[Rana abdo]

How can i get results of roughness function (Delta u+)after simulation and get its contours on the model in fluent

[NickFL]

I am confused on what you are trying to obtain. The roughness height is specified at the surface. Go to the wall boundary condition and you can see the roughness height and coefficient.



You could plot the velocity profile normal to the wall. Probably what would be easiest would be to export this into MATLAB or Excel and then produce u+. Then from there you could determine the Δu+.

[Rana abdo]

Could you tell me how to choose the correct Y+ value for each roughness height and which turbulance model should i use for roughness ?
If i use kw sst model shouldnt the y+ value be 1 but also i think that the roughness height should be less than the height of the centre of the first cell yp so i have to use k-e model with standard wall functions is my information correct or what am i miss understanding ?

[LuckyTran]

Originally Posted by NickFL

I am confused on what you are trying to obtain. The roughness height is specified at the surface. Go to the wall boundary condition and you can see the roughness height and coefficient.

You could plot the velocity profile normal to the wall. Probably what would be easiest would be to export this into MATLAB or Excel and then produce u+. Then from there you could determine the Δu+.

Roughness function (e+) is defined in Nikuradse's dissertation and the work of his predecessors in Prandtl's engineering group.

Roughness function you get after simulating the case and getting the pressure drop, friction factor, friction velocity, and thereafter the roughness function from its definition.

kwSST has wall functions you can use it for wall y+ greater than 1. You do not have to use any particular turbulence model. For sand-grain type roughnesses you can use the roughness height option in Fluent, but large scale roughnesses like rib turbulators you have to mesh explicitly.

[Rana abdo]

I need help in correlating real peak to valley roughness with sand grain roughness in fluent are there any papers that can guide me for roughness on ships ?