UDF for Pulsed flow
 

Hi all ,I’m new in fluent and particularly UDF, I want to model a system that a gas is inlet and it flows for 3s and doesn’t flow for 3s alternatively and continuously. I wrote a udf for this problem But it don't do correctly.
Please, guide me.
Thank you very much

#include"udf.h"
DEFINE_PROFILE(inlet_x_velocity, t, position)
{
face_t f;
real flow_time = RP_Get_Real("flow-time");
int i;
begin_f_loop(f, t)
{
for(i=0; i<=flow_time; i++)
{
if(flow_time >= i*6 && flow_time <= i*6 +3)
F_PROFILE(f,t ,position)=0;
else
F_PROFILE(f,t,position)=0.58425;
}
}
end_f_loop(f, t)
}

Try this one.

Thank you very much in advance.

regards

Hi Blackmask, if I want to model a system that a gas is inlet and it flows for 0.05s and doesn’t flow for 0.05s alternatively and continuously, What do I do?

Change

int i = (int)(flow_time/3.0)%2;

to

int i = (int)(flow_time/0.05)%2;

I change this but the udf can't do correctly

Please explain in more details. What is the time step you choose in your calculation? Make sure that the time step is at least one order smaller that the period of the pulsating flow.

Hi Dear Vahideh
please see Chapter 8 of the ANSYS FLUENT UDF Manual.

/************************************************** *********************
vprofile.c
UDF for specifying steady-state velocity profile boundary condition
************************************************** **********************/
#include "udf.h"
DEFINE_PROFILE(inlet_x_velocity, thread, position)
{
real x[ND_ND]; /* this will hold the position vector */
real y, h;
face_t f;
h = 0.016; /* inlet height in m */
begin_f_loop(f,thread)
{
F_CENTROID(x, f, thread);
y = 2.*(x[1]-0.5*h)/h; /* non-dimensional y coordinate */
F_PROFILE(f, thread, position) = 0.1*(1.0-y*y);
}
end_f_loop(f, thread)
}

/************************************************** ********************
unsteady.c
UDF for specifying a transient pressure profile boundary condition
************************************************** *********************/
#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) = 101325.0 + 5.0*sin(10.*t);
}
end_f_loop(f, thread)
}

udf
 

Hi all ,I’m new in fluent and particularly UDF, I want to model a system that a gas is inlet and it flows for 3s and doesn’t flow for 3s alternatively and continuously in steady state. I wrote a udf fo r this problem But it don't do correctly.
Please, guide me.
Thank you very much.


#include"udf.h"
DEFINE_PROFILE(inlet_x_velocity, t, position)
{
face_t f;
real flow_time = RP_Get_Real("flow-time");
int i = (int)(flow_time/1.0)%2;
begin_f_loop(f, t)
{

if( i)
F_PROFILE(f,t ,position)=0;
else
F_PROFILE(f,t,position)=0. 2;
}
end_f_loop(f, t)
}

you want to run a steady state or a transient case? you say one thing, but your problem suggests something different.

The Model is a tube being inside water intermittent (pulse), but when I use the code is not there is a change in the results, When change my time
I do not know how or where I put the time flow

hello, i'm currently try your code.. but it seems not working. could you please teach me how to write udf...?

"It seems not working" is not very helpful. Please be more detailed.

(Does it give errors? Warnings? Wrong results? Fluent crashes? Your computer destroyed in a fire? Nothing happened?)

Thank you for you reply Sir..
so i was trying to simulate gas-solid fludized bed dryer with pulsed flow... 0.2 m/s inlet velocity in +y direction, frequency 1 Hz (
0s -> 0.5s it flow 0.2m/s
0.5s -> 1s the flow stop at 0 m/s
1.0s -> 1.5s the flow again at 0.2m/s , repeat continously

and when i simulate the volume fraction..it doesn't show any pulsed effect..more likely constant velocity..
i'm also trying to change the frequency into 3s flow...3s stop just to see wether the udf code is working properly or not..and it show the same..

here the copy of my udf code for 3S flow..3S stop flow
==================================

#include"udf.h"
DEFINE_PROFILE(inlet_y_velocity,t,position)
{
face_t f;
real flow_time = RP_Get_Real("flow-time");
int i = (int)(flow_time/3)%2;
begin_f_loop(f,t)

{
if (i)
F_PROFILE(f,t,position)=0;
else
F_PROFILE(f,t,position)=0.2;
}

end_f_loop(f,t)
}

===============================
note: i still very beginner in fluent, especially in udf... so i don't know wether when we have to add "space" "." or ";" , and anything about coding