Propeller scour phenomenon in the presence of a quay-wall and currents

Investigating the interaction between flow intensity and a ship propeller jet scouring process is paramount to predict scour dimensions in mooring sites in navigation channels, for instance. While the condition of still water is typical in protected mooring sites, in other real-world conditions, like docking in waterways, the presence of an additional flow approaching a rotating propeller can induce changes in the propeller jet hydrodynamics and in turn in the scouring process. Note that, although ship-hull and rudders influence the jet propagation and the flow field, the present research project aimed at studying the propeller-inducing effects only. Literature studies that have relied on this assumption are rarely found, with only a few examining the impact of the intensity of the flow on the propeller jet scour. This study presents an experimental campaign aimed at assessing the effects of flow intensity on propeller jets in confined conditions. Specifically, three different flow intensities and three propeller distances from a vertical quay-wall were tested. The findings are presented through profiles of the scoured bed, and bathymetries at the equilibrium condition and empirical formulas for calculating the principal dimensions of the scour holes are given. To explore the intricate hydrodynamics and understand how the intensity of the flow affects the scour hole development, and to investigate boundary effects on the flow field, we performed Reynolds-Averaged Navier– Stokes (RANS) simulations. These simulations were applied to the three-dimensional scoured bathymetry in a state of equilibrium. The satisfactory match between numerical results and sampled velocities at the equilibrium stage ensures the reliability of the simulations. To the authors’ knowledge, these configurations had not been previously simulated, owing to the complexities involved in computing a moving mesh in presence of a bathymetry and a confining vertical wall. The results offer the first numerical demonstration of boundary effects on the characteristics of propeller jets both in the presence and in the absence of an additional channel flow.