Fluids

Fluids

Superficial velocity in Ansys Porous resistance

    • eric1234598765
      Subscriber

      Hi,

      In Ansys Fluent user guide, it says how to calculate pressure drop through porous media, which is:

    • Robert Woolhouse
      Ansys Employee
      Check 7.2.3.8.6 in https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v221/en/flu_ug/flu_ug_sec_bc_porous_media.html I tend to leave the porous formation as default, superficial velocity.
    • eric1234598765
      Subscriber
      Hi, I've read 7.2.3.8.6 and 7.2.3.8.7. Interestingly, I though the answer is in 7.2.3.8.7 , which is:


      The picture above is the part of 7.2.3.8.7. It says that Fluent assume porous the 100% open media, in other word, no solid part in simulation world, and people who define the pressure drop through porous media must use superficial velocity to determine either permeability or inertial coefficient.
      For those using physical velocity form in the porous zone, user guide tells the answer in 7.2.7.1 in the "Important" section, which says that the pressure drop factors are still based on the superficial velocity.


      Anyway, Fluent uses superficial velocity to determine pressure drop factors no matter which velocity formulation is chose.
      Thanks for the quick and useful answer, however, since Fluent says that using physical velocity can get the more accurate solution, could you tell me why you would use the superficial velocity to compute the porous zone?





    • Robert Woolhouse
      Ansys Employee
      Physical velocity will speed up flow to mimic the effect of a reduced space in the porous media. But, and this is why I rarely use it, is the porous media slowing the flow, or speeding it up? Generally a porous zone forces flow to go around it, or creates a more tortuous path for the flow: the latter adds a pressure loss but not any increase of speed. Finally, if the physical velocity works you have a larger area with a higher velocity so momentum is potentially too high.
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