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Fluid structure interaction of Piano Key Weirs
Published in Sébastien Erpicum, Frédéric Laugier, Michel Ho Ta Khanh, Michael Pfister, Labyrinth and Piano Key Weirs III – PKW 2017, 2017
F.J.M. Denys, G.R. Basson, J.A.v.B. Strasheim
Although the assessment of the separation bubble and shear boundary is useful, an examination of the actual transient flow field is far more revealing. Whereas the bubble is relatively easy to observe and record in a laboratory setting (using Acoustic Doppler Velocimeters, see Section 2.1), the transient flow field is more difficult to obtain. Calibrated numerical models, however, can be used to exhibit the instantaneous vectors across the entire flow field. An example of such a field, represented by vorticity (a measure of turbulence), at relatively low overflow heads (H/P = 0.5), is shown in Figure 4 and Figure 5 (for symbol definition, see Erpicum et al. 2011). It shows the generation of a vortex sheet along the entire upstream edge of the inlet key. As it moves downstream, it rolls up into vortices which merge, grow in size, and start to form the typical horseshoe vortex shapes. These vortices are then dragged by the flow to the top of the transverse wall where they overtop the crest.
Experimental investigation of the effect of sail geometry on the flow around the SUBOFF submarine model inspired by the dolphin’s dorsal fin
Published in Ships and Offshore Structures, 2023
Mohsen Rahmani, Iraj Jafari Gavzan, Mojtaba Dehghan Manshadi
The study of the effects of a particular vortex generator on reducing the horseshoe vortex shows that the vortex produced in the opposite direction of the horseshoe vortex reduces the adverse effects of the horseshoe vortex up to 50%. The Reynolds number of the submarine model affects the effect of the vortex generator, so that in higher Reynolds, the effect of the vortex generators is more significant (Liu et al. 2011). In addition to the shape of the vortex generators, their size and arrangement also significantly affect their impact, so generators with counter-rotating arrangement at pitch angles less than 30 degrees almost eliminate the secondary separation on the model surface. It also weakens the horseshoe vortex and reduces the drag force and vortex flows around the submarine model. By selecting the appropriate size of the vortex generator, controlling the separation of the boundary layer is more effective, and the separation line can be aligned precisely with the submarine centreline. As a result, the separation area becomes smaller, the drag force decreases, and the submarine hydrodynamic performance improves (Manshadi et al. 2017; Liu et al. 2019) studied noise suppression of a scaled submarine model by leading-edge serrations.
Hydro-morphodynamic model with immersed boundary method for local scour at bridge piers
Published in ISH Journal of Hydraulic Engineering, 2022
J. K. Vonkeman, G. R. Basson, G. J. F. Smit
Despite the perceived limitations of the proposed coupled fully 3D hydro-morphodynamic model, it has been demonstrated that the velocity flow field, the horseshoe vortex and the subsequent maximum scour at the nose of a bridge pier can be modelled successfully to simulate results from the experimental work. In order to resolve the crucial horseshoe vortex, a very fine computational mesh with an advanced turbulence model is required. However, the sediment transport submodels of the proposed model are very sensitive to the mesh resolution, which are ascribed to the diffusion resulting from the discretization of the IB method. The implication is that the diffusion coefficient should be calibrated for the mesh resolution and that the subsequent reduction in erosion of the sediment bed should be compensated by an increase in the dimensionless entrainment coefficient (and vice versa). Nevertheless, the IB method may be considered robust and superior relative to the ALE method in the case of complicated topologies of massive erosions.