Improved Modeling of Unsteady Free Surface, Pressurized and Mixed Flows in Storm-Sewer Systems

The main aim of this thesis is to advance our understanding of the process of flood-wave propagation through storm-sewer systems by improving the methods available for simulating unsteady flows in closed conduits ranging from free surface flows, to partly free surface-partly pressurized flows (mixed flows), to fully pressurized flows. Two fully-conservative, computationally efficient and robust models are formulated in this thesis. In the first model, pressurized flows are simulated as free surface flows using a hypothetical narrow open-top slot (“Preissmann slot”). In the second model, free surface and pressurized flows are treated independently while interacting through a moving interface. In the first model, a gradual transition between the pipe and the slot is introduced and an explicit Finite Volume (FV) Godunov-type Scheme (GTS) is used to solve the free surface flow governing equations. This model is called the modified Preissmann model. In the second model, both free surface and pressurized flows are handled using shock-capturing methods –specifically GTS schemes. Open channel-pressurized flow interfaces are treated using a shock-tracking-capturing approach. In this case, cell boundaries are introduced at the location of open channel-pressurized flow interfaces, subdividing some regular cells into two subcells, resulting in a variable mesh arrangement that varies from one time step to the next. For boundary conditions, an intrinsically conservative second-order accurate formulation is developed.