[Josyula]

Hi,
I am trying to superimpose a pulsatile (sinusoidal) profile on an existing parabolic profile, at the inlet of a rectangular microchannel, whose hydraulic diameter is 77.1 micron.

I have written a UDF for the same and which is shown below:

#include "udf.h"
#include "math.h"
DEFINE_PROFILE (unsteady_velocity,thread,position)
{
real x[ND_ND];
real y;
real Par;
face_t f;
real t = CURRENT_TIME;
begin_f_loop (f,thread)
{
y = x[1];
Par = 0.0122*(1-((y*y)/(38.55e-06*38.55e-06))); /* Parabolic profile where r = 38.55e-06*/
F_PROFILE (f,thread,position) = Par+(0.5*sin(2*3.141592654*1.333*t)); /*Parabolic + Pulsatile profile (Asin(2*pi*freq*t))*/
}
end_f_loop (f,thread)
}

After interpreting and hooking the profile to the inlet, I am getting a uniform profile at the inlet instead of a pulsatile profile, even after a very long timestep.

Can anyone tell me what could be the problem with the UDF?

Thanks.

[ComputerGuy]

Originally Posted by Josyula

Hi,
I am trying to superimpose a pulsatile (sinusoidal) profile on an existing parabolic profile, at the inlet of a rectangular microchannel, whose hydraulic diameter is 77.1 micron.

I have written a UDF for the same and which is shown below:

#include "udf.h"
#include "math.h"
DEFINE_PROFILE (unsteady_velocity,thread,position)
{
real x[ND_ND];
real y;
real Par;
face_t f;
real t = CURRENT_TIME;
begin_f_loop (f,thread)
{
y = x[1];
Par = 0.0122*(1-((y*y)/(38.55e-06*38.55e-06))); /* Parabolic profile where r = 38.55e-06*/
F_PROFILE (f,thread,position) = Par+(0.5*sin(2*3.141592654*1.333*t)); /*Parabolic + Pulsatile profile (Asin(2*pi*freq*t))*/
}
end_f_loop (f,thread)
}

After interpreting and hooking the profile to the inlet, I am getting a uniform profile at the inlet instead of a pulsatile profile, even after a very long timestep.

Can anyone tell me what could be the problem with the UDF?

Thanks.

Sure -- you're not ever assigning a value to the x-array (you should use C_CENTROID), and thus it is always returning its default value.

ComputerGuy

[Josyula]

Originally Posted by ComputerGuy

Sure -- you're not ever assigning a value to the x-array (you should use C_CENTROID), and thus it is always returning its default value.

ComputerGuy

Hi,

Sorry for the late reply.

How and where do I incorporate the C_CENTROID macro?

[Daniel Tanner]

Try putting it in here, otherwise the you have not set x so y=x[1] will not give the required answer.

begin_f_loop (f,thread)
{
F_CENTROID(x,f,thread);
y=x[1];
.....

[Josyula]

Originally Posted by Daniel Tanner

Try putting it in here, otherwise the you have not set x so y=x[1] will not give the required answer.

begin_f_loop (f,thread)
{
F_CENTROID(x,f,thread);
y=x[1];
.....

Thank you Daniel!