Preprocessing

Preprocessing

Many unnecessary wall and internal boundary conditions added in fluent

    • Tim Weber
      Subscriber

      Hi

      I wanted to investigate a FDM extrusion system. The model I created with DesignModeler, it consists of 9 bodies, 8 solids and 1 fluid streaming/moving through the system.

      Then I went on to creat a mesh. I checked all the contacts that were made and named them (they were all correct), used name selection for all important features. Then moved on to the setup portion and I encounter issues that I don't know how to deal with:

      The cell zone conditions are correct, fluids and solids are correctly assigned

      The boundary conditions are the issue:

      • It creates the interior boundray conditions for all the bodies, but then there are 13 other interior boundary conditions
      • It creates an interface for every contact in meshing, twoa target and source, which kinda makes, since there are two walls touching. Every interface makes a wall boundary conditiond which:
        • Does not have a shadow, cannot be displayed either. In other fluent analyses that I have made, the wall could always be displayed and I had never only interfaces.
        • And then I cannot use system coupling as a thermal condition either. But this is what I want when the walls are in contact and heat just flows through them.
      • The fluid comes in contact with different part (thus also materials) on its way through the system. In meshing, a contact was made between every part and the fluid. But in the set-up, there is a wall made throuout the hole system which cannot be coupled again like above and I have to choose a material from the solid list, but it is a fluid.

       

      So, is the double wall (double interface) normal?, how can I couple them to the sytem, why do I have so many interiors? And why does it make interfaces and not walls to begin with?

    • Rob
      Ansys Employee

      The walls associated with the interface zones are to account for pairs that don't fully overlap. They aren't visible, and are generally left alone. Interior zones represent the surface between connected cell zone but are also created to contain all of the facets of the cells within a fluid (or solid) zone, again, the latter are left alone. 

      In your model, none of the parts are connected, and unless you're moving these you may want to look at multibody parts to get a conformal mesh. You'll then have no interface pairs. 

      • Tim Weber
        Subscriber

        ''The walls associated with the interface zones are to account for pairs that don't fully overlap''

        • Contact areas never fully overlap, they coincide, do I understand that wrongly?

        I read up on the multibody parts and it sounds exactly like what I need, but what exactly do you mean with not moving? I guess in a dynamic analysis?, and not a fluid moving through a pipe because it is not actually moving when analysed only the nodes have a velocity. Do I understand that correctly?

         

    • Rob
      Ansys Employee

      The surface pair coincide where they overlap. If the two faces are different sizes then there will be an area on one, the other, or both that doesn't coincide. Equally, if there's a gap between the faces they neither coincide nor overlap. The English language is wonderful.... 

      By moving I mean bits of solid sliding/rotating relative to another part. If the geometry is fixed then nothing is moving. The fluid is flowing, but the mesh/geometry isn't. 

    • Tim Weber
      Subscriber

      I see, with coincide, I meant that the end of both surfaces is on the same plane the means no material/volume of one part is inside the other, there faces are just touching. But I understand your explanation.

      Just to follow up on the multibody solution. When I combine all the parts into one body and then proceed to the fluent setup, it creates interior boundary conditions of the connection/touching of two bodies. If those bodies got assigned two different materials, I get a warning that same bodies have different materials.

      But if I make them walls, I have to decide on a material of that wall, and since there are two different materials touching, there is no unique solution. Or does it just not matter what kind of material that is chosen at that wall?

    • Rob
      Ansys Employee

      If the wall is zero thickness between the solid blocks then the material doesn't matter: the material of the solid does. Equally, the warning is there so you check whatever Fluent is telling you to look at, if it's not important you can ignore it. 

Viewing 4 reply threads
  • You must be logged in to reply to this topic.