BCs for k and epsilon at walls with y+=1
 

Hello everybody,

I would like to know the following for OpenFOAM 2.1.1:

when setting up a turbulent flow case with a mesh that leads to y+ values of 1 I do not need to use wall functions.
What is the correct BC for k and epsilon in such a case
Are they fixedValue=0 or
zeroGradient?

Similar question for k-omega models also.

I have found this post
http://www.cfd-online.com/Forums/ope...m-1-5-dev.html
but it refers to previous OF releases

Thanks!

Hi Vangelis,

To my understanding you would (theoretically) set both at fixedValue = 0, as there is no turbulence possible in the viscous sublayer. And as there is no turbulence, you also can't have dissipation of turbulence.

I say theoretical because actually setting the BC's to 0 would result in a division by zero in the OpenFOAM implementation. In practice you would therefore set them to a very small value, for example fixedValue = 1e-12.

Best regards,
Sylvester

Hi Sylvester!

Thank you very much for your reply.

Best regards

Vangelis

Hi Sylvester

I forgot to also specify that
nut should also be set to fixedValue=0
like k, right?

Vangelis

Hi Vangelis,

Or use nutLowReWallFunction, which makes the patch accessible from yPlusRAS.
From nutLowReWallFunctionFvPatchScalarField.H:
regards,
Sylvester

ps. Can we perhaps expect improved OpenFOAM pre-processing in ANSA v13.3?

We are trying to do this.
And in this sense thank you for your help!

so you mean that it is better to use
nutLowReWallFunction

so that afterwards I can get values for y+?

Otherwise it would be the same as setting fixedValue=0 for nut at walls?

Hi Vangelis,

Yes, from what I can gather it is better to use the nutLowReWallFunction. But I haven't done much work with low Re turbulence models, so I may be wrong here.

Best regards,
Sylvester

Thanks again Sylvester!