Learning Forum

[Pegah Mehrabian]

I use ANSYS for two-way coupling FSI simulation(CFX+ Transient Mechanical). I am interested to study the VIV (Vortex-induced vibration) of a circular cylinder. This is a URANS study. The turbulence model is SST with 1% turbulence intensity (for the Reynolds number range between 3000-10000). The Advection Scheme is high resolution, the transient scheme is second-order backward Euler, and the turbulence Numerics is high resolution. This model isn't able to predict not only the onset of resonance but also the tube response amplitude. If you have any suggestions for me, please help me.

(Ps: I strongly ask you to don't mention the simple tutorial video of the FSI simulation of ANSYS as an answer to my question. Thanks in advance)

[rfblumen]

I would consider using a scale-resolving turbulence model instead of the URANS approach.  Try using the Stress-Blended Eddy Simulation (SBES) model.  You might also include turbulence transition modeling.  Of course, you'll need to have an appropriate mesh proximal to the cylinder with y+~=1 and 10-15 inflation layers in the boundary layer.  Using this approach allows for reasonable prediction of the Strouhal number, so it should be appropriate for your FSI application.

[Pegah Mehrabian]

Thank you for your reply. Could you please tell me your opinion about changing the Advection scheme to Upwind and the transient scheme to first-order backward Euler? I tried these options and the results are more close to the experiment. I was wondering why the more precise scheme gives me the wrong answer.

[rfblumen]

The solution is strongly dependent on the turbulence model used.  I would not use Upwind or 1st Order Backward Euler even though they generate a solution closer to experiment.  You're correct in your assessment that you're getting the right answer for the wrong reasons when using these approximate methods.  Use the SBES turbulence model.

[Pegah Mehrabian]

Could you please give me your idea about "Transitional turbulence" specifically speaking "intermittency model" which is available in ANSYS CFX? instead of switching to Fluent and SBES turbulence model?

[rfblumen]

The SBES turbulence model is available in both Fluent and CFX. Transitional Turbulence model may be turned on in CFX and could be used in addition to the SBES model in CFX.  The Transitional Turbulence models predict transition to turbulence using empirical correlations.  Please refer to "4.1.11. Ansys CFX Laminar-Turbulent Transition Models" in the CFX Modeling Guide for further details.