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Experimental Measurement and Numerical Model of Dunes Drag Coefficients
A. Motamedi, M. Galoie,
Volume 22, Issue 2 (9-2018)
Abstract
In order to investigate the flow formation on dunes, the experimental data from a flume 12 meters long, located in Hydraulic Lab at Technical University of Graz (Austria), were collected. In this study, dunes (particle sizes of 13 and 6 mm) in a 2-D plan were developed with the wavelength of 1 meter, the lee angle of 8 degree, and the crest heights of 4 and 6 cm; these were uniformly installed across the width of flume. The analysis of the experimental flow velocity profiles measured by ADV and PIV technology and the numerical profiles modeled by SSIMM showed that in the same hydraulic conditions, there was no significant relation between drag coefficients of particles on dunes and flow discharge variation, while the water depth reduction caused a sudden increase in the drag coefficient up to 66%. Also, reducing particle size of the dune increased the drag coefficient and there was a significant relation between particle size (diameter) and dune formation, so that in smooth crested conditions, as compared with the sharp crested dune, the drag coefficient was increased up to 32%.

Effects of Cutoff Wall Shape and Size of Dam Gates on Vortex Formation Upstream of Dams
M. Eskandari, M. Heidarnejad, A. Egdernezhad,
Volume 27, Issue 3 (12-2023)
Abstract
The formation of vortices behind the gates of diversion dams is an operational challenge. Such vortices lead to vibration and corrosion in the gate, reducing the lifetime and raising the operational cost of the dam. This study investigated these vortices and their formation. It was found that the gate or cutoff wall was not the only explanation for the vortices; the closed side gates also contribute to vortex formation. Furthermore, an increase in the gate width reduced vorticity; the vortex size experienced a 200% reduction as the gate size increased by 200%. The cutoff wall diameter was another determinant. An increase in the cutoff wall diameter raised vorticity. The vortices increased by 50% as the wall diameter increased by 150%.

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