SnappyHexMesh collapse at the boundaries giving negative volume cells
 

Hi everyone,

I've been struggling for quite a long time to do a mesh with snappyHexMesh. Finally when the mesh quality was quite good for the castellated and the snap part, I had to add the layers. I can't manage to get the proper layers that I would need to run the CFD simulation, as the mesh is collapsed at the boundaries and I get negative volume cells.

In the end, only 7 cells are illegal if I set up the FeatureAngle from the layer addition to 180, but as you can see in the images, the layers get collapsed at the boundaries...

I've tried to changed the type of patch and add layers, but it didn't worked out. I also tried to add another *.stl for the boundaries but it didn't work out either.

Does anybody know how I can fix this? I have attached the snappyHexMesh file and some figures of the problem.

Thank you!!!

Clara

Greetings,

Dear Clara,;)

this is the issue which I were struggling with for about a couple of month & finally shoot the target.
if it is possible, attach your case dictionaries like blockMesh &... with the steps you are following.
maybe me or someone else can work on it in our own way.

anyhow, you should first be sure of the "addLayer" parameters which are in a correct manner for your case or not. you should try & error all conditions for your parameters.

GoodLuck
metti.

Dear Metti,

I've managed to finally add the layers, but however, I've learnt that it is really tricky and it really depends on the geometry and the other two parts of the mesh generation (castellated and snap). The key parameters that I had to play with were the expansionRatio and the finalLayerThickness, so in the end I manage to generate a maximum number of 4 layers, which for my case, I believe it is enough!

I've added the final snappyHexMesh file and the blockMesh. I hope this can help someone else in the future...

Cheers!

Clara