Roughness Models Suggestions
 

Hi All,

I am solving a problem involving rough surface under laminar flow conditions in a microchannel. In order to model roughness, I can do one of the following.

Explicitly "position" the rough surface randomly on an ideal smooth surface using rectangular/triangular shapes & then simulate them with a well refined mesh at the wall boundary.

OR

Can I use a porous zone to simulate a rough surface effectively? Since, this will represent a momentum sink, I feel it should be possible.

OR

How about using a modified viscosity near the rough surface zone higher than normal viscosity of fluid?

I am unable to make the choice between these alternatives & would appreciate any advice OR other way out for this case.

Thanx a lot for all your co-operation.

Swarup.

Re: Roughness Models Suggestions
 

Dear Swarup,

I am not working in this field, but I would like to make the following suggestion.

The presence of roughness are known to trigger transition to turbulence, wherin the viscosity is increased. Thus, it seems quite logical and comparitively easier if you make use of the third option, compared to the others. Also, it is a nice option if you can check if the flow remains fully laminar throughout inspite of the roughness introduced, otherwise the flow would turn more complex.

Regards,

Ganesh

Re: Roughness Models Suggestions
 

Hi Ganesh,

You are very right about flow transition to turbulent flow but that seems to be a grey area. Actually, I am using FLUENT 6.2 & I doubt whether it (or any other CFD software) will be able to predict this transition. There is only one explicit claim by CFX I guess. Low Re k-e or transitional k-w are limited in their accuracy & only realistic solution strategy is said to be DNS!!

In this situation, I think I will have to stick to steady laminar flow assumption but I am still waiting for some clue. Thanx a lot for your prompt response & suggestions.

Swarup.