Modeling of broad crested weirs by using dynamic similarity and CFD

Abstract

Broad crested weirs and steps are used to regulate the flow in the channel, increase the water level at the upstream side, and measure the discharge. The construction of the broad crested weirs is more practical and also they are more stable compared with the other types of weirs. To serve in accordance with the purpose of their construction, broad crested weirs should be designed and built by considering certain criteria. Before the hydraulic structures are built, model experimental setups are constructed in the laboratory and problems to be encountered are tried to be determined. However, there may be differences between the structure to be built in real life (prototype) and model due to scale effect. These possible differences must be determined and necessary measures must be taken. In this study, the model and prototype of the broad crested weir are constructed in two different open channel systems by using Froude similarity. The geometric similarity between model and prototype is determined as Lr = 4. 44 experimental data were collected from model and prototype. The results obtained from the model and prototype are compared according to hydraulic similarity rules. In addition to the physical experimental setups, numerical models were created using the ANSYS Fluent for the model and prototype separately. By comparing the numerical model and physical experimental setups, optimum mesh size is tried to be determined. According to the results obtained from experimental setups, differences were observed in the position of critical flow depths and downstream water levels due to scale effects.