turbulence, RANS model

[cris2015]

Hi everyoone,

I'm using a RANS model, with k-epsilon turbulence model (IH2VOF).

One of the options in the model setup is to 'activate turbulence' and then specify 3 parameters (turbulence seed parameter, eddy viscosity and a parameter for boundary layer turbulence).

My question is if I choose not to include turbulence what is happening to the equations? they became NS?

Many thanks

 

[RustyWater]

I'm not familiar with IH2VOF, but in most environmental-scale models turbulent motions are not resolved, and the diffusive effect of turbulence is parameterized by a closure (such as k-epsilon). If you turn the turbulence closure off, you could still (very roughly) capture turbulent mixing by supplying a constant eddy viscosity. Turning the turbulence closure off and using only molecular viscosity (e.g. approx 1e-6 m^2/s for water) will drastically underestimate friction effects and it's possible the model become unstable, as well.

As far as the equations becoming Navier-Stokes: if you have no turbulence closure calculating an eddy viscosity, and no prescribed eddy viscosity, then the equations would be Navier-Stokes (instead of Reynolds-averaged Navier-Stokes, which includes turbulence via an eddy viscosity).

 

[cris2015]

Many thanks for your reply, it was very helpful!