How to implement a new numerical model on the conventional CFD-DEM?

I try to implement a new numerical model called "Fictitious Particle Method” on the conventional CFD-DEM. This method uses for systems that have particles with a large difference in size (10 to 20 times).

In this method, the amount of momentum exchange between the fluid and the solids is estimated by assuming that large solid consists of small, dense fictitious particles. (as shown in the below figures)

For the implementation of this method, I need to change some equations that used in conventional CFD-DEM. Such as:
• Gas void fraction equation
• Sauter mean diameter that used in Reynolds number and β equation
• The average velocity of all solids existing in a computational cell.
• The equation of drag force acting on particles and coarse solid.
Finally, my question is how and with which subroutines can these changes be made?

Thank you very much for your help.


I was able to find subroutines that need to be changed. But unfortunately, I had a problem. The solid volume fraction inside cells that are completely occupied by the large particle is not calculated correctly.

In fldvar_mod.f, a function called EPS is defined that calculates the value of a solid volume fraction as follows:

EP_s = ROP_s(IJK, xxM)/RO_S(IJK,xxM)

But in cells that are completely or partially occupied by the large particle, the values of RO_S and ROP_s are calculated to be zero, and therefore EP_s is equal to NaN(Not a Number).

Now the question is, how can I get the correct volume fraction for a large solid inside a cell?

P.S: In the method that I will use, measures have been devised so that the volume fraction of gas inside the cell is not zero, and I will not encounter any errors in this regard. At the moment it is only necessary to be able to get the amount of solid volume fraction inside the cell.

Thanks for your help