CFD investigation of flow in scour protection around a mono-pile with the volume-averaged k-ω model

The study numerically investigates the flow behaviour around a mono-pile with scour protection under steady and oscillatory flow conditions. A hydrodynamic model based on volume-averaged Reynolds-averaged Navier-Stokes (VARANS) equations with the volume-averaged k-ω turbulence closure is developed and implemented in OpenFOAM. Three porosity transition types, i.e., constant, linear and parabolic, near the interface between stone cover and free flow are firstly evaluated in two-dimensional models. The simulated results, i.e., flow velocities, turbulence levels and bed shear stresses, are compared to previous experiments under steady and oscillatory flow conditions. The parabolic transition shows the best agreement with the measurements and is therefore used in the developed model. Under steady current, a three-dimensional model is validated against experimental measurements including flow features both inside and outside of the scour protection around a mono-pile and it exhibits relatively good performance. Further, the volume-averaged k-ω model shows better agreement to experiments in porous medium compared to results from k-ω SST and volume-averaged k-ε models. The model is applied to investigate the flow patterns under oscillatory flow condition. The results show that a horseshoe vortex is formed and it penetrates the entire scour protection, which generates high flow velocities and bed shear stresses; erosion is most likely to occur at the area in the presence of vortex, which poses a threat to the pile stability. The simulations demonstrate the ability of the developed model to evaluate the flow behaviour in scour protection