HYDRODYNAMIC MEASUREMENTS AROUND MOVING PROFILES: FLAPPING FLIGHT, WATER TURBINE, AND OSCILLATING PROFILE

In the field of the fluid mechanics, the team HYDEE (Hydrodynamics and Environmental flow section) of the institute Pprime is involved in the understanding of flows around moving profiles for environmental applications, the maritime transport, the renewable energy production, The research interests cover fundamental aspects of unsteady flows with moving structures, turbulent free-surface flows, environmental flows and mixing through different national and European programs. Fundamental contributions to optical flow measurements include PIV stereoscopy PIV measurement techniques and recently free surface measurement and volumetric measurement techniques have been obtained

Session C8: Development of Criteria for the Design and Dimensioning of Fish-Friendly Intakes for Small Hydropower Plant

Abstract: To conciliate the hydroelectric production and the restoration and protection plans of migratory species, in particular salmon (Salmo salar), sea trout (Salmo trutta) and eel (Anguilla anguilla), and more generally the longitudinal continuity for fish species, it is necessary to avoid or at least reduce damages to fish passing through turbines. The best way to reduce fish mortality would be to install fish-friendly turbines, but it is not a cost-effective solution on existing installations and in the present state of the art their use is very limited in terms of head and discharge ranges. Transforming conventional intakes into socalled “fish-friendly” ones is therefore considered as one of the most acceptable solutions. We present here the development of criteria for the design and dimensioning of fishfriendly intakes for small hydropower plants in France (up to ≈ 100 m3/s until now). These criteria were established from the feedback following the evaluation of existing downstream bypasses in France and abroad, and from hydraulic studies on downscale models. Fish-friendly intakes comprise a trashrack designed to guide fish towards its downstream end and to the entrances of bypasses, through which fish safely reach the tailwater. Criteria concern (1) the clear space between bars to avoid the passage of fish through the trashrack and via turbines, (2) the inclination or angulation of the rack to guide fish towards the bypasses located at its downstream end, (3) the normal velocity through the rack to avoid fish impingement, and (4) the number, positions, dimensions, and discharge of bypasses to collect the fish. New formulae have also been proposed to evaluate head-losses for inclined or angled trashracks with low bar-spacing

Numerical simulations of fish-friendly angled trashracks at model and real scale

Several amphihaline species, such as silver eels, suffer high mortality rates during their downstream migration, due to their passage through turbines. The combination of adapted trashracks (inclined or angled screen, lower bar spacing, …) with bypasses can efficiently prevent these mortalities. A numerical study has been carried out with such angled trashracks. Numerical results with model scale racks were validated against previous experimental results on model trashracks, resulting from head loss and velocity distribution measurements (Raynal et al., 2013). Real scale racks were then computed in order to evaluate the influence of both the bar spacing and the channel width on velocity distributions in real dimensions. The mesh generation and the numerical simulations were performed by the open source CFD software suite OpenFOAM. The trashrack solid comprised basic elements, individually created using CAD software and directly inserted in OpenFOAM’s mesh generation utility. For small scale configurations, grid refinement was applied at the flume walls, at trashrack bars and downstream of the trashrack, whereas only bars were refined for real scale racks. The resulting number of cells ranged between 100,000 and 1,500,000. Steady state results were obtained by solving the Reynolds-averaged Navier-Stokes (RANS) equations for an incompressible and monophasic flow. The k-ε, k-ε-based RNG, k-ω, k-ω-based shear stress transport (SST) and Spalart-Allmaras models were examined to select the most appropriate one in terms of computation time and result accuracy. Results show that the k-ε-RNG is the model best agreeing with experimental results. Two-dimensional calculations seem to provide quite satisfactory results although both the head losses and the size of the recirculation zone downstream of the trashrack are slightly under-estimated. Real scale results confirm experimental ones and show that the bar spacing slightly effects upstream velocity profiles. Downstream of the rack, simulations with different flume width demonstrated that the size of the recirculation zone is proportional to the channel width

Study on fish-friendly inclined and angled trashracks

This paper presents the results on trashrack head losses obtained by Raynal et al. [2013 a,b], [2014] for several configurations. More especially, it compares the head loss formulae proposed in these studies with various equations from the literature to improve energy losses prediction in fish-friendly configurations. These new predictive laws of head losses are applied to the renovation of a hydropower plant and show that inclined trashracks or angled trashracks with streamwise bars are reliable solutions when the bar spacing is reduced

Closure to “An experimental study on fish-friendly trashracks: part I & II”

The Authors thank the Discussers for their observations on our two papers. Four main points, related to head-loss predictions for angled trashracks, have been underlined by the Discussers and are discussed here.[...

An experimental study on fish-friendly trashracks – Part 2. Angled trashracks

Experimental results for fish-friendly trashracks placed in an open water channel are presented. Model trashracks with different bar shapes, spacing and angles were tested. The numerous configurations provided results on head losses and on changes in velocity along the rack for a large range of situations, including fish-friendly trashracks. Previous head-loss equations found in the literature were applied to these configurations and were compared with measurements. A new head-loss equation is proposed that takes into account the effect of the different tested parameters. Velocity measurements provided new results and answers concerning downstream-migration aspects such as admissible approach velocities and guidance efficiency as a function of the trashrack angle

An experimental study on fish-friendly trashracks – Part 1. Inclined trashracks

Experimental results are presented for trashracks placed in an open water channel with different bar shapes, spaces between bars and screen inclination angles. The numerous configurations provided results on head losses and on changes in velocity along the rack for a large range of situations, including fish-friendly trashracks. A new head-loss equation is proposed that takes into account the effect of the different tested parameters and demonstrates the need to separate the effect of the trashrack bars, which is directly related to the inclination of the trashrack, from the effect of the transversal elements such as spacer rows whose effect on the flow is not altered by rack inclination. Velocity measurements also adduce rules for efficient water intakes complying with fish-friendly criteria

Hydrodynamique de prises d'eau munies de plans de grilles orientés

Dans le cadre des directives européennes SER (Développement d'Énergie Renouvelable), DCE (Directive Cadre sur l'Eau), et des plans de restauration de la continuité écologique (Trame bleue, Plan de gestion de l'anguille), la nécessité de limiter, voire d’annuler, les dommages liés à la dévalaison des poissons au niveau des centrales hydroélectriques (mortalités au passage par les turbines) apparaît comme une priorité. Les contraintes biologiques de nombreuses espèces de poissons, essentiellement migratrices, doivent alors être intégrées dans la conception des prises d’eau dites ichtyocompatibles, au même titre que les dimensionnements hydraulique et mécanique. L’objectif est d’obtenir des taux de survie des poissons dévalant proches de 100% au niveau de chaque aménagement, de manière à limiter l’impact cumulé sur les axes de migration [...

Downstream fish passage technologies for small-to-medium hydropower plants: part I

Hydropower plants (HPPs) can block or delay fish migration and cause fish injuries or mortalities during the turbine passage. In the scope of the EU Horizon 2020 research project "Fishfriendly Innovative Technologies for hydropower" (FIThydro), different solutions for downstream migration are studied, applied and compared in different test cases. In particular, Fish Guidance Structures (FGS) with a behavioral or physical effect on fish can be effective solutions to protect and guide downstream migrating fish towards bypasses at water intakes of HPPs. However, these structures should not impair the hydroelectric operation. In this first part, inclined and angled bar racks with low bar spacing are proposed as a solution for small to medium hydropower plants. In the second part of Albayrack et al, 2019, solutions for medium to large HPPs are discussed. Head loss and upstream and downstream velocities fields are important criteria to choose the most efficient solution for both fish protection and hydroelectric operation. In this paper, different solutions with low bar spacing are proposed and discussed for two small and medium HPPs in relation to these different criteria