3 Replies Latest reply on Feb 8, 2013 12:54 PM by Andrew Vassallo

    Pressure as inlet condition – does it work?

    Michal Heliks

      Hello

       

      When I set pressure as inlet condition and volume flow as outlet condition my task isn´t able to converge or finishes with different values of flow between inlet and outlet. Is it possible to set it in this way for cetrifugal pumps tasks (local rotating region)?  With swapped conditions it works well.

       

      Thanks

      Michal

        • Re: Pressure as inlet condition – does it work?
          Andrew Vassallo

          I am also interested in this as well.  I typically analyze flow through pressure regulators and most of the time I have a fixed supply pressure and a known outlet pressure, but the flow rate through the regulator is unknown.  I have the same issue with mismatched inlet/outlet flow rates when I specify pressure boundary conditions at both the inlet and outlet.

           

          In addition, depending on how the mesh is consustructed, I may also see a pressure at the outlet (surface parameter - average pressure) that differs considerably from that specified as the outlet boundary condition.  I don't understand this, since I assumed that the boundary condition would be a fixed value.  The calculated pressure resulting at the outlet should exactly match the boundary condition, right?

           

          I have been searching for other information on this example without success so far.

          • Re: Pressure as inlet condition – does it work?
            Jared Conway

            Can pressure be used as an inlet condition? Yes, but most commonly it is used when you have a pressure on both ends. (you're driving flow rate based on 2 pressure conditions)

             

            The more likely cause of your issue is the outlet volume flow rate, the developers do not recommend using that in your BC

            definition. However, I have seen it work as long, you just need to be sure you understand the assumptions that it makes and that they are valid for your situation.

             

            When you say it isn't able to converge, can you elaborate on what you mean? What goals do you have defined? What criteria are you using for stopping? What causes the solution to stop...etc. It may just be that you need to remove the default option to stop the solution when it reaches a max of 4 iterations or choose the option "all criteria have been acheived".

             

            Andrew, I'd recommend opening a separate thread for your question. Mismatched flow rates doesn't make sense. Have you checked mass flow rate vs volume flow rate? Regarding the pressures if you're using environmental pressure you might need to look at total pressure if it becomes an inlet. Would need more information to understand the issue. It could be similar to Michal's (stopping criteria) but it sounds different.