Improved Modeling of Unsteady Free Surface, Pressurized and Mixed Flows in Storm-Sewer Systems
Leon, Arturo S.
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https://hdl.handle.net/2142/83328
Description
Title
Improved Modeling of Unsteady Free Surface, Pressurized and Mixed Flows in Storm-Sewer Systems
Author(s)
Leon, Arturo S.
Issue Date
2007
Doctoral Committee Chair(s)
Garcia, Marcelo H.
Department of Study
Civil Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Language
eng
Abstract
"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. For boundary conditions, an intrinsically conservative second-order accurate formulation is developed. The proposed formulation for boundary conditions maintains the conservation property of FV schemes and does not require any special treatment to handle shocks at boundaries. Comparisons between simulated results and experiments reported in the literature show that the two formulated models can accurately describe complex flow features---such as negative open channel-pressurized flow interfaces, interface reversals, and open-channel surges---that have not been addressed well, or not considered at all, by previous models. Numerical simulations also show that the formulated models are able to produce stable results for strong (rapid) transients at field scale. In general, the scope of this work is limited to single-phase flows (liquids). However, a simplified model for air-water mixture flows, valid only when the amount of gas in the conduit is small, has been implemented in the pressurized flow regime. This work does not include the prediction of any type of air entrainment or air release."
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