Boiling Simulation got DIVERGED when running in the coarse mesh

Dear admin,

Finally, after several trial and error, my simulation is working and giving the result with sufficient value against the experimental value. It seems that the mesh is not the main factor of the boiling model because when I try to use another option with the same mesh, they could give us good results.

Unfortunately, this particular boiling option can't capture the behavior of the boiling inside the domain within low refinement mesh or coarse mesh. Have you any reasonable idea why it could happen for the boiling case?

Thank you,

Best regards,

Luthfi

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Comments

  • RobRob UKForum Coordinator
    edited October 2019

    Have you checked whether the issue is with the formation of the bubbles or their transport into the flow?  

  • DrAmineDrAmine GermanyForum Coordinator
    edited October 2019
    Coarse resolution near the wall higher resolution in the bulk: these are passpartout. I made boiling runs with yplus around 20 or lower and that was okay for the particular case.
  • farizanluthfifarizanluthfi Member
    edited October 2019

    Dear rwoolhou,

    Thank you for your response. Actually, I'm not sure about that, have you any idea on how to check that in fluent? Highly appreciated for your concern and support.

    Best regards,

    Luthfi

  • farizanluthfifarizanluthfi Member
    edited October 2019

    Dear Amine,

    Yes, I absolutely agree with that. I made boiling runs with higher mesh near the wall too, unfortunately for lower mesh it always got floating point in the middle of a simulation. Do you have any recommendations for this issue?

    Highly appreciated for your support.

    Thank you,

    Best regards,

    Luthfi

  • RobRob UKForum Coordinator
    edited October 2019

    Careful looking, look for non-physical velocity spikes.  Not something we can easily diagnose without the files, which isn't something we can cover via the community: nonANSYS staff are free to do this. 

     

  • farizanluthfifarizanluthfi Member
    edited October 2019

    Dear rwoolhou,

    Can you please demonstrate it how to do it? Highly apologize on this matter due the users are still new one on ansys kinds of stuff.

    Thank you,

    Best regards,

    Luthfi

  • RobRob UKForum Coordinator
    edited October 2019

    No, as I said we're severely limited in how much knowledge we can use/share on here.  Have a look at the results and see if anything looks odd. 

  • DrAmineDrAmine GermanyForum Coordinator
    edited October 2019
    Check the heat flux partitions as well as report max value of vapor phase velocity and temperature.
  • farizanluthfifarizanluthfi Member
    edited October 2019

    The boiling options for this simulation is RPI wall boiling model (Non-equilibrium) with k-epsilon model and Non-Equilibrium Wall Fn. Here is the phase interaction that I specified for this case:

    Drag : Ishii

    Lift : Moraga

    Wall lubrication : Antal et al

    Turb. Dispersion: Lopez de Bertodano

    Turb. Interaction: Troshko-Hassan

    Heat: Ranz-Marshall

    Mass : boiling

    Boiling model :

    Bubble departure diameter : tolubinski-kostanchuk

    Frequency of bubble : cole

    Nucleation Site density : lemmert-chawla

    Area influence coeff : delvalle-kenning

    Use correction model with fixed yplus value 250

    Surface tension : specified

    Interfacial area: ia-symmetric

    For pressure velocity coupling is Coupled with First Order option in all spatial discretization. The way I run the model is by applying the Energy URF at 0.1 and gradually increase until 0.5. Unfortunately, the result is giving that error at floating point like I take a pict in the previous comments.

    Any recommendation is highly appreciated. 

    Thank you,

    Best regards,

    Luthfi

     

  • RobRob UKForum Coordinator
    edited October 2019

    Have a look at the results from about 7500 iterations: what's happening? Also monitor volume fraction of vapour. 

  • DrAmineDrAmine GermanyForum Coordinator
    edited October 2019

    How does the geo look alike?

  • DrAmineDrAmine GermanyForum Coordinator
    edited October 2019

    Switch all forces off, focus only on drag and turb dispersion. The later switch it a bit later and do not use here Lopez et al.

  • DrAmineDrAmine GermanyForum Coordinator
    edited October 2019

    Check if buoyancy is well defined and check the void profile in the volume.

  • farizanluthfifarizanluthfi Member
    edited October 2019

    Dear rwoolhou,

    Please kindly check the parameters that I took there in the previous comments. Have you any idea on that one why it could be happened?

     

    Dear Amine,

    Thank you for your reply. I have shown you my geometry for the boiling case, it's a helical coiled tube with 2 turn. The details of the tube is:

    inner diameter: 0.00498 m , outer diameter: 0.00603 m , coil diameter: 0.13 m , pitch: 0.0403 m , total length: 0.82 m

    For the phase interaction that you mentioned, is it from the beginning of the iterations or how? and for the turb. dispersion, do you have any recommendations that suitable for my case?

    The buoyancy that I used is based on the density of the vapor at saturation temperature and for the void profile, I can't specified it due to the floating point at 7800 iterations. Any guidance is highly appreciated on this matter.

    Thank you,

    Best regards,

    Luthfi

  • RobRob UKForum Coordinator
    edited October 2019

    Look at the flow field: ie plot contours of stuff and see what's going on. 

  • farizanluthfifarizanluthfi Member
    edited October 2019

    For the boiling case, I run with steady-state with pressure based. Also I read some forums that for running the boiling, usually they will use UDF part. Do you have any recommendation on the UDF that I have to set up if necessary?

    Thank you,

    Best regards,

    Luthfi

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