I am running a multiphase simulation with the particle model. I expect the area density to be related to the volume fraction and particle diameter by
A_int = 6 * volfrac / d
When I plot the area density in Post, I find that this is the case almost everywhere but for a few locations. Why is that?
The particle model is strictly only valid for continuous-disperse flows. The area density is clipped when the volume fraction of the disperse phase exceeds a maximum value, which by default is set to 0.8. The clipping makes the area density go to zero when the disperse phase volume fraction goes to 1. This is done to represent the fact that the area density for slug flow is found to be lower than value assuming spherical particles. This is implemented with:
IF( VOLFRN_D(I).LE.MaxVF(I) ) THEN
VFR_MOD = VOLFRN_D(I)
VFR_MOD = MaxVF(I) * ( VOLFRN_D(I)-ONE ) / (MaxVF(I) - ONE )
If you want to change the maximum volume fraction, from which the clipping starts you can change the `Maximum Volume Fraction for Area Density` under INTERPHASE TRANSFER MODEL