Numerical Simulation Of Scour Around A Pipeline Using Two-phase Model

The stability and structural integrity of pipelines can be influenced by scour below pipelines which may lead to significant structural failure,hence a good understanding of the scour mechanism is paramount.Scour below pipelines is a complicated two-phase fluid-sediment process.Various numerical methods have been proposed to simulate scour,such as potential flow theory,single-phase models.However,these numerical methods have limitations,such as their reliance on calibrated empirical parameters,as their lack of considering the interaction between fluid and sediment and as their inability to provide detailed information.Considering the effect that sediment exerts on the turbulence,a modified k-? turbulent model is used in this paper to complete a two-phase sediment model.Based on the open-source software OpenFOAM,the two-phase sediment model is applied to simulate scour around a pipeline.The novelty of this work is to use the two-phase sediment model to study the influence of initial gap between pipelines and bed on the different characteristics which include the contour of fluid velocity,the evolution of bed profile,the sediment transport rate and the pressure distribution on the pipeline surface,leading to new findings that enhance the current understanding of the underlying mechanisms of the scour process.The simulated scour evolution and bed profile are found to be in good agreement with published experimental results.When the pipeline scour reaches the equilibrium,with the increase of the initial gap(G)between the pipeline and the bed,the depth S decreases linearly.According to the two-phase simulation results,the relationship between S and G is obtained.The sediment transport rate is calculated using the concentration and velocity of particle.The numerical results reveal three scour stages:onset of scour,tunnel erosion,and lee-wake erosion.Fluid velocity and the sediment transport rate show that during the tunnel erosion stage,the particle motion and fluid-particle interaction are particularly intense,suggesting that single-phase models,which are unable to account for fluid-particle interactions,may be inadequate.The pressure coefficients on the pipeline surface show that the scour depth dominantly affects the flow features around the lower side of the pipeline.The suitable initial gap is a necessary condition for the generation of downstream vortices.