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August 17, 2009, 15:01 
velocitydependent diffusivity

#1 
New Member
Mark Porter
Join Date: Aug 2009
Posts: 2
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I am using starcd (version 4.06). I need to define a velocitydependent diffusivity coefficient for a passive scalar. I have worked out that I need to write a subroutine using pordif.f. What I can't figure out is how I access the magnitude of the velocity that has already been calculated by starcd. My calculation is very simple:
PORODF = 0.0522*v + 1e8 where v is the velocity magnitude at every location in my volume. It seems like should be very easy, but I can not find any documentation regarding this matter. Thanks in advance. 

August 17, 2009, 19:58 

#2 
Senior Member
Pauli
Join Date: Mar 2009
Posts: 185
Rep Power: 9 
At the top of pordif.f you should have this line:
INCLUDE 'usrdat.inc' It will provide U,V,W in global cys. See nom.inc for details. usrdat.inc & nom.inc will appear in your ufile directory when you compile (star ufile). 

November 5, 2009, 14:18 
directiondependent difusivity

#3 
New Member
Mark Porter
Join Date: Aug 2009
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Thank you for the reply Pauli. I know this is very late, but we had some license issues here and I haven't been able to use starcd in awhile. Thus, I now return to my problem. I implemented the velocitydependent diffusivity for each region in my model domain as follows:
Code:
IF(NPPOR.EQ.1) THEN PORODF = 0.00152*SQRT(UL**2 + VL**2 + WL**2) + 3.6431E10 ENDIF My other concern is that in porous media flow the diffusivity becomes a tensor (similar the alpha and beta tensors that are implemented in starcd). But the diffusivity is treated as a scalar. In the code above I technically need a PORODF for each component (x,y,z) of flow. It appears that I need additional if statements that identify each component of flow. For example, the if statements should look something like this: Code:
IF(???.EQ.1.AND.NPPOR.EQ.1) THEN PORODF = 0.00152*UL + 3.6431E10 ENDIF IF(???.EQ.2.AND.NPPOR.EQ.1) THEN PORODF = 0.00152*VL/10 + 3.6431E10 ENDIF IF(???.EQ.3.AND.NPPOR.EQ.1) THEN PORODF = 0.00152*WL/10 + 3.6431E10 ENDIF Thanks in advance. porter 

November 5, 2009, 15:03 

#4 
Senior Member
Pauli
Join Date: Mar 2009
Posts: 185
Rep Power: 9 
U is velocity in the global CSYS. UL is the velocity in the porous media CSYS. I don't know if it is superficial or otherwise.
It looks like diffusivity is implemented as isotropic (i.e. a scalar). I have no idea how you can make it otherwise. I don't think your psuedocode would work. Both are good questions for CDadapco support. 

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