how to start CEL in CFX after the flow converges?

jason580315 · November 6, 2016, 14:19

I was using a UDF in fluent after the flow converges to calculate the scalar shear stresses (3D) in the flow field. Now I need to do the same in CFX. How to do that? If I set the function in CFX-Pre, will that start to calculate the scalar from the beginning?

ghorrocks · November 6, 2016, 18:43

Shear stress is in the results file by default. You will need to look under the "..." button to access it.

jason580315 · November 6, 2016, 19:20

Thanks for your reply, Glenn. I believe the shear stress you mentioned is wall shear stress. But the scalar shear stress (3D) I need is calculated by the formula attached in the figure. It is the scalar shear stress in any point in the flow field. In Fluent, we usually couple the UDF to calculate it after the flow converges. But I'm new to CFX and don't know if there is way to do that in CFX.

ghorrocks · November 6, 2016, 19:34

No, I was not referring to wall shear stresses.

It looks like in a normal simulation you do not have shear stresses, but you do have velocity gradients. It is straight forward to calculate the shear stresses for constant viscosity fluids from that (or your formula, if you like). The variables are named "Velocity w.Gradient Z" and all the other combinations.

I have not tested this but I suspect if you define a variable viscosity fluid then I think it puts the shear stresses in the results file.

jason580315 · November 6, 2016, 21:07

It seems that all the velocity gradients in my equation are available in the results as you mentioned. Let me try if I can define a expression or variable using those gradients to calculate the scalar shear stress. Thanks a lot!

November 6, 2016, 14:19	how to start CEL in CFX after the flow converges?	#1
jason580315 New Member Jason Join Date: Oct 2016 Posts: 11 Rep Power: 10	I was using a UDF in fluent after the flow converges to calculate the scalar shear stresses (3D) in the flow field. Now I need to do the same in CFX. How to do that? If I set the function in CFX-Pre, will that start to calculate the scalar from the beginning?

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November 6, 2016, 18:43		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	Shear stress is in the results file by default. You will need to look under the "..." button to access it.

November 6, 2016, 19:34		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,872 Rep Power: 144	No, I was not referring to wall shear stresses. It looks like in a normal simulation you do not have shear stresses, but you do have velocity gradients. It is straight forward to calculate the shear stresses for constant viscosity fluids from that (or your formula, if you like). The variables are named "Velocity w.Gradient Z" and all the other combinations. I have not tested this but I suspect if you define a variable viscosity fluid then I think it puts the shear stresses in the results file.

November 6, 2016, 21:07		#5
jason580315 New Member Jason Join Date: Oct 2016 Posts: 11 Rep Power: 10	It seems that all the velocity gradients in my equation are available in the results as you mentioned. Let me try if I can define a expression or variable using those gradients to calculate the scalar shear stress. Thanks a lot!