2.5.13 DEFINE_DPM_SWITCH

Description

You can use DEFINE_DPM_SWITCH to modify the criteria for switching between laws. The function can be used to control the switching between the user-defined particle laws and the default particle laws, or between different user-defined or default particle laws.

Usage

DEFINE_DPM_SWITCH( name, p, ci)

Argument Type	Description
symbol name	UDF name.
Tracked_Particle *p	Pointer to the Tracked_Particle data structure which
	contains data related to the particle being tracked.
int ci	Variable that indicates if the continuous and discrete phases
	are coupled (equal to $1$ if coupled with continuous phase, $0$
	if not coupled).
Function returns
void

There are three arguments to DEFINE_DPM_SWITCH: name, p, and ci. You supply name, the name of the UDF. p and ci are variables that are passed by the ANSYS FLUENT solver to your UDF.

Pointer p can be used as an argument to the macros defined in Section  3.2.7 to obtain information about particle properties (e.g., injection properties).

Example

The following is an example of a compiled UDF that uses DEFINE_DPM_SWITCH to switch between DPM laws using a criterion. The UDF switches to DPM_LAW_USER_1 which refers to condenshumidlaw since only one user law has been defined. The switching criterion is the local humidity which is computed in the domain using a DEFINE_ON_DEMAND function, which again calls the function myHumidity for every cell. In the case where the humidity is greater than $1$, condensation is computed by applying a simple mass transfer calculation. Otherwise, one of ANSYS FLUENT's standard laws for Vaporization or Inert Heating are applied, depending on the particle mass. The UDF requires one UDML and needs a species called h2o to compute the local humidity.

/**********************************************************************
   Concatenated UDFs for the Discrete Phase Model that includes a     
   usage of DPM_SWITCH                                                
***********************************************************************/

#include "udf.h"
#include "dpm.h"
#include "surf.h"  /* for  macros: RP_Cell() & RP_Thread()        */
#include "prop.h"  /* for function: Saturation_Pressure() (of water) */

static real dpm_relax=1.0; /*dpm source relaxation */

real H2O_Saturation_Pressure(real T)
{
  real ratio, aTmTp;

  aTmTp = .01 * (T - 338.15);
  ratio = (647.286/T - 1.) *
    (-7.419242 + aTmTp*(.29721 +
                 aTmTp*(-.1155286 +
                 aTmTp*(8.685635e-3 +
                 aTmTp*(1.094098e-3 +
                 aTmTp*(-4.39993e-3 +
                 aTmTp*(2.520658e-3 -
                 aTmTp*5.218684e-4)))))));
  return (22.089e6 * exp(MIN(ratio,35.)));
}


real myHumidity(cell_t c,Thread *t)
{
  int i;
  Material *m=THREAD_MATERIAL(t), *sp;
  real yi_h2o=0,mw_h2o=1.0;
  real r_mix=0.0;

  if(MATERIAL_TYPE(m)==MATERIAL_MIXTURE)
  {
   mixture_species_loop (m,sp,i)
   {
     r_mix += C_YI(c,t,i)/MATERIAL_PROP(sp,PROP_mwi);

     if (0 == strcmp(MIXTURE_SPECIE_NAME(m,i),"h2o") ||
  (0 == strcmp(MIXTURE_SPECIE_NAME(m,i),"H2O")))
     {
 yi_h2o = C_YI(c,t,i);
 mw_h2o = MATERIAL_PROP(sp,PROP_mwi);
     }
   }
  }

  return ((ABS_P(C_P(c,t),op_pres) * yi_h2o / (mw_h2o * r_mix)) /
                H2O_Saturation_Pressure(C_T(c,t))) ;
}

#define CONDENS 1.0e-4

DEFINE_DPM_LAW(condenshumidlaw,p,coupled)
{
 real area;
 real mp_dot;
 cell_t c = P_CELL(p);               /* Get Cell and Thread from */
 Thread *t = P_CELL_THREAD(p);  /* Particle Structure using new macros*/

 area = 4.0* M_PI * (P_DIAM(p)*P_DIAM(p));

 /* Note This law only used if Humidity > 1.0 so mp_dot always positive*/
 mp_dot = CONDENS*sqrt(area)*(myHumidity(c,t)-1.0);

 if(mp_dot>0.0)
 {
   P_MASS(p) = P_MASS(p) + mp_dot*P_DT(p);
   P_DIAM(p) = pow(6.0*P_MASS(p)/(P_RHO(p)* M_PI), 1./3.);
   P_T(p)=C_T(c,t); /* Assume condensing particle is in thermal
          equilibrium with fluid in cell */
 }

}

/* define macro that is not yet standard */

#define C_DPMS_ENERGY(c,t)C_STORAGE_R(c,t,SV_DPMS_ENERGY)

DEFINE_DPM_SOURCE(dpm_source,c,t,S,strength,p)
{
  real mp_dot;
  Material *sp = P_MATERIAL(p);


  /* mp_dot is the (positive) mass source to the continuous phase */
  /* (Difference in mass between entry and exit from cell)         */
  /* multiplied by strength (Number of particles/s in stream)      */

  mp_dot = (P_MASS0(p) - P_MASS(p)) * strength;

   C_DPMS_YI(c,t,0) += mp_dot*dpm_relax;
   C_DPMS_ENERGY(c,t) -= mp_dot*dpm_relax*
MATERIAL_PROP(sp,PROP_Cp)*(C_T(c,t)-298.15);
   C_DPMS_ENERGY(c,t) -= mp_dot*dpm_relax*
MATERIAL_PROP(sp,PROP_latent_heat);
}


#define UDM_RH 0
#define N_REQ_UDM 1
#define CONDENS_LIMIT 1.0e-10

DEFINE_DPM_SWITCH(dpm_switch,p,coupled)
{
 cell_t c = P_CELL(p);
 Thread *t = P_CELL_THREAD(p);

 if(C_UDMI(c,t,UDM_RH) > 1.0)
  P_CURRENT_LAW(p) = DPM_LAW_USER_1;
 else
 {
  if(P_MASS(p) < CONDENS_LIMIT)
   P_CURRENT_LAW(p) = DPM_LAW_INITIAL_INERT_HEATING;
  else
   P_CURRENT_LAW(p) = DPM_LAW_VAPORIZATION;
 }
}

DEFINE_ADJUST(adj_relhum,domain)
{
 cell_t cell;
 Thread *thread;

 /* set dpm source underrelaxation */
 dpm_relax = Domainvar_Get_Real(ROOT_DOMAIN_ID,"dpm/relax");

 if(sg_udm<N_REQ_UDM)
    Message("\nNot enough user defined memory allocated. %d required.\n",
            N_REQ_UDM);
 else
 {
  real humidity,min,max;

  min=1e10;
  max=0.0;

  thread_loop_c(thread,domain)
  {
   /* Check if thread is a Fluid thread and has UDMs set up on it */
   if (FLUID_THREAD_P(thread)&& NNULLP(THREAD_STORAGE(thread,SV_UDM_I)))
   {
    begin_c_loop(cell,thread)
     humidity=myHumidity(cell,thread);
     min=MIN(min,humidity);
     max=MAX(max,humidity);
     C_UDMI(cell,thread,UDM_RH)=humidity;
    end_c_loop(cell,thread)
   }
  }
  Message("\nRelative Humidity set in udm-%d",UDM_RH);
  Message(" range:(%f,%f)\n",min,max);
 }/* end if for enough UDSs and UDMs */
}

DEFINE_ON_DEMAND(set_relhum)
{
 adj_relhum(Get_Domain(1));
}

Hooking a DPM Switching UDF to ANSYS FLUENT

After the UDF that you have defined using DEFINE_DPM_SWITCH is interpreted (Chapter  4) or compiled (Chapter  5), the name of the argument that you supplied as the first DEFINE macro argument will become visible in the Custom Laws dialog box in ANSYS FLUENT. See Section  6.4.13 for details on how to hook your DEFINE_DPM_SWITCH UDF to ANSYS FLUENT.