Numerical Analysis And Validation Of South Valencia Sewage Collection System Diversion.

Arnau Bayon-Barrachina, Francisco J. Vallés-Morán, Petra Amparo Lopez-Jimenez

Tuesday 30 june 2015

16:30 - 16:45h at Europe 1 & 2 (level 0)

Themes: (T) Water engineering, (ST) Computational methods

Parallel session: 7E. Engineering - Computational

The old Sewage Collection System (SCS) of south Valencia, Spain, had to be recently diverted to avoid interference with the city high-speed railway works. The proposed modification of this channel is extremely sensitive, as it must handle flow rates up to 100m³/s. In the present work, the stretch most prone to suffer from hydraulic issues is numerically analyzed. This part of the project consists of an initial curved inlet followed by a WES type weir, where flow also expands while becoming supercritical. The resulting high shear stresses and dynamic loads have to be bounded within the modified stretch of the channel, as the old works were not designed for this purpose. To do so, a stable hydraulic jump is forced to occur as upstream as possible thanks to a stilling basin that includes macro-roughness elements for energy dissipation purposes. In order to analyze the hydraulic performance of the described design, a three-dimensional model based on the open-source CFD platform OpenFOAM is presented. In this model, turbulence is treated using three widely used RANS approaches, namely: Standard k-epsilon, RNG k-epsilon and SST k-omega, whose accuracies are compared caeteris paribus. Structured meshes of different element size are tested, and the model sensitivity to this parameter is analyzed. The air-water interface must be accurately defined, as the flow under study is gravity-driven and non-pressurized. To do so, an Eulerian-Eulerian volume method is used. As a result, a full physically consistent description of the flow is achieved and so a wealth of variables can be estimated. In order to assess the accuracy of the model, some variables regarding the water surface level are compared to experimental data. These experimental results are obtained from a 1:20 scale physical model, where Froude similarity is achieved and scale effects are proven not to be significant. Good agreement between numerical and experimental results is achieved despite the complexity of the system under study. In the light of the results, the model proposed can be applied to accurately model similar hydraulic structures.