Minimum Aspect Ratio

Jordan_kal · June 28, 2021, 06:32

Hello all,

I am relatively new to fluent . Can someone help me with the below warning

"Warning: Min. aspect ratio less than 1 at 2190 nodes"

What is the significance of this warning and will this effect the calculation. I am simulating flow through a nasal cavity.

Thanks

Martin_Sz · June 30, 2021, 05:53

Aspect ratios concern the length:width ratio of the element - usually if this is greater than 1:3 a warning can be set to appear, but in theory aspect ratios shouldn't affect the solution

Jordan_kal · June 30, 2021, 06:08

Thank you very much

meto1992 · October 25, 2021, 09:29

I also faced this issue and my solution diverged. Did you manage to solve this problem?

LuckyTran · October 25, 2021, 11:28

A cell aspect ratio less than 1 means you have cells where the corners have been squished inwards compared to the faces. This is usually very bad and means the cell is really skewed and will almost always lead to divergence either locally in that cell or in the entire solution.

Locate these cells in your mesh and play with your mesh settings to make it better.

meto1992 · October 26, 2021, 02:03

I changed the method of the prism generation from uniform to last aspect ratio and this error didn't appear at all but my solution still diverges. I use the exact same sizing in Ansys mesher and I get no divergence issues with that tetra mesh. But when I use the Fluent mesher with the same sizing values, I get divergence. I used tetra and poly-hexcore mesh in Fluent mesher and the result is the same even though the max. skewness is about 0.65. Any ideas about what I might be doing wrong? I wanted to use the Fluent mesher to generate Poly-Hexcore grid.

LoGaL · October 26, 2021, 06:24

Check also orthogonal quality on top of the skewness. Sometimes i had good skewness but bad orth quality. What are you simulating?

meto1992 · October 26, 2021, 11:59

My min ortho quality is about 0,09 and I don't fail the mesh quality check in Fluent as well. I'm simulating a multi-element F1 car wing in ground effect.

June 28, 2021, 06:32	Minimum Aspect Ratio	#1
Jordan_kal New Member Jordan Join Date: Jun 2021 Posts: 12 Rep Power: 4	Hello all, I am relatively new to fluent . Can someone help me with the below warning "Warning: Min. aspect ratio less than 1 at 2190 nodes" What is the significance of this warning and will this effect the calculation. I am simulating flow through a nasal cavity. Thanks

June 30, 2021, 05:53		#2
Martin_Sz Senior Member Marcin Join Date: May 2014 Location: Poland, Swiebodzin Posts: 232 Rep Power: 12	Aspect ratios concern the length:width ratio of the element - usually if this is greater than 1:3 a warning can be set to appear, but in theory aspect ratios shouldn't affect the solution Jordan_kal likes this. __________________ Quick Tips and Tricks, Tutorials FLuent/ CFX (CFD) https://howtooansys.blogspot.com/

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June 30, 2021, 06:08		#3
Jordan_kal New Member Jordan Join Date: Jun 2021 Posts: 12 Rep Power: 4	Thank you very much

October 25, 2021, 09:29		#4
meto1992 New Member Metin Join Date: Oct 2021 Posts: 5 Rep Power: 4	I also faced this issue and my solution diverged. Did you manage to solve this problem?

October 25, 2021, 11:28		#5
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,672 Rep Power: 65	A cell aspect ratio less than 1 means you have cells where the corners have been squished inwards compared to the faces. This is usually very bad and means the cell is really skewed and will almost always lead to divergence either locally in that cell or in the entire solution. Locate these cells in your mesh and play with your mesh settings to make it better.

October 26, 2021, 02:03		#6
meto1992 New Member Metin Join Date: Oct 2021 Posts: 5 Rep Power: 4	I changed the method of the prism generation from uniform to last aspect ratio and this error didn't appear at all but my solution still diverges. I use the exact same sizing in Ansys mesher and I get no divergence issues with that tetra mesh. But when I use the Fluent mesher with the same sizing values, I get divergence. I used tetra and poly-hexcore mesh in Fluent mesher and the result is the same even though the max. skewness is about 0.65. Any ideas about what I might be doing wrong? I wanted to use the Fluent mesher to generate Poly-Hexcore grid.

October 26, 2021, 06:24		#7
LoGaL Senior Member Lorenzo Galieti Join Date: Mar 2018 Posts: 373 Rep Power: 12	Check also orthogonal quality on top of the skewness. Sometimes i had good skewness but bad orth quality. What are you simulating?

October 26, 2021, 11:59		#8
meto1992 New Member Metin Join Date: Oct 2021 Posts: 5 Rep Power: 4	My min ortho quality is about 0,09 and I don't fail the mesh quality check in Fluent as well. I'm simulating a multi-element F1 car wing in ground effect.