code_saturne User's Forum

Dear support and users,
I have a question regarding the roughness:
when we set the roughness different to zero, what exactly changes in the code?
I looked in the theory guide, and apparently, the roughness is used for the calculation of the friction velocity. Is that all? or did I miss something?
I guess the roughness is also used for the linear head loss calculation.
My best regards,
 
Stéphane

Hi Stéphane,
Actually, the roughness (dynamic or thermal) is only used for wall-functions. The code never sets by itself a head loss in the calculation. For example, here are two wall functions, the first for a smooth wall and the second for a rough wall:
u/u * = 1/kappa . ln(yu * /nu) + B

u/u* = 1/kappa . ln(y/y 0 ) + E
Rough walls can also be used to model forests or buildings in atmospheric flows.
David

Hi,
Thank you for your answer David.
Stéphane