Fluids

Fluids

Mass conservation check in FLUENT gives surprising results …

    • nepomnyi
      Subscriber

      Hello dear ANSYS community.


      I am performing mass conservation check for my ANSYS FLUENT 2019R2 air-water 3D flow simulation in vertical pipe (done with Eulerian model).


      I ran my simulation --> during the simulation there wasn't reversed flow at the outlet --> once the simulation was completed I compared mass flow rates at the inlet and at the outlet.


      I got that the magnitudes of the mass flow rates were almost the same (within the accepted tolerance region) - but they had different signs!


      My flow is laminar and vertical (mostly one directional - though it is 3D). My pipe is aligned with the Y axis. My flow is in the positive Y direction. Therefore my mass flow rates must be positive. Still my mass flow rate at the inlet is positive and my mass flow rate at the outlet is negative - but their magnitudes are equal.


      My boundary conditions are:


      - pressure outlet


      - velocity inlet (I specified velocity as "magnitude, normal to the boundary" - I am pretty sure that's the problem because outward normal vectors for the inlet and outlet boundaries are obviously in the opposite directions).


      I was wondering if anybody could help me please to understand whether it is some sort of ANSYS technical issue or my simulation is wrong and I do in fact have reversed flow at the outlet.


      I am ready to provide additional information upon request.


      Thank you in advance.


      Ivan

    • Keyur Kanade
      Ansys Employee

      it shows you got good mass balance. 


      the -ve sign for mass flow rate at outlet is - flow going out of domain. 


      +ve sign at inlet - flow in coming into the domain. 


      please go through help document. 


      Regards,


      Keyur


       


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    • nepomnyi
      Subscriber

      @kkande thank you very much!


      Ivan

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