Numerical investigation of local scour around twin piles under steady current using CFD-DEM coupling method

In recent years, the local scour has developed into a major threat to the safety of offshore group piles. The numerical simulation methods are useful tools in investigating the key mechanisms behind local scour. However, conventional simulation methods often neglect the microscopic sediment behavior, thus impeding a more profound understanding of the scour mechanism. In this research, the CFD-DEM method was applied to investigate the local scour around twin piles. And the coarse grain method and porous media model were incorporated to enhance simulation efficiency. The CFD-DEM model was constructed and validated using experimental data. Based on the validated model, a series of local scour simulations around twin piles were conducted under different arrangements. The time-development curves of scour depth were analyzed, and the variation of the equilibrium scour depth with pile spacing exhibits good agreement with the dates from previous studies. Based on the simulation results, the flow field, scour pit morphology, sediment flux, and microscopic behavior of sediment around twin piles were analyzed under different arrangements, and four key mechanisms of twin piles' local scour were observed and analyzed during this process.