[DHSYNE]

Hello I am simulating the motion of particles in an unsteady fluid (air) field by coupling DEM code as UDF with Fluent. The drag force is calculated in DEM, and it will be passed back to Fluent as a source term. But the error will occur when the particles are dense (e.g. 10,000 5um particles agglomerate together). In that case, when the drag force is passed back to Fluent as the source term, the flow field cannot converge (abnormal residual fluctuations), resulting in excessive local flow field velocity and errors.

Below is the source term code. I can be sure that the drag force is calculated correctly because if the source term is not activated, everything looks reasonable.

DEFINE_SOURCE(xmom_source,c,t,dS,eqn)
{
real source = 0.;
if(initialized)
{
int cellIndex = C_UDMI(c,t,0);
source = cfdcell[cellIndex].dragFX/C_VOLUME(c,t);
}
dS[eqn] = 0.0;
return source;
}

Can someone help me? I have been stuck with this problem for many days. Thank you