Different roughness heights (ks and Cs) for groudn plane of External Flow Volume

Using SimScale
1

Hello there,

I want to use different roughness heights (ks and Cs) for certain parts of ground plane of the External Flow Volume. Like for instance in the advice of Blocken (Fig. 16 in: Blocken, Bert: Computational Fluid Dynamics for urban physics: Importance, scales, possibilities, limitations and ten tips and tricks towards accurate and reliable simulations. In: Building and Environment 91 (2015), pp. 219-245.
https://pure.tue.nl/ws/files/7993534/687442152079717.pdf ).
Cartesian box does not help. I think, more something like a Cartesian sheets, where I can define the roughness height ks&Cs. Or a Custom walls that covers only part of an object’s face…

Any help is welcome. THANKS.
All the best.

2

Hi @jjansman

Maybe this article is helpful: How to Model Wall Roughness in CFD? | Knowledge Base | SimScale

You can also find an example which seems similar to what you’re going for in this tutorial.

Cheers
Igor

3

This link indeed could provide the solution, if it would describe how the elipses on the ground surfaces were made: “Therefore, we modeled the air domain in CAD software and split the ground surface.”
So how is this split done? I am not able to find a function in SketchUp (as that will become ‘sheets’ in SIMSCALE, which are not recognised). I also see no option in SIMSCALE ‘Edit CAD’. Or do I overlook that option?
Hope you can direct me in some way. Sorry and thanks for your patience
All the best

4

Hi @jjansman,

I’d strongly recommend that you go with a software other than SkecthUp for CAD, especially running our OpenFOAM based analysis types. OnShape is a great option we use internally - in it you can split a face by drawing a sketch and using the “Split face” tool.

6

Thanks, I will familiarise with OnShape.