Numerical model for three-dimensional scour below a pipeline in steady currents

A three-dimensional numerical model is established for simulating scour propagation in spanwise direction under a sub-sea pipeline in steady currents. In the model, flow is simulated by solving the Reynolds averaged Navier-Stokes equations with a k-ω turbulence model. The bed development is modelled by conservation of sediment mass. Calculations are carried to simulate local scour development below a pipeline that has been investigated experimentally. The input conditions of the simulation are set as closely as possible to those used in the physical tests reported in literature. The embedment depth of the pipeline was 0.2 pipeline diameter. It was found that scour development in the spanwise direction is mainly caused by the flow velocity around the span shoulders, where the gap between pipeline and bed is small. In the middle of the scour hole, the scour process is similar to that observed in the 2D laboratory tests and 2D numerical results reported in previous studies. The simulation demonstrates the capability of the 3D model although the calculated propagation speed of scour hole in the spanwise direction of pipeline is slightly lower than that measured in the tests.