Applications of Computational Fluid Dynamics in The Design and Rehabilitation of Nonstandard Vertical Slot Fishways

Abstract

Vertical slot fishways are increasingly common structures for the passage of a wide variety of migratory fish and contribute to the maintenance of fish diversity in fragmented rivers. These structures are designed with several geometric arrangements and, consequently, flow patterns through them can be shaped to present suitable characteristics for the fish species. To aid in the design of vertical slot fishways, a three-dimensional numerical model was used to simulate the flow for different geometric configurations. An existing vertical slot fishway with nonstandard dimensions was initially modeled and validated. This geometry was used as a reference design. Modifications to the reference design, such as the insertion of cylinders, changes in the baffle shape and position of the vertical slots, as possible rehabilitation measures, were proposed and tested. In summary, five different designs were evaluated with several slopes, totaling 17 geometries. Hydraulic parameters, flow patterns, maximum velocities, velocity fields and turbulence kinetic energy in the pools were analyzed. The results indicate that the maximum velocity values were between 9% and 68% higher than those obtained by the theoretical equation. This indicates that maximum velocities can be underestimated for nonstandard vertical slot fishways if a simplified evaluation is conducted. The insertion of cylinders in the region close to the slot reduces the maximum velocity up to 8.2%. The positioning of the vertical slots on alternating sides increases the maximum values of turbulence kinetic energy and the regions subjected to higher values. However, this configuration provided greater energy dissipation and reduction of velocities by up to 27%. Thus, modifications in nonstandard vertical slot fishways can be useful in future design or rehabilitation of existing structures in order to provide velocities and turbulence more friendly for a higher number of fish species.

Assessment of Retrofitted Ramped Weirs to Improve Passage of Potamodromous Fish

“…Thus, to assess the effects of hydrodynamics on the fish behavior, numerical modelling (the 3D CFD model FLOW-3D ® ) was used in this study to characterize influential hydrodynamic variables, such as velocity magnitude, TKE, and water depths, present in each configuration tested, in order to identify areas of high velocity and turbulence gradients that might have affected the fish movements. Over the last few years, 3D CFD models have proved to be a practical and robust tool to characterize hydrodynamics on several hydraulic structures, being widely used for the assessment of fish passages (e.g., studies on functioning over a wide range of discharges, prediction of suitable conditions for fish), optimization of designs, and evaluation of different retrofitting solutions [52][53][54][58][59][60][61][62][63][64]. However, given that uncertainty in CFD modelling for environmental fluid mechanics in complex flow fields, like the flow field in the vicinity of a macro-scale roughness (e.g., wake region), can arise from a very wide range of sources, care should be taken when performing a numerical model study [65].…”

A Numerical Study of Fluid Flow in a Vertical Slot Fishway with the Smoothed Particle Hydrodynamics Method

“…(3) With a relatively simple velocity field, the effects of various execution parameters can be more readily investigated and made available for future SPH studies. (4) By using a 3-D model, results herein are easily compared with those in Sanagiotto et al, (2019) [7], where data from another 3-D model is calibrated against the same 3-D field data [12,18] used for comparison in this work. Thus, a useful comparison between the two 3-D models is possible.…”

“…There are various methods and guidelines to design a VSF, whose main aim is to effectively dissipate the energy of the inlet jet and to create flow conditions in the pool that enable the fish to ascend without undue stress, i.e., (1) to simply pass via the slot at their preferred water depth, and (2) to rest in the recirculation regions, where low levels of energy dissipation constitute favorable resting areas [6]. Flow in VSFs is considered favorable for three reasons: (1) in the transition region between consecutive pools, fish have the option to select the depth of passage, since the opening is across the depth; (2) in each pool, there is generally a large resting region where the velocities are much lower than in the main jet, which can be very favorable when a high number of pools are needed to overcome the vertical gradient; (3) the main jet, where the maximum velocities are found, clearly identifies the upstream direction, which minimizes the chances of disorientation of fish along the route [7]. It should be noted that these features do not necessarily provide suitable flow conditions by themselves, since vortices can entrap the fish, as explained in Odeh et al, (2002) [8].…”

“…Despite the possible three-dimensional local velocity gradient in the slot zone, the flow in major areas of the pool is quasi two-dimensional (Wu et al, 1999 [14]; Liu et al, 2006 [15]). Recent studies employed various depth-averaged 2-D models (Cea et al, 2007 [16]; Bermúdez et al, 2010 [17]; Bombač et al, 2017 [18], and also several 3-D models (Masayuki et al, 2009 [19]; Ferrand et al, 2013 [20]; Duguay et al, (2017) [21]; Gisen et al, 2017 [22]; Umeda et al, 2017 [23]), which continue to be employed for VSF optimization (Li et al, 2019 [24] and Sanagiotto et al, 2019 [7]). Field measurements in Bombač et al, (2015) [12] that are used for calibration of the numerical model presented in this work confirm that the flow in the observed VSF is mostly 2-D, with the exception of flow in the vicinity of the slot.…”

Combination of experimental and numerical approaches to determine the main characteristics of skimming flow in stepped spillways

“…Three-dimensional flow simulations were performed using the Ansys CFX software, which uses the finite volume method (Ansys Inc., 2013) and has a history of successful use for CFD simulations of various hydraulic structures (Arantes, 2007;Arantes et al, 2010;Dettmer et al, 2013;Gabl & Righetti, 2018;Sanagiotto et al, 2019aSanagiotto et al, , 2019b.…”