Discussion Question: Forested Areas and Terrain - Drag Based Models

[hgopalan]

I wanted to start a discussion on the inclusion of forested areas and Terrain using simple drag based models. The most common method for inclusion of trees uses the drag force model

F_i = - Cd LAD(z) AF |u_i| u_i

C_d - Drag coefficient, LAD - Leaf area density ; AF - Area fraction covered by trees.

Trees are usually represented by rectangular boxes and it is straight-forward to include them.

The drag model has also been applied to buildings as demonstrated in Fast-Eddy by modifying the force term as follows:

F_i = - alpha_m AF / Delta |u_i| u_i

where alpha_m is a constant and Delta is cell size function.

Ref: https://doi.org/10.1029/2020MS002141

This method can also be in-principle used for terrains by marking cells to apply the forcing. I noticed the possibility of including STL for EB methods in AMREX. How easy will it be to access the classes within the AMR-Wind framework?

[marchdf]

A couple of thoughts:

• we have a "discussion" tab for this repo so maybe it makes more sense to move this discussion there ;)
• Do I understand that you want to use the EB capability to "tag" cells using an STL geometry? And then apply a forcing in those cells? There might be an easier way to do that...

[hgopalan]

Will do it next time :).

Yes. I want to evaluate immersed solid method and apply the forcing to the tagged cells.