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-   -   Difference b/W vol. avg. velocity and superficial velocity (http://www.cfd-online.com/Forums/fluent/85711-difference-b-w-vol-avg-velocity-superficial-velocity.html)

 mwtengr March 4, 2011 20:25

Difference b/W vol. avg. velocity and superficial velocity

hi all
i have a little confusion, i will be very thankful if someone can clerify it:
if i use the superficial velocity (vol. flow rate/X-Area) then permeability can be given using the darcy's law as follows:
K = mu*v_s/delta p; where v_s is superficial velocity, and delta p is the gradient of the pressure (pressure drop per unit length).
In fluent i can get the volume averaged velocity under Reports-> volume integrals->, my question is that is this vol. averaged velocity is the same as the superficial velocity, and can i use it to calculate the K above.
thanks

 Amir March 5, 2011 09:20

Hi,
I don't think so. if you compare superficial and physical velocities, you can understand their differences.
superficial kind is a type of velocity that doesn't consider solidity for velocity increment in porous media and can change through your media but volume average type is totally different!
in other words, volume average of superficial velocity is volume average one. but for calculating average permeability you can use above procedure.

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