Numerical modelling of skimming flow over small converging spillways

Nunes, F. and Matos, J. and Meireles, I. (2018) Numerical modelling of skimming flow over small converging spillways. In: Protections 2018 (3rd International Conference on Protection against Overtopping), 6-8 June 2018, Grange-over-Sands, UK.

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Abstract

Recently, a significant number of embankment dams have been considered unsafe due to inadequate spillway capacity and predicted overtopping during extreme flood events. The use of stepped overlays for overtopping protection has proven to be cost effective and has gained acceptance worldwide, particularly in the USA. An interesting alternative configuration to the typical stepped spillway of constant width is the use of converging chute walls. This spillway typology enables the increase of the crest length in relation to the chute width at the toe, allowing a decrease of the head above the crest, for identical discharge, and complying with possible width constrains at its downstream end. However, a wall deflection induces undesired cross-waves by increasing the flow depths in the vicinity of the wall, which should be taken into account for design purposes. This study presents a 3D numerical study using the Computational Fluid Dynamics (CFD) code FLOW-3D®, with simulations performed using a RANS approach coupled with the RNG k-ε turbulence modelling. Some main flow characteristics along the converging spillway, for smooth and stepped inverts, were evaluated and compared with those previously acquired on a physical model with a 1V:2H sloping chute, typical of the downstream slope of small embankment dams. The results show that, in general, a good agreement was found between numerical and experimental data along the nonaerated flow region, on both smooth and stepped inverts, namely regarding flow depths in the chute centreline and at the chute sidewalls, as well as velocity profiles in the chute centreline.

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