5 Replies Latest reply on Jan 15, 2014 11:48 AM by Jared Conway

    Flow Simulation Question

    Mahyad Mohammadieh

      I have a model of a large tube with a side extrusion, which I am trying to flow Nitrogen through. The inlet is the side extrusion and the outlet is the top of the tube. I have set up all of the general settings. Under analysis type, I have checked off gravity to account for it. Under fluids I have added nitrogen. Wall conditions and Initial Conditions I have left as is and did not change anything. For my boundary conditions. I put an inlet mass flow on the inside of the side extrusion of 0.0002083 kg/s which should be the Nitrogen. I put a static pressure of 2 Torr on the inside of the top of the tube as my outlet. The model is capped off and sealed so the Check Geometry test gives me no errors. It is a very simple model, 1 inlet 1 outlet, and it only takes about a minute to run. For some reason my results don't look appropriate. When looking at the flow trajectories inside the tube you can clearly see that the nitrogen does not flow as it should. The trajectory lines do not appear to come in on the inlet and go out through the outlet. When I play the animation of the trajectories, the trajectory lines just appear in a random location in side the tube and disappear in a random location as well. I have ran this simple model a few times now, and each time I am getting different incorrect results. I have also changed the boundary conditions a bit (ie. double the flow, double the pressure) to see if anything differs, but the inlet and outlet are still incorrect, and do not behave as they should. Any ideas what I might be doing wrong? I can provide pictures if necessary.

        • Re: Flow Simulation Question
          Chris Michalski

          A picture is always helpful.

          I know that I have heard people say that the methods used by Flow to solve problems may not be ideal for low pressure, and 2Torr is definitely low pressure.

          Have you added any goals?

          Have you set the calculation control options or is it simply running 4 travels and stopping?

          I would at least recommend setting your initial conditions to a pressure close to your 2Torr (assuming you want to know what happens once at vacuum, not during the evacuation process.