A Finite Volume Model for Mixed Surface-Pressurized Flows in Drainage Systems

This paper presents a Finite Volume (FV) scheme for simulating free surface flows, pressurized flows and their simultaneous occurrence (mixed flows). The free surface region is modelled using the 1D Saint-Venant equations, the pressurised region is modelled using the classical 1D compressible waterhammer theory and the interface is modelled by enforcing mass, momentum and energy relations at a shock. The proposed approach is able to simulate mixed flows without restriction of the type of flow in the free surface region. The results show that the proposed model is robust and able to (i) accurately describe complex flow features—such as positive and negative open channel-pressurized flow interfaces, interface reversals, and open-channel surges, and (ii) simulate negative pressures in the pressurized flow regime (not presented in this paper due to space limitations).