well, check your mesh, again, you assign a wrong patch as out-flow

your mesh has wrong assigned patch, also severely non-orthogonal face, build new mesh

How didi you find the wrong boundary.
I was using checkMesh, and it looks everything is ok.

your mesh configure is fine, as i said before, you assigned wrong patch as out-flow, you can see each patch by paraview, just click on patch name , and remove other patch name on paraview ;)

Hi Nimasam,

Thank you.
I changed the out-flow patch.
And now it can calculate, but some problems still exist, see figures below

There is no flow in the area (blue region) around the cylinders (represented by the gray circle). I have double checked the wall boundary, and it's right. So what's wrong with the blue region?

In the second figure, large velocity is found at the surface. Note different scale for these two figures. I gave a symmetryPlane boundary for the surface. Why did it cause big value at the surface?

If you want, find the case at
https://www.dropbox.com/s/vb3ge8jm4t...linders.tar.gz

i feel you need to increase cells number in z direction to atleast 4 cells, maybe it solves your problem

Hi Nima

I increased the cells number in z direction to 8, but it didn't work.
Do you have any other ideas on this?
Thank you.