Why fan boundary condition does not operate at an operating point

    • PTW99


      I am trying to model and validate the air flow in simple circular air duct i place fan boundary condition at 0.1 m right before outlet as you can see my system in Pic.1. I set an inlet as Pressure inlet and outlet as Pressure outlet (Pic.2,3) and specify my fan curve with piecewise-linear (Pic.4). Then plot the result of simulation an average pressure distribute in each cross sectional area (Pic.5) then plot system characteristic curve with fan curve to determine where the operating point is (Pic.6). But as you can see from the simulation result it has system head 28.3 Pa but the fan provide head at 77.3 Pa. I have no idea why it is not operate at the operating point.

      Thank you in advance

      ** Blue circle dot is system head and blue triangle dot is system provide head

      ** I also try to extend the duct length but the result is still the same


      Pic.1 System

    • Surya Deb
      Ansys Employee
      How are you obtaining the system curve?
      It seems that your system resistance is quite low and so intersects the fan curve at a lower point. [The blue line].
      Regards SD

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