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-e) 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.

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Experimental and numerical study of the characteristics of side weir flows

The three-dimensional two-equation k–ω turbulence model is applied to obtain the characteristics of flow past a rectangular floor slot located in a rectangular closed conduit. The predictions of the numerical simulation are validated using existing experimental data. The model faithfully reproduces the flow behavior including flow separation in the expanding flow region downstream of the slot. In particular, the model predictions agree well with the experimental data related to pressure and velocity fields. As such, following proper model validation, the numerical model can yield design data pertaining to flow characteristics for different discharge ratios and slot width ratios for many other slot flow situations encountered in engineering practice.

Numerical model for flow past a slot in a rectangular conduit

The well-known Schwarz-Christoffel transformation and the free streamline theory are used to solve the problem of flow past a lateral outlet housed in a two-dimensional conduit. The solution presented can be applied to lateral outlets which are fitted with a barrier that can be set at arbitrary inclinations. For the more general case, where the barrier inclination is arbitrary, numerical techniques were used to obtain the solution. The contraction coefficient and the inclination of the flow issuing out of the outlet are obtained as functions of the velocity ratios.

B. L. Carballada

Papers

Two Dimensional Lateral Flow Past a Barrier