7.6 Limitations of Parallel UDFs

The macro PRINCIPAL_FACE_P can be used only in compiled UDFs.

PRF_GRSUM1 and similar global reduction macros (Section  7.5.4 cannot be used in DEFINE_SOURCE UDFs in parallel ANSYS FLUENT. As a workaround, you can write a DEFINE_ADJUST UDF that calculates a global sum value in the adjust function, and then save the variable in user-defined memory. You can subsequently retrieve the stored variable from user-defined memory and use it inside a DEFINE_SOURCE UDF. This is demonstrated below.

In the following example, the spark volume is calculated in the DEFINE_ADJUST function and the value is stored in user-defined memory using C_UDMI. The volume is then retrieved from user-defined memory and used in the DEFINE_SOURCE UDF.

#include "udf.h"

static real spark_center[ND_ND]={20e-3, 1e-3}; 
static int fluid_chamber_ID = 2;

DEFINE_ADJUST(adjust, domain)
{
 real vol, xc[ND_ND], dis[ND_ND], radius;
 cell_t c;
 Thread * tc;

 tc = Lookup_Thread(domain, fluid_chamber_ID);

 radius = RP_Get_Real("spark/radius");

 vol = 0;
 begin_c_loop_int (c, tc)
    {
     C_CENTROID(xc, c, tc);
     NV_VV(dis, =, xc, -, spark_center);

     if (NV_MAG(dis) < radius)
         {
          vol += C_VOLUME(c, tc);
          }
     }
 end_c_loop_int (c, tc)
 vol = PRF_GRSUM1(vol);

 begin_c_loop_int (c, tc)
    {
     C_UDMI(c, tc, 1) = vol;
    }
 end_c_loop_int (c, tc)
}

DEFINE_SOURCE(energy_source, c, t, dS, eqn)
{
  #if !RP_HOST
    real xc[ND_ND], dis[ND_ND];
    real source, radius, vol, CA, rpm, start_CA;

    rpm        = RP_Get_Real("dynamesh/in-cyn/crank-rpm");
    start_CA   = RP_Get_Real("spark/start-ca");

    CA = rpm*CURRENT_TIME*6+RP_Get_Real("dynamesh/in-cyn/crank-start-angle");

    if(CA>=start_CA&&CA<(start_CA+RP_Get_Real("spark/duration")*rpm*6))
      {
         radius = RP_Get_Real("spark/radius");
         vol = C_UDMI(c, t, 1);

         C_CENTROID(xc, c, t);
         NV_VV(dis, =, xc, -, spark_center);
         if (NV_MAG(dis) < radius)
           {
            source  =
            RP_Get_Real("spark/energy")/RP_Get_Real("spark/duration")/vol;
           return source;
            }
         else
            {
             return 0;
             }
      }
    else
      {
       return 0;
      }
  #endif
}

Interpreted UDFs cannot be used while running in parallel with an Infiniband interconnect. The compiled UDF approach should be used in this case.