Fluids

Fluids

Wrong results in ANSYS Fluent

    • 3LMOON
      Subscriber

      I am using ANSYS fluent 2020 R1 in my MSc dissertation (University of Aberdeen) to model sea-water flow over a circular cylinder (fluid properties: density=1023.6 kg/m3,viscosity=.00091 kg/m.s) using 4 values of Re (100,1000,10000 and 10^6). I am trying to obtain drag coefficient and flow contour maps, but i am getting wrong results. Note that I have seen some tutorials on Youtube and I followed them but still getting wrong results different from what is available on the published resources.

    • Rob
      Ansys Employee

      Check the reference area as drag coefficient is a derived quantity and the mesh: is it fine enough at the surface to pick up the shedding? 

    • 3LMOON
      Subscriber

      Thanks for your reply.


      the diameter of my cylinder is .6096 m. for the meshing my I put an element size of 300 mm and for the inflation I put an element size of 20 mm to have finer meshing around the cylinder.is it fine enough ??


      for the reference area as well as the length I put .6096 m.


      What would you suggest ?

    • Rob
      Ansys Employee

      Check the sizing, and also try local refinement (adaption). 

    • 3LMOON
      Subscriber
      Thanks for your reply. I have done that but still getting wrong Cd values as well as the contour flow maps.
    • Rob
      Ansys Employee

      What's wrong with the flow field? Pictures will help.

    • 3LMOON
      Subscriber

    • 3LMOON
      Subscriber

      As it is clearly seen that vortex shedding is not shown, although that Re = 100.

    • Rob
      Ansys Employee

      Do you expect shedding at 0.15mm/s around a 0.5m diameter pipe? 

    • 3LMOON
      Subscriber

      As per my understanding, vortex shedding is a function of Re number. Also, from the literature it is mentioned that vortex shedding starts from Re= 40( critical Re) and in all my cases Re is higher than this value. 


      If you have a better explanation as well as better understanding for this subject, I am happy with that and I will appreciate it, because my background is petroleum engineering so that I am not familiar to this subject.


      Thanks.

    • Rob
      Ansys Employee

      Pass, I've not looked at the theory in years.  However at the speed you're using I'd not expect anything much to happen. 

    • 3LMOON
      Subscriber

      one more question, about the models, when to use each one??


      Thanks for your replies.

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