[DHSYNE]

Hello friends.

I am modeling a transient particle-gas system inside a tube. The particle trajectories are calculated externally using UDFs, so I have to pass back the drag forces as source terms to take into account the effect of the particles on the gas flow.

I found that fluent had difficulty converging in the case of dense particles accumulated in one or more cells (porosity becoming less than 0.5). As a result, the gas flow velocity can suddenly become very high due to the inability to converge.

I tried to reduce the time step of Fluent (gas flow) to 1e-7s, and it worked well for dilute particle cases. But the problem still occurs when more particles are injected. Can anyone give me a suggestion to solve this problem?
Thanks!



*****Here is the udf for source terms*****:
DEFINE_SOURCE(xmom_source,c,t,dS,eqn)
{
real source = 0.;
if(initialized)
{
source = C_UDMI(c,t,1)/C_VOLUME(c,t);
}
dS[eqn] = 0.0;
return source;
}
C_UDMI(c,t,1) stores the drag force on particles.

[DHSYNE]

Can anyone help with this problem?