Two-phase simulation of scour using a hybrid RANS-LES turbulence model

The coastal environment is meeting numerous anthropogenic changes especially with the increased implementation of bottom-fixed Offshore Wind Farms. Few feedbacks are available for these recent infrastructures facing a complex turbulent marine environment made of combined waves and currents. In the presence of a pile, strong hydrodynamical eddies structures form that are responsible for the scour process which may lead to the failure of the wind turbine. Former two-phase flow simulations of this problem [1] have been performed using the Reynolds-Averaged Navier-Stokes approach for turbulence modelling and they have shown some limitations to reproduce the main features of the scour process. Turbulence modelling was argued to be the major bottleneck. In order to further investigate this problem, an extensive study of the numerical simulation of the flow hydrodynamic around a wall-mounted cylinder has been carried out using a hierarchy of turbulence models including RANS, hybrid RANS-LES and LES. The range of Reynolds numbers is too large to allow for a well-resolved LES and therefore hybrid RANS-LES is essential to reproduce main hydrodynamical features at an affordable cost. In this study we evaluated the k-omega SST model coupled with the Improved Delayed Detached Eddy Simulation [2] and the Scale-Adaptative Simulation [3]. All the simulations have been performed using OpenFOAM an open-source Computational Fluid Dynamics toolbox. Our simulations suggest that the k-ω SST SAS is the best model for this configuration. It has been adapted for the two-phase flow Eulerian-Eulerian approach and implemented in sedFOAM [4]. Preliminary results of the two-phase simulation of Roulund and co-worker experiments [5] shows very encouraging results in terms of morphological features at short-time scales. These results will be presented during the conference together with in-depth analysis of the sediment transport fluxes.

References

[1] Nagel T., Chauchat J., Bonamy C., Liu X., Cheng Z. and Hsu T. - J., Three-dimensional scour simulations with a two-phase flow model, Advances in Water Resources (2020).

[2] M. S. Gritskevich, A. V. Garbaruk, J. Schütze and F. R. Menter, Development of DDES and IDDES Formulations for the k-ω SST Model, Flow Turbulence Combust (2012).

[3] F. R. Menter and Y. Egorov, A scale-adaptative simulation model using two-equation models, American Institute of Aeronautics and Astronautics Paper (2005).

[4] J. Chauchat, Z. Cheng, T. Nagel, C. Bonamy, and T.-J. Hsu, Sedfoam-2.0: a 3-d two-phase flow numerical model for sediment transport, Geoscientific Model Development (2017).

[5] Roulund A., Sumer B. M., Fredsøe J. and Michelsen J., Numerical and experimental investigation of flow and scour around a circular pile, Journal of Fluid Mechanics (2005).