[djendara]

HI , I HAVE A GREAT PROBLEM WHEN I HOOK AN SOURCE TERM ,I FIND DIFFERENT RESULTS SPECIALLY WHEN I RUN TWO CALCULATION HAVE SAME STRICTURE EXP : POISSON EQUATION USING "UDS" VS HEAT EQUATION USING ENERGY EQUATION IN FLUENT USING SIMPLE ALGORITHM I FOUND THE FOLLOWING RESULTS :

1 /WHEN I RUN EQUATION WITH INTERPRETED SOURCE TERM FOR ENERGY GIVE REASONABLE RESULT

2 /WHEN I RUN EQUATION WITH INTERPRETED SOURCE TERM FOR ENERGY GIVE HUGE VALUES

THE UDF ARE :

DEFINE_SOURCE(ENERGY_SOURCE, c, thread, dS, eqn)

{

Domain *d = Get_Domain(1);

int fluid_ID = **;

Thread *t_fluid = Lookup_Thread (d,fluid_ID);

Source = C_T(c,t_fluid);

dS[eqn]=1;

return Source;

}

DEFINE_SOURCE(POISSON_SOURCE, c, thread, dS, eqn)

{

Domain *d = Get_Domain(1);

int fluid_ID = **;

Thread *t_fluid = Lookup_Thread (d,fluid_ID);

Source = C_UDSI(c,t_fluid,0);

dS[eqn]=1;

return Source;

}

WHY COMPUTING HEAT EQUATION BY UDS GIVE HUGE VALUES WHEN USING UDF SOURCE TERM
PLEASE HELP !

[pakk]

YOU GET DIFFERENT RESULTS BECAUSE YOU PUT DIFFERENT THINGS IN. THERE IS NO REASON TO EXPECT THAT THE TWO UDFS GIVE THE SAME RESULT, WHY ARE YOU THINKING THAT?

Also, why are we screaming?

[djendara]

Hi, i put same characteristic for the diffusive steady stat equation
1/same diffusivity coefficient
2/same boundary condition
3/same solver (simple algorithm ,second order)
the same source term that are is motioned
but only difference is energy vs uds
i have use cv=1 and rh0=1 and i deactivate relation between viscosity and energy equation to conserve the same stecture like uds

[pakk]

If you don't add sources, is UDS0 completely identical to temperature? In the results, I mean?

[djendara]

YES Mr PAKK WE ARE KNOWING THAT THE UDS IS IDENTICAL TO ENERGY EQUATION AFTER SOME MODIFICATION I CONFESS THAT , THE PROBLEM HERE IS WHEN WE INTERPRET THE TEMPERATURE LIKE AN SOURCE IN IN ENERGY EQUATION IT'S OK BUT IN THE TURN IF WE SET UDS_0 SOURCE IN UDS EQUATION IT GIVE IN THE HUGE VALUE
EXAMPLE YOU CAN SET SOURCE TERM = 1 IN UDS_0 IT WILL BE 300 IN THE RESULT
I USE ANSYS FLUENT 2020 R2 ACADEMIC

[pakk]

I DIDN'T ASK IF YOU KNOW THAT THEY ARE EQUAL. I ASKED IF YOU SAW THAT THEY WERE EQUAL IN THE RESULTS. PLEASE SHOW PICTURES OF THE UDS0 AND TEMP WITHOUT SOURCE TERMS.

AND WHAT DOES IT MEAN THAT 1 WILL BE 300 IN THE RESULTS? THAT SOUNDS WRONG, 1 SHOULD BE 1.

Why do you scream like that? It's not so polite..

[AlexanderZ]

you may put just a value instead of any macro here:
Source = C_UDSI(c,t_fluid,0);
for instance
Source = 300;

and it should be equivalent to
Source = C_T(c,t_fluid,0);
in case temperature is 300

if you have different result, it means, your Scalar field is defined wrong in way

[djendara]

OK I , ESTIMATE THE SOLUTION OF THE PROBLEM SINCE THE THE STEADY EQUATION DEPEND OF TWO PARAMETER IN WHICH ARE THE DIFFUSIVITY RATIO AND SCALAR SOURCE TERM OR IN BETTER THE RATIO SCALAR SOURCE AND DIFFUSIVITY COEFFICIENT R=Sf/Df
BUT INSPITE OF THIS I DONT KNOW IF I MAKE MULTIPLICATION OF SOURCE TERM WITH CELL VOLUME OR NOT IN MY UDF