Two Way FSI using LES turbulence and dynamic mesh with Fluent

- July 13, 2019 at 2:58 am
  
  MemoriseXuxu
  Subscriber
  
  Now I want to perform a two way FSI simulation in Fluent ,but here comes the problem that the LES turbulence model requires the second order implicit transient formulation.However, in the dynamic mesh module, the first order is required, which is necessary in the two way FSI simulation.
  
  As a result ,I want to hear whether you are faced with the same problems like that.
  
  As for the solution I come up with the few thoughts:
  
  1.Switch formulation to first order to satisfy the dynamic mesh.By doing so, I don't know whether it will affect the accuracy of LES turbulence.
  
  2.Switch formulation to second order to satisfy the LES. As a result, it will lead to negative cell in the SYSTEM COUPLING and cannot calculate further.
  
  So I want to know whether the thought can work or not.
- September 28, 2020 at 5:57 am
  
  paraprapa
  Subscriber
  
  What did you end up doing in this case? I am observing FSI instability, particularly, CFD solution doesn't converge within coupling iteration (10 and even more). It keeps oscillating at each coupling iteration (not coupling step) and doesn't converge at the end of it. I chose the second option you mentioned- went in TUI and asked dynamic mesh to allow second order formulation. I tried tuning system coupling stabilization coefficient...doesn't help. I think the boundedness in time is messed up when new mesh is created and this is causing the problem but I am not sure about it. This is annoying. Tbh, Fluent dynamic mesh has lot to improve- in other areas too. n
- September 28, 2020 at 6:15 am
  
  paraprapa
  Subscriber
  
  Based on what I read: If I choose first order option for LES, only the low frequencies are unaffected and can be reasonable. Might have to live with this. n

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