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-   -   Ugly mesh around cylinder (http://www.cfd-online.com/Forums/star-ccm/101595-ugly-mesh-around-cylinder.html)

rks171 May 8, 2012 11:58
Ugly mesh around cylinder
 
I can't seem to get a nice looking mesh around a cylinder I'm modeling. See picture below. The cylinder goes perpendicular to the screen. The flow is in the same direction. This is a cross-sectional shot of the cylinder in the flow field. I don't see why I can't get the prism layer to be nice consistent squares around the cylinder. Why does the trim mesh have so many non-square funky looking cells?

http://s13.postimage.org/u5cpt8vyr/cylinder_mesh.jpg


Here's the mesh portion of the summary report if that helps:

Code:
| +-1 Mesh 1        Verbose Output        false
  | | |          OOC translation        false
  | | |          Per-Region Meshing        false
  | | |          Use Parallel Meshing        false
  | | |          Interpolation Option        Nearest neighbor
  | | |          Interfaces        []
  | | |          Regions        [Body 1]
  | | +-1 Models                 
  | | | +-1 Prism Layer Mesher        Stretching Function        Geometric Progression
  | | | |          Stretching Mode        Stretch Factor
  | | | |          Gap Fill Percentage        49.0
  | | | |          Minimum Thickness Percentage        10.0
  | | | |          Layer Reduction Percentage        10.0
  | | | |          Boundary March Angle        50.0
  | | | |          Concave Angle Limit        0.0
  | | | |          Convex Angle Limit        360.0
  | | | |          Near Core Layer Aspect Ratio        0.0
  | | | |          Generate Standard Cells Only        false
  | | | |          Improve Subsurface Quality        true
  | | | +-2 Surface Remesher        Do curvature refinement        true
  | | | |          Do proximity refinement        true
  | | | |          Do compatibility refinement        false
  | | | |          Retain geometric features        true
  | | | |          Create aligned meshes        true
  | | | |          Minimum face quality        0.05
  | | | |          Enable automatic surface repair        true
  | | | `-3 Trimmer        Coordinate System        Laboratory
  | | |            Do mesh alignment        false
  | | |            Template mesh type        Hexahedra
  | | |            Template mesh growth type        Simple
  | | |            Run Optimizer        true
  | | +-2 Reference Values                 
  | | | +-1 Base Size        Value        0.05 m
  | | | +-2 Automatic Surface Repair        Connected surface count limit        None
  | | | | |          Connected surface size limits        None
  | | | | +-1 Minimum Proximity        Minimum Proximity        0.05
  | | | | `-2 Minimum Quality        Minimum Quality        0.01
  | | | +-3 CAD Projection        Project to CAD        true
  | | | +-4 Maximum Cell Size        Size type        Relative to base
  | | | | `-1 Relative Size        Percentage of Base        10000.0
  | | | |            Absolute Size        5.0 m
  | | | +-5 Number of Prism Layers        Number of Prism Layers        1
  | | | +-6 Prism Layer Stretching        Prism Layer Stretching        1.5
  | | | +-7 Prism Layer Thickness        Size type        Relative to base
  | | | | `-1 Relative Size        Percentage of Base        1.0
  | | | |            Absolute Size        5.0E-4 m
  | | | +-8 Surface Curvature        Enable curvature deviation distance        false
  | | | | `-1 Basic Curvature        # Pts/circle        36.0
  | | | +-9 Surface Growth Rate        Surface Growth Rate        1.3
  | | | +-10 Surface Proximity        # Points in gap        2.0
  | | | |          Search Floor        0.0 m
  | | | +-11 Surface Size        Relative/Absolute        Relative to base
  | | | | |          Size Method        Min and Target
  | | | | +-1 Relative Minimum Size        Percentage of Base        1.0
  | | | | |          Absolute Size        5.0E-4 m
  | | | | `-2 Relative Target Size        Percentage of Base        10.0
  | | | |            Absolute Size        0.0050 m
  | | | `-12 Template Growth Rate        Default Growth Rate        Medium
  | | |            Boundary Growth Rate        Medium
  | | `-3 Volumetric Controls

Paulh May 8, 2012 13:59
My guess is that you're cutting plane is located on a plane of cell faces. Try moving your section location just a bit. Your problem might be just a visualization issue.

rks171 May 8, 2012 14:03
I also thought that, but when I moved the plane, the mesh looks almost the same. I didn't mention that the cross-sectional area doesn't change at all. The cylinder and flow section dimensions are constant moving in the z-direction (in and out of the screen). So I don't see why mesh cell dimensions and cross-sectional area should change in the z-direction. At least, I don't want it to be changing in the z-direction.

ryancoe May 8, 2012 16:11
Meshing a circular cylinder with cubes will inherently result in misshapen cells.

Alternatively, you could use a cylindrical mesh (gridgen and pointwise can do this, but Star-CCM+ cannot). Within Star-CCM+, you could try the polyhedral mesh...

rks171 May 9, 2012 14:35
I was able to improve this mesh simply by reducing the base size of my mesh cells from 0.05 m to 0.03 m. I played with a lot of other features, too, but that seems to be the one that made the funny looking cells go away around the cylinder.

http://s17.postimage.org/52auo6yzf/c...mesh_fixed.jpg


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