Best meshing settings

Hi everyone, I’m trying to set up an outdoor airflow simulation for my dissertation, I’m trying my best to figure out how OpenFoam and Butterfly work, but the meshing always gets me confused, and I’m not able to figure out the best mesh settings for my simulation, can someone give me some help on this point? Which settings I can use to get a better meshing? when following the standart air flow simulation file my meshes are always a bit coarse for visualization.
Hope you all ar fine, safe and well.
Best regards
CFD TEST (645.8 KB)

@minggangyin can I ask for some guidance of yours for this one? I’m trying my best to understand the workflow, but still can’t find the best way to mesh and optmize my simulation

Here are the files I’m using, the Rhino file is a simplified 3d model of a street in my city in 3 different times, 1940, 1980 and 2020, I’m trying to figure out the best way to mesh the model and have nice results

hi @Dconforte

it will help for you to write down exactly the physical phenomenon you are trying to capture.
Is it the wind around a specific building, is it a public space, is it for the whole urban area? focus on pedestrian ? on facades?
My point is that CFD isn’t meant to capture reality but to approach it with a “controllable” amount of error possible. Once you clarify your intention then you can define how much detail or simplifications you can do to ease the whole process.

There’s a lot to dig about meshing, please find here a pdf which is very useful to understand meshing. The area of interest should be more refined than what is next to it, and so on, gradually.

Your wind tunnel should have enough space windward, sides and leeward to allow for the fluid to develop physically, this depends on the type of geometry your are testing. Make tries and with time you’ll find out.
Best practice is if H is the height of your highest building then you could account for:

  • windward, sides and top 3-5xH
  • leeward 12-15xH

From your wind tunnel, you’ll define a blockmesh cellsize, say 6m. Blockmesh will subdivide the wind tunnel in cells of 6m on the side. If you are working with only building massings, you can aim for 1m cell size at those surfaces. Each level of refinement divides by 2 the cell size.
Level 0: 6m
Level 1: 3m
Level 2: 1.5m
Level 3: 0.75m (near the 1m you are aiming for).

Perhaps start with this and then you can dive into more settings such as:

  • Grading
  • Surface features

Hope it helps somehow,

Good luck

The grading

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Hi @OlivierDambron, first of all, thank you soo much for the explanation, summarizing. I’m trying to assess each outdoor variable in separate, comparing each variable’s behaviour to built density during the years (since I’m evaluating the street’s morphology from 1940 to 2020, how it developed and etc), so, I’m trying to evaluate the whole area.
I’ll keep on digging into Butterfly’s workflow, for now I’m only trying to achieve the best meshing settings in order to visualize windspeed behaviour and results comparing to built density.
And again, thank you so much for your help, best regards!