10 Replies Latest reply on Dec 2, 2013 3:01 AM by Luc Spruyt

    Determine rotation of flowmeter rotor

    Luc Spruyt

      Dear members,

       

      I'm working on a project with flowmeters.

      The question is, what is the best design for the worm in order to get te best efficiency in a flow meter.

      I've added a picture to show the model.

       

      I know it is possible to determine equilibrium rotation of a propeller in ambient flow.

      Set a goal for the torque around the axis for all the faces of the propeller and see if it's driving or resisting.

       

      I did some testing to see the difference between selecting ALL faces or just ONE as a " sensor " face to determine the "+" or "-" vallue of the torque.

      The vallues are quit different and therefore I'm doubting my analysis.

       

      Question:

      - Is it neccesary to select ALL the faces of the rotor?

      - Is there an alternative for placing a sensor goal to measure the equilibrium rotation?

       

      Thanks in advance.

      Luc Spruyt

      3D Assist

        • Re: Determine rotation of flowmeter rotor
          Bill McEachern

          Best efficiency would be achieve by calibrating a low solidity rotor - that would be my guess - don't have a worm gear with high solidity (100%).

          Flow sim is not hte best tool for this analysis. The rotating frame approximation is not well suited to this problem. However an iterative scheme (trail and error) may get you in the ball park but I am not even sure what you would look to compare the assumed rotor speed to the actual rotor speed to see when it would be balanced. It isn't initially obvious to me at least. The "efficieny" would be the pressure drop that the meter induces across it. You can always assume the rotor speed is the same as the pitch of the worm and go from there but that seems a bit dicy.

            • Re: Determine rotation of flowmeter rotor
              Luc Spruyt

              Hello Bill,

               

              Thanks for the reply.

              The thing is I need a proper goal/sensor to determine wether the rotor is not causing any obstruction.

              And there will be obstruction when the RPM of the rotor is much to high or to low.

              The spiral/worm in front of the rotor is fixed and guiding the flow to achieve maximum thrust on the rotor.

              I would like to see the effect of changing the angular twist of the spiral.

              It would effect the RPM and therefore I need a goal to measure this change.

              I am willing to run several trail and error analysis as long as I can rely on the goal/sensor value.

               

              The advice of setting up a surface goal and measure driving or resisting troque is ok with me. (article ID x344 26-12-2006)

              Is it neccesary to apply the surface goal on ALL the surfaces or will 1 surface do the job.

              Eventually the only thing we need to know is if the torque will be "+" or "-".

              Or is there another work around for this matter.

              Is there another way to set up a reliable goal !!

               

              Thanks again.

              Regards Luc


                • Re: Determine rotation of flowmeter rotor
                  Jared Conway

                  I think you are violating too many assumptions of the frozen rotor approach that flow uses. Would suggest setting up a know case before you try design with flow. Also, work with your var on this. I wouldn't spend too much time on it until you can confirm the application is applicable to frozen rotor.

                   

                  The limitations are well defined in the kb, tech ref and solving eng problems docs.

                   

                  If you're good with the ball park that bill describes, go for it. But don't be blown away by weird inconsistent results. If you want an opinion, build a sample model that you can post with your questions.