Author(s): Kimberley Kasischke; Mario Oertel

Linked Author(s): Mario Oertel

Keywords: Fast fourier transformation; Flow fluctuations; Hilbert-huang transformation; Large eddy simulation; Vertical slot passes

Abstract: Vertical slot passes (VSP) are used for fish migration in the nearfield of hydraulic structures such as dams. Their presence is important to ensure good ecological conditions and to meet the requirements of the European Water Framework Directive (EU-WFD). Nowadays, numerous experimental and numerical investigations are available, dealing with discharge coefficients, flow patterns, and design equations. But still, not all hydraulic processes on VSP are described in detail, and especially fluctuations represent a major research deficit. The present investigation consequently deals with a flow analysis and occurring fluctuations on an exemplary numerical VSP model. The used CFD code is FLOW-3D, and the free surface is described via the Volume-of- Fluid method (VOF), while Large-Eddy-Simulations (LES) were performed. Hilbert-Huang Transformation and Fast Fourier Transformation are used for further result analysis. Results show, that for specific boundary conditions, larger time-dependent fluctuations might occur, next to basic turbulent flow structures and small scaled fluctuations. These fluctuations come along with frequencies of a couple of seconds up to minutes and they can change flow behavior and basic flow principles on the structure. The results and findings will be used for further, more detailed design investigations to define more precise dependence and regularity.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0125-cd

Year: 2023