Author(s): M. Mossa
Linked Author(s): Michele Mossa
Keywords: Local scour; Hydraulic structures; Coastal structures; SPH modeling; Erosion
Abstract: Local scour is an important issue in the stability and protection design of hydraulic and coastal structures. Inappropriate scour design and evaluation may lead to failure of the structure, environmental pollution, and significant economic losses. An important element consists in the evaluation of the maximum value of local scour and erosion and their development over time. Some case studies in laboratory channels will be described, even in the presence of oscillating hydraulic jumps, and in wave tanks. Comparisons between numerical and experimental results will also be presented. By way of explanation and as an example of the case studies that will be presented, in one of the studies we numerically focus on the vorticity generation mechanism in a scour hole developed downstream of a grade control structure in sand-bed channels, providing a full hydrodynamic picture of the scouring process. The liquid-granular flow has been simulated through a Weakly Compressible SPH (WCSPH) scheme with a two-equation turbulence model, where the two phases are treated as continua with different physical and rheological properties. The validity of the numerical scheme adopted here was checked against the experimentally observations of the local scour holes downstream of hydraulic jumps. As experimentally observed, our results indicate that there are three regions: the first is dominated by a jet-like flow characterized by a high velocity, which plays an important role in the scour process; the second is dominated by a clockwise local vortex at the position of the maximum scour depth; the third is dominated by velocity vectors mainly directed in the longitudinal direction of the channel. The equilibrium configuration of the flow field and bed topography is reached after a transient period in which the system oscillates between two flow patterns: (i) the scour hole shows a relatively steep hump downstream of it, increasing the free surface elevation and generating a B-jump type with a counterclockwise rotating macro-vortex structure which pushes the main flow towards the bed, where strong erosive action is observed; (ii) the scour shows a relatively modest inclination of the scour cavity, leading to the formation of a wave jump dominated by a clockwise rotating macro-vortex structure.
Year: 2023