[hwet]

This code appears to work fine (not really) after weeks of attempts.
The idea was to make the particle reflect if a certain condition was fulfilled.

The particle does reflect, and quickly attains the gas speed so the reflected speed i suppose doesn't really matter.

But... still curious to know what it was and tried to print the reflected components, the values are very illogical.

''The printed new velocity components are: -1.3e+38 5.9e-323 1.9e-323.'' Also using printf and not message0 as I have other issues trying to compile the UDF so just interpreting it at the moment.

#include "udf.h"

DEFINE_DPM_BC(drop_col_wet_scrubber, particle_data, thread_face, f_index, f_normal, dim)

{

real vsqr=0;                                                     /*Initializing the variables*/
real vmag=0;
real vn=0;
real normal[3];
real collision_weber_number;
int i, idim=dim;

for (i=0; i<idim;i++)
    {       
    vsqr += P_VEL(particle_data)[i]*P_VEL(particle_data)[i];         /*Taking all dimensions into consideration*/
    vmag += sqrt(vsqr);
    printf("The velocity magnitude is: %e\n", vmag);             /*From specified node only*/
    
    
    collision_weber_number=(P_RHO(particle_data) * P_DIAM(particle_data) * vmag*vmag) /0.072;                /*Weber number calculation*/
    printf("The collision Weber number is: %e\n", collision_weber_number);
    }

      for(i=0; i<idim; i++)
      normal[i]= f_normal[i];
   /*   printf("The fnormal vector components are: %d %d %d\n", f_normal[0],f_normal[1],f_normal[2]);  */
      
      
if   (collision_weber_number >=500)                              /*Critical weber number values from experiments/literature*/
     {return PATH_END;
     }
else if (1 <=collision_weber_number <500)
     
     /*Compute normal velocity*/
     {
     for(i=0; i<idim; i++)
     vn +=P_VEL(particle_data)[i]*normal[i];
     
    /*printf("The face normal vector is: %d %d %d\n", normal[i]); */
     printf("The normal velocity is: %e\n", vn);
              
              
     /* Subtract off normal velocity*/
     for(i=0; i<idim; i++);
     P_VEL(particle_data)[i] -= vn*normal[i];

     /*Add reflected normal velocity*/
     for(i=0;i<idim; i++)
     P_VEL(particle_data)[i] -=vn*normal[i];
    
    /*Store new velocity in P_VEL0 of particle*/
    
    for(i=0;i<idim; i++)
    P_VEL0(particle_data)[i]= P_VEL(particle_data)[i];

    printf("New velocity components are: %e %e %e\n", P_VEL(particle_data)[i]);

    return PATH_ACTIVE;
}
else 
  {return PATH_END;
    }
    
}

The printed new velocity components are: -1.3e+38 5.9e-323 1.9e-323.

[`e`]

You have three %e's in your printf() function but only one value to provide these three values: P_VEL(particle_data)[i] where 'i' is your last dimension (idim-1).

[hwet]

They are certainly more logical now! But i am certain I did try that before, well one of the things about beginner programming, might have something else wrong when I tried displaying all three of them before, thanks!