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Different drag coefficients for different zones in computational domain

    • ariyan zare
      Subscriber

      Hi

      I have developed a simple Drag force model code. my computational domain includes 4 different zones. the drag coefficient formulation is the same for all zones, except the constants will change. To specify which formulation applies to each zone, I plan to utilize conditional statements with the "IF" condition based on the zone_ID. could you please help me on how and where I should consider "IF" statement and which macro should be used?


      #include "udf.h"

      DEFINE_EXCHANGE_PROPERTY(DRAG,c,mix_thread,s_col,f _col)
      {
      Thread *gas, *liq;
      real r_vel_g,z_vel_g,r_vel_l,z_vel_l,abs_u,slip_r,slip_ z,rho_g,void_g,mu_g,drag_f;

      /* find the threads for the gas(primary) */
      /* find the threads for the liquid(secondary) */
      gas=THREAD_SUB_THREAD(mix_thread,s_col);
      liq=THREAD_SUB_THREAD(mix_thread,f_col);

      /* find phase velocity and properties */
      r_vel_g=C_U(c,gas);
      z_vel_g=C_V(c,gas);
      r_vel_l=C_U(c,liq);
      z_vel_l=C_V(c,liq);
      slip_r=r_vel_g-r_vel_l;
      slip_z=z_vel_g-z_vel_l;

      /* absolute slip */
      abs_u=sqrt(pow(slip_r,2)+pow(slip_z,2));

      /* properties */
      rho_g=C_R(c,gas);
      mu_g=C_MU_L(c,gas);
      void_g=C_VOF(c,gas);

      /* drag calculation */

      /* Zone_ID=1 */
      drag_f=121564*mu_g/void_g+11*rho_g*abs_u;

      /* Zone_ID=2 */
      drag_f=141266*mu_g/void_g+21*rho_g*abs_u;

      /* Zone_ID=3 */
      drag_f=181786*mu_g/void_g+11*rho_g*abs_u;

      /* Zone_ID=4 */
      drag_f=201454*mu_g/void_g+51*rho_g*abs_u;

      return drag_f;
      }

    • Rob
      Forum Moderator

      The problem you face it tagging the cell to the cell zone - that's doable, but may not be easy. 

      Why is drag different between zones, and how many coefficients do you need? 

      Note, I can give some pointers but need to tread carefully around the "expert knowledge" rules staff work to. 

    • ariyan zare
      Subscriber

      Hi Rob

      Thank you fo your kind reply

      drag coefficient is different between zone because of porous matrix and celar fluid domains. As both permeability and porosity can affect the gas-liquid interaction formulation I need to define different fomrulation for different zones. consider the following equation from the aforementioned code:

      drag_f=121564*mu_g/void_g+11*rho_g*abs_u;

      I want to keep the same drag coefficient fommulation while adjusting the constants 121564 and 11 for four different zones (zone_ID=2,4,6,7). 

      Can I use the following code?

      /* Zone_ID=2 */
      if (mix_thread == 2)
      drag_f=121564*mu_g/void_g+11*rho_g*abs_u;


      else if (mix_thread == 4)
      /* Zone_ID=4 */
      drag_f=141266*mu_g/void_g+21*rho_g*abs_u;


      else if (mix_thread == 6)
      /* Zone_ID=6 */
      drag_f=181786*mu_g/void_g+11*rho_g*abs_u;


      else if (mix_thread == 7)
      /* Zone_ID=7 */
      drag_f=201454*mu_g/void_g+51*rho_g*abs_u;

       

    • Rob
      Forum Moderator

      Try it, I'm not sure if you need c or mix_thread in this case. 

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