CFX Solver exited with warning

musa19 · September 27, 2020, 14:46

Hi I am using CFX solver for an oscillating airfoil. I am hereby attaching the cfx.out file content in txt file.

It says negative volume and skewness warning, but I checked my mesh, there is no negative volume or badly skewed elements. I am attaching pictures. Kindly help me. Thanks in advance.

Steffen595 · September 27, 2020, 16:52

is it 2Dor 3D? Maybe at the tip, if its a sharp edge, then it made a twisting surface? Maybe make a small fillet there?

musa19 · September 27, 2020, 17:08

Hi Steffen, thank you for your reply. It is a blunt TE. The mesh is good at the TE. Any other reason. I am not able to figure out. I even improved the mesh further. But same issue.

Steffen595 · September 28, 2020, 04:10

maybe there is a surface or its a multi-body part?

Opaque · September 28, 2020, 08:06

It seems you are repositioning the coordinates, not displacing them.

For this type of problem (where there is periodic boundary motion), I usually follow:

Use mesh deformation with the automatic blended mesh stiffness option and Displacement Relative to Initial Mesh

For the moving boundary, I use an expression for the displacement in Cartesian Coordinates. I rarely use the Location option.

Perhaps there is an error in the motion of the boundary.

musa19 · September 28, 2020, 14:08

Hi Opaque,
Thank you for your time and reply. I will follow up your suggestions. I see there are two types of displacements, specified and periodic..which one should I select.
Will the expressions change for x, y and z coordinates as I have put in case of specified location? For now, I am using Initial X *cos(ai)-Initial Y * sin(ai), Initial X *sin(ai)+Initial Y * cos(ai) and Initial Z, where ai is mentioned expression.

Can you please clear my concept. I am using this first time. Thank you.

September 28, 2020, 08:06		#5
Opaque Senior Member Join Date: Jun 2009 Posts: 1,862 Rep Power: 33	It seems you are repositioning the coordinates, not displacing them. For this type of problem (where there is periodic boundary motion), I usually follow: Use mesh deformation with the automatic blended mesh stiffness option and Displacement Relative to Initial Mesh For the moving boundary, I use an expression for the displacement in Cartesian Coordinates. I rarely use the Location option. Perhaps there is an error in the motion of the boundary. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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September 27, 2020, 16:52		#2
Steffen595 Senior Member Join Date: May 2012 Location: Melbourne Posts: 161 Rep Power: 14	is it 2Dor 3D? Maybe at the tip, if its a sharp edge, then it made a twisting surface? Maybe make a small fillet there?

September 28, 2020, 04:10		#4
Steffen595 Senior Member Join Date: May 2012 Location: Melbourne Posts: 161 Rep Power: 14	maybe there is a surface or its a multi-body part?

September 28, 2020, 14:08		#6
musa19 Member PENANG Join Date: Aug 2017 Location: Malaysia Posts: 40 Rep Power: 9	Hi Opaque, Thank you for your time and reply. I will follow up your suggestions. I see there are two types of displacements, specified and periodic..which one should I select. Will the expressions change for x, y and z coordinates as I have put in case of specified location? For now, I am using Initial X cos(ai)-Initial Y sin(ai), Initial X sin(ai)+Initial Y cos(ai) and Initial Z, where ai is mentioned expression. Can you please clear my concept. I am using this first time. Thank you.