[blerli_91]

Dear Forum,


For future projects I want to implement alternative Drag laws for the DDPM model. For getting experience in UDF programming (I am quite new to the topic) I am trying to recreate the Fluent Build-In Drag law by Wen and Yu. I have a 1D test case for comparison of the original drag law and my UDF. For comparison I am using a DPM-Sample at the Outlet for a patched Flow-Field.
According to UDF Manual the Define_DPM_Drag should return an expression equal to: . First I tried to directly insert the Wen-Yu Cd given in the Theory Guide into the expression:




However, I was not able to recreate the results of the original Drag Law. So I guess I will need another formulation for Cd? Maybe someone has experience with that? I am not sure which kind of expression I should use for : in case of Wen-Yu.
The code I was using.:

#include "udf.h" 

#include "dpm.h" 

DEFINE_DPM_DRAG(particle_drag_force,Re,tp) 

{ real drag_force, void_s,void_g; 

 cell_t cell; Thread *thread_s, *mix_thread;  

cell=P_CELL(tp); 
 
 mix_thread=P_CELL_THREAD(tp);  

thread_s = THREAD_SUB_THREAD(mix_thread,1); 

void_s = C_VOF(cell, thread_s);  void_g =1-void_s ; 
 //drag_force = 18.0 * pow(void_g,-2.65) * (1 + 0.15 * pow(void_g * Re,0.687))/void_g ;
 
drag_force = 18.0 * (1 + 0.15 * pow(void_g * Re,0.687))/void_g ; 
return (drag_force); }

Thank You and Best Regards