**Two-Phase Flow Simulation of Tunnel and Lee-Wake Erosion of Scour below a Submarine Pipeline**

#### **Antoine Mathieu \*, Julien Chauchat, Cyrille Bonamy and Tim Nagel**

Laboratoire des Ecoulements Géophysiques et Industriels (LEGI), Centre National de la Recherche Scientifique (CNRS), University of Grenoble Alpes, Grenoble-INP, F-38000 Grenoble, France

**\*** Correspondence: antoine.mathieu@univ-grenoble-alpes.fr

Received: 29 July 2019; Accepted: 13 August 2019; Published: 19 August 2019

**Abstract:** This paper presents a numerical investigation of the scour phenomenon around a submarine pipeline. The numerical simulations are performed using SedFoam, a two-phase flow model for sediment transport implemented in the open source Computational Fluid Dynamics (CFD) toolbox OpenFOAM. The paper focuses on the sensitivity of the granular stress model and the turbulence model with respect to the predictive capability of the two-phase flow model. The quality of the simulation results is estimated using a statistical estimator: the Brier Skill Score. The numerical results show no sensitivity to the granular stress model. However, the results strongly depend on the choice of the turbulence model, especially through the different implementations of the cross-diffusion term in the dissipation equation between the *k* − *ε* and the *k* − *ω*2006 models. The influence of the cross-diffusion term tends to indicate that the sediment transport layer behaves more as a shear layer than as a boundary layer, for which the *k* − *ε* model is more suitable.

**Keywords:** two-phase flow; scour; pipeline; numerical modeling; turbulence modeling
