Learning Forum

[Asif Shahriar Nafi]

For Eulerian Multiphase flow:

As far I know, UDF of the momentum source term has to be hooked for each phase inside the "cell zone condition" (i.e., for phase 1, phase 2, etc.)

For example:

say for phase-1: x-momentum source term UDF is 

 

DEFINE_SOURCE(xmom_source,cell,thread,dS,eqn)

{

       PHASE1_U_Velocity = C_U(cell, thread);

       PHASE1_VOF = C_VOF(cell, thread);

       source = PHASE1_VOF*PHASE1_U_Velocity;

       return source ;

}

 

From my understanding, C_U and C_VOF here will give the Phase 1 velocity and volume fraction only. To calculate my source term, I need the PHASE2 velocity and volume fraction as well. how do I get both of them for Phase 2 inside that particular cell. 

Thanks in Advance 

 

 

[Rob]

You need to access the phase thread, so start reading here   https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v241/en/flu_udf/flu_udf_GenPurposeLoopingMacros.html%23flu_udf_sec_THREAD_SUB_THREAD

[Asif Shahriar Nafi]

If my understanding is correct:
for water (phase 1) - air (phase 2) flow (Eulerian Multiphase): 

A UDF for Phase 1 x-momentum source can be written as:

DEFINE_SOURCE(xmom_source,cell, mixture_thread, dS, eqn)

{    

    int phase1_domain_index = 0;           /* primary (water) phase-1 index is 0     */
    int phase2_domain_index = 1;           /* secondary (air) phase-2 index is 1    */

    Thread *mixture_thread;               /* mixture-level thread pointer */

    Thread *water = THREAD_SUB_THREAD(mixture_thread,phase1_domain_index); 

    Thread *air = THREAD_SUB_THREAD(mixture_thread,phase2_domain_index);

       water_U_Velocity = C_U(cell, water);

       water_VOF = C_VOF(cell, water);

       air_U_Velocity = C_U(cell, air);

       air_VOF = C_VOF(cell, air);

 

       source = water_VOF*water_U_Velocity*air_VOF*air_U_Velocity;

       return source ;

}

Please let me know if my assumption is correct ?
Thanks in Advance

[Rob]

Looks about right. Best approach is to build a simple model and test. We're unable to give UDF advice on here beyond what's in the manual, or "very obvious" in code snippets.