Mesh Expansion Factor- Acceptable range

saisanthoshm88 · June 28, 2012, 07:40

Could some one please let me know the acceptable range of mesh expansion factor in CFX.

I found many threads related to this on cfd-online but none of them seem to suggest the acceptable range.

I have a maximum mesh expansion factor of 146 and it is seen with less than 1 % of the elements. It is a hexahedral mesh and i'm using the SST turbulence model

ghorrocks · June 28, 2012, 08:22

You can't find a general rule for this because there isn't one. Some models are super sensitive to eg (eg surface tension) yet some models are quite accurate despite horrible expansion ratioes (eg low Re flows). And if the elements are aligned with the flow it is much more tolerable than if it is at an angle.

I realise that does not help you much. So the best approach is to try a few different mesh qualities and work it out for your specific model.

Danial Q · June 28, 2012, 23:14

I guess in documents it is recommended to be less than 20. But still, depending on model it should be checked accordingly.

June 28, 2012, 07:40	Mesh Expansion Factor- Acceptable range	#1
saisanthoshm88 Senior Member --------- Join Date: Oct 2010 Posts: 303 Rep Power: 17	Could some one please let me know the acceptable range of mesh expansion factor in CFX. I found many threads related to this on cfd-online but none of them seem to suggest the acceptable range. I have a maximum mesh expansion factor of 146 and it is seen with less than 1 % of the elements. It is a hexahedral mesh and i'm using the SST turbulence model ordinary likes this. __________________ Best regards, Santhosh.

June 28, 2012, 23:14	HI Glenn	#3
Danial Q Senior Member Danial Join Date: Nov 2011 Posts: 179 Rep Power: 14	I guess in documents it is recommended to be less than 20. But still, depending on model it should be checked accordingly.

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June 28, 2012, 08:22		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143	You can't find a general rule for this because there isn't one. Some models are super sensitive to eg (eg surface tension) yet some models are quite accurate despite horrible expansion ratioes (eg low Re flows). And if the elements are aligned with the flow it is much more tolerable than if it is at an angle. I realise that does not help you much. So the best approach is to try a few different mesh qualities and work it out for your specific model.