How to get a snapped mesh with SnappyHexMesh?
I am new in OpenFoam and study it now. I just start it from a simple model.
Though it is small model, I still met some problems. Hopefully I can get your support.
The model consists of three parts : Extr1, Poro, Extr2. Each of them consists of inlet, outlet, and wall. I am now doing the multiregions meshing for these three parts together with snappyhexmesh. But I cannot get a perfectly snapped mesh. The edges and somewhere in the faces look not very smooth. I have struggled with this for a week. :(
Could someone help me a little bit? I attached the case folder and the pictures which indicate the results I have obtained. I have written the commands I ran the case in command.txt. I am now using OpenFOAM 2.2.0
I have tried to add the featureEdges for all of them and increase the surface refine mesh level, it is better now, but the surface is still not so flat. Could anybody tell me why?
Really thank you for your kind support!;)
Try to align your blockMesh with your geometry (start with its real bounding box). This should give you much better results.
Greetings to all!
@Jackie: Sorry, I don't enough time to go through testing this. Please check the tutorials at the following link for more ideas: http://openfoamwiki.net/index.php/Sn...als_and_Guides
Conforming a hexmesh to a general geometry implies a few things.
If you want to have a 'perfect' mesh with only orthogonal cells you can not expect it to fit the surface of
And vice versa,
if you want the mesh to fit your geometry perfectly you can not
expect it to consist of only perfectly shaped hex cells.
So it is up to the user to decide what you want the most, good conformity or good quality, usually you can not have both.
Therefore it is a good thing if you can align the mesh with the geometry, since this will allow the mesh to conform to the geometry with less modifications, and not do what you have done here...
You can play with these parameters and see how they affect the mesh.
Start by setting everything to 90, which should make the mesh fit as good as possible given the resolution.
If this looks good you can start reducing the numbers and see what happens.
Below I've made a few such tests just to illustrate how the mesh is unable to conform to the surface when you
start reducing the maxNonOrtho value.
Watch how the surface starts to look 'wavy' as the maxNonOrtho is lowered.
here's a new version of snappyHexMeshDict
just some more pics
Mesh Quality in Nikla's Experimnent
It would be very very nice if you can also the mesh quality for the above experimental cases. like the results form checkMesh. I am also now experimenting with these parameters. As far as I can understand in the above experiments of yours the mesh quality should be relatively bad for the case with all 90(good surface fit). But my question is if we have a lot of non-orthogonal and skewed faces then the simulation may not converge .. am I correct ... ??
That exactly is my problem now. I am trying to get a good mesh of a blower. But I cannot get the number of skewed faces low. I am getting about 300 skewed faces (total number of faces ~18Millon ) and my solver(MRFSimpleFoam) is not converging. I think these 300 skewed cells are causing it to diverge. Any suggestion on this issue ?? Any one ?? ..
my first question is obvious.
Are you 100% sure that it is the mesh quality that is the cause of the divergence?
I have found that usually the cause lies in the choice of the initial values of k and epsilon.
What is the initial turbulent viscosity (or length scale)?
Mesh Quality in Nikla's Experimnent
Thank you for the reply. I think the turbulence settings are good because, the same parameters gave me ok solution previously. I mean the solution converged. But as I wanted to get good solution I started to look at the mesh and make improvements and experiments with mesh quality parameters. And am caught in this problem I mentioned
..still havent answered my question though
Sorry I was away from the data so could not post it. I am using a k-omega model for turbulence and my turbulence values are :
inital K = 0.0015
initial Omega = 5
Both are uniform on the inlet which is a 140x140(mm) square
I have an inlet flow rate of 0.0011 m3/s
Thank you in advance.
ok, those values are pretty acceptable, so thats not it then.
dont know then.
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