Numerical simulation of transient flow in storm sewers using standard and improved McCormack scheme

This paper describes the results of the first part of the research project which aims at developing a hydraulic model for simulation of unsteady flows in storm sewers ranging from gravity flows to surcharged flows resulting with water outflow on the ground surface and propagation of inundation in the flooded area. The paper focuses on the development and assessment of a second-order explicit numerical scheme for unsteady flows in sewers, but only in a single pipe at this moment, without any special elements such as manholes or drop shafts and with no water overflowing problem. The problem of water flow in sewer system pipes is associated with some specific phenomena occurring in conduits during storm events. If the pipes start to be fully filled with water, there is a transition from free surface to pressurized flow. Then, the vice versa effect can be observed. Such transitions are also possible in sewers when the discharge is controlled by control devices, such as gates for example. Moreover, the rapidly varied flow with some hydraulic local effects such as hydraulic jumps or bores can appear during extreme rain episodes. The appropriate modeling techniques have to be applied to solve these problems. The ‘Preissmann slot’ concept is implemented to simulate the pressurized flow. The original and improved McCormack scheme is used for transcritical flow simulation. The calculated results obtained for some benchmark tests are compared with numerical solutions and laboratory measurements published in the technical literature.