Three-dimensional numerical modelling of wave-induced scour around piles in a side-by-side arrangement

Abstract

The paper presents the numerical modelling of wave-induced scour around piles in a side-byside arrangement using the open-source CFD model REEF3D. The model solves the Reynolds-Averaged Navier-Stokes equations to calculate wave hydrodynamics. The turbulence under the wave action is calculated using the k-ω model. The free surface is captured with the level set method. The simulated flow field is coupled with the morphological module in REEF3D to simulate the scouring process. The morphological evolution of the sediment bed is based on the Exner formula. For a more realistic calculation of bed scouring and deposition, the modified critical bed shear stress on a sloping bed together with a sand slide algorithm is implemented in the morphological model. First, the model is tested for numerical modelling of wave-induced scour around a single pile. The study presents wave generation and the scouring process in a full-sized and a reduced-length numerical wave tank (NWT) using the relaxation and the active wave absorption method. Furthermore, a discussion on the partial temporal decoupling for the time scales of the morphological and the hydrodynamic models is made. The simulated result shows that the fully developed waves and resulting scouring can be modelled in a reduced-length NWT with the same quality as seen for a full-sized NWT. The validated model is then used to simulate the wave-induced scour around piles in a side-by-side arrangement. The capacity of the model to simulate wave-induced scour in the gap between two piles along with the free surface is demonstrated. The results show the variation of the normalised maximum scour depth S/D with the gap ratios G/D and the Keulegan-Carpenter number. The formation of the jet effect between the piles with different G/D values is also discussed.

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