[Bohr1ng]

Hello all,

I am currently working on calculating the aerodynamic damping of the three "vanes" shown in the attached figure of the flow analysis window (CFX 17.0). I am following the procedure outlined in this paper (Note that my geometry is non-rotating and the flow is incompressible):https://www.researchgate.net/publica..._Blade_Damping

In addition, I am referencing the aerodynamic damping calculation of an initially stationary beam here:
https://www.singularityeng.com/singu...icting-damping

Just like in both references, I first calculated the mode shapes of the vanes using ANSYS Mechanical, and then prescribed the normalized displacements to the unsteady CFX simulation. The mesh motion for the vanes is then generated based on the displacements calculated from the modal analysis. All other boundaries are set to a stationary mesh motion, and the unsteady simulation is initialized by a previous steady state run. The mesh is an unstructured, tetrahedral mesh with about 22 million elements. My problem arises about 6 or 7 timesteps into the unsteady run when the solver generously lets me know my mesh has collapsed:
"A negative ELEMENT volume has been detected. This is a fatal error and execution will be terminated. The location of the first negative volume is reported below."

The location of the collapse occurs on the vane "fillets", where the geometry becomes quite complex next to the domain wall (shown by the yellow star in the second attachment). My solution to this was to split the vanes and fillets apart, and only model the mesh motion for the vanes. Upon doing this, my mesh still collapses but this time at the truncated trailing edge shown in the third attachment. I then decreased the maximum vane oscillation amplitude to about 2% of the chord length - still collapsing.

I am looking for some guidance or any information to prevent this error from occurring, as I do not have much experience with mesh deformation. I have also attached the .out file of the most recent run. My guess is it has to do with the mesh, but since time is limited, I wanted to get some other insight before I dive into that. This is my first post, so please let me know if I need to provide any more information. Thanks in advance for your help.

flow_domain.jpg

vane1.jpg

vane2.jpg

Unsteady_CFD1_002.txt