Kombination klein- und großskaliger physikalischer Modellierung zur Optimierung der Spüleffizienz von Laufkraftwerken

The scaling of physical models is common due to spatial, flow-related, and economic constraints. Free-surface models based on Froude similarity result in model Reynolds numbers that deviate from nature. Scaling of sediments faces limitations, as at large scales, natural fractions would need to be replaced by others, leading to distortions. The University of Natural Resources and Life Sciences, Vienna (BOKU), hosts the new BOKU River Lab, ideal for large-scale experiments up to a 1:1 scale. Despite the advantages of large-scale experiments, scaled models retain their relevance as long as the prevailing limitations are considered. The goal of the study was to highlight the advantages of small- and large-scale modeling and to examine the application of laser-optical flow measurement techniques through specific experiments. The study focuses on bedload transport in rivers in the context of Run-of-river hydropower plants. Methodologically, both small-scale (1:20) and full-scale (1:1) models were employed. The impact of weir gate positions on flushing efficiency was analyzed in a 1:20 model, revealing a distinct influence. The 1:1 experiment could simulate smaller grain sizes that could no longer be used in the scaled model to make statements about sediment transport behavior at mean flow rates. For the free-flowing conditions on a 1:1 scale, a similar relationship between sediment transport and velocity profile was found as in the scaled model. This study shows the advantages of combining small and large-scale modelling experiments.