[Donald_Wu]

Hi,

I am doing a CFD wind tunnel test for a front wing geometry on Ansys fluent meshing for my final year project.

I have been trying to get the minimum orthogonality to be 0.1 or above but can't seem to be able to increase it much above 0.01. This problem occurred when inflation layer was added.

Inflation Layer conditions:

• Uniform
• Growth rate: 1.1
• Number of layers: 20
• First Height: 0.000016

Other conditions:

• Body of influence: Mesh size 0.1m
• face meshing on the front wing geometry: Mesh size 0.005m
• Poly-hexcore used

Any help will be much appreciated.

Thank you

[siw]

Most likely that the aspect ratio of the elements is too high. Presumably, you've calculated that first layer height based on a required y-plus value.

As a test, change to Smooth Transition for 5 layers (defaults). Is that OK? If you now increase the number of layers (without changing anything else) how does the element quality drop?

Watch these: https://courses.ansys.com/index.php/...undary-layers/

[Donald_Wu]

Originally Posted by siw

Most likely that the aspect ratio of the elements is too high. Presumably, you've calculated that first layer height based on a required y-plus value.

As a test, change to Smooth Transition for 5 layers (defaults). Is that OK? If you now increase the number of layers (without changing anything else) how does the element quality drop?

Watch these: https://courses.ansys.com/index.php/...undary-layers/

Yes, the first layer height is based on a required y-plus value.

Number of layers, Min Orthogonality
5, 0.1615
7, 0.1064
10, 0.0963
13, 0.0638
15, 0.0278
17, 0.0383
20, 0.0096

Thank you

[siw]

Did you try the Smooth Transition method?

However, my guess would be that with the lowest height first layers (thus highest aspect ratio) then a slight distortion of the high aspect ratio adversely affects the minimum orthogonal quantity. Then then only way to reduce the aspect ratio of the first element is to decrease the surface element size on the regions of concern. Can you put a local face sizing (maybe you need to split the face in SpaceClaim and put in in a Names Selection aka Group in SpaceClaim, and see how that affects the quality metric.

[Donald_Wu]

Originally Posted by siw

Did you try the Smooth Transition method?

However, my guess would be that with the lowest height first layers (thus highest aspect ratio) then a slight distortion of the high aspect ratio adversely affects the minimum orthogonal quantity. Then then only way to reduce the aspect ratio of the first element is to decrease the surface element size on the regions of concern. Can you put a local face sizing (maybe you need to split the face in SpaceClaim and put in in a Names Selection aka Group in SpaceClaim, and see how that affects the quality metric.

Yes, I did try Smooth Transition.

I tried decreasing the surface mesh size at the affected region and the orthogonality increased.

Thanks for helping!