Document Type : Original Article
Abstract
Labyrinth weirs are often a favorable design option to regulate upstream water elevations and increase flow capacity; nevertheless, it can be difficult for engineer to optimal design due to the complexities of nappe behavior, many geometric design and hydraulic variables. A level of sedimentation in upstream and submergence in downstream of the weirs are parameters, which affects on the performance of these structures. In this research the effect of different levels of tail water (one third and two third of weir height) and upstream sedimentation level (non-sedimentation and in sedimentation level of 90 percent of weir height) on the discharge coefficient of different geometers of trapezoidal labyrinth weirs for two conditions, that was investigated experimentally. The analysis of results indicated that increasing tail water depth to one third of weir height didn’t affect on the discharge coefficient of weirs. by increasing tail water depth to two third of weir height, air cavity volume under nappe decreased. Therefore, the flow pattern of the nappe changed from leaping to clinging condition and upstream head decreased. As a result, the labyrinth weirs discharge coefficient in non-sedimentation and sedimentation level of 90 percent of weir height increased about 3.3 to 12.2 and 2.1 to 9.2 in maximum discharge, respectively in comparison un-submergence tail water. The statistical equation for estimation of the discharge coefficient of trapezoidal labyrinth weirs for upstream sedimentation and submerged conditions was developed.
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