4 Replies Latest reply on Oct 10, 2014 6:07 PM by Jared Conway

    inlet,outlet and rotating flow

    Siew Goh

      I am new to CFD modelling. I tried to simulate the flow of the rotating disk with an inlet flow and an outlet pressure (please refer to the sectioned view of the model below). However, the outlet flow rate is different from the inlet flow rate. I just wonder is that related to my setup.

      Model.JPG

       

      General Setting:

      Analysis: Internal , exclude cavities without flow condition

      Gravity: Y component (-9.81 m/s^2)

      Rotation: local region

      Flow: Air

      Boundary condition:

      local rotating region- 219.94 rad/s

      Real Wall - Stator

      Inlet volume flow- 0.033 m^3/s , uniform, absolute

      Environment pressure outlet

      The diameter of inlet is 40 mm and outlet is 50 mm.

       

      Results:

      Volume flow rate.JPG

       

        • Re: inlet,outlet and rotating flow
          Chris Michalski

          Without being able to see your geometry from a 3D perspective to know what the rotating disc DOES, the simple answer is: you haven't run enough iterations for the calculations to converge.  Because you define the inlet flow that is always stable, but the software has to determine how that inlet flow creates a pressure wave, and how it propagates, and continue refining that until it stabilizes.

          As you can see, it initially WAY overshoots the outlet, then over-corrects.  It will oscillate like this (getting smaller each time) until the model is stable.

          You should look into adding a goal to the outlet flow to track whether it has converged.

          1 person found this helpful
          • Re: inlet,outlet and rotating flow
            Jared Conway

            before you get too caught up in the results, make sure you've checked that your rotating region is valid for flow simulation. a rotating disk would probably be better handled with a moving wall.

             

            also the way it looks, i think you're breaking the rules about axisymmetry for rotating regions which would cause an issue similar to what you describe because of the way the regions are generated. (they are like inlets and outlets)

             

            check the kb and the tech refs for more info

            1 person found this helpful
            • Re: inlet,outlet and rotating flow
              Siew Goh

              Dear Chris and Jared,

                       Thanks you for your tips. Both methods are useful. The calculation converge at the end of simulation after I increase the number of iterations while by setting the rotating disk as moving wall, I get same inlet and outlet flow rate at the beginning of the simulation. However, both give me similar result at the end of the simulation. Both methods work in my case.

               

              Kind Regards,

              Siew