Fluids

Fluids

Dynamic Mesh First Layer Height Collapsing/Expanding

    • tsprengeler
      Subscriber

      Hi all,

      I am simulating an airfoil with dynamic flaps, to do this I am using a UDF to control the shape and dynamic mesh to re-mesh. I am using diffusion and remeshing at every time step. The problem is, when the flap deflects downward the first layer cells on top start to stretch and the first layer height is greatly reduced and the first layer cells on the bottom begin to collapse as the edge moves downward until eventually there is a negative volume. It seems as though only the boundary is moving and the first layer height is changing but the rest of the mesh is not reacting to the movement.


      If anyone has any input it would be greatly appreciated.


      Thomas

    • Karthik R
      Administrator
      Hello What type of mesh are you working with? Can you share a few screenshots of your failed mesh as well as your dynamic mesh settings?
      Karthik
    • tsprengeler
      Subscriber
      I'm working with a hex mesh of an airfoil, the upper and lower surfaces of the airfoil have a UDF with applied motion that deflects the leading and trailing edges a prescribed amount that varies with time. The movements are relative in size to the time step of the problem. This problem worked perfect in 2D with zero mesh issues and now that I moved to 3D I'm having a bunch of issues. The span is 4 inches and the movement is uniform across the entire span, the sides are symmetry so I set the side symmetry boundaries to deforming with remeshing and smoothing, for smoothing I am using diffusion. No matter what I set the diffusion parameter to the issues appear in the same place. There is deforming elements under the airfoil where the deflection is occurring but it seems to only be near the symmetry BC and not the interior elements, like I mentioned previously this worked perfect in 2D so I'm stumped as to why I cant get this working with a 3D set up.

      Thanks
      Thomas

    • tsprengeler
      Subscriber

    • tsprengeler
      Subscriber

    • tsprengeler
      Subscriber

    • tsprengeler
      Subscriber

    • tsprengeler
      Subscriber

    • tsprengeler
      Subscriber

    • Karthik R
      Administrator
      Hello:
      Remeshing does not work on hex meshes. If you attempting to use remeshing, you need to have a tetrahedral mesh. This is the reason for the negative volumes.
      Karthik

    • tsprengeler
      Subscriber
      I did not know that.
      This mesh is the same exact mesh as my 2D case and that worked perfect with just smoothing. This 3D mesh is a direct copy of the 2D just extruded 4 inches. What could cause the issue with the 3D model? Even if I turn off remeshing I get the same results.

      Thomas
    • tsprengeler
      Subscriber
      This is the same exact mesh but in only 2D using the same UDF, same dynamic mesh settings, and at the same time step. The mesh deformation is very uniform with zero left handed faces.


    • tsprengeler
      Subscriber

    • tsprengeler
      Subscriber

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