Two-Phase Simulation of Wave-Induced Tunnel Scour beneath Marine Pipelines

Abstract

An Eulerian two-phase flow model was presented and employed to investigate wave-induced tunnel scour beneath marine pipelines. The model is based on the Euler-Euler coupled governing equations for the fluid and sediment phases, i.e., time-averaged continuity and momentum equations were solved for both phases with a modified k-ε turbulence closure for the fluid phase. Fluid-particle, particle-particle, and fluid-structure interactions were implemented in the simulation. The model accounts for the interphase momentum exchange by considering the drag, lift, and added mass forces. The flow model was validated against an oscillatory flow around an isolated cylinder and a cylinder close to a rigid wall. The two-phase model was also validated against an oscillatory sheet-flow motion above a plane bed. Then, the two-phase model was used to simulate the wave-induced tunnel scour beneath the pipeline laid on a plane erodible bed. Comparison between the numerical results and experimental measurements indicates that the model simulates the bed profile successfully during the tunnel scour stage. Investigations revealed that the tremendous sediment transport takes place during the tunnel scour stage under high turbulence intensity. A phase-lag was observed between the flow velocity in the scour hole and the free stream velocity.