Fluids

Fluids

How to choose interpolation scheme near interface for VOF?

    • ansysuser
      Subscriber

      Hello,


      In the Fluent manual, section 18.3.4, there is a discussion of different schemes for interpolating near the interface of two phases in the VOF model. For example, the geometric reconstruction, donor-acceptor, etc.  But there is no mention of how to choose one or the other and I do not see anywhere in the dialog boxes where these options are listed.

      How can I choose one of these schemes in Fluent?  


       


      Thanks

    • Karthik R
      Administrator

      Hello,


      You can pick the method from Solution Methods in Fluent. Here is a screenshot.



      Hope this helps.


      Best,


      Karthik

    • ansysuser
      Subscriber

      I see. Thank you.

      That does help, except in my drop down list I only have Compressive and Modified HRIC.  I was hoping to use Geo-Reconstruct because it looks like it will help with the phases mixing too much.  Do I need some other setting enabled before the Geo-Reconstruct is available?  Please let me know.

      The problem I am having is that the phases (liquid water and incompressible air) are mixing way beyond what is physical.  Here is an example of the contour of the water phase fraction 1 second after an air bubble rises to the top of a closed container. The container is 1cm wide with 0.1mm mesh sizing. In reality, no such massive phase gradient would exist like this.  I am wondering if Coupled Level set would be a better way to go.   Any suggestions would be helpful.  




    • Karthik R
      Administrator

      Hello,


      These options depend on your analysis type as well as your pressure-velocity coupling. If I remember correctly, steady VoF with coupled solver will not show you Geo-Reconstruct. However, a transient analysis with SIMPLE coupling should show you the Geo-Reconstruct option.


      Best,


      Karthik


       


       

    • ansysuser
      Subscriber

      Thanks again, Kremella.


       


      I am performing a transient analysis with SIMPLE, as shown in the SS below.


       


    • Karthik R
      Administrator

      Hello,


      Which version of Fluent are you using?


      Best,


      Karthik

    • ansysuser
      Subscriber

      I am using the version that came with Workbench 2019 R3

    • Karthik R
      Administrator

      Could you please change your VoF model to Explicit and check your Solution Methods? Are you seeing all the options now?


    • Keyur Kanade
      Ansys Employee

      The options depend on explicit and implicit formulation. 


      For your reference, 



      Regards,


      Keyur


       


      If this helps, please mark this post as 'Is Solution' to help others.


      Guidelines on the Student Community


      How to access ANSYS help links


       

    • ansysuser
      Subscriber

      Thanks, Kremella. Yes, I was able to change to Geo-Recon by selecting explicit. However, the solution is now not correct.  


      Thanks, kkanade. I am not sure what those plots are supposed to be, but I do see there is a difference!  

      For my problem, the issue is that I am getting way too much phase mixing to be physical.  See the contour plot above.

      At the start of the simulation, I have a water zone and an air zone (with patching) that have a vertical boundary between them. Then the solution starts.  Here is the difference at time step 8.  Note the implicit solution evolves into a very nice motion that looks physically correct, except the extreme amount of phase mixing. The explicit formulation gets these strange ripples.  Any suggestion would be much appreciated. (Note I had to drop the time step size to keep convergent. All other settings are the same except the Geom-Recon for the explicit formulation.)



       

    • Keyur Kanade
      Ansys Employee

      For explicit, geo-reconst is recommended. 


      Can you please show some image with model for boundary conditions used?


      Regards,


      Keyur


       


      If this helps, please mark this post as 'Is Solution' to help others.


      Guidelines on the Student Community


      How to access ANSYS help links


       

    • ansysuser
      Subscriber

      Thank you kkanade.


       


      I just discovered that when I loaded the case and data files into the new Fluent module to try the explicit method, the wall contact angle was reset to the default value of 90 degrees. I am unsure why this happened, as all other settings remained unchanged.  As such, I will run with the correct contact angle and come back to start another post if needed.


       


      Thanks again, I appreciate everyone's efforts.

Viewing 11 reply threads
  • You must be logged in to reply to this topic.