Preprocessing

Preprocessing

Topics relate to geometry, meshing, and CAD

How to Generate hex mesh with high quality and lower acceptable number of elements in ANSYS Meshing?

    • Mohamed Abdulazim
      Subscriber

      Hello Everybody,


      I am trying to generate a structured mesh with improved orthogonality for a rectangular channel with tilted perforated baffles as a heat transfer case. I use ANSYS meshing for that case, but the resulted mesh elements are very high in number, about 6000000 or higher, and the resulted mesh elements are tetrahedrons, also when I export it to the fluent, the program recorded error message mentioning that the memory run out and the mission aborted automatically. Moreover, when I tried to modify the shape by slicing option in the design modeler in the hope of making hex mesh, the resulted mesh has a very low orthogonality quality about lower than 0.003 and the aspect ratio is too high about 1200. I am really depressed about this situation. Any help will be appreciated. Thanks in advance.  


       


       


      Meshing after slicing around baffles,but the orthogonality is too low  

    • peteroznewman
      Subscriber

      I suggest you delete all the holes in all the baffles. That will make it possible to have an all Hex mesh.



      I understand removing the holes changes the flow slightly compared with having holes, but at least you will get a result that is a good approximation to the original baffles. When you have a better computer, you can put the holes back in.  Another way to approximate the holes is to make the solid body without holes slightly porous to account for the flow that goes through the baffle.


      Another observation is there are at least five sets of double baffles. You could slice out one segment with an upper and lower baffle to make the geometry edits to make a good hex mesh. When that is working, you can make four more copies in a pattern or use Periodic Symmetry to rebuild the full length model.

    • Rob
      Ansys Employee

      The other observation is that we can include baffles in Fluent as thin walls: no need to model them as a solid body. That may effect the flow around the baffle tips, but will have the benefit of significantly reducing the cell count. 

    • Mohamed Abdulazim
      Subscriber
      Thank you very much, Peter,for your kind reply. You suggested making a slice for one set of upper and lower Baffles, how could I do that in order to reach a fully developed flow condition for reaching a constant local heat transfer coefficient, as you know. In other words, what is the exact position for slicing? When I make periodic symmetry, Do you think that the variations from the beginning of the channel to the end of it would be sensible for the solver and can be seen in the contours or the pattern will be similar for each set of the Baffles and variation couldn't be seen .
    • Mohamed Abdulazim
      Subscriber
      Thank you very much for your kind help,rwoolhou . I'm going to try this method, it's a good idea.
    • peteroznewman
      Subscriber

      If you are interested in a fully developed flow condition, Periodic Symmetry delivers that solution. A pair of baffles occurs at a repeating pitch length, that is the important parameter. It doesn't matter where you slice out the periodic section. If you slice it at 25% between the upper and lower baffles on the input side, you will have 75% on the output side. Keep it simple and just slice halfway between the baffles. In any case, the Periodic BC will make the inlet flow conditions identical with the outlet flow conditions.  I'm not sure how that works with a Thermal model. Maybe rwoolhou can comment.


       If you are interested in seeing how the flow develops, then you can't use Periodic Symmetry.

    • Rob
      Ansys Employee

      Thanks Peter. There are a few limitations for thermal periodic flow (relating to solids, and what temperature/heat flux boundaries you can use) but they're simple enough to set up. The issues are all covered in the section of the Heat Transfer chapter of the User's Guide outlining the periodic boundary. 


      Slitting mid way is a good idea: don't split over the baffle as that may break the rules and always makes it more complicated than it needs to be. 

Viewing 6 reply threads
  • You must be logged in to reply to this topic.