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-   -   Passive Scalar boundary conditions (http://www.cfd-online.com/Forums/star-ccm/109984-passive-scalar-boundary-conditions.html)

francesco12 December 2, 2012 08:41

Passive Scalar boundary conditions
 
Hello,

I am performing a simulation of the advective-diffusive mass transfer for the oxygen in a fluid.
I have a bifurcating pipe (an artery and a vein), with a velocity inlet, a velocity outlet, and a pressure outlet as boundary conditions.
I'm using the passive scalar model to simulate the oxygen, and I would like to impose the normal concentration gradient, on the two outlets,
but since I'm using a velocity and a pressure as boundary conditions, I can only impose a specified value on those faces.
For what concerns the other boundaries, I have a concentration sink on the wall of the pipes (with a specified value of 0), and a constant concentration on the inlet.
I have also tried to use the flow-split condition, but sometimes the solution start diverging because of a recirculation on the cells of the boundary layer, even if I try extend the pipe to damp the recirculation.
The Schmidt number I'm using is quite high (2700), and I noticed that if I change the constant value on the outlets from 0 to 1 the solution for the passive scalar remains the same, on the other hand, imposing the gradient would be conceptually more correct.
Does anyone have any suggestion?

Thanks in advance,

Francesco

siara817 December 13, 2012 04:15

I hope I understood correct. If you want to have a normal distribution of a phase (oxygen) you can use lagrangian multiphase mode. Then the second phase will be defined as a normal distribution.


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