Scour modeling based on immersed boundary method: A pathway to practical use of three-dimensional scour models

Local scour around structures is an important hydraulic phenomenon that involves multiple coupled physical processes, including turbulent flow, sediment transport, and the evolution of erodible bed. This paper presents a new three-dimensional (3D) scour model, ibScourFoam, which is based on an immersed boundary method. This model is capable of dealing with scour around complex structures and thus it paves the way for practical use of 3D scour models. A special wall function has been developed to overcome the non-smoothness problem of wall shear stress in previous immersed boundary methods. Smooth and accurate wall shear is of critical importance for successful simulation of scour. The model was validated against cases reported in the literature and one flume experiment conducted in this work. The validation case of flow and scour around a vertical pile was reproduced well by our model. The flume experiment is for scour around a partially-buried, horizontal cylinder placed on a foundation. The horizontal cylinder is of finite length and the scour is initiated by flow contraction. The model revealed the distinct stages of scour in the experiment. The complex process of undermining and exposure of initially buried cylinder and foundation was captured well by the model.