Approach Flow Depth Influence on Nonlinear Weir Discharge Capacity

The high hydraulic efficiency and the compactness of nonlinear weirs favor their use in several rehabilitation or new dams projects. Main types of nonlinear weirs are labyrinth and piano key weirs.The purpose of this paper is to provide indications on the influence of the approach flow depth on the discharge capacity of these nonlinear weirs. To do so, a series of experimental tests have been carried out in the laboratory of Engineering Hydraulics of the Liege University. A labyrinth and a piano key weir have been tested in channel configuration (upstream flow width equal to the weir width) considering various dimensionless dam heights. A large range of discharge has been tested for each case. The results show that the dimensionless dam height increase may decrease up to 8% of the labyrinth weir discharge capacity while it has only very limited but opposite effects for the piano key weir

Discussion of Discharge coefficient for free and submerged flow over Piano Key Weir

The Authors made an interesting contribution to the assessment of the discharge coefficient of Piano Key Weirs (PKW). The Discussers were impressed to read that the Authors conducted some 600 tests thereby producing nearly 3000 data points

Flow structure in a compound channel: benchmarking 2D and 3D numerical models

The benchmarking test of 2D and 3D numerical models on a compound channel flow with a rectangular-shaped main channel and a rectangular-shaped floodplain was carried out by the IAHR Working Group on Compound Channels. The selected test case is the flume experiment by Nezu and Tominaga (1991). Nine depth-averaged 2D models and four 3D models participated in the benchmark. In the 2D models, the depth-averaged streamwise velocity profiles in the lateral direction were compared. In the 3D models, velocity components in three directions as well as the distribution of the turbulence kinetic energy in a cross-section were compared. Through the comparison, the applicability and limitations of each model are highlighted and discussed with regard to the model characteristics.Konferencija je održana na daljinu (on-line), bez fizičkog prisustva i sav materijal se nalazi na web-stranici organizatora skupa

Experimental Assessment of the Influence of Fish Passage Geometry Parameters on Downstream Migrating Atlantic Salmon (Salmo salar) Smolts Behavior

The fragmentation of rivers caused by the construction of dams and weirs disturbs fish migration and poses a threat to fish populations and aquatic biodiversity. Fish passages around hydraulic structures aim to restore river connectivity; however, the effective design of fish passages is a challenging problem that depends on several processes. The present experimental study investigated how the characteristics of a trash rack at the entrance of a fish passage for downstream migration affects fish behavior and subsequently the effectiveness of the fish passage. A series of experiments was carried out to systematically analyze the behavior of Atlantic salmon smolts in a flume with two outlets featuring the same 1:1 physical model of the entrance of a downstream passage with or without a trash rack. The parameters that were tested were the spacing of the vertical round bars of the trash rack, the location of the trash rack at the fish passage, and the velocity gradient at the entrance of the passage. Aggregated results showed that only 34% of the fish selected the outlet with a trash rack to exit the flume while 66% preferred the unobstructed outlet. More fish swam through the outlet with the trash rack when the spacing of the vertical bars increased from 10 cm to 20 cm and when the rack was placed in the higher velocity region compared to the lower velocity one. These results show that a trash rack acts as an obstacle to Atlantic salmon smolts passing through a downstream passage. When possible, trash racks should be avoided at the entrance of downstream fish passages

Advances in Spillway Hydraulics: From Theory to Practice

Over the past decades, significant advances have been achieved in hydraulic structures for dams, namely in water release structures such as spillway weirs, chutes, and energy dissipators. This editorial presents a brief overview of the eleven papers in this Special Issue, Advances in Spillway Hydraulics: From Theory to Practice, and frames them in current research trends. This Special Issue explores the following topics: spillway inlet structures, spillway transport structures, and spillway outlet structures. For the first topic of spillway inlet structures, this collection includes one paper on the hydrodynamics and free-flow characteristics of piano key weirs with different plan shapes and another that presents a theoretical model for the flow at an ogee crest axis for a wide range of head ratios. Most of the contributions address the second topic of spillway transport structures as follows: a physical modeling of a beveled-face stepped chute; the description and recent developments of the generalized, energy-based, water surface profile calculation tool SpillwayPro; an application of the SPH method on non-aerated flow over smooth and stepped converging spillways; a physical model study of the effect of stepped chute slope reduction on the bottom-pressure development; an assessment of a spillway offset aerator with a comparison of the two-phase volume of fluid and complete two-phase Euler models included in the OpenFOAM® toolbox; an evaluation of the performance and design of a stepped spillway aerator based on a physical model study. For the third topic of spillway outlet structures, physical model studies are presented on air–water flow in rectangular free-falling jets, the performance of a plain stilling basin downstream of 30° and 50° inclined smooth and stepped chutes, and scour protection for piano key weirs with apron and cutoff wall. Finally, we include a brief discussion about some research challenges and practice-oriented questions

Hydraulic Behavior Assessment of Type A and Type B Piano Key Weirs from Experimental and Numerical Results

Since their development, as a result of an improvement of labyrinth weirs, Piano Key Weirs (PKWs) have been implemented as (a) a flood safety structure for gravity dams, allowing to also increase their storage volume, and (b) in river systems to increase the water level for hydropower or navigation purposes. The rectangular folded crest, consistent with apexes inclined by turns in the upstream and in the downstream direction, turns the PKW a device with a high discharge capacity, especially useful during wet extreme events. Nevertheless, several modifications have been implemented in the PKW geometry, capable to improve and, in some cases, worsen their efficiency. Herein, an experimental and numerical assessment, using the ANSYS Fluent Computational Fluid Dynamics (CFD) software, of the discharge coefficient is presented for two PKW configurations, evaluating the specific discharge over the upstream, downstream, and lateral crests, the velocity in the inlet and outlet keys, and the water surface profile, as well. The investigated configurations are a symmetric type A, designed following the recommended optimal values, and a type B model, with the same geometric features as type A. Results showed that for the specific geometries, the type B is more efficient for lower head; however, once the filling of the outlet key occurs, the type B efficiency is reduced, leading to type A becoming more efficient

Pressure and velocity on an ogee spillway crest operating at high head ratio: Experimental measurements and validation

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