Tuesday 31 December 2013
Mesh quality
• For
the same cell count, hexahedral meshes will give more
Accurate solutions,
especially if the grid lines are aligned with the
Flow.
• The
mesh density should be high enough to capture all relevant
Flow features.
• The
mesh adjacent to the wall should be fine enough to resolve
The boundary layer
flow. In boundary layers, quad, hex, and
Prism/wedge cells are
preferred over tri’s, tets, or pyramids.
• Three
measures of quality:
– Skewness.
– Smoothness
(change in size).
– Aspect
ratio.
Skewness
Two methods to define skewness are:
·
Based on equilateral volume :
o
Skewness = (optimal cell size – actual
cell size) / (optimal cell size)
o
Applied to only tri and tet meshing.
o
This method on meshing follows Delaunay
triangulation theorem.
o
Default method used in ansys for tri and
tet meshing.
·
Based on the deviation from a normalized
equilateral angle
o
Skewness = Max [ {(θmax -90)/
90}, {(90 – θmin )/90}]
o
Applies to all cell and face shapes,
used generally for quads.
o
Used for prisms, pyramids, etc.
Smoothness
and aspect ratio
- Change is mesh size should be gradual or smooth
- Aspect ratio is the ratio of longest edge length to the shortest edge length. It is equal to 1 for an equilateral triangle or square.
Checking For Quality
·
