Flow Volume Extraction and Parametric Mesh (snappyHexMesh)

I saw a great post in the documents about the Fluid Volume Extraction method for creating an enclosure for CFD. Based on a post I read earlier today, using the enclosure method would allow me to keep my Topological Sets and Mesh Assignments when I regenerated the volume. For meshing, I always use the Parametric Mesher (snappyHexMesh) because I have a lot of control of the elements and sizes. When combining these two concepts (Fluid Volume Extraction and Parametric Mesher), I still have the same issue that I lose all Topological Sets and Mesh Assignments. Am I missing something or is this working as designed?

Let me check that and get back to you asap Bryce!



I did a bunch of playing with this today and I have figured out the issue. Parametric Meshing will work with Fluid Volume Extraction for external aerodynamics if you make your bounding box slightly larger than the domain. Doing this will allow you to maintain all of your topological and boundary condition assignments when you recalculate or change your mesh.


Everything is working great in my test project but I have found one small downside; the outermost layer of cells on all sides of the enclosure are slightly warped due to the snapping process. I don’t think it is enough to mess with results as long as you are following good domain sizing suggestions (13L, 10W, 6H). Below is a picture of what I mean.


In the end I think this is going to save me a bunch of time and will definitely help me with streamline the meshing and case setup process.


Excellent deduction of the issue and solution for the problem!!!

Is the difference in size exactly one Level 0 grid size (looks close)? If not it might be worth trying that.

That is just a crazy hunch I have because of other meshing/sim issues that I am investigating…

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I tried a couple of different methods that all have similar results. The key is to make sure that the bounding box does not snap to the surface of your enclosure. If your bounding box is less than half a L0 width away, then it will snap to the surface and mess you up. If you go more than a half width away then you are fine. In the end I just added to my Model Calculations sheet for an updated fluid domain. You can view my spreadsheet here if you are interested: External Aerodynamics Mesh and Model Calculations


Awesome Bryce!

This investigation has been on my to-do list and I am more happy that you solved it right now! :slight_smile:



Love your spreadsheet!

I’ll merge it with my quick and dirty one I have been using.

@jousefm I think that there should be a Wiki that has a spreadsheet like this and explains how to use it, be careful Bryce, jousef might be looking for new power users :wink:

I will probably schedule either a hangout session (still one open with you :wink: ) or a private chat with Bryce…and you have some good senses Dale! Already offered Bryce a PowerUser status 4 days ago :slight_smile:

Cheers guys and keep up your great work - super inspiring to see you interact in such a way :+1:


Not quite sure what you mean…

It was about the y+ documentation and what we can make with the big posts you have created so far. It has to be in a compact form and I could integrate it into a video with some additional theoretical background :slight_smile:

Sorry, still lost, did I miss a hangout?
How is one still open for me?
My Y+ experience lately is still in a flux, really want to figure out those ‘Eddy Viscosity plots’ that seem to be able to verify that you’ve captured the BL correctly in the layers we make…

I’m working on my SEO requirement right now. I had a little trouble finding a fun and engaging problem, but I’ve got it now. It’s going to turn into a whole series by the time I am done. My plan is to step through initial meshing and model setup, advanced model setup, and finally some design optimization. Should be pretty cool. Should have the first one done today or tomorrow though. Get that Power User button warmed up for me @jousefm.


No not at all but we discussed it briefly in the PowerUser’s group - still in planning as you are in a flux as mentioned :slight_smile: Once you seem to be ready we are good to go. Will also TeX this as a guide then! :+1: