Understanding flows over channel floor with cross-sectional joints
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2022-08-02Autor
Poza Sánchez, Patricia
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One of the main elements of hydraulic plants are the spillways. The main
purpose of this element is to discharge water from the basin when it reaches
levels above the safety limits. Therefore, spillways are designed to withstand
large water flows and high pressures. However, poor channel design can lead
to high pressures at the joints of the concrete slabs that make up the channel
and result in fatal landslides. Clear examples are the accidents at Oroville
Dam in 2017, Dickinson Dam in 1954, and Big Sandy Dam in 1983. The
objective of this project is to develop a numerical model to analyze the
behavior of the flow over the spillway and to study the relationship between
the flow velocity and the uplift pressures generated at the channel slab joints.
For this purpose, a lot of research have been made in the field trying to
understand the water behavior over a spillway, but few have focused on the
uplift pressures under the slabs due to the stagnation of the water. Some
experiments made by the Bureau of Reclamation analyzed the flow over the
joint for different situations. In 1976, Mr Perry L. Jonshon studied
experimentally the pressures generated on the linings in an open channel,
while Warren Frizell tested, in 2007, the pressures under the slabs in a close
water tunnel. The aim of the current project was to develop a numerical model
to predict accurately the behavior of the flow over the joints and compare it
to the experimental results.
Computational Fluid Dynamics (CFD) has been used as the main tool in the
numerical analysis. This software has been continuously used by many
scientists during the years and many investigations have verify the accuracy
of the tool to predict the fluid over a spillway. Three different joint geometries
have been studied, sharp-edged, chamfer-edged and radius edged joints. All
the cases have been analyzed for sealed and vented situations and compared
between them.
The current project has obtained great results regarding the uplift pressures
and flow behavior over the joints compared to the experimental tests. The
numerical model shows a maximum of 6% of deviation related to the
experimental results for sealed configurations, while the vented
configurations take deviations of around 15%. This increase is expected to be
due to the lack of information of the discharge flow rate, for this reason, the
results related to the analysis over a slope with a free surface are considered
trusty enough. The study shows similar results for different slopes
configurations which explains that the gravity is not the main force of the
study as it was previously expected