Author(s): Gerrit Fiedler; Martin Henning; Roman Weichert

Linked Author(s): Gerrit Fiedler, Martin Henning, Roman Weichert

Keywords: Fishways; Attraction flow; Auxiliary water systems; Supply structures; Flow homogenization

Abstract: Building fishways at large river dams with hydropower presents a challenging task: the operational discharge of the fishway is often not sufficient to establish an adequate attraction flow. In order to add auxiliary discharge, supply structures are constructed near the entrance pool. Therefore, fish biologists demand a slow and homogeneous supply velocity with low turbulence rates to prevent negative effects on passing fish. However, these requirements are hard to meet since fishway-guidelines are unspecific in terms of design recommendations and space is limited near hydropower plants. Usually, the auxiliary flow is taken from the headwater and fed to the supply structure, wherein it propagates as a jet with high flow velocities. Jets have a low rate of homogenization and long structures are necessary for homogeneous flow to develop. For this reason, homogenization elements are necessary to enable shorter supply structures. Although many studies about jet homogenization in e.g. outlet structures or sedimentation basins exist, no studies are available that focus on such restricted spatial conditions. Six homogenization elements for jet homogenization were evaluated by means of CFD models and a new defined evaluation criterion for homogeneity. Results show, that conventional baffle-like structures show insufficient homogenization rates. Significantly better results were achieved by the use of static mixers, which are well-established for mixing highly viscose fluids in chemical industries and tested here in terms of jet homogenization for the first time. In conclusion, a consistent evaluation criterion for homogeneity in supply structures and a space saving homogenization element are presented.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221051

Year: 2022