (b/B= 1, 0.7, 0.5, 0.3). Onedimensionalflow equation is presented from the integration of both analytical and physical based solutions. A coefficient of discharge has been introduced to represent the complex functions in the equation and to overcome any uncertainties. Intensive experiments were carried out to evaluate the discharge coefficient in terms of the most significant parameters such as: the geometry of the weir, upstream head and tail water levels, artificial aeration of the weir on downstream face. The results are presented in the form of non-dimensional figures from which the flow rate can be calculated in conjunction with the proposed flow equation. The present results indicate that (1) truncated weirs designed within the limitations from this study can be used as flow measuring structures with sufficient accuracy up to f5%; (2) stability and accuracy of this measuring system are achieved where the threshold condition of (h >20 mm) or (h/P, >0.I) are provided; (3) weirs with side contraction of (b/B 0.5) are more efficient; (4) direct evaluation of discharge coefficient, Ca, is not recommended for the condition of submerged flow over the weirs; (5) modular limit of the flow over the weir has to be checked for an accurate evaluation of the flow. This limit is determined in terms of the weir geometry and head water level; (6) in case of the submerged flow, a reduction factor known as submergence coefficient,Y, is introduced to evaluate the actual flow rate over the weir in terms of the relative tail and head water levels (t/h), and side contraction ratio (b/B); (7) these types of weirs are efficient enough by a degree of submergence up to t/h< 0.3; (8) artificial aeration has no significant effect on the flow capacity over truncated weirs.