wall roughness with SST turbulence model in CFX10
 

I'm trying to set a wall roughness using the SST turbulence model in CFX-10. The documentation says it is a beta feature and there are posts (dating from 2005 and CFX 5.6) saying you can set a roughness modifying the .ccl file. (http://www.cfd-online.com/Forum/cfx_...cgi/read/10419)

I've tried to set the extra parameters but I've got the error: 'TURBULENT WALL FUNCTIONS' is not allowed in FLOW/DOMAIN:Domain 1 /BOUNDARY:wall/BOUNDARY CONDITIONS. And setting just the roughness (whithout changing any other parameters) give the exact same result than the computation without any roughness.

Has anyone set a wall rougness with SST in CFX 10? Thank you for your help.

Re: wall roughness with SST turbulence model in CF
 

Dear Vincent,

I imagine you want to access the turbulent wall function for the momentum boundary condition closure. You should add the TURBULENT WALL FUNCTIONS within WALL INFLUENCE ON THE FLOW. For example,

BOUNDARY CONDITIONS:

WALL INFLUENCE ON THE FLOW

Option = No Slip

TURBULENT WALL FUNCTIONS:

Option = Rough Wall Omega Automatic

END

END

END

Hope this help, Opaque

Re: wall roughness with SST turbulence model in CF
 

Thanks a lot. I accessed the turbulent wall function with this syntax. But Cfx pre says that the Option you mentioned (Rough Wall Omega Automatic) is an 'Invalid Option parameter'. Was it just an example or is there really some automatic option for the turbulent wall functions when using a wall roughness and the SST turbulence model?

Re: wall roughness with SST turbulence model in CF
 

Dear Vincent,

There are two options named Rough Wall Omega Automatic and Rough Wall Omega Scalable. Neither of them is allowed in the GUI for 10.0 or 11.0.. Maybe 12.0 has it.

There is an additional parameter that can be added to the Rough Wall Omega Scalable named Rough Wall Minimum Yplus to determine the specific yplus for that boundary.

Regards,

Opaque

Re: wall roughness with SST turbulence model in CF
 

Thank you opaque for your help. But I still can't set properly a roughness with cfx-10 and the SST turbulence model.

When I just include the roughness in the .ccl it doesn't change anything to my result without any roughness. And when I include the extra parameters mentionned under, my result is different but doesn't depend on the value of my roughness... Has anyone succeeded to implement a roughness with the SST model?

Extra parameter I used :

FLOW:

EXPERT PARAMETERS:

effective viscosity type = 2

END

END

and :

WALL INFLUENCE ON FLOW:

Option = No Slip

TURBULENT WALL FUNCTIONS:

Option = Scalable

Minimum Yplus = 2.5

END

END

Re: wall roughness with SST turbulence model in CF
 

Dear Vincent,

Unfortunately, I do not understand why is not picking up your roughness data. Have you updated to 11.0? I do not recall if there were any problems with the 10.0 rough wall model for SST. Have you contacted help desk already about this issue?

On a different topic, who adviced you to change the effective viscosity type from its default value to 2? Help desk?

Regards,

Opaque.

Re: wall roughness with SST turbulence model in CF
 

I'm still using cfx-10.0. I saw the advice on the effective viscosity in a previous post : http://www.cfd-online.com/Forum/cfx_...cgi/read/12758

I've not contacted help desk yet. I tell you what they advice me if I do.

Thanks again,

Vincent

Re: wall roughness with SST turbulence model in CF
 

Dear Vincent,

Unfortunately, I do not understand why is not picking up your roughness data. Have you updated to 11.0? I do not recall if there were any problems with the 10.0 rough wall model for SST. Have you contacted help desk already about this issue?

On a different topic, who adviced you to change the effective viscosity type from its default value to 2? Help desk?

Regards,

Opaque.