Computational Investigation of Scour Around Square Piles Oriented at 45 deg and 90 deg in Wave–Current Flows

Square piles are widely utilized in coastal engineering due to their economic efficiency and robustness in resisting large forces in the coastal environment. However, the removal of sediment particles due to the approaching flow around such structures, known as scour, raises concerns about the stability and safety of the structure. Therefore, this study investigates scour around square piles placed at 45 deg and 90 deg angles in wave–current flows. A newly developed sediment transport module within the open-source REEF3D framework is developed, incorporating a three-phase semicoupled approach with level-set method (LSM) for realistic representation of sediment bed and free surface interfaces. The developed model is first validated against experimental results of circular and square pile scour in different flow conditions, such as steady current, wave-only, and wave–current flows. Furthermore, the effect of the combined wave–current parameter (U_cw) and Keulegan–Carpenter (KC) number on the normalized equilibrium scour depth (S/D_w) is explored. This study provides new insights into how square pile orientation modifies bed topography and equilibrium scour depth in wave–current flows. Numerical results demonstrate that a higher S/D_w value was observed for larger U_cw and KC numbers for both piles. It is revealed that in wave-only and combined wave–current flows with low KC numbers (KC < 10), square piles oriented at 45 deg experience greater scour depths than those oriented at 90 deg. However, at a higher KC number (KC = 18), square piles oriented at 90 deg exhibit greater scour depths compared to those at 45 deg.