Boundary conditions for simulating complex storm-sewer systems in free surface, pressurized and mixed flow conditions

This paper describes part of the work presented in León et al. (2009), which presents integrated boundary conditions (BCs) for simulating free surface, pressurized, and the simultaneous occurrence of free surface and pressurized flows (mixed flows) when the free surface region is modeled using the 1D Saint-Venant equations and the pressurized region is modeled using the 1D compressible waterhammer equations. The present paper describes the results of the application of the integrated boundary conditions for modeling free surface, pressurized, and mixed transient flow conditions in two test cases. The first test case is a hypothetical test and the second is an experimental work in an oscillation tube performed by the authors of this paper. Computational Fluid Dynamics (CFD) modeling results were used as frame of comparison for the first test case and experimental results besides CFD results were used for the second one. The results show that the integrated boundary conditions can be used with good accuracy for simulating complex storm-sewer systems in free surface, pressurized and mixed flow conditions. The integrated boundary conditions are general and they can be used to simulate point and storage junctions with any number of inflowing and outflowing pipes. The integrated boundary conditions were implemented in the Illinois Transient Model (ITM), which has been used to study hydraulic transients in the Calumet system of the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC). The results of the latter study are not presented in this paper.