Conceptual Approach for Positioning of Fish Guidance Structures Using CFD and Expert Knowledge

Horizontal bar racks used as fish protection measures at hydropower plants have rapidly gained importance in recent years. Despite the large number of installed racks in Europe, systematic investigations of the hydraulic losses and velocity fields were missing. To fill these research gaps, the hydraulic performance of horizontal bar racks was systematically investigated in a laboratory flume for a large number of rack parameters and different hydropower plant layouts. The results of the head loss assessment are published in a paper entitled Head Losses of Horizontal Bar Racks as Fish Guidance Structures, whereas the present paper focuses on the velocity fields. The measurements show that the bar shape, the horizontal approach flow angle, and the clear bar spacing have only a minor effect on the velocity fields. In contrast, bottom and top overlays might enhance the fish guidance efficiency for bottom and surface oriented fish, while the asymmetric downstream velocity field can reduce turbine efficiencies. The hydropower plant layout strongly affects the approach flow field to horizontal bar racks. For block-type hydropower plants, the installation of a dividing pier or partial opening of the spillways improves the flow field for better fish guidance.

Section: Engineering Application Considerationsmentioning

confidence: 99%

Velocity Fields at Horizontal Bar Racks as Fish Guidance Structures

Meister

Fuchs

Beck

et al. 2020

“…Such bars are important for fish guidance racks, which typically consist of bars angled to either the side wall or the ground plane to guide downstream migrating fish to an appropriate bypass [9,10,13,14,18]. Furthermore, many empirical equations are based on undisturbed, uniform inflow conditions [116]. However, inflow conditions to trash racks at HPPs are much more complex [117,118] and also depend on the design of the HPP [2,32].…”

Section: Further Limitations and Potential Future Research Topicsmentioning

confidence: 99%

Large Eddy Simulations of Flow Past Circular Cylinders to Determine Head Loss Coefficients of Circular Bar Trash Racks with Perpendicular Inflow Conditions

Zöschg

2024

Trash racks installed at hydropower plants cause head losses that reduce energy output. Previous research has thoroughly investigated head losses through both experimental and field studies. However, only a limited number of numerical studies have been performed, which have shown significant simplifications in terms of model complexity. In this study, the head loss coefficients ξ of circular bar trash racks (CBTRs) were analyzed using 3D Large Eddy Simulation (LES). Specifically, a single submerged bar oriented perpendicular to the flow direction was studied under homogeneous inflow conditions while (i) the blocking ratio P was varied between 0.043 and 0.444, and (ii) the flow velocity U was varied between 0.3 and 1.0 m/s. The model parameters were selected primarily based on the extensive literature on flow past circular cylinders, particularly at a Reynolds bar number Reb of 3900. To ensure the validity of the parameters, systematic independence tests were performed, including simulations with three and five bars in the computational domain. The results confirmed the suitability of 3D LES as an appropriate tool to determine ξ of CBTRs. In general, ξ decreased continuously with decreasing P and increased with increasing U when Reb ≥ 3981, which is consistent with comparable flow parameters observed in previous studies of flow past circular cylinders. Notably, the study found that the empirical formulas used for comparison tended to underestimate ξ when P was relatively low. Finally, the potential of the presented approach for future applications was discussed in detail.

“…Usually, these bar racks are oriented perpendicular to the flow direction. In an integral approach to fish protection described by Calles et al [12], a properly functioning bypass is essential for successful downstream migration [49]. The observed searching behavior of fish from one side of the bar rack to the other indicates a possible guiding effect, which might help fish to find a bypass located at the side of the bar rack.…”

Section: Passing the Barriermentioning

confidence: 99%

Retrofitting of Existing Bar Racks with Electrodes for Fish Protection—An Experimental Study Assessing the Effectiveness for a Pilot Site

Haug

Auer

Frees

et al. 2022

Downstream-migrating fish in rivers tend to follow the main current, and are in danger of swimming through the turbines at run-of-river hydropower plants, possibly causing high mortality rates. To avoid these losses, fish must be prevented from entering the turbines. Most existing vertical bar rack systems (used for turbine protection) however usually do not ensure proper fish protection due to large bar spacings. FishProtector technology enables the retrofitting of existing bar racks (i.e., the mechanical barrier) with additional electrodes to create a hybrid barrier. The induced electric field in the water aims to create a behavioral barrier to prevent fish passage through the bar rack. In this study, ethohydraulic experiments to investigate the effect of such a behavioral barrier on fish were performed. In detail, the fish-protection rate at a bar rack with a bar spacing of 30 mm was tested in five different scenarios: (i) a bar rack without electrodes (reference), and four electrified setups with electrode spacings of (ii) 80 mm, (iii) 120 mm, (iv) 160 mm, and (v) 200 mm. A flow velocity of 0.23 m/s was chosen to replicate the situation at a planned pilot site. The study was conducted in an outdoor laboratory flume using small fish of several local riverine species, mostly cyprinids and minnows. The results show that the mean fish-protection rate in the experiments could be increased from 62% in the reference setup up to 96% in the electrified setups.