How necessary is the addLayers step on SHM?
 

Hello everyone!

I am writing you in order to ask you about snappyHexMex, and more especifically about its third step, addLayers.

I have been modelling the air current that flows around a tall building whose size is (30x45x184). I have used a uniform flow and the ABL flow from the turbineSiting tutorial.
My initial 10x10x10-cells-mesh extents from 290 meters before the building until 1020 after it, then 380meters from every side of the building and 370 meters in the z axis from the ground. I also have used SHM, but only around the building itself.
However, i would like now to refine a small surface over the ground before the building or even the whole ground, depending on the number of cells that are involved, in order to analyse how the initial flow evolves.

Now, my point is, since i will probably have a larger number of cells because of this new mesh over the ground, I wonder about quiting the addLayers step. Consequently, I would have a small reduction in my RAM exigence that could be very helpful and useful.

However, I also think on how bad could it be to the accuracy of the analysis. My current SHM have just one refinement surface for all the building which goes through levels (3 6) and it uses 3 nCellsBetweenLevels. Additionally, the .emesh uses level 3 too and the final added layers are 5.

Finally, my question is how useful is this final step in such a big mesh. For instance, having 5 layers of just a few centimeters over a building of 184 meters high.

Anyway, I will post my snappyHexMeshDict and if you need any other post, just ask me for it and i will rapidly post it.

Im sorry if my vocabulary is not accurate or especific, I am just a beginner and I am trying to get it better.

Regards

Pelayo