Current-induced scouring around a submarine pipeline using a multi-phase flow model with different inter-phase drag models

Abstract

This paper numerically investigates scouring beneath a submarine pipeline induced by the current. The simulations use an Eulerian–Eulerian multi-phase model for sediment transport developed in OpenFOAM (the open-source Computational Fluid Dynamic toolbox), which can capture fluid–particle–structure interactions. The model implements the Hybrid Fictitious Domain-Immersed Boundary (HFD-IB) method for representing the pipeline structure in the computational domain. The simulated flow fields are validated by experimental data for the developed flow around a pipeline over scoured beds, resulting in favorable results for velocity profiles. Further, three inter-phase drag models, the EF (Engelund and Fredsøe, 1976), RZ (Richardson and Zaki, 1997), and ERZ (Lee and Huang, 2018) are applied and subsequently examined in simulating pipeline scouring, particularly the effects on the flow field, sediment transport, and the resulting scour profile during the onset and tunnel erosion stages. The models produce consistent results with the measured scour profile. All models show that buoyancy is dominant in driving the sand movements within and near the bed surface in both stages. Meanwhile, the drag force is dominant for sand transport above the bed where the inter-phase relative velocity is high. However, the three models differently capture the physical behaviors of the particle response time and relative velocity near the bed surface and within the bed, which impact the computed drag force and, thus, the resulting scour profile.