Novel design of composite broad-crested weir for determining open-channel emissions

Abstract

The current study deals with a composite broad-crested weir which is specially designed with the unique idea for a ‘constant discharge coefficient (Cd) of 0.6’. It is investigated experimentally and numerically. The available designs of the weir are unable to give constant Cd over a wide range of discharge as ‘Cd’ itself is relative to the head over the weir crest. Therefore an attempt is made to restrict Cd value to 0.6 irrespective of the variable head on the weir crest. This is achieved by adjusting the widths of the weir. With the novel objective, Cd is frozen to constant value and instead of it, ‘b’ is allowed to vary. The weir so designed is capable of producing constant Cd over a wide range of discharge and hence will be helpful from the viewpoint of field applications. Under existing laboratory conditions, the research reports for emissions varying from 20 to 100% of the design discharge. The numerical performance of the CBC weir through FLOW 3D is experimentally validated to examine the crest width effect and head over weir crest. In the experiments, Cd is found to vary proportionally with discharge from 0.518 to 0.648. The R-value is 0.999, with a mean error in discharge measurement being much less. HIGHLIGHTS The available designs of the weir are unable to give constant Cd over a wide range of discharge as ‘Cd’ itself is relative to head over weir crest.; Thus, an attempt was made to restrict the Cd value (0.6) irrespective of the variable head on weir crest.; This is achieved by controlling head over weir by adjusting the widths of weir.; With the novel objective, Cd is frozen to a constant value and instead, ‘b’ is allowed to vary.;

Keywords

• cbc weir design
• discharge coefficient
• head
• measurement