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Simulating an air-heater for a moving steel tube (rigid body)

    • 1829116


      I am trying to heat a steel tube using impingement heating in an heater I modeled. As seen, the air flows in the -z direction to heat the tube that moves in the x direction at a constant speed. I am facing a problem in simulating the moving steel tube. I tried creating a dynamic mesh and using UDF but it is giving me:

      "Warning: incorrect cg motion UDF Tube on zone 8 (assuming no motion)"

      I tried then setting the governing equation for the steel tube and its wall bu the momentum tab is not appearing for the wall of the tube.

      Thankful for any help

    • KR
      Apologies for the delayed response on this one. Seems to have fallen through the cracks. How are you planning to move the tube? Is this using a UDF? Have you tried assigning this to the cell zone?
    • 1829116
      Thank you Karthik for you answer.
      I have tried both options but none seems to do the job. When i give the solid zone (Steel Tube) a velocity as a moving solid., the solution comes out with the tube not moving. When using UDF with a dynamic mesh, the error i mentioned is showing.
      I am yet to find a solution with moving solids in FLUENT. Everyone uses moving walls since they are interested in the airflow. For me, I am interested in the moving solid and its wall temperature. I have also been trying to use the FSI method using FLUENT, Transient Structure and system coupling but the last is giving this "the specified end time cannot be greater than the end time specified by Transient Structural: 1." The tutorial i followed suggested to keep Transient structure end time to one since the transient simulation should be run by System Coupling.
      Can you advice on these errors? Also, do you agree that FSI is the correct solution for my problem?
    • Steve
      Ansys Employee


      Hadi, the errors will be a consequence of incorrect setup.

      However, you haven’t offered any explanation why you’re trying to physically move the tube in the model. You explain that you are moving it in the x direction at a constant speed. Unless you need to capture flow and thermal effects relative to other stationary (or differently moving) objects you are likely over-complicating the modeling setup. A common approach is to move the air relative to the object (similar to a car in a wind tunnel).

      Other approaches are available as well depending on your objective.The other approach you suggested (applying a velocity to the solid) can also be a sensible approach, essentially introducing the relevant ‘convective’ terms to the solid relative to the surrounding zone.

      ’Physically’ moving the object is a much more involved simulation method (and computationally higher) – I would recommend avoiding this unless the objective requires you to do so.

      Similarly, you need to consider whether you are trying to capture continnuous operation (steady state) or short heat-up/ cool-down (transient) conditions. Try to explain your modeling objective to attract the most relevant advice.


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