[barracuda]

Hello. I am new to OpenFoam. I would like to create simulation of wind affected by trees and a house. I know how to create the house, but if I want to add some trees near it or a small forest adjacent to the house, how to do it. The problem is that if I create a mesh of tree, the wind would behave like the tree is solid obstacle - but in real, there is a lot of spaces. To create a real tree would take too much resources for calculation. Any tips how to solve that problem? Is there some simple solution?

PS: dynamic meshing is not needed
PS2: I Found this https://www.researchgate.net/publica...in_urban_parks
which shows the case which is not ideal because the trees seems to be simple blocks/obstacles.

[RobertHB]

How about implementing the trees as a region of lower porosity?

[barracuda]

I have no experience how to do that. Yesterday I worked with some Sketchup models of trees. I found some trees with simple polygons geometry, which I exported to gmsh. There I have created the mesh.

I could try both. I could try simulation with the trees and then to try the region with smaller poresity and to compare both results.

[RobertHB]

The page explains how to use different fvOptions entries, e.g. the explicitPorositySource. Unfortunately it is partly in japanese, but you can use google translate and the important part is in english.

Source: http://www.geocities.jp/penguinitis2...fvOptions.html

[barracuda]

I have modified and exported these trees, to .geo and mesh files. Anyone interested - free for use.
https://sourceforge.net/projects/aut...h.zip/download

You can check it out if you know how to make it better (clear, simple, less edges), your help is welcome. I tried to make them as simple as possible, but with tree 3, there are some soft/dashed lines, which could be removed but IDK how to do that.

[barracuda]

Could you pleas suggest me which case to use, when I want to simulate the wind in 3D space effecting the trees and house? Till now I was met with the tutorials and cases which use 2D space and pipe or walls where you define the inlet, outlet, etc. However it is not clear to me how can I define the 2D environment which is open ("outdoor"; not closed). So for example when I want the wind to blow from east to west, how should I define the direction. Of sure, I can be interested in 2D solution too, but my final goal is to see the 3D results. Now I am trying to make to work pitzdaily case according "OpenFoam CFD Tutorial | Laminar Flow Through a Pipe 3D | Part 2/4" (Vijaya Kumar), this one is 3D but this is the "enclosed" environment, where the inlet and output is defined.

[RobertHB]

Originally Posted by barracuda

However it is not clear to me how can I define the 2D environment which is open ("outdoor"; not closed).

You could use cyclic boundary conditions at the side patches of your domain. And then define the velocity via a velocity magnitude in the fvOptions dictionary.

So for example when I want the wind to blow from east to west, how should I define the direction.

Assuming your z-axis is your vertical axis, e.g. the one parallel to your trees, then your x-axis may be your E/W direction and your y-axis be your N/S direction.

[barracuda]

Thank you for your answer.

[Rojj]

I wonder if this could help

https://github.com/OpenFOAM/OpenFOAM...35e58e842cb681

"atmosphericModels: Added Lopes da Costa porosity and turbulence models
Specialized variants of the power law porosity and k epsilon turbulence models
developed to simulate atmospheric flow over forested and non-forested complex terrain."

It is a new feature in openfoam 6. I have not tested it myself yet, but planning to do it soon.

https://openfoam.org/release/6/

[barracuda]

Thank you for your reply but I do not do the things which I did at that time, so I am not a developer in this branch anymore.

[shaiashe]

Hi,

@Rojj did you ever get around to trying this package? do you know of any existing tutorials for use of the porosity model?

thanks,