Experimental Investigation of Arched Sharp-Crested Weir Flow and Comparing it with Rectangular Weir

Abstract

The hydraulic behavior of the arched sharp-crested weirs is investigated and compared with rectangular weirs in this research. For this purpose, a laboratory study was made on a physical model, including weirs with four different arc lengths each with five different heights. Experiments were carried out in free flow condition and in both aerated and non-aerated cases of weirs. Laboratory data were discharge rate and water head amount on weir. The water head on weir has been read over the course of various discharge flows over a range of about 3–140 l/s. Test results proved that the arched weir discharge coefficient, while seriously dependent on the $\frac{H}{P}$ ratio, is also a function of the weir arc length. The variations of this coefficient with respect to $\frac{H}{P}$ ratio are nonlinear and different from rectangular weir one. It will be reduced and attain an almost constant amount by increasing the ratio. Experimental results show that the circle discharge coefficient amount is bigger than rectangular one in $\frac{H}{P}$ values less than 0.2 and it is smaller than one in $\frac{H}{P}$ ratio more than 1.2. Moreover, arched weir discharge value is always more than the rectangular weir in the same status. In the range of present experiments, increments of the arched weir discharge relative to the rectangular vary from 10 up to 80%. It depends on the height and length of the weir crest.