[Kukka]

Dear all,

I am working with swirl flow confined in a cylinder. The center of rotating inner vortex undergoes displacement with time.

I wrote a UDF to run with fluent 16.2. Basically, I need the coordinates of the points with least pressure on a plane with time. Though I am getting the values of least pressure on that plane, yet I am unable to extract the coordinates - in my case it is x-y plane with z direction coinciding with the axis of cylinder.

My programming skills are not good enough. I am sharing to what I have been able to do so far.

#include "udf.h"
#include "mem.h"
#include "metric.h"

DEFINE_ADJUST(least_pressure,d)
{
face_t f;
Thread *t;
real x[ND_ND];
float pressure;
int zone_ID;
float coordinate[ND_ND];
float least_press = 10000;
FILE *fp;

thread_loop_f(t,d)
{
zone_ID = THREAD_ID(t);
if(zone_ID == 7)
{
begin_f_loop(f,t)
{
pressure = F_P(f,t);
if(pressure<least_press)
{
F_CENTROID(x,f,t);
NV_V(coordinate, =, x);
least_press = pressure;
}
end_f_loop(f,t)
}

fp = fopen("pressure_writer.txt","a");
fprintf(fp,"%f* ",coordinate);
fprintf(fp," %f\n",least_press);
fclose(fp);
}
}
}


Could anyone simply point out where am I going wrong? This I ran in serial mode as I have least idea of programming for parallel processing.

Regards,
Kukka

[AlexanderZ]

Originally Posted by Kukka

Dear all,

I am working with swirl flow confined in a cylinder. The center of rotating inner vortex undergoes displacement with time.

I wrote a UDF to run with fluent 16.2. Basically, I need the coordinates of the points with least pressure on a plane with time. Though I am getting the values of least pressure on that plane, yet I am unable to extract the coordinates - in my case it is x-y plane with z direction coinciding with the axis of cylinder.

My programming skills are not good enough. I am sharing to what I have been able to do so far.

#include "udf.h"
#include "mem.h"
#include "metric.h"

DEFINE_ADJUST(least_pressure,d)
{
face_t f;
Thread *t;
real x[ND_ND];
float pressure;
int zone_ID;
float coordinate[ND_ND];
float least_press = 10000;
FILE *fp;

thread_loop_f(t,d)
{
zone_ID = THREAD_ID(t);
if(zone_ID == 7)
{
begin_f_loop(f,t)
{
pressure = F_P(f,t);
if(pressure<least_press)
{
F_CENTROID(x,f,t);
NV_V(coordinate, =, x);
least_press = pressure;
}
end_f_loop(f,t)
}

fp = fopen("pressure_writer.txt","a");
fprintf(fp,"%f* ",coordinate);
fprintf(fp," %f\n",least_press);
fclose(fp);
}
}
}


Could anyone simply point out where am I going wrong? This I ran in serial mode as I have least idea of programming for parallel processing.

Regards,
Kukka

Hello,
try this code

#include "udf.h"
#include "mem.h"
#include "metric.h"

DEFINE_ADJUST(least_pressure,d)
{
face_t f;
Thread *t;
real x[ND_ND];
float pressure;
int zone_ID;
real coordinate;
float least_press = 10000;
FILE *fp;

thread_loop_f(t,d)
{
zone_ID = THREAD_ID(t);
if(zone_ID == 7)
{
begin_f_loop(f,t)
{
pressure = F_P(f,t);
if(pressure<least_press)
{
F_CENTROID(x,f,t);
coordinate = x[0];
least_press = pressure;
}
end_f_loop(f,t)
}

fp = fopen("pressure_writer.txt","a");
fprintf(fp,"%f* ",coordinate);
fprintf(fp," %f\n",least_press);
fclose(fp);
}
}
}

Best regards

[Kukka]

Dear AlexanderZ,

Thanks a lot for your reply and support. It worked for me and I have started getting the x-coordinate values for minimum pressure. Now I would try getting both x- and y-coordinates, simultaneously, and I hope it would just be the same as for X.

The planes which it recognizes are the boundaries and not the planes which we create manually inside the solver (FLUENT). So as a trial, I monitored at outlet boundary to generate this data. Do I need to go with cell marking to generate a boundary at my desired location (which would be, of course, inside the fluid domain) where actually I will be monitoring? Any idea on this?

I look forward to hearing from you.


Best Regards,
Kukka

[AlexanderZ]

x-axis is x[0]
y-axis is x[1]

y_coordinate = x[1];

Regarding monitors, you may use this approach:

If you need to get values from your domain across y-axis, for instance y=0,
you may make a loop over all faces(for 2D), and monitor if x[1] == 0, than you save pressure (or whatever you want)

I hope you got my idea.

Best regards

[pakk]

You do everything right, except for printing the answer. You do that by:

fprintf(fp,"%f* ",coordinate);

The %f tells that you want to print a single number, but "coordinate" is a combination of three numbers. So that does not work.

Instead, what you can do:

fprintf(fp,"(%f,%f,%f) ",coordinate[0],coordinate[1],coordinate[2]);

This has three %f's, so you tell that you want to print three numbers, and then you specify which three numbers.

==Edit: I was responding to the original question, did not see that there was already an answer==

[Kukka]

Dear AlexanderZ,

Thank you for your extended support. I would return to my institute on Tuesday and give it a try.

I hope now it should work well :-)

Best Regards,
Kukka

[Kukka]

Dear Pakk,

Many thanks for your suggestions :-)

I will run this code and incorporate your suggestions as well.


Best Regards,
Kukka