Effect of Weir Height on Flow Features of Duckbill Weir

Duckbill weirs do not have a straight crest in the direction perpendicular to the flow. The plan view of the weir consists of multiple and broken linear crests that increase its effective length. The advantages of this type of weirs are their higher discharge capacity, easy aeration as well as low fluctuations of water surface at the weir upstream. In this study, discharge coefficient of the duckbill weir is investigated numerically. Numerical modeling is carried out by Fluent v. 6.2. The simulated velocity and pressure field are coupled by using Piso method. Reynolds governing equations, turbulence k –ε model, and the Volume of Fluid (VOF) model are numerically solved to define pressure and velocity. Also a few equations are proposed to define the relationship of discharge coefficients with some dimensionless hydraulic Parameters. Results showed that as the height of weir is increased, the discharge coefficient increases and the value of discharge coefficient is constant after H/P = 0.3 and is fixed on 0.47. Also the increase in weir height has a significant effect on the increase in the duckbill weir on discharge coefficient, which is an important factor in designing these weirs. Equation 8, with error value of 0.01695, is presented as the best equation to estimate the discharge coefficient over duckbill weirs.