Hydraulic performance of circular crested oblique weirs

The present study attempted to improve the discharge capacity of oblique weirs by rounding their crests. Twenty-four oblique weir models have been tested in which oblique angle (alpha), weir height (P) and crest diameter (D) were changed. Analysis of the results shows that the discharge (Q(OC)) increases with the increase of effective head above crest (He). Values of discharge coefficient (C-D) are found decreasing slightly with the increase of (He/P) and (He/D) values and weirs of small oblique angles give lower values of C-D. An empirical expression is presented to determine C-D in terms of He/P, He/D and alpha (in radian) with a correlation coefficient of 0.90 and a standard error of 0.01. The highest discharge capacity is obtained from a weir having alpha = 20 degrees, P = 20 cm, D = 4 cm and D/P ratio = 0.2 in which the percentage increase in discharge is ranging between 147% and 175% compared to sharp crested normal weir. Comparison of the present study results with those of other investigations shows that circular crested oblique weirs offer higher discharge capacity compared with some other weir shapes. A simple design method is recommended through which the lasting dimensions and the head-discharge relationship of the weir can be predicted. (C) 2020 The Author. Published by Elsevier B.V. on behalf of Faculty of Engineering, Ain Shams University.