Abstract
This paper presents an experimental and numerical study of transient flow from pressurized flow to open channel free surface flow in a horizontal circular pipe. A one-dimensional (1D) depth-averaged velocity model is developed to study the unsteady flow in mixed pressurized-free surface flow, which can be occurred due to the rapid movement of a gate. The numerical approach is an interface tracking and after finding the interface position, pressure drop is considered at the interface. To evaluate the numerical model performance, some experiments were conducted in a straight circular pipe using water and air as two fluids. In order to generate the undular bore, in some cases a weir was used at the open end of the pipe. The results of the comparisons lead to the conclusion that the pressure drop at the interface is very important. Results also showed that in the case of free overfall, the hydrostatic and Bouussinesq models can reproduce air cavity front shape with reasonably good agreement with experiments.
