Fluids

Fluids

extremly high turbulence intensity

    • AgriCFD
      Subscriber

      Hi,


      currently I do a transient calculation (k-epsilon) on a fast rotating (3000rpm) mower unit. I only simulate one rotor.


       


      The Problem:


      Simulation is running for a few time steps (approx. 5-30, depending on the initial flow field). The residuals are high but very evenly. Then Epsilon residual starts vibrating. Then, suddenly I get a floating Point exeption, with the residuals always being below 1e-01.


      Console Output:
      Divergence detected in AMG solver: epsilon
      Error at host: floating point exception
      Error at Node 0: floating point exception


      I found an area of extremly high turbulence variables (turbulent intensity: >1500%). I think this is the problematic area, but I dont know what to do. Can someone help me out with this Problem.


      I tried a lot of Things:


      - created a better mesh ()


      - enlarged the fluid domain around the mower (with smaller Domain I had backflow and high turbulent viscosity ratio)


      - reduced the relaxation factors


       


      Possibly interesting: I did the same calculation with a rotational Speed of 300rpm and the Simulation is running without Problems. But even in this case the turbulence in the problematic areas is extreme (turb. intensity > 200%). Is there a possible reason for this?


       

    • DrAmine
      Ansys Employee

      Better mesh with low aspect ration, lower skewness and low cell volume change. I won't touch anything else before ameliorating the grid in the areas where you think that is related to that. Just have a look into the areas where you high TVR, locate them and check the values of the mesh metrics. 

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