[ANSYS Meshing] High skewness problem

rrr311 · February 5, 2015, 16:10

Hi miquiita,

Hexahedral meshes will provide you accurate results, particularly if they are aligned in the flow direction, and the number of elements/cells would be much lower when compared to the tetrahedral mesh. Lesser elements, lesser computational time and memory. Hexa meshes also resolves the boundary layer flow conveniently. Hexas have a better numerical accuracy when compared to tets but a lot of work has been done in the last 10-15 yrs that numerical accuracy comparison might not hold too good in future. Hexa can't be used for all the geometries as it might be too difficult/time consuming. For such complex geometries, prefer tets.

A good CFD solution requires a lot of effort. Just because you have a good mesh doesn't mean that you have an accurate solution. There are studies like mesh convergence and time sensitivity which will help you reach the best solution. Hope this helps!

Best,
Rahul

miquiita · February 5, 2015, 18:59

Hi thanks again.

I got this message "The selective body meshing is not being recorded, so the meshing may not be persistent on an update. If you want to record the order of the body meshing, please use the Mesh Worksheet to track the meshing steps. Please see Selective Meshing documentation for more details."

Does this mean the meshing cant be used that I created?

Also trying to follow the tutorial I did:
1. Created a slice through the fan and the cylinder around it.
2. Slice the face from under the fan cylinder and to the ceiling.
3. Created a method with Hexa mesh in meshing of the two bodys next to eachother on the floor in the room.

I feel like I missing something, but I cant see what. Do not want to change the inflation of the fan. Just the skewness in the picture.

Should I slice it different?

rrr311 · February 5, 2015, 19:07

Can you share your geometry file?

miquiita · February 5, 2015, 19:23

here is the dropbox link

miquiita · February 5, 2015, 19:25

https://www.dropbox.com/s/cstdb63cxnt8nms/Geom.igs?dl=0

Igna · April 15, 2015, 05:59

Hi miquiita,
Hi everybody,

Reducing the size of the element will not always reduce the quality problem!

I realize that on general options-->Sizing--> Used Advanced Size Function On can help a lot for getting a better mesh quality. You can chooose Curvature, Edge or boths. That means that your mesh will considerer curvatures and edges and thus generating a better meshing. I got also quality problems and just adjusting Curvature ON in my case the problems went away

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February 5, 2015, 16:10		#21
rrr311 Member Rahul Join Date: Jun 2013 Location: Pennsylvania, USA Posts: 31 Rep Power: 13	Hi miquiita, Hexahedral meshes will provide you accurate results, particularly if they are aligned in the flow direction, and the number of elements/cells would be much lower when compared to the tetrahedral mesh. Lesser elements, lesser computational time and memory. Hexa meshes also resolves the boundary layer flow conveniently. Hexas have a better numerical accuracy when compared to tets but a lot of work has been done in the last 10-15 yrs that numerical accuracy comparison might not hold too good in future. Hexa can't be used for all the geometries as it might be too difficult/time consuming. For such complex geometries, prefer tets. A good CFD solution requires a lot of effort. Just because you have a good mesh doesn't mean that you have an accurate solution. There are studies like mesh convergence and time sensitivity which will help you reach the best solution. Hope this helps! Best, Rahul

February 5, 2015, 18:59		#22
miquiita Member Michelle Join Date: Aug 2014 Posts: 92 Rep Power: 12	Hi thanks again. I got this message "The selective body meshing is not being recorded, so the meshing may not be persistent on an update. If you want to record the order of the body meshing, please use the Mesh Worksheet to track the meshing steps. Please see Selective Meshing documentation for more details." Does this mean the meshing cant be used that I created? Also trying to follow the tutorial I did: 1. Created a slice through the fan and the cylinder around it. 2. Slice the face from under the fan cylinder and to the ceiling. 3. Created a method with Hexa mesh in meshing of the two bodys next to eachother on the floor in the room. I feel like I missing something, but I cant see what. Do not want to change the inflation of the fan. Just the skewness in the picture. Should I slice it different?

February 5, 2015, 19:07		#23
rrr311 Member Rahul Join Date: Jun 2013 Location: Pennsylvania, USA Posts: 31 Rep Power: 13	Can you share your geometry file?

February 5, 2015, 19:23		#24
miquiita Member Michelle Join Date: Aug 2014 Posts: 92 Rep Power: 12	here is the dropbox link

February 5, 2015, 19:25		#25
miquiita Member Michelle Join Date: Aug 2014 Posts: 92 Rep Power: 12	https://www.dropbox.com/s/cstdb63cxnt8nms/Geom.igs?dl=0

April 15, 2015, 05:59		#26
Igna New Member Ignacio Join Date: Sep 2014 Location: Braunschweig, Germany Posts: 2 Rep Power: 0	Hi miquiita, Hi everybody, Reducing the size of the element will not always reduce the quality problem! I realize that on general options-->Sizing--> Used Advanced Size Function On can help a lot for getting a better mesh quality. You can chooose Curvature, Edge or boths. That means that your mesh will considerer curvatures and edges and thus generating a better meshing. I got also quality problems and just adjusting Curvature ON in my case the problems went away