I want to use bf to simulate the outdoor wind environment of a series case of parametric building models.
Before that, I hope to make people believe that the results of bf are credible, so I found some actual wind tunnel data, the database provides the experimental wind profile and the wind pressure coefficient of each surface, I hope to use the simulated results Compare with wind tunnel results (Cp, wind pressure coefficient)
But I found that the boundary conditions in bf seem to use log law mode, and the boundary conditions of the wind tunnel experiment data I found are all power law modes. Is there any way to modify them in butterfly
Or is there any other way to confirm the credibility of bf, so that I can continue to use it (this series of software is really cool, and at the same time very convenient and efficient)
Butterfly’s credibility is based on OpenFOAM’s credibility. OF is a simulation engine that has been thoroughly validated through the years in many studies. If you wish to understand it’s credibility a literature review on comparisons between OF and other engines would be useful. Additionally, BF will use RANS models by default, which is another field of comparisons that you can look into (RANS vs other models like LES).
As for your custom ABL function as far as I know that will have to be scripted somehow, using the power law equation. There was something called groovyBC which allowed you to do things like that but I haven’t used it and not even sure it exists in OF right now. Perhaps you could look into OF documentation for more information?
From my experience btw, log law is more than sufficient. Perhaps again look into the literature of comparisons between simulation and wind tunnel and see if they considered this.
Thank you very much for your reply, perhaps I can try again to find wind tunnel data using the LOG LAW mode;
If validation data is still ultimately missing, perhaps I could do some summarization and collation of the extensive literature on openfoam simulation about building wind environments, including how they illustrate accuracy (e.g. grids or comparison with other software), and put them into my paper to confirm the authority of openfoam and butterfly
Thanks again for your reply, I think I just specifically want to use butterfly because of its convenience!
An application that allows modification of boundary conditions is mentioned in a literature that uses openfoam simulation and validation.
But I’m not quite sure how I should use it yet, as I’m just starting out with butterfly and don’t know much about openfoam in practice.
Anyway, here’s my latest discovery, and below is the link to this software. I thought maybe you guys could use it to better refine Butterfly or conduct other research? http://openfoamwiki.net/index.php/Contrib_setDiscreteFields
Dear TheodorosGalanos，
Thank you for mentioning groovyBC, I finally found a similar code;
I directly rewrite the U file in the 0 file generated by butterfly to groovyBC type, and write the formula, the program seems to run normally
Assuming this is correct, my question is: do I still need to rewrite other boundary conditions at 0 file,such as k files and epsilon files, etc. The wind tunnel data contains k data, But they don’t seem to be as easy to describe with a coordinate formula as a velocity wind profile.
Maybe these questions seem awkward, I’m still hoping for some help, thanks very much!
Concerning the boundary conditions I’m really not sure. I would guess the abl inlet conditions for k, epsilon might need to be changed but not really sure because I’ve never used power law personally.
Perhaps try with your current set up first and see what the validation results show?
I would love to see your comparisons against the wind tunnel studies.
There will in theory always be difference on the two.
In the wind tunnel your model is typically 3D printed in 1:400 and small few mm probes leaves anything small scale negletable due to tolerances. And you may see Reynolds scaling.
In cfd you can have higher resolution in your outputs although if the turbulence is slightly off, then the shape of the wake around corners or behind towers may change completely.
For Urban comfort you should be okay in most cases with RANS and 12/16 directions if you have a good mesh and the ABL is correct. Don’t use this method for structural loading, safety, facade pressure etc though.
Have in mind that your roughness around your site will play a huge role.
