1-Way FSI CFX to Mechanical - Imported loads (pressure/forces) not matching?

MElsawy · August 16, 2018, 15:36

Hi everyone, I am trying a very simple example of flow going through a 90 degree bend pipe. After my CFX sim, which I verify the results with hand calcs for a simple 90 degree bend pipe flow, I import the load (pressure) to a static mechanical analysis and expect to get the same forces I get from CFD?

However, when I look at the imported loads summary I find that they dont match. Is this due to a meshing issue or how does ANSYS Map the pressures from CFD to nodal forces in static mechanical? Does my solid (pipe) mesh has to match exactly the fluid (water inside pipe) mesh at the interface between them? It shows 100% of forces are mapped but they still dont match (not within 5% of each other)

Here is what the imported load summary shows:
https://imgur.com/a/biVualR

My current mesh in ANSYS Mechanical is alot more finer which is recommend by looking at the documentation provided by ANSYS (take a look here at the bottom of the page): https://www.sharcnet.ca/Software/Ans...teraction.html

Your feedback is appreciated.

ghorrocks · August 16, 2018, 20:31

FSI can handle non-matching meshes.

Does the force balance improve when you refine the mesh?

MElsawy · August 16, 2018, 20:43

Quote:

Originally Posted by ghorrocks

FSI can handle non-matching meshes.

Does the force balance improve when you refine the mesh?

I did not try several meshes, but I did notice the results do vary greatly when the mesh is different. I was hoping someone had experience with this issue. Maybe ai can try several runs tomorrow with different meshes (although I am still fairly new to usinf ANSYS workbench) and post here to help anyone with a similar issue.

ghorrocks · August 16, 2018, 20:51

If your results are changing between meshes that is a big sign your mesh is not fine enough. There is no point looking at other issues until you have a mesh fine enough to be accurate.

MElsawy · August 16, 2018, 20:54

Quote:

Originally Posted by ghorrocks

If your results are changing between meshes that is a big sign your mesh is not fine enough. There is no point looking at other issues until you have a mesh fine enough to be accurate.

My CFD results are converged and dont change with changing ghe mesh. I am talking about the import load step, thats what changes and even with a super fine mesh (the screenshot shown) it still doesnt match. You can try a very quick example of a simple pipe with a bend. Would you like me to upload my model?

evcelica · August 21, 2018, 16:52

Just checking, is the position and orientation of the pipe elbow the same in both models?
There seems to be a pretty huge discrepancy here.

MElsawy · August 21, 2018, 16:54

Yeah they are the same exact model. I am importing the geometry from CFD to mechanical using workbench. You are free to do a quick trial using a simple geometry. The results change with different mesh in mechanical but they never seem to match close enough to be reliable?

power.pwoer123 · February 1, 2022, 03:33

Quote:

Originally Posted by MElsawy

Hi everyone, I am trying a very simple example of flow going through a 90 degree bend pipe. After my CFX sim, which I verify the results with hand calcs for a simple 90 degree bend pipe flow, I import the load (pressure) to a static mechanical analysis and expect to get the same forces I get from CFD?

However, when I look at the imported loads summary I find that they dont match. Is this due to a meshing issue or how does ANSYS Map the pressures from CFD to nodal forces in static mechanical? Does my solid (pipe) mesh has to match exactly the fluid (water inside pipe) mesh at the interface between them? It shows 100% of forces are mapped but they still dont match (not within 5% of each other)

Here is what the imported load summary shows:
https://imgur.com/a/biVualR

My current mesh in ANSYS Mechanical is alot more finer which is recommend by looking at the documentation provided by ANSYS (take a look here at the bottom of the page): https://www.sharcnet.ca/Software/Ans...teraction.html

Your feedback is appreciated.

Hi
Did you solve this problem? I am confronting the same issue. in my case, the pressure load which is plotted in Fluent is not the same as the imported pressure which is shown in Ansys Mechanical.

Opaque · February 1, 2022, 08:47

Wrong forum?

power.pwoer123 · February 2, 2022, 01:50

Quote:

Originally Posted by Opaque

Wrong forum?

nope!
it is related to both CFX and Ansys mechanical.

August 16, 2018, 15:36	1-Way FSI CFX to Mechanical - Imported loads (pressure/forces) not matching?	#1
MElsawy New Member Moustafa El-sawy Join Date: Aug 2018 Posts: 4 Rep Power: 7	Hi everyone, I am trying a very simple example of flow going through a 90 degree bend pipe. After my CFX sim, which I verify the results with hand calcs for a simple 90 degree bend pipe flow, I import the load (pressure) to a static mechanical analysis and expect to get the same forces I get from CFD? However, when I look at the imported loads summary I find that they dont match. Is this due to a meshing issue or how does ANSYS Map the pressures from CFD to nodal forces in static mechanical? Does my solid (pipe) mesh has to match exactly the fluid (water inside pipe) mesh at the interface between them? It shows 100% of forces are mapped but they still dont match (not within 5% of each other) Here is what the imported load summary shows: https://imgur.com/a/biVualR My current mesh in ANSYS Mechanical is alot more finer which is recommend by looking at the documentation provided by ANSYS (take a look here at the bottom of the page): https://www.sharcnet.ca/Software/Ans...teraction.html Your feedback is appreciated. mossgoms likes this.

August 16, 2018, 20:31		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,732 Rep Power: 143	FSI can handle non-matching meshes. Does the force balance improve when you refine the mesh? __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

August 16, 2018, 20:51		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,732 Rep Power: 143	If your results are changing between meshes that is a big sign your mesh is not fine enough. There is no point looking at other issues until you have a mesh fine enough to be accurate. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

February 1, 2022, 08:47		#9
Opaque Senior Member Join Date: Jun 2009 Posts: 1,819 Rep Power: 32	Wrong forum? __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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August 21, 2018, 16:52		#6
evcelica Senior Member Erik Join Date: Feb 2011 Location: Earth (Land portion) Posts: 1,171 Rep Power: 23	Just checking, is the position and orientation of the pipe elbow the same in both models? There seems to be a pretty huge discrepancy here.

August 21, 2018, 16:54		#7
MElsawy New Member Moustafa El-sawy Join Date: Aug 2018 Posts: 4 Rep Power: 7	Yeah they are the same exact model. I am importing the geometry from CFD to mechanical using workbench. You are free to do a quick trial using a simple geometry. The results change with different mesh in mechanical but they never seem to match close enough to be reliable?