CFD Online Discussion Forums - [snappyHexMesh] Speeding up snappyHexMesh when using many regions

Hi All,

I am currently working with snappyHexMesh to create a flow geometry through a packed pebble bed with several thousands of spherical pebbles (I need to resolve the flow through the bed to account for heat transfer, etc...).

I have two options for working with snappyHexMesh. One option is to use surface mesh STL files for the pebbles, but these end up being 5-10 GB and present some memory limitations for my specific problem (running in parallel actually loads the full surface mesh on every processor, overflowing memory). It also adds another step of complexity, because if I rearrange my packed bed of pebbles, I have to regenerate surface mesh files, format them for snappyHexMesh, etc...

The other option is to simply make a list of regions using searchableSpheres with the known list of pebble centers. This results in a really simplified workflow for me, and I avoid any possible quality issues with the surface meshes that I've run into with the other option. However, it seems like adding several thousands of searchableSphere regions causes a significant slowdown in snappyHexMesh's performance. I'm actually very surprised by how significant this slowdown is. Even just generating the patches for a few thousand searchableSphere regions takes 100s to 1000s of seconds, and then each step of snappy is also significantly slower than when using the surface mesh option.

I would really prefer to use the searchableSpheres option because of the simplified workflow and avoiding surface mesh quality issues, but the slowdown is very severe. Ultimately I would actually like all of the pebbles to be in a single cellZone. Is there any way to speed up this process? Is it possible to put multiple searchableSpheres into a single region? Is there any possible way to speed up this process?

Currently my geometry and refinementSurfaces entries look like this:

Code:

 sphere0 {

    type searchableSphere;

    centre (0.2446325 0.163559 6.296035);

    radius 0.025;

}

 

 sphere0 {

    level (0 0);

    faceZone sphere0;

    cellZone sphereZone;

    cellZoneInside inside;

    faceType baffle;

}