Abstract

Side weirs are extensively used in hydraulic engineering, irrigation, and environmental engineering applications which involve flow measurement and regulation. Flows through side
weirs are typical examples of spatially varied flow (SVF) with decreasing discharge.

The flow emerging out from the side weir is three-dimensional (3D) due to variations in the water surface profile. These flow characteristics can be obtained by experimental methods,numerical modeling or by theoretical analysis. The present study is confined to the rectangular
side weir located in a horizontal rectangular channel having zero sill height. Experiments were performed on the rectangular side weir to locate the stagnation zone, the region of separation and the water surface profile. A Laser Doppler Anemometry (LDA) unit was used to measure
the mean and turbulent velocity components of the flow. Experimental results are analyzed to find the detailed flow characteristics using data related to the velocity distribution, velocity vectors, separation streamlines, stagnation point and water surface profiles for different weir flow configurations.

The predictions of the 3D numerical turbulence model were validated using the experimental
results. The 3D equations, Reynolds’s averaged Navier-Stokes (RANS) equations and the twoequation
renormalized relations (RNG k-ε) were verified using experimental results. The
volume of fluid (VOF) scheme was incorporated in the model to find free surface profiles of the
open channel flow configuration denoting the side weir flow. The simulation result provided
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detailed analysis of flow patterns, velocity distributions, water surface profiles, flow separation zone, stagnation zone, and separation streamlines. In general, the experimental data validated the predictions of the numerical model. The location of the stagnation point on the near wall
was also determined based on the existing ideal flow analysis of Michell for flow past a rectangular outlet in a 2D conduit and was shown to be close to both test results and model predictions.