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-   -   UDF: source, fixed value for a given region (http://www.cfd-online.com/Forums/fluent/31030-udf-source-fixed-value-given-region.html)

 Ming March 4, 2003 16:21

UDF: source, fixed value for a given region

Hi,

If there is any friend here once worked on UDF, source term, please give me some help.

It is a 2-D, species transport, laminar flow in a slit. Pure water enters the slit. I want to set a fixed value of species A in the middle of the slit.

I can not find a way to let Fluent know this. It can take a UDF for a source term, but not for a fixed value. If I use same UDF, and select "fixed value" in boundary setting for Fluid, then it will give a message saying 'void value expected'.

I also tried Adapt-separate skill trying to separate this middle region and specify a species fraction value for it, but after I separated that region, it still belonged to Interior type rather than fluid type, therefore shutting the door of setting value.

Thanks for any suggestions.

Ming

 Murali March 4, 2003 18:23

Re: UDF: source, fixed value for a given region

<font face = "courier new">My suggn is more of a trick/workaround.

Choose a scalar equation to represent the species. Set source for scalar = 0. Also u have the choice of 'turning off' the convective term in the UDS panel. This way you are going to solve for the following scalar equation:

dS d<sup>2</sup>S
-- = D ---
dT dl<sup>2</sup>

where l is x,y or z (einstenian notation). Now set the boundary condition for the scalar to be the value which you want to fix in 'all' the boundaries. This will ensure that the scalar will have a fixed value through out the system and your problem is fixed (?).

Murali

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