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-   -   Interface Matching and Field Function problems (http://www.cfd-online.com/Forums/star-ccm/66041-interface-matching-field-function-problems.html)

 PLUH July 3, 2009 11:20

Interface Matching and Field Function problems

Good day.

I'm a fairly new to CFD and am currently working on Star-CCM+ 4.02.007 on OpenSuse 11.1.

First off, im trying to simulate the fluid flow through an annular packed bed with the bed being presented by a porous region in my model. I however also have to take the inlet header into account. This means that i have 24 interfaces between my header and bed.

Now when i run the surface remesher the output window shows that some of the edges of the interfaces were matched using "edge zipping" while other others were "conformally matched". Is this any cause for worry?

Secondly, since the pressure drop over the packed bed (porous) region isn't correctly predicted by the availible models (Ergun's equation was used in defining the inertial and viscous resistance of the porous region) I want to ajust the Dynamic viscosity in this porous region by means of a field function.

Say the dynamic viscosity is 1.79e-5 Pa.s and for the porous region i want a value 11 times that of the normal unmodified dynamic viscosity and the porous region extends from a height of Z=0.0m to Z = 0.6m I then define my field function as follow:

((\$\$Position("Cylindrical")[2] >= 0.0 && \$\$Position("Cylindrical")[2] <= 0.6)?(1.79e-5)(1.79e-5)*11))

When i test the field function by plotting it in a scalar scene it works fine. When i go to Continua - Pysics 1 - Models - Gas - Air - Dynamic Viscosity and change the input from "Constant" to "Field Function" and apply the above mentioned field function I suddenly get an error message saying that the field function is incorrecty defined.:confused:

I have checked that its defined as a scalar and that the units are also Pa.s but the problem doesn't want to go away.

Is this even possible and am i doing something wrong? Is there an alternative way of doing this?

Any help will be greatly appreciated and sorry for the long post.

Thanks

Henco

 highnelly July 4, 2009 02:44

May be this will not be of any use but did you try using the scalar "\$Centroid" to define position.

Also its seems like you don't have a colon in your equation; does that matter?

As regards your meshing is the edge zipper the tool that does the conformal matching for inter region boundaries? If so I don't think you need to worry once it actually meshed for you.

 PLUH July 5, 2009 06:15

Highnelly

As for the meshing, i really dont know about the meshing, it might ba that star-ccm+ uses the edge zipper to match the perimeters of interface surfaces.

As for the using \$\$Centroid in the field function, that cleared up the problem. Thanks again. But now i'm wondering, why \$\$Centroid works but \$\$Position doesn't? Any Ideas?

Thanks again for the help, really appreciate it