Fluids

Fluids

Threads and subthreads at an interface

    • LukeM
      Subscriber

      I have found very little information about subthreads in the user manual, so I am looking for clarity on the topic. From my understanding, threads are computer-defined groupings of cells; subthreads split each thread into regions where each phase resides. Is that correct? 


       


      The complication arises at the interface between two phases. Assuming VOF is the multiphase model in the simulation, a cell at the interface could have a "Phase1" volume fraction of 0.5. Does the cell belong to the subthreads of both phases? Does it belong to neither? 


       


      Additionally, in a UDF DEFINE macro based on a single cell (like DEFINE_SOURCE), is the thread argument passed to the UDF the thread or the subthread? If it is a subthread, as some of my experimenting seems to suggest, how can I know which phase it represents? 


       


      Lastly, if I want to call a cell flow variable macro such as C_R(c,t) for a cell potentially at the interface, which thread should I pass to the macro? The parent/super thread? One of the subthreads? 


       


      Thanks in advance.

    • DrAmine
      Ansys Employee

      1/The threads are duplicated in multiphase flows: you will have mixture, phase and interaction threads. The latter almost never used. All these information are in the manual. For your cell at the interface, you can access based on the thread different information based on the model used. Saying every cell will belong to all threads: the bulk and the phase ones.


      2/It depends on where it is hooked


      3/It depends on what you want to get: If t correspond to the primary phase thread then C_R is the density of that phase. Again everything is steered by the thread you are working on /looping through.


       


       

    • LukeM
      Subscriber

      1)   If I'm understanding you correctly, the subthreads have less to do with dividing the cells in the thread and more to do with the phases. Is that correct? Also, if you could provide the article(s) in the manual that discusses the mixture, phase and interaction threads you alluded to, I would greatly appreciate it. I have scoured the manual trying to find information on the topic, but I could not find a thorough description. 


       


      2)   It seems like you're suggesting that, if the UDF is hooked at the phase-level, the thread argument will be the subthread (phase-level thread). But if the UDF is hooked to the bulk region, then the UDF argument will be the "super thread". Is that correct? 


       


      3)   To continue in the example of C_R before, if I pass in the bulk, "super" thread, it will provide the overall, bulk density for that cell. But if I pass in the subthread, C_R will provide the local density of that phase. Again, is that correct? 


       


      Thanks for the help. 

    • DrAmine
      Ansys Employee
      There are some exceptions as some variables are only accessible on phase thread and only model dependent. The post processing in Fluent will give you an idea which variables are available for bulk and for phase level.

      In the help look after multiphase specific data types.
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