[FlavioC]

Hello to everyone. I am studying the reflect condition for inert particles, I use the code that appears in the udf fluent manual

DEFINE_DPM_BC(bc_reflect,p,t,f,f_normal,dim)
{
   real alpha;
   /* angle of particle path with face normal */ 
   real vn=0.; 
   real nor_coeff = 1.; 
   real tan_coeff = 0.3; 
   real normal[3]; 
   int i, idim = dim;    
   real NV_VEC(x); 
   #if RP_2D 
   /* dim is always 2 in 2D compilation. Need special treatment for 2d axisymmetric and swirl flows */ 
   if (rp_axi_swirl) 
   { 
      real R = sqrt(p->state.pos[1]*p->state.pos[1] + p->state.pos[2]*p->state.pos[2]); 
      if (R > 1.e-20) 
      { 
         idim = 3; 
         normal[0] = f_normal[0]; 
         normal[1] = (f_normal[1]*p->state.pos[1])/R; 
         normal[2] = (f_normal[1]*p->state.pos[2])/R; 
      } 
      else 
      { 
         for (i=0; i<idim; i++) 
         normal[i] = f_normal[i]; 
       }
   } 
   else 
   #endif 
   for (i=0; i<idim; i++) 
   normal[i] = f_normal[i]; 
   if(p->type==DPM_TYPE_INERT)
   { 
      alpha = M_PI/2. - acos(MAX(-1.,MIN(1.,NV_DOT(normal,p->state.V)/ MAX(NV_MAG(p->state.V),DPM_SMALL)))); 
      if ((NNULLP(t)) && (THREAD_TYPE(t) == THREAD_F_WALL))
      F_CENTROID(x,f,t); 
      /* calculate the normal component, rescale its magnitude by the coefficient of restitution and subtract the change */ 
      /* Compute normal velocity. */ 
      for(i=0; i<idim; i++) 
      vn += p->state.V[i]*normal[i];
      /* Subtract off normal velocity. */ 
      for(i=0; i<idim; i++) 
      p->state.V[i] -= vn*normal[i]; 
      /* Apply tangential coefficient of restitution. */ 
      for(i=0; i<idim; i++) 
      p->state.V[i] *= tan_coeff; 
      /* Add reflected normal velocity. */ 
      for(i=0; i<idim; i++) 
      p->state.V[i] -= nor_coeff*vn*normal[i];   
      /* Store new velocity in state0 of particle */ 
      for(i=0; i<idim; i++)
      p->state0.V[i] = p->state.V[i]; 
      return PATH_ACTIVE; 
   }
   return PATH_ABORT; 
}

But I change the tangent coefficient value setting it to one since the collision should be elastic. Then, I compare the particles trajectories using the UDF and the boundary condition type :reflect. The trajectories are so different. Can someone please explain it to me?