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holtwong April 4, 2012 06:14

Surface mesh not sticking to surface
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I have been trying to make an unstructured tetra mesh (specifically of a turbine blade) with and without prisms.
I am finding that every time I generate the volume mesh, the surfaces which should be smoothly curved become very "bumpy" with ridges and individual bumps appearing which do not conform to the smooth geometry surface.

I was not aware of this happening until I used the mesh in FLUENT, which results in very spotty results due to the random ridges and bumps.
The most affected area is the external wall of the aerofoil which is a simple curved surface. There is no curvature in the spanwise direction, if you know what I mean.
The geometry has been fixed to a very small tolerance, a factor of 50 smaller than the elements in the problem area.
To make it fit the geometry again, I have to do a "project nodes to nearest surface" on all the surface nodes.
This is not such a big problem with a tetra mesh, but when I put in prisms on the surface, the bumps and ridges reappear, much larger, and this time some of the prisms which should be right on the surface actually end up inside the aerofoil. This means when I project the surface nodes to the surface, it turns some of the prisms inside out!

This seems really strange because I would have thought that when the volume mesh is created, it should stay faithful to the geometry unless otherwise specified, and when I grow prism layers in a tetra mesh, I would have thought it should keep the surface mesh (on the surface from which the prisms are growing) where it is rather than moving it about.
Can anyone help?
Attached are two images before and after prisms of one of the aerofoil surfaces

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