Author(s): Robert Feurich; Stefan Thonhauser

Linked Author(s): Robert Feurich

Keywords: air entrainment; computational fluid dynamics (CFD); volume of fluid (VOF); hydropower plant (HPP); measurements

Abstract: TIWAG-Tiroler Wasserkraft AG has been operating Schwarzach Hydropower Plant (HPP) on the River Schwarzach in East Tyrol´s Defereggental since 2007. In the course of an expansion of the power plant capacity a fish pass and a measuring and controlling structure for the residual flow had to be refurbished. This structure controls the flow via an overflowed slide gate, causing a falling water jet into a basin. At the outflow end of the structure there are another slide gate as bottom outlet and a standard overflow weir. The first tests of the hydraulic structure showed an unexpected behaviour of the water levels in the basin. Air entrainment, caused by the flow rate depending geometry of the falling water jet into the basin, was suspected to have a strong impact on the flow pattern and water levels in the basin. For a detailed investigation of this flow situation in the structure a commercial 3D numerical code using the Volume of Fluid (VOF) method for free surface representation has been applied. In addition, on-site tests and measurements were carried out to improve and support the numerical results. Through a combination of on-site measurements and details of the numerical results it was possible to understand the complex flow patterns. The surface instabilities and air entrainment are now prevented by a diving wall, blocking the incoming jet. In combination with the raised crest of the outflow overflow weir a solution for reliable flow control operation over the whole measurement range was found.

DOI: https://doi.org/10.3929/ethz-b-000675921

Year: 2024