Fluent, Dynamic Mesh, Negative cell volume detected

    • dl11

      I want simulate a 2 Stroke linear free piston. Therefor I have to come over dynamic meshing. I started to build this piston, where one face have to follow a translational sine movement, and other face is pushed and pulled due to the aerodynamic force (and it’s mass of 1 kg). And all I get is something like this:
      •    Update_Dynamic-Mesh failed. Negative cell volume detected.
      •    Zone-surface:invalid thread[2]
      •    There is no active aplication

      I can’t get this simulation to run, without incredible tiny time steps, so I thought there a have to be some issues with my settings. Here is a link with the file:


      I read many chapters of the Fluent Useres Guide and also tried serval settings which I found while googling the problem. This is what I came up with:
      •    Using Tetrahedral instead of hexahedral should reduce negative cell velamina, but didn’t helped in my case.
      •    For the fluent-surface interaction of piston, I should use the 6DOF, or in my case the 1DOF
      •    Since my mesh is deforming quite a bite (later when adding the overflow channel of the Piston-controlled inlet port)  I should use at least smoothing instead of Layering for the dynamic mesh method, or may be even remeshing.
      •    Implicit mesh update is recommended while using 6DOF and with it, I should get rid of the tiny timesteps.
      •    If I get it right, the cylinder surface should me a stationory wall the following Piston-controlled inlet port could be stationary zone.

    • seeta gunti
      Ansys Employee



      Please go through the following tutorial on two stroke engine with dynamic meshing. 



    • dl11

      Hay Setta,

      thanks for this link, i am aready familar with it. But since I am trying to simulate a free pistion, most of theese thechnis like layering does not work on my example.

    • Rob
      Ansys Employee

      Please can you post some images, as staff we can't download files. Geometry and mesh would be a good starting point. 

Viewing 3 reply threads
  • You must be logged in to reply to this topic.