Turbulence is an extremely important physical process, especially when studying wave breaking or wave impacts on a structure. However, OpenFOAM® does not provide by default incompressible turbulence models for multiphase systems (i.e. models that take into account the density variation between the air and water phases). This often results in a well-known excessive wave height damping (due to the increasing nut) as the simulation progresses, due to turbulence build-up.
Today olaFlow CFD is presenting a library that provides modified versions of k-ε and k-ω SST turbulence models to simulate correctly multiphase systems and mitigate this effect.
Moreover, a new variation of the k-ω SST model, recently proposed in an excellent paper by Devolder et al. (2017) to model free surface cases (e.g. waves) correctly, is also included. Their model features an additional buoyancy term that helps suppress the spurious turbulence generation at the free surface.
This new library is part of the olaFlow supplementary materials repository:
It is hosted in the turbulenceMultiphase folder and includes the source code and a tutorial to test the effects of the turbulence models, as in the videos below.
You can follow the link for full information on how to download and compile this module and use it in you cases.
The turbulence models have also been tested on a more meaningful context in which waves break on a 1:10 slope. These results make clear the importance of running a density-aware turbulence model to prevent turbulence build-up in two-phase simulations.
It can be noticed that the dissipation of OpenFOAM default models is excessive and that the model presented in Devolder et al. (2017) shows the best performance among all.
References
Devolder, B., Rauwoens, P. & Troch, P. (2017)
Application of a buoyancy-modified k-ω SST turbulence model to simulate wave run-up around a monopile subjected to regular waves using OpenFOAM®.
Coastal Engineering, 125, 81–94.
doi:10.1016/j.coastaleng.2017.04.004
Devolder, B., Troch, P. & Rauwoens, P. (2018)
Performance of a buoyancy-modified k-ω and k-ω SST turbulence model for simulating wave breaking under regular waves using OpenFOAM®.
Coastal Engineering, 138, 49–65.
doi:10.1016/j.coastaleng.2018.04.011