Numerical simulations of flow over a side weir for diversion structures and water intakes

Abstract

Side weirs are hydraulic structures used to divert the excess flow from a main channel into a lateral one at diversion structures or intakes, in order to control the water surface elevation or reroute part of the discharge. Flow over a side weir is considered to be a typical case of spatially varied flow, with decreasing discharge along the main channel and varying water surface elevation along the lateral crest. The objective of the paper is to apply various numerical modelling approximations (1D, 2D and 3D) using HEC-RAS and ANSYS Fluent software to virtually reproduce the flow characteristics over the side weir along the diversion canal of the Valea Iasului hydropower plant (HPP), on Argeş River (Romania). Different geometries, mesh types and sizes and the appropriate initial and boundary conditions are used for two HPP operating scenarios (fully functional and completely shut down). The water surface elevation profile along the weir crest is computed, together with a qualitative comparison between the shape of the simulated flow nappe and in-situ visualizations. Quantitative results from the numerical simulation cases are given in terms of the computed upstream and downstream weir rating curves.