Topics relate to Fluent, CFX, Turbogrid and more

Volume rendering last species CFD post

    • jonny

      Hi i am using CFD post and the volume rendering tool two show the sifferent species within a micture of a 3D flow. however when i apply this to the last species the volume generated is the negative of the the species volume (for example the volume of the domain subtract mess fraction of that species). I know that that the fluent calculates the volume of the last species as 1 minus teh volume of the other species however i dont know how to stop this from happening iin CFD post. can someone help me? Thanks


    • rfblumen
      Ansys Employee

      When you create a variable composition mixture, at any given control volume the sum of the components must be exactly one.  To enforce this, one of the components must act as the constraint (i.e. whatever is left over in the control volume must be that component in order for the mass fractions to sum to one).  In your case, you're showing that the constraint component is filling most of the volume when using Volume Rendering.  This implies one of two things:

      1.) The mass flow rate of the constraint into the model component is much larger than that of the other components.

      2.)  The case isn't converged such that mass imbalances are low.  Depending on how the case was initialized, the model might have contained all or mostly the constraint component at the beginning of the simulation.  If the simulation was stopped before the model was converged and the flow imbalances were minimal, one might see mostly the constraint component in the model.

      You can also verify the volume rendering by creating planes in the model and coloring by the component mass fraction.

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