Numerical Analysis of Flow Parameters over the Cylindrical Weir Using Flow3D Model

Cylindrical weir is one of the most common structures for measuring flow rate in open channels. Cylindrical weir is one type of broad-crested weirs that has extensive application due to its stable flow pattern and ease of passing suspended solids. Therefore, in this article, flow over a 7.5 cm diameter cylindrical weir in the rectangular channel was simulated using k-ε turbulence model in three-dimensional flow3D model. Validation was performed with experimental results. The obtained root mean square error of comparison between numerical discharge coefficient and physical values was 0.3427, which represents a good agreement of hydraulic characteristics obtained from numerical and physical models. It was also observed that discharge coefficient value of cylindrical weir was greater than 1.0. Dimensionless ratio of hydraulic head to crest radius was an effective parameter on discharge coefficient, such that its 100% increase enhances discharge coefficient more than 100%. In the numerical model of cylindrical weir, such parameters as velocity, pressure, flow depth and kinetic energy and turbulence were analyzed and compared in some sections of the channel with respect to the weir. Results showed that depth and pressure in the upstream have larger amounts than in the downstream. But, results of velocity were opposite the pressure and hydraulic head. Finally, a relationship was provided for determination of kinetic energy of the flow over the cylindrical weir.