Mesh independent study

kmgraju · June 4, 2015, 00:52

Dear all
I have a question on the following statement

"A mesh independent study was performed by varying number of elements and I compare the velocity values at different points and the computed velocity values differed by less than 0.3%."

But I heard from one of my friend's that this is not the scale to check the accuracy of the result (or) independency of the mesh elements.

I ask the cfd expert here what is the answer for this?

Thomas MADELEINE · June 4, 2015, 04:44

depending on the case you study.
For me a mesh independence study should focus more on thing that are hard to catch with a coarse mesh (boundary layer, thermal transfer, etc) and so in macro value that are affected by this (Total Pressure drop, maximal massFlow in a nozzle, drag or lift force on blade).

If you only want the velocity in the middle of nowhere, a quite coarse mesh is perfectly able to suit you.

that's only my point of view, maybe other people here have different one

ghorrocks · June 4, 2015, 05:11

Thomas is correct. If you only need to know the velocity in the middle of the flow you can get that with a coarse mesh, so there is no need to go fine. But if you want accurate heat transfer on a surface you will need to be very careful with your mesh.

That is why mesh sensitivity is not only dependent on what type of flow you are modelling but also what sort of result you are trying to get and how accurate you want them.

June 4, 2015, 00:52	Mesh independent study	#1
kmgraju Senior Member Govindaraju Join Date: Apr 2010 Posts: 209 Rep Power: 17	Dear all I have a question on the following statement "A mesh independent study was performed by varying number of elements and I compare the velocity values at different points and the computed velocity values differed by less than 0.3%." But I heard from one of my friend's that this is not the scale to check the accuracy of the result (or) independency of the mesh elements. I ask the cfd expert here what is the answer for this?

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June 4, 2015, 04:44		#2
Thomas MADELEINE Senior Member Thomas MADELEINE Join Date: Oct 2014 Posts: 126 Rep Power: 12	depending on the case you study. For me a mesh independence study should focus more on thing that are hard to catch with a coarse mesh (boundary layer, thermal transfer, etc) and so in macro value that are affected by this (Total Pressure drop, maximal massFlow in a nozzle, drag or lift force on blade). If you only want the velocity in the middle of nowhere, a quite coarse mesh is perfectly able to suit you. that's only my point of view, maybe other people here have different one

June 4, 2015, 05:11		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	Thomas is correct. If you only need to know the velocity in the middle of the flow you can get that with a coarse mesh, so there is no need to go fine. But if you want accurate heat transfer on a surface you will need to be very careful with your mesh. That is why mesh sensitivity is not only dependent on what type of flow you are modelling but also what sort of result you are trying to get and how accurate you want them.