[Kerouac]

I everyone,
currently I'm trying to solve numerically the multiphase flow in a semi-cylinder (the problem is symmetrical with respect to a given plane passing through the center of the cylinder; on that plane a symmetry b.c. has been imposed).
What I want to impose is a fully-developed flow as boundary inlet condition; the expression for the velocity profile, if the problem was 2D-axisymmetric, would be the following:

u(r)=-10.1424*r^3+0.0516*r^2-0.0197*r+0.087

does has anyone idea about how to write the UDF?

Thanks in advance,
Kerouac

[anan12345]

Did you try using Fluent's expressions? If I remember correctly, you can define radius as (x**2+y**2) and write your expression directly into Fluent's GUI without ever needing to compile a UDF for it.

[pakk]

It's a DEFINE_PROFILE condition. The manual has an example.

My hint would be to start with that example, and change the equation to yours. If this is giving you problems, please be more specific on which step is giving you problems.

[Kerouac]

I solved the problemby myself.
The idea is that to write a normal udf for velocity inlet, as it was a complete circular cross section in 3D domain. The symmetry does not have influence on the profile, because the inlet flow field is simply symmetrized.
I will post the complete udf, for those which have a similar problem:

#include "udf.h"
#include "math.h"
DEFINE_PROFILE(inlet_y_velocity, thread, index)
{
real y[ND_ND]; /* this will hold the position vector */
real x;
real z;
real a;
face_t f;
begin_f_loop(f, thread) /*loops over all faces in the thread passed in the DEFINE macro argument*/
{
F_CENTROID(y,f,thread);
x =y[1];
z =y[1];
a = pow((pow(x,2)+pow(z,2)),0.5);
F_PROFILE(f, thread, index) = -10.142387415545718*a*a*a+0.051610679345377*a*a-0.019652442143266*a+0.087031654863898;
}
end_f_loop(f, thread)
}

Best regards,
Kerouac