[Nicholas_A]

Hi,


I'm using the Ansys Fluent multiphase DPM model to investigate particle focusing in microchannels. For this, I've written an UDF to incorporate the net lift force acting on the particles (see below). However, after compiling and hooking my UDF, Fluent crashes and exits upon starting the calculations with following error messages:


By only adding a couple lines of code at a time and running the simulation, I was able to determine the lines causing the problem. The problem is caused by following lines where I try to fetch the fluid velocities:


Ufx = C_U(c,t); /* local fluid x-velocity in cell */
Ufy = C_V(c,t); /* local fluid y-velocity in cell */
Ufz = C_W(c,t); /* local fluid z-velocity in cell */


When I replace the velocities by constants, the UDF works and Fluent doesn't crash or exit the simulation. Does anyone have an idea as to why these lines are causing the problem? I've posted the full UDF below.


Thanks in advance


Full UDF:


/* UDF for computing the lateral displacement of particle suspended in fluid flow*/
#include "udf.h"
#include "mem.h" /* cell indexing header */
#include "dpm.h" /* particle properties even though declared in the macro arguments */
#include
DEFINE_DPM_BODY_FORCE(net_lift_force,p,i)
{
/* declaration of variables */
double w, Dh, Ufx, Ufy, Ufz, Gx, Gy, Gz, rho, a, Fx, Fy, Fz, FL,
c_volume, Renx, Reny, Renz, crDh, mu, aUfx, aUfy,
aUfz, Clx, Cly, Clz;
cell_t c = P_CELL(p); /* the cell initialization in which the particle is present*/
Thread *t = P_CELL_THREAD(p); /* thread initialization */
c_volume = C_VOLUME(c,t); /* Volume of cell particle is currently in */
Dh = 0.000013929; /* Hydraulic diameter of channel */
crDh = pow(c_volume, (1./3.)); /* Hydraulic diameter of cell */
mu = 0.001003; /* dynamic viscosity of water at 20°C */
rho = C_R(c,t); /* local density of fluid in cell */
Ufx = C_U(c,t); /* local fluid x-velocity in cell */
Ufy = C_V(c,t); /* local fluid y-velocity in cell */
Ufz = C_W(c,t); /* local fluid z-velocity in cell */
aUfx = fabs(Ufx); /* absolute local fluid x-velocity in cell */
aUfy = fabs(Ufy); /* absolute local fluid y-velocity in cell */
aUfz = fabs(Ufz); /* absolute local fluid z-velocity in cell */
/* local Reynolds number calculation*/
Renx = (rho*aUfx*crDh)/mu;
Reny = (rho*aUfy*crDh)/mu;
Renz = (rho*aUfz*crDh)/mu;
/* Determination of lift coefficient based on local Reynolds number */
if(Renx<15.)
Clx = 0.5;
else
Clx = 3.4368*(pow(Renx, -0.714));
if(Reny<15.)
Cly = 0.5;
else
Cly = 3.4368*(pow(Reny, -0.714));
if(Renz<15.)
Clz = 0.5;
else
Clz = 3.4368*(pow(Renz, -0.714));

/* Calculate ratio of local velocity to hydraulic diameter */
Gx = (Ufx)/Dh;
Gy = (Ufy)/Dh;
Gz = (Ufz)/Dh;
a = P_DIAM(p); /* particle diameter */
/* Lift force magnitude calculation */
Fx = Clx*rho*pow(Gx,2)*pow(a,4);
Fy = Cly*rho*pow(Gy,2)*pow(a,4);
Fz = Clz*rho*pow(Gz,2)*pow(a,4);
/* Lift force vector calculation as resultant of shear rate tensor */
if (i==0)
{
FL = (Fy+Fz);
}
else if (i==1)
{
FL = (Fx+Fz);
}
else if (i==2)
{
if (P_POS(p)[2]>0.0000075)
{
FL = Fx+Fy;
}
else
{
FL = -(Fx+Fy);
}
}
else
FL = 0;
return (FL/P_MASS(p));
}