[faiazk]

Dear All,

I am relatively new to Openfoam. I am trying to perform a grid independence study using different turbulence models over a small building model. I am trying to simulate the atmospheric boundary layer flow throughout the domain. It is expected to have refined meshing towards the ground and gradually getting coarser away from the ground. I have 40 meters in vertical direction and have 200 cells with expansion ratio of 1.3. The meshing looks acceptable and also the pressure measurement obtained on the building surface is pretty close to experimental results using this mesh. However, I want to get appropriate yplus value for k epsilon and k omega models.

when I try to find the yplus value at each time step I found very high values which is telling me that something is not right.

y plus values seems to change a lot at each time step. but here I am showing a sample result for yplus.

for patch ground: y+ min:7961.96, max: 65989.3, average: 53993.8

I only get reasonable value when I increase the nu value in transport properties dictionary. But, I think I cannot just play with nu values to adjust yplus numbers. right?


Please enlighten me on what to do in order to get desirable yplus value for each turbulence model .

Thanks in advance.

Regards,
Faiaz

[mzzmrt]

You have to remesh the domain according to the required yPlus.
For a target yPlus value the distance of the first grid point to the wall must be calculated first and meshing must be done accordingly.
As an example with your case; when you target average yPlus ~1 and your first grid distance to the wall is z, to get a correct mesh this first grid distance must be z/54000 etc.