Simulation of Flow Characteristics Over Semi Cylindrical Weirs Using Ansys CFX Numerical Model

Weirs are the most important and very applicable barriers built across channels to control the flow of water or change its direction. They are also widely used in current measurement in open channels and many hydraulic engineering studies. The advantage of the semi-cylindrical and circular crested weirs as compared with other structures and measuring instruments is their higher discharge coefficient, stability of flow pattern, non-obstruction by floating materials, simplicity of design, durability, wide applicability and economics. One of the newest and most useful software in the field of computational fluid dynamics is Ansys CFX, which provides fairly reliable results. This software, which benefits from the continuity and momentum equations and the application of a turbulence model, was used to simulate flow over three semi cylindrical weirs with different radii in a laboratory study. After selecting the optimum mesh size for simulating the flow in the multiphase form of the fluid model, the k-ε, RNG k-ε and k-ω turbulence models were used to simulate the flow, and the results of the numerical solution was compared with the collected data extracted from experimenting with the physical models. The mesh size selection was based on the optimum mesh, root mean square error, mean absolute error and the coefficient of determination. The results showed that for cylinder with 4, 6, 7 cm radius, the discharge coefficient ranged from1.2 to 1.4. Furthermore, both the flow and the discharge coefficient increased with an increase in the radius. Moreover, the location of minimum pressure on the weir moved upstream with incremental discharge in conformity with previous studies.