A nested SPH approach for simulating propeller jet wakes over scoured bathymetry

This work presents a numerical investigation of the three-dimensional hydrodynamics generated by a propeller jet (PJ) operating above a scoured bathymetry (SB), a configuration frequently encountered in harbour basins and navigable waterways where propeller-induced flows lead to local bed erosion. Accurately modelling the interaction between the propeller jet, the equilibrium scour geometry, and the surrounding flow field remains computationally demanding, due to the coexistence of highly localised turbulent structures and the large spatial scales typical of laboratory and field settings. To address this multiscale challenge, a nesting strategy is developed within the Smoothed Particle Hydrodynamics (SPH) framework. The approach couples a high-resolution SPH domain, dedicated to resolving the near-field hydrodynamics of the propeller jet, with a larger domain discretised at coarser resolution, representative of the overall experimental environment. This formulation enables an efficient transfer of flow information across scales, substantially reducing computational costs while retaining the essential dynamics of the jet–bathymetry interaction. The numerical model is validated against laboratory measurements obtained under steady current conditions, showing good agreement in terms of velocity distributions, jet spreading, and flow structures influenced by the scoured bed. Additional simulations under still-water and regular-wave conditions further demonstrate the robustness of the proposed methodology. Overall, the results confirm the suitability of the nested SPH approach for simulating fully three-dimensional propeller-induced flows interacting with complex bed geometries.