Think this is indeed not correct what I had. I used a flow region height of 40m (2.5H) and my object of interest was H=16m high. So now I changed the flow region height to 100m (6H).
I used 10m, more or less 20times the z0. By the way I see this also a (lower) recommendation for terrain scale 6 by SIMSCALE: a factor of 10.
I don’t understand this point: I set the roughness height in the boundary ‘Custom’. Anyway I use a boundary layer for all surfaces of the flow region. Perhaps I misunderstand this point?
If I look in the Mesh quality file I see:
nonOrthogonality
Acceptable range: 0 to 88
min: 0
max: 89.96142835721949
average: 15.115932162422554
standard deviation 11.87045328471216
median: 14.786002566388524
99.9-th percentile: 56.65718636249987
99.99-th percentile: 67.50480604953317
99.999-th percentile: 77.50601308919153
So this looks all ok, correct? By the way what is: ‘pot-flow initialisation’?
At this moment I used the default meshing, the manual of Fineness setting did not work for me (all setting above 7.5 and 10 cause same issues). It looks the the Roughness height of ground is a reason for terminated Runs. A Roughness height of 1m works mostly, but a 3, 5 or 10m Roughness height causes Gauge pressure field started diverging (see another mail thread: Gauge pressure field started diverging - #9 by jjansman ).
Thanks for your help. I am slowly getting there.