Roughness of ground plane internal flow area

Using SimScale
1

I am simulating a village with a traditional wind mill and thus I have an internal flow region around this. The ground plane of this flow region includes the buildings. So what roughness should I put on this ground plane? I first though 10m, but thinking more on this that does not sound well, as this 10m roughness will also be ‘included’ on the tops of the buildings, correct? So I think a much smaller roughness should be more realistic (say 1m).
Any thoughts/hints/help/links?

Thanks!

2

Hi @jjansman, thanks for your post on the forum :slight_smile:

I see an old forum post you made where my colleague Ricardo answered your question on that, his answer seems to be correct:

Did you find anything wrong in it? Please let me know!

Best,
Igor

4

Hello Igor,
Ricardo’s input was useful and it helped me at that moment, but I am now wondering if my thinking was correct! I was using this roughness to keep the same z0 over the whole space. But of course I had also buildings and do these buildings now also get this roughness on top of them? In that case it is doubling (?) the roughness, or not?
In my possible ignorance I thought that the roughness would only play for the surface height (=0), but perhaps the roughness is also working on all surfaces of the buildings (which are part of the flow area, or not).
So I am doubting my own thinking.

All the best.

P.S. I really appreciate the great feedback I receive from SIMSCALE support (aka you), it is always to the point and helpful. THANKS.