Fluids

Fluids

Problem with Expression

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    • tianxiao
      Subscriber

      Hello Everyone

      Recently I am working with the Expression in Fluent. And I have defined a constant in Expression as a Parameter, which I want to change between simulations. And I noticed that, after I change the value of this expression, nothing happens. Only when I restart the Fluent again, the model knows that I have a new Value of that expression? So do I always need to restart fluent again to update the value in the expression?

      regards

      Tianxiao

    • Kishan Konannavar
      Ansys Employee
      Hello
      Just for clarification, could you let us know what steps do you execute after changing the values of the expression and additionally steps before you restart Fluent (when you see the updated value).
      Thank you
      Regards
      Kishan.
    • tianxiao
      Subscriber
      Hello Kishan I changed the Value of this expression, which is used in a source term. After changing I direktly click the "calculate" again without touching other settings, and nothing happens. Then I turn off the fluent, restart and click the "calculate", then it works.
      Regards
      Tianxiao
    • Nikhil Narale
      Ansys Employee
      Hello
      Usually it is not required to restart the fluent to update the expression. However, I am finding it difficult to grasp the issue with the information provided.
      Would you mind elaborating the expression?

      Nikhil
    • tianxiao
      Subscriber
      Hi Nikhil
      I defined the following expressions in fluent:
      the one "rho_cat" is a contant without unit:
      as you can see, "rho_cat" are being used in "S_h2", "S_h2o"......
      as a Example "S_h2" are used as a source-term for the species "h2" as in the following picture:
      And My Problem ist, wenn I change the "rho_cat" between two calculations, nothng happens to "S_h2". Only wenn I restart the fluent again, the solver seems to notice that the source term is also changed.
      After 15 Iterations with rho_cat=10:


      Now I change the rho_cat to 15 (It seems nothing happens):
      After I restart the fluent (Now the solver noticed my modification of "rho_cat"):

      regards
      Tianxiao




    • Kishan Konannavar
      Ansys Employee
      Hello
      Do you monitor S_h2 or a quantity affected by rho_cat? Because the snapshots attached are of residuals.

      Regards
      Kishan
    • tianxiao
      Subscriber
      hi yes you are right, S_h2 did changed, But the results (for example, a temperatur plot) are not changed. That means, the source term is not updated, even though the expressions are already updated.
      (S_h2 changed)
      (nothing happens to my results (and I am quit sure the source term will influence the results strongly))

      regards
      Tianxiao
    • Rob
      Ansys Employee
      How is the source and the zone temperature linked? If you monitor the volume fraction (for instance) does that change? If that constant changes all values equally what does it achieve?
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