[NachtErfinder]

Hello all,

I'm planning to study the transient response of turbulence models in pulsatile flow. In order to do so, I would like to set up a UDF boundary condition that varies in both time and space.

Initially, my geometry will be a simple 2D channel. I would like to program the following UDF Boundary Condition on the inlet:

Pf (x, t) = DeltaP0[1 + a cos(w t + pi/2)]x/L_x

where x/L_x is zero at the center line and 1 at the channel wall.

I have successfully programmed a UDF Boundary condition dependent on just time, but I don't know how to incorporate the spacial dependency in the code. I have very limited programming experience with C.

Does someone on these forums know how to write such a function? Any help would be appreciated.

Here is the code I have been using (dime dependent, uniform in space)


#include "udf.h"

DEFINE_PROFILE(unsteady_pressure, thread, position)

{

face_t f;

real t = CURRENT_TIME;

begin_f_loop(f, thread)

{

F_PROFILE(f, thread, position) = 0.00017-0.00017*cos(6.28319*t);

}

end_f_loop(f, thread)

}


Thanks in advance!

[litzj]

This is part of UDF which I have used before.

x[ND_ND] means spatial variables in grid.

If u use that variable correctly, u can present your one





DEFINE_SOURCE(zmomu_source, cell, thread, dS, eqn)
{

/* plasma source constant */

real x[ND_ND];
real source;
source = 0;

C_CENTROID(x, cell, thread);

thrust = 0.02; /* thrust value (N/m) */

/* Plasma region set up */

b_bottom = 0;
b_left = 0;
rat3 = thrust/0.015;
rat4 = thrust/0.015;
xmax = 0.005*pow(rat3, 0.33);/*0.001*(0.667e-3*(V+V0) - 1.333);*/
lamda = 1.2*xmax;
ymax = 0.0013*pow(rat4, 0.33);/*0.001*(0.167e-3*(V+V0) - 0.333);*/
lmax = 0.02;
b_x = 0.3-lmax;


check_bottom = b_bottom;
check_left = b_left;
check_top = b_bottom + ymax;
check_right = b_left + xmax;
check_minx = b_x;
check_maxx = check_minx + lmax;
/*xs = b_left;*/
ys = b_bottom;

/*C_CENTROID(x, cell, thread);*/

/* Apply source term to region inside the four inequalities */

if ((x[1]>=check_bottom)&&(x[1]<=check_top)&&(x[0]>=check_minx)&&(x[0]<=check_maxx))
{
for(i=0; i<=40; i++)
{
if((x[2]>=(check_left+lamda*i))&&(x[2]<=(check_right+lamda*i)))
{
A1 = (9.86)/(4*xmax*ymax);
xs = check_left + 0.01*i;
source = thrust*A1*sin(3.14159*(x[3]-xs)/xmax)*cos(3.14159*(x[1]-ys)/(2*ymax));
dS[eqn] = 0;
}
if((x[2]<=(check_left+lamda*(i+1)))&&(x[2]>=(check_left-xmax+lamda*(i+1))))
{
A1 = (9.86)/(4*xmax*ymax);
xs = check_left - xmax + lamda*(i+1);
source = -thrust*A1*sin(3.14159*(x[3]-xs)/xmax)*cos(3.14159*(x[1]-ys)/(2*ymax));
dS[eqn] = 0;

}
/*else{
source = 0;
dS[eqn] = 0;
}*/
}
}
else
{
source = 0;
dS[eqn] = 0;
}

return source;
}