CFD Online Discussion Forums - Energy Source Term for Sub-Region

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Energy Source Term for Sub-Region

Hello, I'm using ANSYS v15. for my masters thesis and I have the following problem:

My thesis is about the Multiphase-Euler-Approach to simulate granular flows under different conditions (yeah, I know DEM would be more efficient but that is what my prof wanted me to do).
I have already finished most of my workload but I simply cannot complete my last problem:

A box is filled with the 2 granular phases as shown in the little paint picture I attached (vf means volume fraction). I want to set the energy source term to be in a very specific area that is heated - so NOT for all the cells inside a certain phase, in fact the area of the energy source term should not be linked to the phases at all. I should be able to fill my box however I want to and the area of the box where I want to modify the energy source term should not be affected by it.
I have already tried everything I know. I simply cannot get the energy source term to be set ONLY for that area and to remain unchanged for everything else.

I'm NOT asking you to solve my problem, but i just want to know if what I want to do is even doable? Can the energy source term be changed only for a certain area or is it always globally? Like it was with my previous simulations where I changed the gravity for the second phase globally.

Is it possible to have a little area where the energy source term is changed? How should I construct the UDF? Because nothing I try is working.

Thanks in advance, I hope I was able to explain my problem properly :)

Including an energy source term dependent on location should be straightforward using the DEFINE_SOURCE macro. Have a read of the section in the UDF manual (there's a description, example and steps on hooking the macro to your cell zone).

The DEFINE_SOURCE macro is called for each cell and therefore you could use a conditional statement to apply a local energy source. For example:

Code:

#include "udf.h" // UDFs require this header file



DEFINE_SOURCE(local_energy_source,c,t,dS,eqn)

{

    real x[ND_ND]; // array of cell coordinates

    real source = 0.; // default the source term to zero



    C_CENTROID(x,c,t); // retrieves the cell coordinates

    dS[eqn] = 0.; // derivative of source term



    if (x[0] > 0.5) // only if this cell belongs in the domain where x > 0.5 m

    {

        source = 1.; // non-zero source [generation-rate/volume e.g. W/m^3]

    }



    return source; // source is returned to solver

}

Thank you e for your code :),
I already tried that but what happens is this:

Fluent goes into the if statement, looks if there are cells with x coordinates >0.5 and then applies the source term to ALL cells, not only to the cells with x coordinates above 0.5.
This is why I was asking, because I can't find the solution to my problem. It seems like the source term can only be applied globally ... :( or am I just very stupid and doing something very wrong?

As I mentioned above, the source term is applied on a cell-by-cell basis. The DEFINE_SOURCE macro is called for each cell and returns a source term for that specific cell (with the cell index c).

Try the UDF I posted above and set the local source term to a very high value to make the temperature field peak in this local region (you may need to modify the conditional statement for your domain).

Thank you very much for your patience. I just figured out my mistake.
When I used UDFs before this last problem, I modified the viscosity and gravity of each phase and I was used to working with absolute values. But as you pointed out the expression should be in W/m³ so I just divided the source term by the volume of each cell .... it works just fine now. Thank you =)