Turbulent viscosity limited to viscosity ratio of
 

Hi,

"Turbulent viscosity limited to viscosity ratio of ....." it this an error? For my simulations, it is for nearly 50% of the total cell count but still, my solution is getting converged. I have also attached a picture with this thread.

Any suggestions are welcome.

Check your boundary conditions and initial conditions. You shouldn't get that warning if a case converges to a reasonable solution. That high of a turbulent viscosity ratio is non-physical / borderline insanity

Thanks for the reply,

I am doing a 2D simulation. I am using open channel wave conditions at the inlet (left) to generate the wave, top and right-hand sides are pressure outlet.

Please let me know if any other inputs are required.

Boundary conditions for turbulence?

Initial conditions for everything?

Actual values for everything... not just their types.


Anything that you left default is likely a culprit and it's likely (my guess) the turbulence BC's and initial conditions.

VoF model, implicit body force, open channel flow and open channel wave BC

K-w SST model, default settings

Numerical beach treatment is activated

Pressure-Velocity coupling-- SIMPLE
Pressure-- PRESTO
Momentum -- Second order upwind
Vol. fraction-- Modified HRIC
Turbulent K.E. -- Second order upwind
Sp. dissipation rate-- Second order upwind
Transient formulation -- second-order implicit
URF -- default values

Those are neither boundary conditions nor initial conditions. Specifically I'm looking for what you specified as the inlet for k and omega and the initial condition for k and omega.

Hint: they'll be numbers.

I think you are looking for these values.

Thanks for your patience

I'm really not interested in your model settings and urf's.

Okay so you have an inlet turbulence intensity of 2% and viscosity ratio of 2. Is the 2 correct? That's a low number but still reasonable for a laminar inlet.

Alright. Now what about the initial conditions? Hint: they're in the initialization pane. What did you do? Standard where you manually set them or did you do some automatic hyrbid/FMG initialization where you have no control? If you don't provide the proper initialization then of course you will into issues with the turbulence viscosity ratio while the case is iterating..

Inlet turbulence intensity of 2% and viscosity ratio of 2, that I have provided from one reference. I don't know how much it is applicable.

I have selected standard initialization and initial values are taken as default.

So your initial condition for k is 1 (which is a very high value) and initial condition for omega is also 1 (which is a very very low value). That's how you end up with these viscosity ratio warnings.


Either you make better guesses. Or keep iterating and pray they go away and eventually converge to the correct values.

Thanks for clearing my doubts.

I have checked with lower values k and omega of 1e-06 (which are very low values). That's removed my error. Before that, I have checked with different values but the error was still there after that only I posted the thread.

I will check as you recommended i.e. lower values of K and higher value of omega. Please can you mention the range of values for k and omega?

Convert your inlet BC of 2% and 2 into k and omega. Or again you can just keep iterating and wait and get the value from the solution.