[snappyHexMesh] snappyHexMesh cell alignment

Miguel Hernandez · March 3, 2022, 19:12

Hello everyone,
with the goal of simulating a free-flowing channel (using interFoam as solver ) I am trying to set up the mesh, but the results are not satisfactory.

The channel has a maximum slope around 10% and is not straight.
For the mesh setup I followed the following steps:

Created the background mesh (blockMesh), without the boundary definitions, large enough to include all the stl geometries.

Created the stl for the definition of the channel (gray stl), inlet, outlet (pink stl) atmosphere (cyan stl), right and green boundary (boundary for air outlet - green and red stl).

The stl files were also used for the definition of the boundary conditions.

Using snappyHexMesh I created the mesh, defining the mesh itself as the internal volume of stl files.

The mesh created allows the simulation for 20 seconds of the 40 sec I've estimated, then it becomes unstable.
I noticed that the cells, due to the curve, are not aligned with the direction of the flow - as seen in the attached image which correspond in the castellatedMesh phase only (is not the "final" mesh I used in my tests simulations) but I think it makes the point.

Is it possible that the instability is due to this non-alignment?
Is possible to align the cell with the flow? If yes, how?

Thanks in advance...

Schermata 2022-03-03 alle 23.57.33.jpg

Schermata 2022-03-04 alle 00.01.50.jpg

AtoHM · March 4, 2022, 06:50

Have you looked at important quality metrics for the mesh? What does the skewness, non-orthogonality look like? Also cellVolumeRatio might be important for mulitphase flows.

You can create a blockMesh that follows roughly the curvature of the channel, this will align the cells and simultaneously improve performance of snappy when snapping the mesh. I would definitely recommend that here.

March 3, 2022, 19:12	snappyHexMesh cell alignment	#1
Miguel Hernandez Member Miguel Hernandez Join Date: Feb 2021 Location: En mi casa Posts: 56 Rep Power: 5	Hello everyone, with the goal of simulating a free-flowing channel (using interFoam as solver ) I am trying to set up the mesh, but the results are not satisfactory. The channel has a maximum slope around 10% and is not straight. For the mesh setup I followed the following steps: Created the background mesh (blockMesh), without the boundary definitions, large enough to include all the stl geometries. Created the stl for the definition of the channel (gray stl), inlet, outlet (pink stl) atmosphere (cyan stl), right and green boundary (boundary for air outlet - green and red stl). The stl files were also used for the definition of the boundary conditions. Using snappyHexMesh I created the mesh, defining the mesh itself as the internal volume of stl files. The mesh created allows the simulation for 20 seconds of the 40 sec I've estimated, then it becomes unstable. I noticed that the cells, due to the curve, are not aligned with the direction of the flow - as seen in the attached image which correspond in the castellatedMesh phase only (is not the "final" mesh I used in my tests simulations) but I think it makes the point. Is it possible that the instability is due to this non-alignment? Is possible to align the cell with the flow? If yes, how? Thanks in advance... Schermata 2022-03-03 alle 23.57.33.jpg Schermata 2022-03-04 alle 00.01.50.jpg

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
[Other] Contribution a new utility: refine wall layer mesh based on yPlus field	lakeat	OpenFOAM Community Contributions	58	December 23, 2021 03:36
[blockMesh] Odd cell distortion when meshing a sphere in BlockMesh or SnappyHexMesh	37269	OpenFOAM Meshing & Mesh Conversion	3	February 20, 2020 04:35
Neighboring cells in tetrahedral mesh	vishwesh	OpenFOAM Programming & Development	9	November 10, 2017 08:06
[snappyHexMesh] Problem with SnappyHexMesh Cell Removal	MoeCFD	OpenFOAM Meshing & Mesh Conversion	0	July 7, 2017 13:55
[snappyHexMesh] SnappyHexMesh and cell orientation region-wise	heksel8i	OpenFOAM Meshing & Mesh Conversion	2	July 23, 2015 03:15

March 4, 2022, 06:50		#2
AtoHM Senior Member M Join Date: Dec 2017 Posts: 703 Rep Power: 13	Have you looked at important quality metrics for the mesh? What does the skewness, non-orthogonality look like? Also cellVolumeRatio might be important for mulitphase flows. You can create a blockMesh that follows roughly the curvature of the channel, this will align the cells and simultaneously improve performance of snappy when snapping the mesh. I would definitely recommend that here.