Sluice gates are commonly used to control discharge and levels, and to monitor discharge. However discharge formulas perform poorly at large opening and large submergence. This study explores the flow structure under such gates in order to verify commonly used assumptions about contraction coefficient and energy losses. The study is based on experimental results acquired in a laboratory flume. The flow structure was determined experimentally by ADV and numerically with RANS simulations performed with Fluent TM for different configurations of submerged gates and different modelling assumptions. Attention is given to the contracted flow and to the recirculating zone upstream of the gate. The experimental results on velocity are consistent with RANS simulations as far as discharge coefficients, wall shear stress and flow structure are concerned. Contraction coefficients were compared with analytical calculations based on potential flow and momentum balance. It is verified that, as usually assumed, the viscosity effects have a limited influence on the flow structure. We show that contraction coefficients should not be considered as constant at large submergence and large opening, which is a reason of the poor performance of the discharge formulas in these regimes.
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