[FFerrario]

Greetings to all users. I am trying to simulate the convective mass transfer of water into a vapor by using an UDF that first stores the magnitude VOF gradient (which is also a way to define the Interfacial Area Density), to then use it to calculate the volumetric flux of the evaporation. I am using a Sherwood model to calculate the MTC. The UDF is as follows:




#include "udf.h"
#include "math.h"
#include "mem.h"
#include "prf.h"
#include "sg_mphase.h"
#include "sg.h"

#define MF_SAT 0.03484 /*At T = 308.2 K for the water phase*/
#define D 2.45e-05
#define g 9.81
#define L 0.15
#define R 8.314
#define A 6.209
#define B 2354.37
#define C 7.559
#define PM_acq 18.1

DEFINE_ADJUST(store_gradient, domain)
{
Thread *t;
Thread **pt;
cell_t c;
int phase_domain_index = 0;
Domain *pDomain = DOMAIN_SUB_DOMAIN(domain,phase_domain_index);
{
Alloc_Storage_Vars(pDomain,SV_VOF_RG,SV_VOF_G,SV_N ULL);
Scalar_Reconstruction(pDomain, SV_VOF,-1,SV_VOF_RG,NULL);
Scalar_Derivatives(pDomain,SV_VOF,-1,SV_VOF_G,SV_VOF_RG,
Vof_Deriv_Accumulate);
}

/*Loop over all the cells in the domain*/
mp_thread_loop_c (t,domain,pt)
if (FLUID_THREAD_P(t)) /*Checks if the threads are fluids*/
{
Thread *ppt = pt[phase_domain_index];

begin_c_loop(c,t)
{
if (C_VOF(c, ppt) != 0.0 && C_VOF(c, ppt) != 1.0)
/*Check for cells that have interfaces*/
{

C_UDMI(c,t,0)=C_VOF_G(c,ppt)[0]; /*VOF gradient along x*/
C_UDMI(c,t,1)=C_VOF_G(c,ppt)[1]; /*VOF gradient along y*/
C_UDMI(c,t,2)=C_VOF_G(c,ppt)[2]; /*VOF gradient along z*/
C_UDMI(c,t,3)=NV_MAG(C_VOF_G(c,ppt)); /* with a unit of 1/m, since it is the gradient of the VOF volume along the axis, I needed the Interfacial area density*/

}

}
end_c_loop (c,t)
}
Free_Storage_Vars(pDomain,SV_VOF_RG,SV_VOF_G,SV_NU LL);


}

DEFINE_MASS_TRANSFER(evap_source,c,t,from_index,fr om_species_index,to_index,to_species_index)
{

Thread *liq = THREAD_SUB_THREAD(t,from_index);
Thread *gas = THREAD_SUB_THREAD(t,to_index);

real m_lg;
m_lg = 0.0;


/*process only done in the interfacial cells*/
if (C_YI(c,gas,0) < MF_SAT && C_VOF(c,liq) != 0.0 && C_VOF(c,liq) != 1.0 )
{
real mu_c = C_MU_L(c,gas) / (C_R(c,gas)); /* density is kg/m3 and viscosity is Pa*s, so Kinematic Viscosity*/
real T = C_T(c, gas) ; /*In K*/
real coeff = A + (B / (C+T));
real Pev = pow (10,coeff) * 100000; /*in Pa*/
real rho_o = (Pev * PM_acq) / (R * T * 1000); /*Saturation rho for water*/
real Sc = mu_c / D ;
real Gr = ((g * pow(L,3))/ pow (mu_c,2)) * (((C_R(c,gas) * C_YI(c,gas,0)) / rho_o)-1);
real Kc = (0.508 * pow(Sc,0.5) * pow(0.952+Sc,-0.25)* pow(Gr,0.25))* D / L; /* in m/s*/

m_lg = Kc *C_UDMI(c,t,3) * C_R(c,gas) * (MF_SAT - C_YI(c,gas,0)); /*kg/m3 s*/
}
else
{

m_lg = 0;

}

return (m_lg);
}


Would you be so kind to help me with debugging the code? It compiles well, but as soon as I start the simulation (after Inizializing), the process stops with a critical error warning. (Also, if I remove the conditional of only checking cells with an interface in the C_UDMI store_gradient Macro, Fluent Crashes, without error. Is it because it has to store too many values for all cells?)



Thank you in advance,
FF.