Experimental and Numerical Investigation of Flow under Sluice Gates

The flow characteristics upstream and downstream of sluice gates are studied experimentally and numerically using Reynolds averaged Navier-Stokes two-dimensional simulations with a volume of fluid method. Special attention was brought to large opening and submergence, a frequent situation in distribution canals that is little seldom addressed in the literature. Experimental results obtained by ADV measurements provide mean velocity distributions and turbulence characteristics. The flow is shown to be mostly two-dimensional. Velocity fields were simulated using renormalization group k-epsilon and Reynolds stress model turbulence models, leading to an estimation of energy and momentum correction coefficients, head loss, and bed friction. The contraction coefficient is also shown to increase with gate opening at large submergence, which is consistent with the energy-momentum balance. This result can be used to derive accurate discharge equation

Experimental and numerical studies of the flow structure generated by a submerged sluice gate

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

Calculation of Contraction Coefficient under Sluice Gates and Application to Discharge Measurement

The contraction coefficient under sluice gates on flat beds is studied for both free flow and submerged conditions based on the principle of momentum conservation, relying on an analytical determination of the pressure force exerted on the upstream face of the gate together with the energy equation. The contraction coefficient varies with the relative gate opening and the relative submergence, especially at large gate openings. The contraction coefficient may be similar in submerged flow and free flow at small openings but not at large openings, as shown by some experimental results. An application to discharge measurement is also presented

Modeling steep-slope flow across staggered emergent cylinders: application to fish passes

Designing efficient rock-ramp fish passes with flows over a bottom with roughness on the same scale as the water depth requires a precise knowledge of hydrodynamics in order to avoid or limit characteristics unattractive for fish, particularly for small fish. This paper considered the numerical modeling of free-surface flow across a steep-sloped ramp covered with staggered surface emergent cylinders. Considering the importance of complex flow features for fish passage, computational fluid dynamics (CFD) was adopted because it is capable of predicting such features. Because of the longitudinal periodicity of the arrangement of the obstacles, cyclic boundary conditions made this fine simulation possible. Two computational meshes (coarse and fine) and two turbulence models [shear stress transport (SST) k-ω and Smagorinsky large-eddy simulation (LES)] were used. The SST k-ω coarse mesh model gives correct time-averaged values, the main flow unstationarities and is usable for rock-ramp fish pass design, but a fine model using LES turbulence closure can provide detailed flow characteristics in the wakes in order to provide possible rest zones, particularly for smaller fish

Discussion of "Revisiting the Energy-Momentum Method for Rating Vertical Sluice Gates under Submerged Flow Conditions" by Oscar Castro-Orgaz, Luciano Mateos, and Subhasish Dey

The discussers really appreciated the efforts to make more solid some usual assumptions used to derive reliable stage-discharge relationships, and the confrontation with field measurements. Energy and momentum equations are generally applied in their standard form, as presented in most hydraulic engineering books. The authors are right to point out that some of these assumptions are simplistic, which introduces biases in the derived relationships. Velocity distribution is one of these assumptions, and trying to improve this distribution is commendable. Head loss is another crucial issue, especially for submerged gates where the presence of the roller above the jet induced large dissipation. The authors also neglected the friction forces and assumed that contraction coefficient (Cc) is the same in submerged flow as in free flow. This assumption was questioned by Henderson (1989), and Belaud et al. (2009) showed how to derive a continuous relationship for Cc between low submergence (Cc about 0.61) and fully open gate (Cc ¼ 1). For submerged gates, there have been a limited number of experimental studies that explored the validity of the most sensitive assumptions. Compared to free flow, much more phenomena need to be quantified, such as head loss due to jet–roller interaction, velocity distributions at the contracted section and downstream measuring section, friction forces between these two sections. The effect of submergence introduces another dimension when trying to elaborate generic relationships. As the practical objectives are to obtain accurate discharge predictions, a common approach is to calibrate corrections using measured discharges, water levels, and openings. This may not be sufficient to validate physically based improvements since several phenomena compensate for each other. The pioneer experimental works used by the authors provided very useful data sets to perform this analysis. This discussion is based on recent experimental and numerical results presented by Cassan and Belaud (2012). Experiments used acoustic Doppler velocimetry at selected locations, for three configurations in free flow and three in submerged flow. Computational fluid dynamics was used in complement, with the objective to interpolate flow characteristics between measuring points and to explore other configurations than those measured. Experiments were essential to verify the validity of the numerical results, based on Reynolds–Average Navier–Stokes simulations with the volume-of-fluid method and Reynolds stress model as turbulence closure model. Notations are those of the discussed paper

A Semi-Analytical Model for the Hydraulic Resistance Due to Macro-Roughnesses of Varying Shapes and Densities

friction model resulting from investigations into macro-roughness elements in fishways has been compared with a broad range of studies in the literature under very different bed configurations. In the context of flood modelling or aquatic habitats, the aim of the study is to show that the formulation is applicable to both emergent or submerged obstacles with either low or high obstacle concentrations. In the emergent case, the model takes into account free surface variations at large Froude numbers. In the submerged case, a vegetation model based on the double-averaging concept is used with a specific turbulence closure model. Calculation of the flow in the roughness elements gives the total hydraulic resistance uniquely as a function of the obstacles’ drag coefficient. The results show that the model is highly robust for all the rough beds tested. The averaged accuracy of the model is about 20% for the discharge calculation. In particular, we obtain the known values for the limiting cases of low confinement, as in the case of sandy beds

Flow and drag force around a free surface piercing cylinder for environmental applications

This paper investigates flows around a free surface piercing cylinder with Froude number F<0.5 and Reynolds number around Re = 50,000. The aim of this work is to gain a better understanding of the flow behaviour in environmental systems such as fishways. The advances are based upon experimental and numerical results. Several flow discharges and slopes are tested to obtain both subcritical and supercritical flows. The drag force exerted on the cylinder is measured with the help of a torque gauge while the velocity field is obtained using particle velocimetry. For the numerical part, two URANS turbulence models are tested, the k-w SST and the RNG k-e models using the OpenFOAM software suite for subcritical cases, and then compared with the corresponding experimental results. With fishways applications in mind, the changes in drag coefficient Cd versus Froude number and water depth are studied and experimental correlations proposed. We conclude that the most suitable URANS turbulence model for reproducing this kind of flow is the k-w SST model

Evolution of flow velocities in a rectangular channel with homogeneous bed roughness.

The flow velocity above large scale roughness is investigated for low and steep slope between 0 and 4 %. The experiments were conducted in the laboratory of Fluid Mechanics Institute of Toulouse -IMFT. For the velocity measurement, the channel is equipped with a fast camera and a lightening system. The originality of the study lies in the application of a particle tracking technique (Particle Tracking Velocimetry). It is a non-intrusive measurement technique to measure instantaneous velocity in two-dimensional fields in stationary and unsteady flows. Analysis of the results is performed by processing images taken by the camera using a developed detection algorithm. A logarithmic distribution has been found for The velocity profiles which are influenced by roughness and slope. The obtained results show a depression of the maximum speed below the free surface. This behavior indicates a delay of the flow in the vicinity of the free surface and this is a direct consequence of the presence of secondary flows in these areas

Study of free surface flows in rectangular channel over rough beds.

This paper presents the results of an experimental and umerical study of fully developed flow in a straight rectangular open channel over rough beds. Conical ribs were placed on the flume bottom to simulate different bed roughness conditions. Acoustic Doppler Velocimetry (ADV) measurements were made to obtain the velocity components profiles as well as the Reynolds stress profiles, at various locations. The experimental results are validated by simulations using an algebraic stress model. These investigations could be useful for researches in the field of sediment transport, bank protection, etc

Session B5: 2D Modelling of Nature-Like Fish Passes

Abstract: The passability of nature-like fishpass depends on water depth, velocity and kinetic turbulent energy. To estimate these values the 2D Saint Venant code can be an interesting tool because it can simulate a large range of geometrical configuration and also take into account the deformation of the free surface. However the flow in a fish pass can reach the limit of the model assumptions as the hydrostatic pressure. As a consequence a series of experiments on down-scale are conducted to validate the numerical results. Velocity and turbulent fields are measured by Acoustic Doppler Velocimeter (ADV) for five combinations of discharge and slope. The comparison between experiments and model shows that the numerical results are relevant for a moderate Froude number which corresponds to fishpass application. Moreover, some crucial data related to passability are extracted from the computation as the maximum velocity location