Mass conservation check in FLUENT gives surprising results …

    • nepomnyi

      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.


    • 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. 




      If this helps, please mark this post as 'Is Solution' to help others.

      Guidelines on the Student Community

      How to access ANSYS help links


    • nepomnyi

      @kkande thank you very much!


Viewing 2 reply threads
  • You must be logged in to reply to this topic.