| A numerical model of mixed flow (free-surface/pressurized flow) was developed. The model takes advantage of the existing similarity between the continuity and momentum equations which govern the unsteady open-channels flow, known as Saint-Venant equations, and those that governing the closed-conduit transient flow. In order to solve the mixed flow, the proposed model used only one set of equations, the Saint-Venant equations, regardless of the flow state (free-surface or pressurized). The proposed model incorporates the Preissmann Slot concept and the transition proposed by Leon et al. (2007). The Saint-Venant equations were solved using the MacCormack scheme and the Method of Characteristics.Initially, the proposed model was compared mathematically with other numerical schemes, and then it was compared experimentally with a physical model built on the Experimentation Fluid Mechanics Laboratory in the University of Puerto at Mayaguez Campus.The results show that the proposed model numerically predicted the variation of the hydraulic head for several situations. Also, the incorporation of the proposed transition by Leon et al. (2007), in the Preissmann Slot was important to avoid instabilities in the simulation. In comparison with the physical model, the results obtained predicted with precision the experimental values while the pipe was completely pressurized. In proximities to the free flow, the proposed model did not predict the experimental values as expected. |
