5 Replies Latest reply on Jul 10, 2014 12:15 PM by Jared Conway

    Tube open to environment

    Johnson Peters

      This is a basic question that I haven't been able to answer yet. I have a simple tube system with a known fluid pressure at the input and fluid flow at the output, where the ouput is open to the environment (i.e. similar to a garden hose). I haven't been able to get good results from my model and so I assumed that I'm probably using SW Flow Simulation for something it wasn't designed for. Is this correct?

        • Re: Tube open to environment
          Jared Conway

          What is the goal of the analysis? To see how things flow out? If so, it won't be a good for for flow. It only handled cases where the whole volume is filled with a single phase. So once it leaves the tube into air, you have 2 phase flow. If it was air , it would be ok.

            • Re: Tube open to environment
              Johnson Peters

              The goal is to examine the static and dynamic pressures and fluid velocity at various points in the system, especially where the tube diameter changes. The fluid is compressed air.

                • Re: Tube open to environment
                  Jared Conway

                  Should be ok if it is air going into air.

                   

                  Do you have a known result you can compare it to?

                    • Re: Tube open to environment
                      Johnson Peters

                      The problem I'm having is that if I use the following BCs:

                       

                      1) Inlet: compressed air pressure, Oulet: fluid flow

                       

                      Fluid velocity and dynamic pressures along tube appear reasonable, but the static pressure along the tube remains similar to the inlet pressure. I was expecting the static pressure to drop near the outlet of the tube.

                       

                      2) Inlet: compressed air pressure, Oulet: atmospheric pressure

                       

                      Static pressure along the tube steadily drops from Inlet pressure to Outlet pressure, but fluid velocities are much too high and dynamic pressures are too low.

                       

                      What I'd like to do is define my Outlet in terms of atmospheric pressure and fluid flow, but SW doens't allow me to give two BCs for the same surface. Not being an expert, my guess was that SW was treating the Outlet  as if the tube was part a closed system and not open to the environment. I think without two BCs at the Outlet SW doesn't know what I'm trying to solve for.

                        • Re: Tube open to environment
                          Jared Conway

                          flow simulation is either setup as pressure pressure where the output will be the flow rate. or flow rate in and a pressure opening at the outlet, the output is the pressure at the inlet.

                           

                          i'm still not sure what the situation is that you are trying to setup to be able to recommend what BCs to use.