Dear all,

We are pleased to announce the release of the "stabRAS" (stabilized Reynolds-averaged stress) library of two-equation turbulence closure models, for use in the open source CFD software OpenFOAM. Versions of the library (as well as a tutorial) are available at:

OpenCFD Ltd.: https://github.com/BjarkeEltardLarsen/stabRAS_v1712

OpenFOAM Foundation: https://github.com/BjarkeEltardLarsen/stabRAS_OF50

foam-extend: https://github.com/BjarkeEltardLarsen/stabRAS_FE31

Background and Motivation: In previous CFD studies of surface waves, there has been a marked and collective tendency to severely over-predict turbulence levels. This is most likely due to the previously described (Mayer & Madsen 2000) conditional instability of two-equation turbulence closure models in the nearly potential flow region, which can lead to exponential growth of the turbulent kinetic energy and eddy viscosity. In our paper published recently in J. Fluid Mech. (Larsen & Fuhrman 2018, https://doi.org/10.1017/jfm.2018.577) we show formally that: (1) such models are in fact unconditionally unstable, and (2) they can be elegantly stabilized with relatively simple modifications. Significant advantages of using stabilized closures are demonstrated in the CFD simulation of both non-breaking and breaking waves, and we recommend that such "stabilized" closure models be utilized in future CFD simulations of surface waves.

To help facilitate this, the "stabRAS" library contains stabilized implementations of several popular two equation turbulence models (standard k-omega and k-epsilon models, as well as several variations) which are widely used in OpenFOAM.

We sincerely hope you might find them useful!

With kind regards,

Bjarke Eltard Larsen & David R. Fuhrman

Technical University of Denmark Department of Mechanical Engineering Section for Fluid Mechanics, Coastal & Maritime Engineering

References

Larsen, B.E. & Fuhrman, D.R. 2018 On the over-production of turbulence beneath surface waves in Reynolds-averaged Navier-Stokes models. J. Fluid Mech. 853, 419-460. doi.org/10.1017/jfm.2018.577

Mayer, S. & Madsen, P.A. 2000 Simulations of breaking waves in the surf zone using a Navier-Stokes solver. In: Proc. 25th Conf. Coast. Eng., pp. 928-941.